Volume 41, Issue 1

Based on CAFE theory and KGT model, the twin-roll strip casting mathematical model was established to solve the dendrite growth and solidification of T2 copper alloy in the molten pool. The influence mechanism of casting temperature, heat transfer, and other technological conditions on the microstructure of strip was analyzed. The results showed that the liquid metal formed 35 µm chilling layer after touching the rollers, and the layer was consisted of a high number of small and equiaxed crystals. Then some grains would appear close to the newly chilling layer, and grow toward the core of molten pool competitively. The dominant grains mainly grew along the 〈001〉 orientation into columnar crystals, and the rest grains that grew out of alignment were eliminated gradually. The number of grains declined, and the radius of columnar grains became coarsening. The Kiss point is a key factor for solidification structure, and the lower location of the Kiss point could limit the growth spaces of columnar crystals, which refined the grains.

Aiming at the problems of poor sensitivity and low accuracy of traditional combustible gas explosion hazard identification methods, the discrete probability model was introduced to design a multicomponent combustible gas explosion hazard identification method. Fem3 model is selected to analyze the diffusion mode of multicomponent combustible gas, and the calculation formula of diffusion velocity is obtained. The explosion limit of multicomponent combustible gas was observed by means of test, and the upper limit of explosion concentration of multicomponent combustible gas was obtained. According to the characteristics of explosion, a multicomponent combustible gas explosion hazard identification device is designed. The discrete probability model is used to identify the explosion hazard of multicomponent combustible gas. Experimental results show that the proposed method greatly improves the recognition sensitivity and accuracy, which fully shows that the proposed method has a better detection effect.

To comprehensively utilize Fe and P in oolitic hematite ore, an innovative method was proposed to enhance P enrichment in the reduced iron during the reduction process. The reduced iron was then converted to low-P-containing molten iron and high-P-containing slag in the presence of CaO–SiO 2 –FeO–Al 2 O 3 slag. In this study, the P content of the final iron after 0–1,800 s dephosphorization was investigated at different slag composition conditions, and the dephosphorization kinetics of the reduced iron was analyzed. The results showed that the P content of the final iron sample decreased rapidly within 600 s of dephosphorization and became almost constant with increasing dephosphorization time to 1,800 s. The basicity, FeO content, and Al 2 O 3 content also affected the dephosphorization rate of the reduced iron. The apparent dephosphorization rate constant ranged from 1.141 × 10 −3 to 2.363 × 10 −3  g·(cm 2 ·s) −1 , and the overall mass transfer coefficient ranged from 2.47 × 10 −3 to 3.38 × 10 −3  cm·s −1 . The rate-controlling step of the dephosphorization process was the mass transfer of P in both the slag and iron phases. The findings of this study provide a theoretical basis for the utilization of refractory oolitic hematite ore.

The effect of hold time with 0, 20, and 40 s on in-phase thermomechanical fatigue (TMF) behavior and life of P92 steel is investigated in this study. TMF tests are carried out under mechanical strain control with strain amplitudes of 0.4 0.4 , 0.6 0.6 , and 0.8 % 0.8\text{\%} , and temperature range of 550–650°C which is closely relevant to the operating condition in power plant. TMF tests are performed in a mechanical strain ratio of R = − 1 R=-1 and cycle time of 120 s. The fatigue life variation follows the sequence of N f 0 s < N f 20 s < N f 40 s {N}_{\text{f}}^{0\hspace{.1em}\text{s}}\lt {N}_{\text{f}}^{20\hspace{.1em}\text{s}}\lt {N}_{\text{f}}^{40\hspace{.1em}\text{s}} for the same mechanical strain amplitude. In addition, the influence of hold time on fatigue life decreases with the increasing strain amplitude. A continuous softening can be observed from the cyclic stress response under all test conditions. Fractographic and microstructural tests indicate that the fracture surfaces are characterized by a multi-source cracking initiation and an oxidation phenomenon. Furthermore, a modified Ostergren model is used to predict the fatigue life and achieves a good predicted result.

Compared with single-sided welding, double-sided welding can melt through thicker workpieces and improve the mechanical performance of the weld. In this work, laser welding with filler wire of 2195 Al–Li alloy plates is conducted via double-sided out-of-sync welding. By combining experiment and numerical simulation results, the influence laws of the weld’s mechanical properties are studied by considering the condition of both sides under different welding parameters. The results show that the welding speed is the key parameter determining the heat input of the weld. In the welds fabricated at slow welding speeds, the cooling rate is greater, resulting in accelerated solidification. The weld solidifies before hydrogen overflows from the weld pool, resulting in increased pore density and weakened mechanical properties. Therefore, welding parameters determine the heat input of the weld and subsequently the mechanical properties. It is shown that a special double-sided welding strategy can effectively control the heat input. Specifically, in contrast to those of the first, the welding parameters of the second side of the weld reduce the wire feeding speed when other parameters are held constant. Compared with the process strategy using identical double-sided parameters, this can slightly increase the heat input and reduce the defects in the weld, which can improve its mechanical properties. In the comparative experiment, the wire feeding speed was reduced from 5 to 3 mm·s −1 , and the tensile strength of the weld was increased by 10%.

The thermodynamic precipitation behavior of the second-phase particles in Nb-containing high titanium microalloyed steel has been studied by calculation in this article. It is revealed that FCC_A1#2 is isomorphic with FCC_A1#3 and the contents of Ti and Nb elements are much higher than that of FCC_A1#3. The influence of different quenching temperatures on microstructure and mechanical properties of steel was also studied. The results indicate that the quenching temperature should be controlled below 1,100°C and the soaking time should not exceed 60 min to avoid abnormal grain growth. The thermodynamic calculation and experimental results have certain theoretical guiding significance for the practical industrial application of high titanium–niobium steel.

As recent advances in additive manufacturing (AM) technology has grown rapidly over the past decades, a wide range of applications in the various field has been proposed. Especially, large-scale 3D printing technology has emerged as one of the most innovative alternatives to the traditional manufacturing process due to its simple, fast, and cost-efficient features. In this article, we proposed a large-scale hybrid manufacturing equipment of the three-dimensional (3D) printer based on fused deposition modeling (FDM) incorporated with CNC machining. Our manufacturing system is designed to produce a product having dimensions up to 3,000 mm × 4,000 mm × 1,200 mm with an extruder having an extrusion rate of 30 mm·s −1 and nozzle area of 15 mm 2 × 15 mm 2 . We also optimized the operating conditions of our equipment including the shape of the nozzle, the temperature of the heater, and the RPM of the machining tool. The performance of the equipment was confirmed by pilot production via sand-casting. We expect that our hybrid manufacturing system can be widely used to produce various shapes of large-scale mold as a cost-effective alternative to conventional methods in the manufacturing process.

TA15 titanium alloy is welded by electron beam welding (EBW) and pulsed Nd:YAG laser beam welding (P-LBW), respectively. Results show that the fusion zone (FZ) is mainly composed of acicular α′ martensite, while the acicular α′ martensite in the FZ of EBW joint is coarser. The quantity of martensite in the FZ of EBW joint is larger and the distribution of martensite is denser. The microstructure of heat-affected zone (HAZ) of the two joints is similar. The HAZ near FZ consists of primary α phase and acicular α′ martensite, and the HAZ near base metal (BM) consists of primary α phase, secondary α phase, and β phase. The hardness in the FZ of EBW joint is slightly higher than that of the P-LBW joint. The tensile strength of both joints is close to that of the BM, but their elongations are decreased to a certain extent. The tensile performance of the EBW joint is slightly better than that of the P-LBW joint. Both joints fail in the BM during stretching. There are many dimples on the fracture surfaces, and the two joints obviously present the characteristics of ductile fracture.

