Volume 36, Issue 3 -

In this present study, the AISI 1025 steel was pack-borided in the temperature range of 1,123–1,273 K for different treatment times ranging from 2 to 8 h. A diffusion model was suggested to estimate the boron diffusion coefficients in the Fe 2 B layers. As a result, the boron activation energy for the AISI 1025 steel was estimated as 174.36 kJ/mol. This value of energy was compared with the literature data. To extend the validity of the present model, other additional boriding conditions were considered. The boride layers formed on the AISI 1025 steel were characterized by the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and the Daimler–Benz Rockwell-C indentation technique. Finally, the scratch and pin-on-disc tests for wear resistance were achieved using an LG Motion Ltd and a CSM tribometer, respectively, under dry sliding conditions.

Hot compression tests of sand casting and centrifugal casting Q235B flange blanks were performed at strain rate range of 0.01–5 s −1 and temperature range of 850–1,150 °C. The evolutions of microstructure and texture were revealed. The constitutive models based on Arrhenius constitutive modeling were proposed by considering the effects of strain on material constants. The results show that recrystallization in centrifugal casting Q235B is more apparent than that in sand casting, resulting in the finer grains and lower flow stress for centrifugal casting Q235B. The intensities of textures slightly weaken with the increase of temperature. At 1,050 °C and 5 s −1 , the textures of sand casting are characterized by strong {001}<100> and {001}<110>, which are related with severe deformation, while the textures of centrifugal casting are composed of {110}<110> and {111}<112>, which are related with dynamic recovery and shear deformation. A good agreement between the predicted and experimental flow stress is achieved and demonstrates that the proposed constitutive models are reliable.

The plasticity, elastic modulus and thermal stability restrict the applications of electrodeposited nanocrystalline Ni-Fe alloy foils. To improve its mechanical properties, the electrodeposited Ni-Fe alloy foils were heat treated within the temperature 900–1,150 °C. The microstructure and texture of the samples were further analyzed with a combination of SEM, XRD and EBSD. The experimental results indicated that the electrodeposited Ni-Fe alloy foil had poor mechanical properties at about 1,000 °C, which was mainly attributed to the development of a mixed grain microstructure. At 900–950 °C, the plastic and elastic modulus were greatly improved, which were owed to the uniformed microstructure and the decrease of structure defects. At 1,050–1,150 °C, the degree of the mixed grain microstructure decreased, resulting in improved plasticity and higher elastic modulus. However, the strength of the foil obviously decreased, which was mainly associated with the increase of the average grain size.

In the view of the exploring novel flame retardants for polymers, modacrylic fibers, which consist of acrylonitrile and vinylidene dichloride, containing metal oxide have been investigated by thermogravimetric–mass spectrometry (TG-MS) analysis. It was found that, among the examined oxides, germanium and antimony oxides formed the corresponding volatile chlorides through the reactions of oxides with hydrogen chloride formed during thermal decomposition of the polymer. The results have been discussed in the framework of thermochemistry. Based on the equilibrium calculation of the polymer–oxide mixture, the predominance diagrams of the M-O-Cl systems ( M  = Sb and Ge) show that the chlorides are the most stable phases at 573 K, at which temperature the major decomposition of the polymer starts. These results suggest that GeO 2 would be a possible candidate of a flame retardant for chlorinated polymers. However, combustion experiments revealed an insufficient performance of the oxide. The inductively coupled plasma with atomic emission spectroscopy (ICP-AES) analysis showed the reactivity of GeO 2 for HCl was inferior to that of Sb 2 O 3 , and X-ray fluorescence spectrometer (XRF) analysis of the solid thermal decomposition products showed that the evaporation of germanium was less intense than that of the conventional antimony system. This result is presumably due to the smaller rate of the chlorination of GeO 2 than that of Sb 2 O 3 .

The 1Cr18Ni9Ti stainless steel with Al-Si/Al-Si-Cr coatings is prepared by slurry process and vacuum diffusion, and the hot corrosion behavior of the stainless steel with/without the coatings is studied under the condition of Na 2 SO 4 film at 950 °C in air. Results show that the corrosion kinetics of stainless steel, the stainless steel with Al-Si coating and the stainless steel with Al-Si-Cr coating follow parabolic laws in several segments. After 24 h corrosion, the sequence of the mass gain for the three alloys is the stainless steel with Al-Si-Cr coating < the stainless steel with Al-Si coating < the stainless steel without any coating. The corrosion products of the three alloys are layered. Thereinto, the corrosion products of stainless steel without coating are divided into two layers, where the outside layer contains a composite of Fe 2 O 3 and FeO, and the inner layer is Cr 2 O 3 . The corrosion products of the stainless steel with Al-Si coating are also divided into two layers, of which the outside layer mainly consists of Cr 2 O 3 , and the inner layer is mainly SiO 2 . The corrosion film of the stainless steel with Al-Si-Cr coating is thin and dense, which combines well with substrate. Thereinto, the outside layer is mainly Cr 2 O 3 , and the inside layer is Al 2 O 3 . In the matrix of all of the three alloys, there exist small amount of sulfides. Continuous and protective films of Cr 2 O 3 , SiO 2 and Al 2 O 3 form on the surface of the stainless steel with Al-Si and Al-Si-Cr coatings, which prevent further oxidation or sulfide corrosion of matrix metals, and this is the main reason for the much smaller mass gain of the two alloys than that of the stainless steel without any coatings in the 24 h hot corrosion process.

