Journal of Materials Engineering and Performance最新文献

Additive manufacturing (AM) is a preferred industrial manufacturing method for modeling and rapid prototyping of physical systems. The final product in AM must have appropriate mechanical properties, such as flexural strength and be of good quality. The selection of printing parameters is essential for this reason. In this study, three critical printing parameters, such as layer thickness (100-200-300 µm), raster angle (0-30-60°), and infill density (40-60-80%) were examined. The analysis of variance method was used to look at the relationship between these parameters and the flexure strength of samples fabricated using the fused deposition modeling technique with polyethylene terephthalate glycol material. The experimental design process was performed using Taguchi L9 orthogonal design. Fuzzy logic-based modeling was applied to estimate the flexural strength. The results demonstrated that the infill density is the most important parameter affecting flexural strength compared to the other parameters. The highest strength of 57.76 MPa was achieved when the layer thickness, raster angle, and infill density were set to 100 µm, 60°, and 80%, respectively. The fuzzy logic provided a high-accuracy estimation of the flexural strength with a maximum percentage error of 2.65%. Consequently, it was determined that the model and experimental results were in agreement.

Hydrogen embrittlement (HE) continues to be a limiting factor in implementing high strength steel alloys in applications such as fasteners. In this work, 9260 bar steel was heat treated to produce quench and tempered (Q&T) martensite and quench and partitioned (Q&P) microstructures at hardness levels between 52 and 54 HRC. The Q&P microstructures consisted of lath martensite, retained austenite, martensite-austenite (M/A) constituents, and intercritical ferrite in some conditions. The Q&P process promoted higher strength and uniform elongation than the Q&T martensite, though also exhibited a relatively low degree of post-uniform elongation except in the lowest quench temperature condition. Slow strain rate tensile and circular notch tensile tests were performed on all conditions after electrochemical hydrogen charging at hydrogen levels of 1–1.5 ppm. The Q&T condition exhibited a better slow strain rate performance and notch tensile strength after hydrogen pre-charging than the Q&P conditions. In the Q&P conditions subjected to slow strain rate tensile tests, a higher HE susceptibility is correlated with higher quench temperatures, which had lower austenite stability and more fresh, non-tempered martensite in the initial microstructure. However, the HE susceptibility was comparable for all of the Q&P conditions in the notch tensile tests.

The development of reliable joining techniques for ceramics and metals is crucial for energy applications, such as fuel cells, nuclear reactors, and high-temperature sensors, most especially for the sealing of hydrothermal sensors to study multiphase flows. However, during one-step active laser brazing it is a serious problem that a high thermal stress concentration can occur at the joint interfaces or on the ceramic side of the joint due to mismatches between the CTEs (coefficients of thermal expansion) and/or elastic constants. The uncontrolled thermal residual stress can lead to cracks and defects in the brazement. In the present work, an elastoplastic finite element method/numerical model was formulated to study the thermal residual stresses developed in the brazement between ceramics and austenitic stainless steel during cooling in active laser brazing. Calculations and comparison experiments were conducted to validate the simulated stress distribution in un-patterned ceramics. Stress analyses were conducted for planar and cylindrical specimen geometries (lab joints) relevant for miniaturized energy sensors. Laser interface patterning was employed to create micro-scale features on ceramic interfaces that reduce thermal stress concentrations. The optimization of the interface designing parameters including hatch size, structure width, pattern depth and metal/ceramic thickness ratio was performed using the Taguchi method with orthogonal arrays. The study suggests that laser interface structuring can modify thermal residual stresses in ceramic-to-metal brazements, thereby increasing the reliability of active brazing joints.

Residual stress plays an important role in the delayed cracking performance of the 22MnB5 hot roll bending pipe. In the present study, the residual stress distribution of the 22MnB5 hot roll bending pipes with different pipe thicknesses is compared. The results show that both the tensile and compressive residual stresses can be traced in the bending zone for the pipe with plate thickness around 1.5 mm. On the contrary, only tensile residual stress obtains in the residual stress measurement positions for the thicker one (~ 2.3 mm). In addition, the thicker 22MnB5 pipe exhibits poor delayed cracking behavior in the solution of 0.1 mol/L HCl for 300 h. Compared with thinner 22MnB5 pipe, high tensile residual stress occurs in the thicker one induced by phase transformation and deformation during the hot roll bending process, deteriorating its delayed cracking performance.