Polyaluminocarbosilane (PACS) as a single-source-precursor of SiAlC(O) ceramic was prepared by reacting a hyperbranched allylhydridopolycarbosilane (AHPCS) and aluminum( iii ) acetylacetonate (Al(acac) 3 ), and the PACS was characterized using gel-permeation chromatography, Fourier-transform infrared spectroscopy, and nuclear magnetic-resonance spectroscopy. The polymer-to-ceramic transformation of the obtained PACSs was investigated by Fourier-transform infrared spectroscopy and thermogravimetric analysis. The ceramic yield of the PACS was approximately 15% higher than that of the original AHPCS at 1,200°C. The phase composition and microstructure of the final ceramics were studied by X-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. The introduction of aluminum to the SiC(O) ceramics suppressed the β-SiC crystal growth and improved the density of the ceramics that were annealed at 1,800°C, which is advantageous for high-temperature ceramics. The aluminum content of the SiAlC(O) ceramics can be readily controlled by the Al(acac) 3 content in the PACS precursors.

In this work, the technology of carbothermic reduction was used to extract iron and remove sodium from red mud. The effect of various parameters like reduction time, temperature, and basicity on melting separation and de-alkalization was studied. At the optimum reduction temperature of 1,450°C, the basicity of 1.5, and reduction time of 12 min, the metallization rate and sodium removal reach 96.63 and 90.62%, respectively. Melting and separating conditions gradually improve with the temperature increasing from 1,350 to 1,450°C. At high basicity ( R = 2), the condition of melting and separation is poor due to a large amount of Ca 2 Al 2 SiO 7 produced, which has a high melting point. Subsequently, in order to explore the aggregation state of iron ions under different basicities, the microstructure of pellets was observed by scanning electron microscopy. It was found that when the basicity is 1.5, the aggregation degree of iron particles significantly increases. X-ray diffraction (XRD) analyses of the reduced pellets indicated that at different basicities, the final phase composition of reduced pellets is mainly Ca 2 Al 2 SiO 7 , which is the basic material for preparing cement materials and glass ceramics. Thus, the carbothermic-reduction method is a sustainable process for dealing with the Bayer bauxite residue.

The reduction swelling behaviors of the fluxed briquettes with basicity (CaO/SiO 2 ) in the range of 0.33–1.33 were determined by adding analytical-grade CaO. Results showed that with the increase of basicity, the diameter, volume, and porosity of briquettes increased gradually, whereas the diameter, volume, and porosity of briquettes decreased when the basicity was greater than 0.83. The volume and porosity of briquettes decreased gradually with the increase in firing temperature. The reduction swelling index (RSI) reached the maximum at the basicity of 0.83. The RSI of fluxed briquettes was fired at 1,230°C, and that at the basicity of 0.83 was 20.12% after 60 min of reduction. The RSI of the fluxed briquettes was 3.16% when the basicity of briquettes was 0 upon firing at 1,300°C. The reducibility and swelling were positively correlated with internal porosity. The higher the swelling of briquettes, the denser was the distribution of iron whiskers. The lower the swelling of briquettes, the more closely the iron particles connected.

The effect of cooling rates on acicular ferrite (AF) nucleation was observed in situ by laser scanning confocal microscopy. The precipitation characteristics of TiN–MnS inclusions, the austenite grain size, and the content and morphologies of AF were analyzed and compared under different cooling rates. The results indicated that with the increase of the cooling rate, the size of TiN–MnS inclusions precipitated in the test steel gradually decreased while the inclusion number increased. When the cooling rate increased from 0.2 to 10°C·s −1 , the average inclusion size decreased from 2.7 to 1.3 µm. The austenite grain size decreased gradually with the increase of the cooling rate, and the larger the cooling rate was, the more uniform the grain size distribution. The AF proportion increased first and then decreased, it reached the maximum when the cooling rate was 5°C·s −1 , which accounted for 82.6%. Meanwhile, the dendrite size decreased gradually, the average length decreased from 30 to 5 µm, and the average width decreased from 2.8 to 0.7 µm when the cooling rate increased from 0.2 to 10°C·s −1 .

To investigate the corrosion behavior of WC–Co composite coating, plasma transferred arc (PTA) welding was applied to prepare WC–Co coating on hull steel EH40 for achieving good metallurgical bonding. The phases of coatings were mainly composed of WC particles, solid solution γ-Co, Fe 3 Ni 2 , SiO 2 and Mo 2 C. After electrochemical test, it can be concluded that Co-based coating with 45% WC content has better corrosion resistance in low temperature marine environment for obtaining denser oxide film. Through X-ray photo electron spectroscopy (XPS) analysis, the main corrosion products of immersion were Co(OH) 2 and Co 3 O 4 . These corrosion products aggregate to form a stable corrosion product film, which plays some protective role for the coating. Hard particle WC is also partially oxidized to WO 3 . The pitting hole of 60% WC is the most serious. Pitting corrosion is easy to occur at the interface defects.

To investigate the thermodynamic stability and the evolution process of inclusions in the Al–Ti deoxidized steels, both laboratory experiments and thermodynamic calculations were conducted in the present work. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and Al 2 O 3 –Ti 2 O 3 –TiO 2 phase diagrams were used to investigate the composition of oxide inclusions after adding various contents of Al and Ti. The results show that the TiO x content of inclusions increases with the increase in titanium addition in steel ranging from 0.31 to 1.88%, and the typical inclusions are transferred from pure Al 2 O 3 to multi-phase Al–Ti complex inclusions and Al 2 O 3 –TiO x complex inclusions with uniform composition. The TiO x content in the inclusions first increased and then decreased with the extension of deoxidation time in the steels with deoxidants of [% Al] = 0.055 and [% Al] = 0.71, and the content of TiO x in the inclusions is highest at 360 s of deoxidation. There is a small amount of pure titanium oxide and liquid Al 2 O 3 –TiO x composite inclusions in the steel with deoxidants of [% Al] = 0.13 and [% Ti] = 1.88 at 120 s of deoxidation, and then this part of inclusions gradually turns into the Al 2 O 3 -rich phase. The predominance diagrams of the Al–Ti–O–Fe system were obtained based on the classical thermodynamic calculation and FactSage calculation with different databases and products. The calculated results were compared with the experimental data, and the discrepancies on the stable region of oxides in the predominance diagrams were discussed. The evolution and transformation of inclusions during the solidification process were analyzed based on FactSage calculation.

