Volume 64, Issue 1

Carbide-free bainite with filmlike retained austenite structure has been reported for its higher wear resistance and toughness compared with conventional bainite and pearlite structure. In order to take advantage from such beneficial structure, this study employs the surface welding method with self-shielded wire electrode containing low carbon (0.15 mass%), high silicon, and nickel on two pearlitic rail steels, R260 and R350HT. The preheating temperature and other welding parameters were carefully selected to avoid too high dilution, which leads to martensite formation. The weld metal, heat-affected zone, and base material were investigated by scanning electron microscopy. Microhardness and wear tests were carried out to ensure improved properties after the surface repair. The results show significant improvements in hardness and wear rate in weld metal compared with the base material.

Aluminum–plastic composites as building materials are widely used for different construction purposes, for instance, for exterior wall cladding, ventilated facades, and interior decoration of buildings, in billboards, trains, and automotive industry. The main goal of this study is to investigate the formability of AA3105/LDPE/AA3105 sandwich composite in detail, which would exhibit a higher formability compared to AA3105 due to its higher strain rate sensitivity and strain hardening exponent. This is of decisive importance for the manufacturing process. The Nakajima tests are performed to experimentally determine the forming limit curves (FLCs) using in situ optical technique digital image correlation. Furthermore, numerical simulations of Nakajima tests are conducted using a modified Gurson–Tvergaard–Needleman damage model to compare the numerically and experimentally determined FLCs. The results show that the sandwich composite underwent inhomogeneous deformation during the Nakajima test, and that the FLC has no typical patterns exhibited by metal sheets. The FLCs predicted by the numerical model used in this study exhibit a very good correlation with the FLCs determined experimentally. The results of the present study provide new insights into the analysis and understanding of the deformation behavior of the sandwich composite sheet that may undergo complex stress and strain states.

Additive manufacturing by laser metal deposition (LMD) requires continuous online monitoring to ensure quality of printed parts. Optical emission spectroscopy (OES) is proposed for the online detection of printing defects by monitoring minute variations in the temperature of a printed spot during laser scan. A two-lens optical system is attached to a moving laser head and focused on a molten pool created on a substrate during LMD. The light emitted by the pool is collected by an ultraviolet–visible (UV–vis) spectrometer and processed. Two metrics are used to monitor variations in the surface temperature: the spectrally integrated emission intensity and correlation coefficient. The variations in the temperature are introduced by artificial defects, shallow grooves, and holes of various widths and diameters carved on a substrate surface. The metrics show sufficient sensitivity for revealing the surface defects, except for the smallest holes with an under-millimeter diameter. Additionally, numeric simulations are carried out for the detection of emission in the UV–vis and near-infrared (NIR) spectral ranges at various surface temperatures. It is concluded that both the metrics perform better in the NIR range. In general, this work demonstrates that spectrally resolved OES suits well for monitoring surface defects during 3D metal printing.

The effect of heat treatment on the microstructure, hardness and wear resistance of modified hypereutectic high chromium cast iron (HCCI) was investigated. The results show that the quenching treatment partially dissolves the edges of the primary carbides, and the sharp corners become rounded and blunt. As the quenching temperature increases, the carbide re-dissolves into the matrix, and the hardness and wear resistance first increase and then decrease. The hardness and wear resistance are the best when quenched at 1000 °C. After tempering, the martensite is transformed into tempered martensite, and the precipitation of secondary carbides increases. As the tempering temperature increases, the secondary carbides gradually become coarser. When the tempering temperature is 500 °C, the hypereutectic HCCI shows the highest hardness and the best wear resistance. When tempered at 400 °C, hypereutectic HCCI shows the best erosion and wear resistance.

In this work, the ASTM A1011 steel substrate has been pack-boronized in the interval of 1123–1273 K for 2–8 h. With the used powders mixture (33.5 wt.% B 4 C, 5.4 wt.% KBF 4 and 61.1 wt.% SiC), the iron boride layers were formed on this steel. The boronized layer/matrix was characterized by a jagged morphology. X-ray diffraction technique was used in order to identify the presence of iron boride phase. Tribological studies were also undertaken to assess the interfacial adherence of boride layer to the substrate and the values of coefficient of friction (COF) for borided and unborided samples. In addition, the mean diffusion coefficient approach was employed to estimate the diffusivity of boron in Fe 2 B. Moreover, this diffusion model has been verified empirically by using an extra boriding condition (at 1248 K for 2 h).

