This study explores the evolution of solidification microstructure of a laser powder bed fusion (L-PBF) martensitic stainless steel during solution annealing and aging. Quasi in-situ experiments using electron backscatter diffraction (EBSD) revealed that the finer, more equiaxed microstructure below the melt pool was susceptible to recrystallization and grain growth during solution annealing. The two distinct solidification microstructures below and inside the melt pool converged into a uniform grain morphology after solution annealing and aging processes. Graphical Abstract: (Figure presented.)

Maraging steel (MS1)-tool steel (P20) bimetals additively manufactured using the laser powder bed fusion technique were studied under different heat treatment cycles and loading conditions. The hardening of P20 and aging of MS1 were performed sequentially on the hybrid samples. The interfacial characteristics and microstructural evolution of the bulk materials were studied using various advanced electron microscopy techniques. The post-processing procedures successfully produced a uniform martensitic structure throughout the MS1-P20 hybrid steels, leading to a less detectable interface under electron backscatter diffraction (EBSD) imaging. The mechanical performance of heat-treated hybrid steels was evaluated using complex loading conditions. 3-point and 4-point bending tests were performed to assess the impact of heat treatments on the mechanical performance of the hybrid steels. The heat-treated samples exhibited higher strength with relatively homogeneous hardness variations and deformed more uniformly in bending conditions.

In this work, the effect of heating rate on the phase transformation temperatures was investigated using dilatometry analysis. Continuous heating and isothermal holding above Ac₃ temperature on microstructural evolutions in additively manufactured (AM) parts of Fe-Cr-Ni maraging stainless steel were studied. The microstructural features developed within the heating processes were characterized employing electron backscatter diffraction and transmission electron microscopy. Austenite reversion was found to take place in two steps for the AM parts by a diffusive mechanism as well as the precipitation reactions. Although grain refinement occurred during the austenite reversion of the continuously heated samples, the microstructure showed a coarser grain size after isothermal heating. The crystallographic orientations developed after the heating processes were different from those of the initial ones implying the absence of the austenite memory effect.

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.

Due to high local cooling rates and non-equilibrium directional solidification conditions, selective laser melting (SLM) processed metals exhibit microstructural and textural features significantly different from the conventionally processed ones. The evolution of crystallographic orientations in a maraging stainless steel (commercially known as stainless steel CX) sample fabricated by the SLM process was studied through experimental and modelling approaches Electron backscattering diffraction analysis showed that the dominant texture components in martensite and austenite phases are <111>|| building direction and <011>|| building direction, respectively. Texture simulation indicated that the formation of crystallographic orientations in the studied sample is the result of two consecutive phase transformations, from initially solidified delta ferrite phase with dominant cube fiber texture to austenite and austenite to martensite.

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.