In fire investigations, the most important aspect is determining the presence of a liquid accelerant at the fire scene. The presence or absence of accelerants is critical evidence during trials for fire cases. Upon exposure to high temperatures, metallic substances undergo oxidation, which can be imparted by accelerants in the fire. Oxides and substrates found on metal surfaces offer valuable information on the characteristics of fire, including exposure temperature, duration, and involvement of a liquid accelerant. In this study, we investigated the oxidation behavior of copper at high temperatures in a simulated flame environment using ethanol combustion. After oxidation, the morphological, oxide phase composition, and microstructural features of specimens were characterized by observation, X-ray diffraction, X-ray photoelectron energy spectroscopy, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopic analysis. The elemental carbon with a hexagonal structure deposited on the sample’s surface was found, which may be incomplete combustion and the chemical composition of ethanol. Copper has a preferred orientation of oxide on the (111) crystal plane, which differs from oxidation in ordinary hot air that is related to the large Coulomb force of the (111) crystal plane. Hot air convection due to combustion may cause large areas of oxide layer on the copper surface to crack and peel. Oxide properties and surface state of metals strongly depended on oxidation duration, temperature, and atmosphere. These data shall offer reference information for determining the presence of combustion accelerants at fire scenes.

Evaluation of the concrete behavior in elevated temperatures is important in terms of first, structural construction safety under specified loadings, and second, measuring the loading capacity to continue operation. Furthermore, concrete behavior at high temperatures is strongly affected by microstructure. The calcium silicate hydrate (C–S–H), a nanostructure which is produced by hydration of cement paste, plays a significant role in enhancing the concrete strength under the impression of thermal fluctuations. Hence, this study investigates the microstructural performance of concrete exposed to high temperatures with a special focus on C–S–H nanostructure. Accordingly, 300 samples were cured for 1, 3, 7, 14, and 28 days in a moist room and then exposed to temperature range of 25–900°C for 2 h to investigate changes in their weight, length, compressive strength, and cracking behavior. Besides evaluating the microstructural behavior of the specimens in different temperatures, several techniques such as SEM, EDX, and XRD have been employed. Based on the results, any changes in the samples’ length, weight, and compressive strength depend on the C–S–H nanostructure behavior. In fact, following water decomposition from the C–S–H nanostructure at 900°C, the structure is partially converted to porous ceramic. These structural changes have caused a decline of 79–100% of the compressive strength. The compressive strength has decreased from 27.6 MPa to about 6 MPa. Also, the weight loss percentage of 28-days-old sample at this temperature was 18.84%. Based on the SEM and XRD results, this decline under high temperature arises due to the collapse of C–S–H nanostructure and formation of calcium oxide in the cement structure.

We established and simulated finite element solidification models of ingots with 180, 380, 800, 1,300, and 1,880 mm diameters, and the solidification process temperature distributions for the five ingot sizes were assessed by Fluent. On this basis, we established a mathematical model for the interfacial heat transfer coefficient between the ingot and the ingot mold, as well as the ingot diameter and solidification time, using the regression analysis method. The results showed that the change law for the interfacial heat transfer coefficients of the ingots with different sizes and times conformed to the change law of the exponential function, and the interfacial heat transfer coefficient and the ingot diameter had a linear relationship. The interfacial heat transfer coefficient, based on a measured temperature of about 36 tons of ingot with an average diameter of 1,500 mm and about 8.5 tons of ingot with an average diameter of 820 mm, was compared to the interfacial heat transfer coefficient calculated by the model. We found that the variation law of the two was essentially the same, indicating that this model could correctly reflect the interfacial heat transfer coefficient between the ingot and the ingot mold in the literature.

In this article, design, fabrication, and testing of SiC/SiC turbine blisk with the fiber’s preform of Spider Web Structure (SWS) subjected to different load spectrums at elevated temperature are conducted. Micro-CT scans are conducted to show the fibers preform and defects inside the SWS-SiC/SiC turbine blisk. For 2D plain-woven SiC/SiC composite under monotonic tensile loading at an elevated temperature of T = 900°C in air atmosphere, the composite ultimate tensile strength is σ uts = 200 MPa with the fracture strain ε f = 0.36%. For SWS-SiC/SiC turbine blisk under the rotation testing, the first and second order natural frequency of the SWS-SiC/SiC turbine blisk are tested using the laser vibration meter. Relationships between the rotation speed, internal damage, and the natural frequency degradation of the SWS-SiC/SiC turbine blisk are established. Under the maximum rotation speed of n = 17,000 rpm at the exhaust temperature of T = 930°C, no damage occurred in the SWS-SiC/SiC turbine blisk. However, multiple coating spalling occurred due to the thermal-chemical coupling failure of the coating under flame impingement. The first natural frequency of the SWS-SiC/SiC turbine blisk decreases by 5% with the increase in the rotating speed from n max = 85,000 rpm to n max = 105,000 rpm, which indicates that there is an internal damage in the SWS-SiC/SiC turbine blisk, which leads to the decrease in the stiffness of the blisk.

It is challenging to efficiently prepare bimetallic composites with excellent metallurgical bonding. Here, we present a strategy, the ultrasonic insert casting (UIC) process, to solve this problem. The ultrasound cavitation effectively destroys the oxide film and promotes diffusion in the UIC-prepared steel/aluminum bimetallic castings, resulting in a uniform reaction layer between steel and aluminum. The reaction layer contains FeAl 3 , Al 8 Fe 2 Si, and Al 4.5 FeSi, and has a higher microhardness than the steel/aluminum matrix, with an average thickness of 8 μm. Moreover, the thickness of the reaction layer increases with the improvement of pouring temperature but the thicker reaction layer (approximately 12 μm) does not bring higher strength. The highest shear strength, about 70 MPa, is approximately three times higher than that without ultrasonic treatment. These results indicate a useful strategy for the low cost and high-efficiency preparation of metallurgical boding bimetallic casting.

The effect of temperature on phase transformation, metallization rate, carbon residue and agglomeration of metal Fe after the pre-reduction of carbon-containing pellets in high-chromium vanadium–titanium magnetite (HCVTM) was investigated. The results indicated that titanomagnetite was finally reduced to metal Fe and (Mg, Fe)Ti 2 O 5 without low valence titanium oxide with increasing pre-reduction temperature from 950 to 1,250℃; Vanadium magnetite produces Fe, VO and VC 0.88 without V, and chromite magnetite produces Fe, Cr 2 O 3 , CrC x and a small amount of Cr. With an increase in the pre-reduction temperature, the metallization rate in the metallized pellets gradually increases, while the content of the residual carbon gradually decreases. Meanwhile, the iron particles precipitated on the surface of ore particles begin to soften into strips and finally agglomerate to form spherical iron particles, which leads to the diameter of iron particles increasing from 8.23 to 182.35 μm. When the pre-reduction temperature is 1,250℃, the maximum metallization rate in the metallized pellets is 92.49 wt% and the minimum content of residual carbon is 10.37 wt%.

In order to improve the alkali metals discharge capacity of slag, the gas-slag balance method was used to carry out the slag alkali metals discharge experiments, the effect of slag composition on alkali metals discharge performance of slag was studied, some suggestions were put forward to optimize the alkali metals discharge performance of slag and the extreme value model was established. The results show that the alkali metals discharge ratio of slag decreased with the increase in the binary basicity and mass fraction of TiO 2 , and increased with the increase in the mass fraction of MgO, Al 2 O 3 and MnO. The change in slag composition led to the change in the solubility of alkali metal oxides in liquid slag, decomposition of alkali metal silicates, structure of the slag in liquid state and viscosity of the slag, and then affected the alkali metals discharge performance of slag. The ability of slag to absorb alkali metals was certain under the condition of fixed composition. With the help of slag alkali metals discharge extreme value model, whether the current slag meets the needs of blast furnace alkali metals discharge could be evaluated. The alkali metals discharge capacity of slag could be improved by optimizing the alkali metals discharge performance of slag combined with experiments and actual production.