Lithium bromide (LiBr) corrosion on austenitic 316 stainless steel (AISI 316) and copper will largely determine the overall performance of refrigeration compression systems. In this work, the corrosion behavior of AISI 316, copper, and brazed joint was studied in LiBr solution at different temperatures by using the polarization curve and electrical impedance spectroscopy. The morphology and chemical composition of the samples before and after corrosion were characterized to elucidate the corrosion mechanism. The passivation film of AISI 316 stainless steel is more prone to breakdown as the temperature increases, and the corrosion resistance of copper and brazed joint also decreases with the increasing temperature. Zero-resistance ammeter technology was employed to analyze the effect of temperature on galvanic corrosion. The degree of galvanic corrosion increases with temperature for all galvanic pairs (AISI 316-Cu, AISI 316-brazed joint, and Cu-brazed joint). For AISI 316-Cu and AISI 316-brazed joint galvanic pairs, AISI 316 functions as the cathode, while copper or brazed joint serves as the anode. For the Cu-brazed joint pair, the brazed joint is preferred to be corroded at room temperature, whereas at 50 and 75 °C, copper corrosion occurs in priority.

The effect of austempering treatment on metallurgical structure of X210Cr12 cold work tool steel inoculated with Ce was researched. Microstructural changes, elemental characterizations, and phase formations of the samples were examined by using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, elemental mapping, and microhardness test. Ce inoculation reduced the grain size, and the austenitizing temperature had a huge effect on the austenitizing process. The austenitizing process increased the hardness by reducing the retained austenite, but the degree was dependent on the austenitization temperature. The austempering treatment improved the hardness resistance by depositing more equal carbides composed of nano-sized carbides. High austempering period and increase of austempering temperature decreased the homogeneity and hardness of the microstructure.

Bake hardening sheets are frequently used materials in the automotive industry. The unique feature of these materials like hardening with the paint baking process is convenient for the manufacturer. Also, the bonding technique is a common issue for assembly lines. With new technologies regarding the welding process after the 1990s, the concept of welding has changed. In this study, the electron beam and laser beam sources, which are still considered new, are used for welding 260 BH bake hardening sheets used in the automotive industry as galvanized and non-galvanized. The characterization analysis of the mechanical behavior of the bonded materials was conducted. The macroscopic and microscopic structural modifications, as well as residual stresses, were measured, and they were compared with each other. From the experiments, very effective results have been found. The results were analyzed in detail from different perspectives in terms of material properties and types of weldment processes.

Ring-stiffened cylindrical shell is the main pressure structure of underwater carrier equipment, and the residual stress and deformation introduced by welding of ring-ribbed frame and cylinder body pose a great threat to the performance and safety of the structure. In this paper, finite element software is used to numerically simulate the residual stress and deformation caused by fillet welding. The influence of welding position, constraint tooling and post-weld heat treatment PWHT on the residual stress and deformation is analyzed systematically. The results show that the gravity has little effect on the welding residual stress and deformation, but it has a significant impact on deformation uniformity. Under the action of restraint, the welding distortion is effectively controlled, but it will lead to the increase of the overall stress level of the structure simultaneously. Heat treatment can dramatically diminish the welding residual stress at the expense of deformation, which may result in structural maladjustment.

Three Longmaxi Formation shale samples from different well depths were analyzed for their total organic carbon (TOC) content and mineral phases. Synchrotron-based multi-energy X-ray computed tomography (CT) slices have been acquired for these samples. Deviations of the sample center away from the harmonic trajectory during X-ray CT imaging were corrected to improve the accuracy of CT reconstructed tomographic slices. The three-dimensional (3D) distribution of porosity and mineral in the samples was derived using the data-constrained modeling (DCM) method. The equivalent spherical diameters of connected pore-organics clusters and the connection probabilities were calculated to evaluate the spatial agglomeration and the spatial correlation of pore-organics in the samples. Numerical results showed that the distribution of the connected regions size and the connection probabilities of pore-organics for three samples have similar characteristics. The connection probabilities versus the distance follow exponential law. The connection probability appeared to be positively correlated to the number of pore-organics connected clusters when the distance between the voxels is shorter than 10 μm. Comparing samples from the three well depths, both the numbers of connected regions and connection probabilities of the samples from a deeper well are higher. The approach would be applicable for structural characterization of other similar materials.