An innovative Wire and Arc Additive Manufacturing combines the well-studied process of arc welding with direct energy deposition. Effect of travel speed 5.0 and 7.5 mm/s on the microstructure and mechanical properties of 5087 aluminum alloy was investigated. Five thousand eighty-three aluminum alloy was used as a substrate material and 5087 aluminum alloy was utilized as a filler material for the walls fabrication. The presence of pores reducing the strength of the overlay weld metal was detected on both overlay welds. The lower welding speed (5 mm/s) resulted in the smaller amount of porosity in comparison to higher welding speed (7.5 mm/s). Average pore area of wall No. 1 was 0.66% and wall No. 2 was 1.13%. It was found that higher welding speed affected the wall width and overlay weld bead geometry. Increase in welding speed led to a narrowing of wall width from 10.23 to 8.44 mm. The microstructure of weld metal matrix consisted of a α-Al substitution solid solution. The tensile strength of parallel to welding direction removed samples exceeded the tensile strength of perpendicular removed samples. It is a result of the cohesion of the layers in the overlay welding direction compared to the non-uniformity of the layers in the perpendicular direction. Furthermore, the tensile strength was higher in the case of travel speed of 5 mm/s in comparison to that of 7.5 mm/s.

Polydimethylsiloxane (PDMS) with multiwalled carbon nanotubes (MWCNT) fillers is a piezoresistive nanocomposite which is conformable, printable, and biocompatible. It is widely employed as a sensing layer in flexible pressure sensors, electronic skin (e-skin) of humanoid robots and as wearable sensors. Piezoresistive nanocomposites show significant increase in their electrical conductivity above a certain percolation threshold. In this work, PDMS + MWCNT-based sensing layers with different nanofiller MWCNT concentrations (2, 4 and 7 wt.%) are screen-printed and their electrical, mechanical, and percolation threshold responses are verified. The static I–V characteristics of the samples for a biasing DC voltage of 0-6 V are studied. The tensile test confirms maximum elongation of more than 50 mm. The change in resistance was minimal for 2 wt.% sample as the MWCNT’s are sparsely distributed and no conducting channels are formed; for the 7 wt.% sensing layer, negligible change in resistance was observed as the conducting channels are broken. The highest change in resistance of 2.4 MΩ was observed after the percolation threshold value of 4 wt.% of the nanofiller concentration was reached. Overall, the 4 wt.% screen-printed piezoresistive nanocomposite layer showed highest sensitivity with a gauge factor of 4.76 and a linear response suitable for industrial applications.

Residual stresses developed during additive manufacturing (AM) can influence the mechanical performance of structural components in their intended applications. In this study, thermomechanical residual stress simulations of the laser powder bed fusion (LPBF) process are conducted for both simplified (plate and cube-shaped) geometries as well as five complex lattice geometries fabricated with Inconel 718. These simulations are conducted with the commercial software package Simufact Additive^©, which uses a nonlinear finite element analysis and layer-by-layer averaging approach in determining residual stresses. To verify the efficacy of the Simufact Additive^© simulations, numerical results for the plate and cube-shape geometries are analyzed for convergence and compared to experimental residual stress results available in the literature. Numerical residual stress results are subsequently compared for five complex lattice geometries. Results suggest that lattice geometry can play a significant role in the distribution and magnitude of residual stresses, which are significant in some applications.

Commercially pure Ti (AMS 4902) was joined using the transient liquid phase bonding technique. The joining process was implemented at various temperatures of 820, 860, 900, and 1000 °C for 90 min under a vacuum atmosphere of 7.99 Pa. The microstructural investigations were carried out comprehensively using scanning electron microscopy equipped with the EDS elemental detector. The mechanical properties were characterized using the microhardness and shear strength tests. Strength properties in terms of ultimate shear strength and ductility were presented as force-extension diagrams. The presence of eutectic intermetallics in the joint centerline indicated that isothermal solidification was not achieved at low bonding temperatures. However, the increase in temperature to 1000 °C resulted in a fully isothermal solidified joint. The elemental gradients between the bonding centerline and the base metal leveled off at high temperatures of 900 and 1000 °C, where the solubility of Ti increased in the Cu crystal structure. A higher hardness of 270 HV with a uniform gradient was also observed across the joint produced at high temperatures of 900 and 1000 °C. A combination of high strength and ductility was obtained for the samples fabricated at 900 and 1000 °C bonding temperatures.

The role of the initial residual stresses (IRS) induced by the milling on the efficacy of laser shock peening (LSP) was investigated numerically on IN718 specimens. Three milling conditions exhibiting high (3.5 μm), medium (1.1 μm), and low (0.6 μm) surface roughness were considered for LSP. Experimentally measured (from XRD) milling-induced sub-surface (up to 60 μm depth) residual stresses were introduced into the simulations of LSP as predefined fields. The role of spot diameter with the IRS on the LSP-induced residual stress was studied systematically. For most cases, the tensile IRS from milling caused a significant decrease in the magnitude of maximum compressive residual stresses induced by LSP.