We performed a laboratory investigation at 1,873 K using a MoSi 2 furnace to study the effect of refractories on inclusions in 55SiCr suspension spring steel. Three types of crucible materials (Al 2 O 3 , MgO·Al 2 O 3 , and MgO–CaO) were investigated. The results of this study indicated that SiO 2 , Al 2 O 3 , and MgO·Al 2 O 3 were not suitable for making 55SiCr suspension spring steel. By contrast, MgO–CaO was a perfect choice for producing 55SiCr suspension spring steel. The advantages of using MgO–CaO crucibles to smelt 55SiCr spring steel were summarized in three aspects as follows: (i) the stability of MgO–CaO was quite good; (ii) a MgO–CaO crucible could act as a desulfurizer and dephosphorizer; (iii) finally, a MgO–CaO crucible could simultaneously remove Al 2 O 3 inclusions.

A novel hot-work die steel 5CrNiMoVNb is developed by optimizing the alloy composition of 5CrNiMoV steel. Thermal stability tests were carried out to compare the hardness evolution of the two steel types. The hardness reduction of 5CrNiMoVNb at 600 and 650°C was only 4.3HRC and 9.6HRC, while that of 5CrNiMoV steel at the same condition was as large as 6.5HRC and 17.5HRC, respectively, which suggests that the thermal stability of the 5CrNiMoVNb steel is more excellent. The thermal stability mechanism of 5CrNiMoVNb was studied based on microstructure analyses and thermodynamic calculations. This suggests that high tempering temperatures cause the coarsening of some carbides and suppress the recovery and recrystallization of the martensite matrix, which is the main reason for the slight decrease in the thermal stability. For the adding of the medium and strong carbide-forming elements, the carbides in 5CrNiMoVNb steel are mainly MC and M 23 C 6 with low coarsening rate coefficient, and the content of these two carbides is almost constant below 670°C. The fine MC and M 23 C 6 carbides showed strong pinning and dragging effects on the dislocations and suppressed martensite recovery and recrystallization. Therefore, the novel hot-work die steel showed excellent tempering softening resistance and thermal stability than 5CrNiMoV steel.

The forming-induced residual stress of metallic parts could cause undesired deformation in the final machining process, especially for the thin-walled parts. Therefore, heat treatment is essential to release the residual stress prior to machining. This study investigates the residual stress change of a forged pure iron part in annealing heat treatment and material removal processes. A modified creep constitutive model with the consideration of microstructure evolution was established to describe the residual stress relaxation in the annealing. Stress relaxation tests were conducted to calibrate the material constants. This constitutive model was then implemented into the finite element model of annealing for the cold-forged semi-spherical shell. The residual stress and the grain size of the shell were predicted at different heating temperatures. The semi-spherical shells were machined to the final thin-walled parts, and the deformation owing to the residual stress release was measured and compared to the simulation results. The heating temperature was determined aiming to minimize the machining-induced deformation as well as to ensure the microstructure. This study could provide guidance to the elimination of the residual stress and the improvement of the geometrical accuracy for thin-walled parts in the machining process.

Titanium alloy Ti6Al4V is widely used in aerospace, shipbuilding, petrochemical, and other industrial fields. Low-speed wire-cut electrical discharge machining (LS-WEDM) has the advantage of high machining accuracy. However, there are few research studies on the comprehensive effects of the electrical parameters of TC4 (Ti6Al4V) made by LS-WEDM on the machining surface. This paper focuses on LS-WEDM machining of titanium alloy TC4 and investigates the effects of electrical parameters on the surface roughness, kerf width, and cutting speed of TC4 specimens based on orthogonal tests. Five electrical parameters are optimized using the grey correlation method and the response surface method. The surface roughness of 1.744 μm, the kerf width of 215.432 μm, and the cutting speed of 24.759 mm 2 ·min −1 are found to be the best process indicators, with errors of 3.3, 3.2, and 12.5% compared with the predicted values. The optimized results show that the surface roughness value is reduced by 50.9%, the kerf width is reduced by 29.4%, and the cutting speed is increased by 23%, which proves the accuracy of the optimized method.

The effect of Cl − concentration on stress corrosion cracking (SCC) susceptibility of high manganese steel was investigated by slow strain rate tensile (SSRT) test, electrochemical test, and immersion test in different NaCl concentration solutions. The results show that the SCC susceptibility of the test steel first increases and then decreases with the increase in Cl − concentration. When the NaCl concentration was 10.5%, the SCC susceptibility was the highest, and the fracture showed river-like transgranular quasi-cleavage morphology, obvious tearing ridge, and strong brittle fracture characteristics. The corrosion current density of the sample first increases and then decreases with the increase in Cl − concentration in the corrosive medium. The corrosion electrochemical reaction and corrosion product layer play a synergistic role in SCC in low concentration Cl − medium. The enrichment of alloying element compounds in the corrosion layer leads to the local acidification below the corrosion layer, which promotes the anodic dissolution (AD) and forms pitting corrosion on the substrate surface. When the Cl − concentration is high, the local AD and hydrogen embrittlement (HE) caused by the dissolved oxygen will be weakened, and SCC susceptibility is reduced.

In view of the characteristics of dynamic basic oxygen furnace (BOF) steelmaking process, prediction models based on backpropagation neural network and incremental learning (BPNN-IL) are proposed for total blow oxygen volume and second blow oxygen volume. The incremental learning is to adjust weights and thresholds of the BPNN according to the difference between the predicted value and actual value of each heat and to adapt to the change in furnace conditions. The combined BPNN-IL models are trained and tested by actual production data, and are further compared with multiple linear regression models and BPNN models. The results show that whether it is total blow oxygen volume or second blow oxygen volume, the BPNN-IL models could provide the most accurate prediction and the introduction of an incremental learning method could further improve the predictive accuracy. So the BPNN-IL method is effective in predicting the oxygen-blowing volume in the BOF steelmaking process.

FeCoCrNiMo high-entropy alloy was melted by vacuum arc melting. The alloys were vacuum annealed at 873, 1,073, and 1,273 K, respectively. X-ray diffractometer (XRD), scanning electron microscope (SEM), simultaneous thermal analyzer, microhardness tester, and universal testing machine were used to study the microstructure, the thermal stability, hardness and compression mechanics of as-cast and annealed FeCoCrNiMo alloys. The results show that the alloy is composed of face-centered cubic (FCC) phase and σ phase in both as-cast and annealed states, and the σ phase and μ phase can maintain structural stability at 873 K annealing temperature. The μ phase decomposes to form the σ phase after annealing at 1,073 K, and part of the σ phase dissolves in the FCC phase when annealed at 1,273 K. Both the as-cast and annealed alloys have a typical dendritic structure. The σ phase is enriched in dendrites, and the FCC phase exists between the dendrites. The microstructure of the alloys in the annealed state is more refined than that of the alloy in the as-cast state. In the 1,073 K annealed state, the FeCoCrNiMo alloy has the highest hardness, yield strength, and fracture strength. The fracture mechanism of the alloy is intergranular brittle fracture and cleavage fracture.