Cooling effects of the cast iron cooling stave were tested with a specially designed experimental furnace under the conditions of different temperatures of 800 °C, 900 °C, 1,000 °C and 1,100 °C as well as different cooling water velocities of 0.5 m·s –1 , 1.0 m·s –1 , 1.5 m·s –1 and 2.0 m·s –1 . Furthermore, the combined heat transfer coefficient of hot-face on cast iron cooling stave ( α h−i ) was calculated by heat transfer theory based on the thermal test. The calculated α h−i was then applied in temperature field simulation of cooling stave and the simulation results were compared with the experimental data. The calculation of α h−i indicates that α h−i increases rapidly as the furnace temperature increases while it increases a little as the water velocity increases. The comparison of the simulation results with the experimental data shows that the simulation results fit well with the experiment data under different furnace temperatures.

In this article, the corrosion behavior of stainless steel 316L in a low melting point novel LiNO 3 -NaNO 3 -KNO 3 -NaNO 2 eutectic salt mixture was investigated at 695 K which is considered as thermally stable temperature using electrochemical and isothermal dipping methods. The passive region in the anodic polarization curve indicates the formation of protective oxides layer on the sample surface. After isothermal dipping corrosion experiments, samples were analyzed using SEM and XRD to determine the topography, corrosion products, and scale growth mechanisms. It was found that after long-term immersion in the LiNO 3 -NaNO 3 -KNO 3 -NaNO 2 molten salt, LiFeO 2 , LiFe 5 O 8 , Fe 3 O 4 , (Fe, Cr) 3 O 4 and (Fe, Ni) 3 O 4 oxides were formed. Among these corrosion products, LiFeO 2 formed a dense and protective layer which prevents the SS 316L from severe corrosion.

MgCl 2 -KCl binary system has been proposed to be used as high temperature reactor coolant. Due to its relatively low melting point, good heat capacity and excellent thermal stability, this system can also be used in high operation temperature concentrating solar power generation system as heat transfer fluid (HTF). The corrosion behaviors of nickel based alloys in MgCl 2 -KCl molten salt system at 1,000 °C were determined based on long-term isothermal dipping test. After 500 h exposure tests under strictly maintained high purity argon gas atmosphere, the weight loss and corrosion rate analysis were conducted. Among all the tested samples, Ni-201 demonstrated the lowest corrosion rate due to the excellent resistance of Ni to high temperature element dissolution. Detailed surface topography and corrosion mechanisms were also determined by using scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS).

Deformation of AZ61-F magnesium alloys with 1 wt % of Al 2 O 3 phase was tested at different temperatures and different strain rates. It was shown that at temperatures 473–523 K and the highest strain rate applied from 1×10 –2 s –1 to 1×10 –4 s –1 , a significant ductility growth was observed. The grain size of 0.6–0.8 μm was reached by severe plastic deformations by means of equal channel angular pressing (ECAP). Secondary Mg 17 Al 12 and Al 2 O 3 phases were identified. Maximum strain was gained at temperature of 473 K and strain rate of 1×10 –4 s –1 .

Ti-17 titanium alloy was treated by laser shock processing (LSP) and the high-frequency fatigue properties were evaluated. The fatigue fracture and the microstructures were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The result shows that the average fatigue life of the LSP sample increases 2.62 times at maximum stress 300 MPa under stress ratio is 0.1. The micro-hardness of the samples subjected to LSP increases 20 % compared with the basic material. The proliferation and tangles of dislocations of Ti-17 occurs and the density of dislocation increases after LSP treatment. The high dislocation density of LSP impacts changes the initiation of crack from corner to subsurface, and hinders the crack extension, thus increases the fatigue performance of the Ti-17.

CMSX 4 and Inconel 625 superalloys were coated by platinum layers (3 and 7   μm thick) in the electroplating process. The heat treatment of platinum layers (at 1,050   ˚C for 2 h) was performed to increase platinum adherence to the superalloys substrate. The diffusion zone obtained on CMSX 4 superalloy (3 and 7   μm platinum thick before heat treatment) consisted of two phases: γ-Ni(Al, Cr) and (Al 0.25 Pt 0.75 )Ni 3 . The diffusion zone obtained on Inconel 625 superalloy (3   μm platinum thick before heat treatment) consisted of the α-Pt(Ni, Cr, Al) phase. Moreover, γ-Ni(Cr, Al) phase was identified. The X-ray diffraction (XRD) results revealed the presence of platinum in the diffusion zone of the heat-treated coating (7   μm platinum thick) on Inconel 625 superalloy. The surface roughness parameter Ra of heat-treated coatings increased with the increase of platinum layers thickness. This was due to the unequal mass flow of platinum and nickel.

In this work, a pleonastic compound, a compound with a composition between hercynite and spinel sensu stricto FeAl 2 O 4 –MgAl 2 O 4 , was synthesized by a non-conventional method of arc-plasma synthesis (APS). The structure of the obtained spinel compound was characterized by means of X-ray diffraction and Mössbauer effect measurements. The microstructure was observed by applying scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) method. It was found that the arc-plasma synthesized material was characterized by a monophasic character, a low-inversion parameter and a compact microstructure.