In this study, cubic coupons of AlSi10Mg alloy were printed using the laser powder bed fusion (LPBF) technique. The effect of heating/reheating cycles on solute trapping and partitioning of alloying elements was investigated using atom probe tomography and transmission electron microscopy. Nano-hardness analysis and uniaxial tensile tests equipped with digital image correlation were employed to investigate the mechanical properties and Poisson's ratio. X-ray micro-computed tomography was utilized to detect strain localization sites along the building direction. Also, the uniaxial tensile test was simulated using finite element analysis to verify the experimental data and predict stress triaxiality. The results showed that the solute trapping and partitioning during the LPBF process results in remarkable changes in phases, their size and morphology, Poisson's ratio, strengthening factor, and consequently mechanical properties. While the tensile sample from top part of the LPBF coupon mostly shows porosity due to floating and entrapment of gases during layer-by-layer fusion/solidification, the sample from bottom part is exposed to sub-surface microcracking induced by residual stresses. The hardness, elastic, and shear moduli, Peierls stress, and cumulative strain energy of the top-part sample are higher than those of the bottom-part sample even though electron backscatter diffraction analyses report similar grain size and texture. Besides, by distancing from the build plate, the Poisson's ratio decreases. Simulation results of both samples indicate that the middle of the gauge is a high-potential area of failure initiation, where the bottom-part sample shows higher stress localization.

The deformation performance of maraging steel samples fabricated using the laser powder bed fusion technique was evaluated using the split Hopkinson torsion bar (SHTB) test. Thin-walled tubular maraging steel samples were deformed under dynamic torsional loading at strain rates of 260 s⁻¹ to 720 s⁻¹ using twist angles varying from 3 to 12°. Microstructural and textural investigations were carried out on deformed samples using the electron backscatter diffraction technique and scanning electron microscopy. Results showed that maraging steel samples fractured when deformed using an angle of twist of 12° and strain rate of 650 s⁻¹. As a result of deformation localization at high strain rates, adiabatic shear bands are developed in some thin-walled tubular torsion specimens deformed using the 12-degree angle of twist, leading to fracture. Textural studies showed that texture weakening occurred with an increment in strain rate ascribable to grain fragmentation. In this study, two models (empirically and semi-empirically) were employed for describing maraging steel performance during high strain-rate torsional loading. Simulation results based on Kobayashi-Odd and Nemat-Nasser models agreed well with the experimental data.

This study aims at assessing the effect of solution heat treatment (at a temperature just below the eutectic temperature) followed by various cooling rates on the microstructure and mechanical properties of additively manufactured AlSi10Mg and the cast counterpart. The mechanical properties were evaluated using a depth-sensing nanoindentation platform. The cast and additively manufactured parts were solutionized at 540 ​°C for 2 ​h followed by water quenching, air cooling, and furnace cooling. Results show extensive microstructural changes (e.g. size and morphology of eutectic-silicon phase) and evolutions in the mechanical properties of the heat-treated materials relative to the as-printed and as-cast ones. Besides, the microstructure and micromechanical properties of the materials broadly alter the cast and additive manufacturing conditions. Depending on the cooling condition, the mentioned cooling cycles directly affect the morphology of eutectic-silicon in both cast and additive manufactured materials starting with silicon fragmentation, then followed by silicon spheroidization, and silicon coarsening. The microstructural evolution affects the local micromechanical properties of the studied materials. The results of this study provide insights into the control of microstructure and hence mechanical properties of AlSi10Mg alloy by addressing suitable heat treatment cycles. This study, for the first time, assesses and compares the effect of various post-fabrication cooling rates in the cast and additive manufacturing conditions in an AlSi10Mg alloy.

Inconel 718 superalloy cylindrical rods were fabricated using the laser powder bed fusion (L-PBF) technology in the vertical orientation. The rods were stress-relieved at 980 °C for 15 min before cutting them from the build plate. The microstructure in this condition exhibited a significant amount of undesirable needle-like δ-phase precipitates and a small amount of interdendritic Laves phase that is finer in size. Differential Scanning Calorimetry (DSC) was used to determine the temperatures for solid-state phase transformations and appropriate temperature for solution-treatment. Solution-treatment was performed at 1065 °C for 1 h, followed by air cooling. The microstructures were characterized with specific reference to δ-phase and Nb segregation. Solution-treatment at 1065 °C was found to result in a significant elimination of micro-segregation (mainly Nb), complete dissolution of δ phase, considerable Laves dissolution, and partly undissolved carbide particles (few nm in size). Solution-treatment did not produce a significant change in the grain morphology (columnar dendritic) on a plane parallel to the build direction but more recrystallized and equiaxed grains were formed on a plane perpendicular to the build direction. The hardness of the solution-treated sample is comparable with wrought 718 alloys but lesser (115 HV) than in the stress-relieved condition attributing to the annihilation of dislocation tangles.