The Al 2 O 3 -based slags are playing important roles in the preparation of Cu–Cr alloy through self-propagating high-temperature synthesis (SHS) – Metallurgy method. However, the current research on Al 2 O 3 -based slag is mainly concentrated on steel metallurgical slag and electroslag remelting slag, and the research on aluminum thermal reduction slag with high content of Al 2 O 3 is still insufficient. Therefore, systematic studies of the physical properties of slag with high aluminum content were carried out in the present work, and the influence of CaF 2 , CaO, MgO, SiO 2 , and Na 3 AlF 6 on viscosities, liquidus temperatures, densities, and surface tensions of high Al 2 O 3 content slags was measured and analyzed. The results indicated that CaO and CaF 2 have positive effects on the physical properties of Al 2 O 3 -based slags, MgO has positive effects when its content is not over 3%, and SiO 2 and Na 3 AlF 6 have negative impacts. CaO, CaF 2 , and MgO (not over 3%) could be used as additives to improve the metallurgical performance of Al 2 O 3 -based slags in aluminothermic reduction–slag refining method.

In this paper, four kinds of coatings Ni + 30% WC, Ni + 15% WC, Ni, and Co are prepared on EH40 steel by laser cladding technology. Electrochemical experiment tests at a simulating low-temperature (–40°C) environment in 0.5 mol·L −1 hydrochloric acid (HCl) solution and 3.5 wt% NaCl solution were conducted, and the polarization curve and electrochemical impedance spectroscopy (EIS) impedance spectrum were obtained. The results show that the Ni + 15% WC coating has the smallest corrosion current and 0.5 mol·L −1 HCl solution and 3.5 wt% NaCl solution have the maximum polarization resistance and impedance arc. Coatings will be treated in a 0.5 mol·L −1 HCl solution and 3.5 wt% NaCl solution at –40°C immersion for 30 days; finally, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used for test passivation films of Ni + 15% WC samples and sample surface morphology after corrosion. XPS results show that Fe, Mo, and Ni elements can form metal oxides in the 0.5 mol·L −1 HCl solution, and Cr, Fe, Mo, Ni, and W elements can form metal oxides in the 3.5 wt% NaCl solution. SEM results display that relatively severe corrosion appeared on the substrate near tungsten carbide in a 0.5 mol·L −1 HCl solution, and coating will be corroded form inside of the coating owing to the corrosive solution will penetrate the substrate. In 3.5 wt% NaCl solution, severe corrosion of the substrate has not been observed; however, the binding part has been obviously corroded.

This article presents a new Ruhrstahl–Heraeus top slag modifier with an enhanced modification effect at an enterprise producing O5 automobile sheets. To compare the modification effect of the original and new modifiers, the thermodynamic and dynamic conditions of the top slag modification were studied by thermodynamic calculations and dynamic analysis. The results showed that the utilization of both modifiers reduced the total iron (TFe) content in the top slag. The new modifier controlled the CaO/Al 2 O 3 (C/A) and TFe content of the top slag to approximately 1.22–1.30 and 6.07–7.97%, respectively. The adsorption capacity of top slag for inclusions was stronger than that of the top slag modified with the original modifier. The concentrations of Al 2 O 3 -type inclusions, Ti x O·Al 2 O 3 composite inclusions, and oxide inclusions were reduced by 13.4, 21.2, and 3.4 per cm 2 with the new modifier compared with the original modifier. The total oxygen content in molten steel was 2.8 ppm lower than that of the original when the new modifier was used. Moreover, the new modifier exhibited a better dynamic condition on the surface of top slag, as determined by R-G-B numerical analysis. Overall, the new modifier improved the dynamic conditions of top slag modification, reduced top slag oxidation, and effectively improved the cleanliness of the molten steel.

There are few studies on the shape and structure of the channel-type induction heating tundish on multi-physics field. Computational fluid dynamics has been used to study the influence of the structure of the tundish on the macroscopic transport behavior of the tundish with channel induction heating. The results show that increasing the depth of the molten pool is conducive to dynamic behavior of multiphase, the deeper the molten pool, the larger the active area, the longer residence time, the more inclusions removal and the higher ratio of plug to dead volume. Meanwhile, the larger the channel diameter, the more inclusions removal in the receiving chamber and channel. The channel induction heating has enough ability to increase the superheat and temperature compensate for the heat loss caused by the excessive residence time of the molten steel in the tundish. The change in the channel structure is crucial to the macroscopic transport behavior of the fluid. The change in channel diameter has the greatest effect on the multi-physics field in the molten pool.

This study shows the application of microwave sintering (MS) on preparing NbC–10Ni and NbC–12Ni cermets, as well as the effect of its microstructure, phase formation, and mechanical properties. Results indicated that NbC–Ni cermets with a fine and uniform structure can be obtained by MS in a relatively short time. And the sintering temperature greatly influenced the microstructure and mechanical properties of NbC–Ni cermets, whereas the effect of dwell time is relatively small. With the increase of the sintering temperature, the microstructure of NbC–Ni cermets experienced sintering densification and grain growth. The strength and toughness increased first and then decreased, and the hardness increased with the increase of sintering temperature. According to the comprehensive mechanical properties, the optimized sintering process is 1,390°C and the dwell time is 15 min. At this time, no new phase formed, but the diffraction peak of the Ni phase shifted. Through analysis, it is found that the improvement mechanisms for comprehensive mechanical properties of NbC–Ni cermets mainly include grain refinement, crack deflection and bridging, and energy absorption of the ductile phase of Ni.

Based on the exit temperature in the aluminium extrusion process, the quality of the aluminium bars is obtained in the industries. Control of temperature plays a significant role to obtain the quality of the aluminium bars or rods. Problems are still encountered in the design of proper temperature control schemes in the industries. A new control scheme is presented here, to address the temperature control in the aluminium extrusion process. Spider-based fractional-order PID controller scheme is simulated for the aluminium extrusion plant using MATLAB and its toolbox. It gives the improved result for reducing the time delay, rise time and settling time in the process. Integral square error performance criteria are considered an objective function. The minimization of objective function gives good results. Comparisons of the presented control scheme with the conventional control methods are presented.

Low-carbon, green and intelligent production is urgently needed in China’s iron and steel industry. Accurate prediction of liquid steel composition at the end of basic oxygen furnace (BOF) plays an important role in promoting high-quality, high-efficiency and stable production in steelmaking process. A prediction model based on the principal component analysis (PCA) – genetic algorithm (GA) – back propagation (BP) neural network is proposed for BOF end-point P and O contents of liquid steel. PCA is used to eliminate the correlation between the factors, and the obtained principal components are seen as input parameters of the BP neural network; then, GA is employed to optimize the initialized weights and thresholds of the BP neural network. The flux composition and bottom blowing are considered in the input variables. The results indicate that the prediction accuracy of the single output model is higher than that of the dual output model. The root-mean-square error of P content between predicted and actual values is 0.0015%, and that of O content is 0.0049%. Therefore, the model can provide a good reference for BOF end-point control.

7N01-T4 aluminum alloy is widely applied to high speed train body material attributed to its excellent comprehensive mechanical properties; however, its high sensitivity to hydrogen stress corrosion would seriously restrict its further application. In this study, the hydrogen-induced stress corrosion of the base metal and the joint was investigated under slow strain rate test to ascertain the characteristics and mechanism of hydrogen-induced stress corrosion cracking of aluminum alloy. By applying the cathode potential, the morphology of tensile port was studied. Results show that under the action of tensile stress, the free atomic hydrogen produced in the corrosion process or absorbed hydrogen diffuses along the grain boundary into the crack tip region, weakens the grain boundary and causes hydrogen embrittlement, thus accelerating the crack propagation and fracture. These properties provide a broader prospect for the application of 7N01-T4 aluminum alloy in high-speed train body.