Titanium and its alloys take attention, especially in aerospace, automotive, and biomedical applications because of their strength, corrosion resistance, and biocompatibility. Titanium components, in general, are produced by sheet metal forming. However, the springback effect is a critical problem in the forming process due to difficult formability of titanium sheets. In the present study, the hot forming process was applied to sheets to investigate the effect of deformation temperature on microstructure, mechanical properties, and springback behavior of commercially pure grade 2 titanium sheets. The springback angles were measured at the CAD model after the sheets were scanned by the 3D scanner. The tensile test, hardness measurements, and microstructural analysis were examined by using specimens that were cut from the sidewall and the bottom of the deformed sheet as U-profile. The results reveal that the microstructure is substantially changed, and the springback is reduced with increasing temperature; thus, optimum results were obtained compared to the data obtained at room temperature.

The combined effect of resin containing nanoclay along with natural fibers elevates the mechanical properties. In addition, the dispersion of nanoclay at the fiber-matrix interface would create strong physical interaction between the two. The significant enhancement in mechanical properties is achieved for the composite containing 30 wt.% abaca fiber content and 2 wt.% nanoclay, which is treated by 8 vol.% NaOH concentration. The enhancement in the mechanical properties can be attributed to the wettability of fiber by the matrix, homogeneous distribution of fibers and nanoclay in the matrix phase and physical interaction between reinforcement and matrix. Increase in the addition of abaca fiber and nanoclay beyond the above mentioned content leads to drop in the mechanical properties. This can be due to many nanoclay agglomerates are not broken down to nano scale during preparation, it may also be the reason for drop in the mechanical properties.

Ultrafine metal wires have been widely used as structural constituents of metal meshes for electromagnetic interference shielding. To investigate the bending property of metal wires during the knitting process, the three-point bending, cantilever bending, and pure horizontal bending methods were carried out and compared. The relationships among the bending property, the twist pitch and the number of twisted wire strings were also analyzed. The specific dependence of the bending stiffness on twist pitch resulted from the internal frictional constraints, and a twist pitch of 4.5 mm was chosen as the optimized twisted parameter. The bending properties evaluated by the three methods were equally sensitive to the twist pitch, and a similar linear trend of bending stiffness with the number of twisted wire strings was found. The values of bending stiffness from the three methods were significantly different, and the descending order was the three-point bending, the cantilever bending, and the pure horizontal bending method. The correlation coefficient of the three methods was higher than 0.935, which is a strong positive correlation. From the investigation came a conclusion that the three-point bending method is more useful in realistic conditions because of its diversity and universality for various bending deformations.

A layer of TiO 2 nanotubes is widely used as a surface application on Titanium (Ti) implants because the nanotubes help promote cell adhesion and provide better cell response than the metal surface. Although several studies have reported the relationship between TiO 2 nanotubes and cell osseointegration rate, the corrosion rate of the TiO 2 nanotube layer under the circumstance of usage has yet to be fully evaluated. In this work, we have studied the effect of surface preparation conditions on the corrosion behavior of a TiO 2 nanotube layer on a pure Ti substrate. The surface of the titanium substrate was prepared by different methods, followed by one-step anodization to obtain a TiO 2 nanotube array. A surface roughness non-contact tester and field emission scanning electron microscope were used to characterize the surface roughness and surface morphology of the as-received, mechanically polished, and chemically polished substrate both pre and post anodization. The corrosion behavior of the prepared substrates was also investigated in Phosphate Buffered Saline solution using potentiodynamic polarization technique. The results suggest that surface roughness at the nanoscale of the prepared surfaces has no relationship with corrosion resistance. However, after anodization, the corrosion rate has a good relationship with the standard deviation of inner tube/pore diameter.