In this study, the ductile iron ingots are cast using a metal mold, and the riser neck diameter is changed to control the micro-shrinkage porosity, which can affect the ultra-low temperature toughness of ferritic ductile iron. The metallographic structure and micro-shrinkage porosity were observed by an Axiovert200 MAT measurer metallographic microscope and an MLA 250 (FEI quanta) scanning electron microscope, and the number and diameter of graphite nodules and micro-shrinkage porosity size were measured by Nano Measurer 1.2 software. The effect of micro-shrinkage porosity on the ultra-low temperature toughness of ferritic ductile iron was studied. It is found that the impact energy of ductile iron decreases with the increase of micro-shrinkage porosity size, and the influence of micro-shrinkage porosity is more obvious with the decrease of temperature. The results point out that the micro-shrinkage porosity becomes the key factor affecting the ultra-low temperature impact toughness of ductile iron when the spheroidization rate of ferritic ductile iron is greater than 98% and the number of graphite nodules is more than 810 mm −2 . The impact energy of ferritic ductile iron can still reach more than 12 J at −70°C when the length of micro-shrinkage porosity is less than 3.7 μm.

Herein, the surface decarburization and oxidation characteristics of Cr–Mo cold heading steel are investigated via optical microscopy, scanning electron microscopy, and electron backscatter diffraction under different temperatures. Furthermore, the competitive mechanisms of decarburization and oxidation are analyzed. The results indicate that the heating temperature considerably affects the decarburization and oxidation characteristics of the steel sample. With an increase in the temperature, the depth of the total decarburization layer increases. The fully decarburized layer is prominent between 750 and 850°C and culminates at 800°C. The oxide thickness parabolically increases, and Cr 2 O 3 is present, which inhibits oxidation. Between 700 and 950°C, the oxidation weight gain is slow. The main structure of the oxide scale is the dense Fe 3 O 4 layer, inhibiting decarburization. The oxidation rate increases at 950°C, and the proportion of loose FeO layer in the oxide scale exceeds 66%, promoting decarburization. At >1,000°C, the surface decarburization and oxidation rate simultaneously increase.

Connecting small pieces of parts manufactured by Selective Laser Melting (SLM) and traditional formed parts into large structural component by using welding technology provides a high-efficiency and low-cost way for expanding additive manufacturing technology. SLMed parts usually exhibit similar or superior tensile strength but lower ductility compared to that of cast or rolled ones due to the rapid cooling and cyclic heating deposition characteristics. What about the weldability of the dissimilar joints of SLMed parts and rolled ones? Whether the properties of the welded joints can be improved by heat treatment under the premise of ensuring the reliability of the joint is unclear. The weldability and the effect of heat treatment temperature on the microstructure and properties of laser-welded joints of SLM-316 L/rolled-316 L are studied in this article. The results show that the joints exhibit good weldability without obvious defects. The low temperature annealing treatment had no significant effect on the multilayered structure and columnar austenite grains, but only changed the morphology and content of ferrite within the grains leading to the slight increase of elongation but decrease of material strength. The corrosion performance was almost unaffected. After solution annealing above 1,000°C, the ferrite was nearly dissolved in the austenite matrix. The austenite recrystallized and the multilayered structure was destroyed, which resulted in decrease of material strength, a slightly improvement in corrosion resistance, and the elongation was greatly enhanced. After the detailed study, it was concluded that the post-weld heat treatment provided an effective way for improving the overall performance of the SLM-316 L/rolled-316 L dissimilar joint.

Nickel base superalloy René 65 is a cast-wrought derivative of René 88DT. Lower cost and comparable physical properties allow René 65 to serve as a promising candidate material for turbine disks in next-generation aeroengines. The cast-wrought route leads to significant segregation of solute elements during solidification of René 65, which should be reduced by a proper homogenization scheme. We use René 65 samples from a Ø 450 mm electros-slag remelting ingot (sample Disk I) and a Ø 250 mm pilot vacuum arc remelting ingot (sample Disk II) to investigate as-cast microstructure and homogenization schemes of the alloy. It is discovered that γ–γ′ eutectic phase, borides–carbides, and TiN are the major precipitated phases in as-cast René 65 and Ti, Nb, Mo, and W are the critically segregated elements. The temperature too high to homogenize René 65 is found to be ≥1,190°C due to defect generation and straightening grain boundaries, whereas 1,140°C is too low due to undissolving γ–γ′ eutectic phase. The acceptable temperature among the selected temperatures is found to be 1,160°C. Thermal compression using homogenized samples reveals that in Disk II 1,160°C for 50 h provides the lowest flow stress. Estimation based on kinetics predicts that the equivalent deformation effect in Disk I is obtained at 1,160°C for 82 h.

The aim of this article is to explore the effect of re-melting times on the microstructure and properties of Fe-based coating. In this study, the Fe-based coating is prepared on 316L stainless steel by laser cladding and laser re-melting. Meanwhile, the microstructure and properties of the coating are studied by 3D laser scanner, Vickers microhardness tester, X-ray diffractometer, and scanning electron microscope. In addition, the effect of laser re-melting times on microstructure formation that is analyzed by numerical simulation. The results show that re-melting can lead to the decrease in coating height, increase in coating width, and increase in both depth and width of melting pool. The hardness of coatings is enhanced by six times compared with the substrate. However, it was found that the hardness of the coating decreased with the increase in laser re-melting times. The abnormal decrease in hardness was analyzed because of the continued growth of crystals in the coating and an increase in the coating dilution rate. The first laser re-melting results in the obvious change of coating crystal. The crystals of the multiple laser re-melting coating continue to grow. Our research results can provide reference for laser multiple re-melting in industry.

With the development of the duplex converter process, the amount of dephosphorization furnace slag is increasing, and it has relatively low basicity. It has been indicated that the recovery of valuable elements from dephosphorization slag by carbothermic reduction has great environmental and economic benefits due to its high content of P, Fe, and Mn. In this work, the experimental slag was reduced by carbon powder in a resistance furnace at 1,550°C. The results show that 76.82% of P, 99.60% of Fe, and 11.82% of Mn in the slag are recycled at basicity 1.0, and the recovery ratios of P, Fe, and Mn are 34.58, 78.89, and 13.85% at basicity 2.0, respectively. The ferrophosphorus obtained from the reduction of the dephosphorization furnace slag can be used as a raw material for steel-making alloy, and the residual steel slag can be used as cement and other building materials. This work provides a reference for recycling and resource utilization of dephosphorization furnace slag.

In order to study the long-time safe storage performance of GaTo modified double base propellant, the accelerated aging tests at 65, 70, 75, and 85°C were conducted. The chemical stabilities, mechanical properties, and microstructure of the propellant samples were characterized by differential scanning calorimeter, bromize-titration, impact resistance testing, and field emission scanning electron microscopy in the aging duration. The results showed that the chemical stability of propellant became worse due to nitrate esters decomposition. The impact resistance degradation is the result of binder network collapse, phase separation between binder and plasticizer, and interfacial dewetting during aging. Hence, the storage life of the propellant at ambient temperature has been evaluated based on stabilizer depletion and impact resistance deterioration via Arrhenius approach

Recently, casting simulations have been used to improve the product quality and the yield during casting. However, there are cases in which the simulation results do not reproduce the defects in the product. Although accurate physical property values are necessary for highly accurate simulations, some physical property values are not dependable. Recently, the occurrence of defects, such as shrinkage porosity, has been compared between simulated results and actual products by varying the physical property values given in the simulation. It has been shown that the heat value of the exothermic sleeve in the catalog used to reduce defects may be approximately one-seventh of the actual heating value. In this study, we developed an adiabatic calorimeter with a simple configuration that can realize actual casting conditions. The heat generated by the three types of exothermic sleeves was measured. No difference in calorific value was observed between the three types of samples, and all were approximately 2 kJ·g −1 . This value is less than the half of that provided in the catalog.

The thermodynamics of the phase equilibria in the Al–Fe–Zn–O quaternary system was studied using the calculation of phase diagrams method to understand the oxidation behavior of the Zn bath surface during galvanizing process. The thermodynamic parameters for the Gibbs energies of the different constituent phases in the binary and ternary systems relevant to this quaternary system were taken mainly from previous studies. In this study, the thermodynamic assessment of the Al 2 O 3 –ZnO system was carried out based on the available experimental data, and some modifications to the thermodynamic model and/or parameters for the Fe–Zn–O ternary system were made to maintain consistency with the thermodynamic descriptions of other binary and ternary systems, making up the Al–Fe–Zn–O quaternary system adopted in this study. The calculated results on the ternary and quaternary systems generally agreed with the available experimental results on phase equilibria. The set of thermodynamic parameters enabled us to calculate the phase equilibria in the Al–Fe–Zn–O quaternary system over the entire composition and temperature ranges.

The effect of rare earth Y on precipitates and textures of the grain-oriented silicon steels, the composition, morphology, size, quantity of inclusions and texture evolution of hot-rolled and cold-rolled oriented silicon steel containing rare earth Y were studied using transmission electron microscopy, field emission scanning electron microscope, and electron backscatter diffraction. The results show that there are mainly spherical or ellipsoidal Y 2 O 2 S precipitates in the Y bearing silicon steel. Rare earth treatment effectively improves the precipitates’ morphology and restrains the precipitation of the long-strip MnS in the hot-rolled plate. Meanwhile, the microstructure is more uniform, and the recrystallized grains on the surface and the fiber structure in the central layer are larger after hot rolling compared with Y-free steel. Furthermore, with the addition of rare earth Y, the unfavorable brass texture and rotational cube texture in the hot-rolled plate are reduced. Meanwhile, the number of shear bands is increased and the strength of the favorable {111} 〈112〉 texture is improved in the cold-rolled plate, which helps develop the Goss texture during the annealing process.

O 2 mixed with CO 2 gas has been successfully applied in converter smelting; however, up to now, there have been few studies regarding the jet characteristics of the mixed injection of the swirl oxygen lance nozzle and the influence of different ambient temperature conditions on jet characteristics compared with common nozzles. In this study, Fluent software was used to simulate the jet characteristics of a four-hole common nozzle and a four-hole swirl nozzle under four different ambient temperature conditions to inject 95% O 2 + 5% CO 2 and analyze the influence of different ambient temperatures on nozzle-jet characteristics. The results show that with an increase in the ambient temperature, the jet-axis velocity and nozzle centerline speed increase. Under the same distance condition, the distance between the maximum radial velocity point of the jet and the centerline of the nozzle becomes larger, with a velocity greater than that of the swirl nozzle. However, the influence of the ambient temperature on the offset of the jet centerline is small. With an increase in the ambient temperature and distance, the jet-axis temperature increases and the temperature of the nozzle centerline decreases. The research results can provide a theoretical reference for the optimal design of a CO 2 + O 2 swirl oxygen lance nozzle.

Aiming at the problem of optimising the temperature field distribution of a multi microwave source agent system, in this work, group consistency is used to explore the multi microwave source agent collaborative tracking strategy to improve both the uniformity of the temperature distribution and the heating efficiency. First, to coordinate the inputting power state information of the multi microwave source agents, a consistency algorithm of non-fully connected communication topology is adopted. Second, according to the efficiency state information of the microwave source agents in different distribution positions of the cavity, the agent group consistency strategy and the group consistency strategy with expected power deviation are used to adjust the power distribution of each agent. Finally, the feasibility and effectiveness of the proposed strategy are verified by using heating materials with different specifications. The experimental results show that compared with the traditional multisource heating method the proposed temperature distribution optimization strategy based on group consistency can improve the temperature uniformity and heating efficiency.

The high-temperature deformation behavior of Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si alloy with initial lamellar microstructure was investigated through performing hot compression experiments at temperatures of 940–1,030°C and strain rates of 0.001–10 s −1 on the Gleeble-3500 simulator. Three kinds of typical flow curves corresponding to different strain rates were distinguished. The deformation activation energy and Zener–Hollomon parameter were obtained through kinetic analysis. By comparing saturated dislocation density with the critical density for dynamic recrystallization, dynamic softening behaviors were identified and verified by the Poliak–Jonas criterion. Furthermore, a piecewise physical-based constitutive model incorporating dynamic softening behaviors was constructed. Finally, microstructures deformed under different deformation conditions were analyzed to further verify the softening behaviors determined by identification criterions.

Welding of Inconel is a difficult task due to its tendency to crack and posing intricacies to the welder. However, it is extensively used in applications where resistance to oxidation at elevated temperatures is required. Therefore, it is important to note that the welding of Inconel alloys is demanding. Under such circumstances, one has to automate the welding of Inconel 617 alloy to eliminate some of the process uncertainties. Plasma arc welding (PAW) is a highly non-linear process that can be automated easily, and it can provide more focussed arc to weld the high strength and creep-resistant alloys. In the present research, PAW process is employed on 2 mm thick Inconel 617 plates by varying the key process parameters, such as welding current and welding speed. Initially, bead on plate (BoP) experiments were conducted to determine the suitable range of welding parameters to weld the super alloy. Subsequently, butt welding of the plates was performed based on the results of BoP welding. Furthermore, a study was conducted to determine the influence of the welding process parameters on the microstructural and mechanical properties of the butt joints.

Based on the three-dimensional field of molten pool and twin-roll strip casting experiments, this work verified the cracking mechanism of the strip by establishing mathematical model and rolling experiments. The results showed that due to the instability of the thermophysical field of the molten pool and the inconsistency of kiss curve height, the newly solidified strip will undergo incompatible deformation through the rolling. The stress concentration will appear around the large reduction area and then form slip bands. When plastic strain exceeds the limit of the metal, the oblique cracks will appear in the slip bands periodically or completely penetrate the strip. In addition, tensile cracks could also be produced by incompatible deformation. Therefore, keeping the uniformity and stability of the thermal physical field in molten pool is the key factor to restrain cracks.

In the precision machining of thin-walled planar components, the initial residual stress of the workpiece could lead to subsequent deformation after machining, which influences the geometrical accuracy of the final parts. Generally, conventional methods, such as stress-relief annealing and vibration stress relief, are implemented to reduce the magnitude of the residual stress. However, the distribution of the residual stress, which is more significant to the machining accuracy for thin-walled parts, is difficult to be adjusted in these methods. This article proposes a novel method to control the stress distribution and magnitude during the manufacturing process and thus reduce the machining-induced deformation for the thin-walled planar part of pure copper. In this method, symmetrical distribution of residual stress is introduced by multi-pass rolling, quenching, stress-relief annealing, and turnover turning. The stress field and deformation of the part are predicted by finite element modeling in the whole process. The part deformation after machining is verified by the experiments. The results show that compared with the traditional stress-relief annealing, this novel method could reduce the part deformation after machining and improve the geometrical accuracy for thin-walled parts.

Aiming at the crane scheduling problem for uncertainty tasks in multi-crane scheduling situation, this article proposes a deep reinforcement learning-based crane scheduling modeling method that is not dependent on mathematical planning and has certain generality. First, the crane scheduling process is integrated into deep reinforcement learning framework in which the orbit space of the crane and the transportation task is environmental information and crane is the intelligent agent. Second, the interactive mode between reinforcement learning algorithm and environment is adjusted to adapt to the combined learning of multi-crane scheduling model. Last, the crane scheduling model for uncertainty tasks is constructed by optimizing reward discount factor, learning rate, and reward function intensive mode. Testing of the model is carried out based on practical crane scheduling in one steelmaking workshop. Scheduling proposal is generated and all crane tasks are completed within the planned time, which verifies the feasibility of this model. Results show that compared with manual scheduling plan, the scheduling proposal based on the new model reduces total task completion time by 11.52%, time of collision of crane routes decreases by 57.14%, and negative crane transportation distance shortens by 55.26%. The high efficiency of the scheduling model is therefore verified.

Exploration of suitable partner materials (so-called buffer layer or n-type emitter) for each light-absorbing material is essential to practicalize various emerging photovoltaic devices. Motivated by our recent discovery of a partner material, Mg(Mg x Zn 1− x ) 2 P 2 , in Mg/Zn 3 P 2 solar cells, the related series of materials M Zn 2 P 2 ( M = Ca, Sr, Ba) is of interest to the application in pnictide-based solar cells. In this study, we synthesize these materials to evaluate the optoelectronic properties concerning photovoltaic applications. To deal with the difficulties of the high vapor pressure and reactivity of the constituent elements, we utilized Sn as a solvent to reduce their activities during heat treatments. Powders that are mainly composed of M Zn 2 P 2 were obtained by crushing the samples after solution growth, although single-phase crystals of M Zn 2 P 2 could not be obtained in this study. The optical bandgap and the ionization potential of each M Zn 2 P 2 were evaluated through the diffuse reflectance and the photoelectron yield spectroscopy measurements of the powder. As a result, we found that CaZn 2 P 2 would be a promising partner material in photovoltaics based on Zn 3 P 2 and ZnSnP 2 .

A fundamental understanding of crystal growth dynamics during directional solidification of multicrystalline Si (mc-Si) is crucial for the development of crystal growth technology for mc-Si ingots for use in solar cells. In situ observation of the crystal/melt interface is a way to obtain direct evidence of phenomena that occur at a moving crystal/melt interface during growth. In this review, some of the phenomena occurring in the solidification processes of mc-Si are introduced based on our in situ observation experiments, after a brief introduction of the history of the development of crystal growth technologies to obtain mc-Si ingots for solar cells.

Due to the detrimental effects of boron (B) on the efficiency of silicon (Si) photovoltaic cells, complete boron removal from Si is necessary to produce solar grade Si (SoG–Si, with a maximum limit of 0.1 ppmw boron). Gas refining is a promising technique for boron removal from Si, in which the thermodynamic equilibrium never establishes. Hence, by starting from any B concentration in the melt, the required limit for SoG–Si will be achieved. This research is devoted to studying the refractory interactions’ effect with melt and the chamber atmosphere on boron removal. For this purpose, gas refining experiments were carried out in alumina and graphite crucibles with H 2 and H 2 –3% H 2 O refining gases. Gas refining in Ar, He, and continuous vacuuming conditions were also carried out to study the effect of chamber atmosphere. The gas refining results are supported by the characterization of the evaporated species by molecular beam mass spectroscopy (MBMS) technique. The MBMS measurements indicated that the boron evaporation occurs by the formation of the volatile species BH x , BO y , and B z H x O y compounds. Most of these compounds are already known in the literature. However, HBO, HBOH, and AlBO (in the case of alumina refractories) were measured experimentally in this work. Results indicate that the evaporation of B in the form of AlBO x compounds leads to higher mass transfer coefficients for boron removal in alumina crucibles. Density-functional theory (DFT) and coupled cluster calculations are carried out to provide a thermodynamic database for the gaseous compounds in the H–B–O–Al system, including enthalpy, entropy, and C P values for 21 compounds.

Silicon was recovered from solar cell Si scraps through 42.5 mol% SiO 2 –42.5 mol% CaO–15 mol% Al 2 O 3 slag refining. The motion behaviors of Si 3 N 4 and SiC were observed in situ and real-time using a high-temperature laser confocal microscope, and the recovery of Si through slag refining was carried out at 1,500°C for 30 min. Results indicated that both SiC and Si 3 N 4 inclusions were concentrated in the slag, and this work provides a clear framework for recycling and reusing solar cell Si scraps.

Silicon solar cells are crucial devices for generating renewable energy to promote the energy and environmental fields. Presently, high-purity silicon, which is employed in solar cells, is manufactured commercially via the Siemens process. This process is based on hydrogen reduction and/or the thermal decomposition of trichlorosilane gas. The electrochemical process of producing silicon has attracted enormous attention as an alternative to the existing Siemens process. Thus, this article reviews different scientific investigations of the electrochemical production of silicon by classifying them based on the employed principles (electrorefining, electrowinning, and solid-state reduction) and electrolytes (molten oxides, fluorides, chlorides, fluorides–chlorides, ionic liquids [ILs], and organic solvents). The features of the electrolytic production of silicon in each electrolyte, as well as the prospects, are discussed.

Zn 3 N 2 (ZN) and ZnSnN 2 (ZTN) are a promising class of nitride semiconductors for photovoltaic and light-emitting-diode applications due to their particular electrical and optical properties, elemental abundance and non-toxicity. So far, most of the experimental results show the degenerate carrier concentration. However, we find that low-temperature growth of these films in a chamber with ultra-high background vacuum can attain a non-degenerate electrical conductivity. This work provides the recent progress of the electrical properties of ZN and ZTN semiconductor thin films. The origins for the high carrier concentrations in ZN and ZTN have been discussed, demonstrating that non-intentional oxygen and hydrogen-related defects play significant roles in such high carrier concentrations. The strategies to suppress the carrier concentrations have also been addressed, such as ultra-high vacuum conditions and low temperature growth.

The tribocorrosion performance of low-temperature steels is vital for use in hostile environments. This study aims to investigate the tribocorrosion behavior of FH36 low-temperature steel with two distinct microstructures of tempered martensite (TM) and tempered sorbite (TS), respectively. Also, the coefficient of friction, surface morphologies, electrochemical properties, and corrosion features of the two steels were investigated. The results showed that the TM and TS steel exhibited outstanding impact toughness values of 239 and 306 J at −60°C, respectively. The friction coefficient and the electrochemical impedance in the TM steel were lower than those of the TS steel, while the scratch was deeper and narrower in the TM steel. Both the microstructure and the electrochemical corrosion affect the wear resistance of the low-temperature steels during the tribocorrosion process. The friction can accelerate the adsorption of Cl − ions that enrich the pits near the scratches, and the pitting of the TM steel was severe.