Gabriel Awuku Dzukey

Selective Laser Melting (SLM) is a type of additive manufacturing or 3D printing technology that makes use of a high-power laser beam to completely melt powder material layer upon layer which solidifies to form the desired part or component. In this experimental study, a careful selection of SLM process parameters (laser power, scan speed, hatching distance, and layer height) was done for the selective laser melting of 316L stainless steel powder material to produce samples with maximum density. A statistical procedure was carried out on the experimental data using the Taguchi's design of experimental technique to optimize the carefully selected process parameters. The obtained results were analyzed using analysis of variance (ANOVA) and signal-to-noise (S/N) ratio with the help of Minitab 18 statistical software to determine the optimal parameters and a regression model was also established. The regression model indicates a linear relationship between relative density and the process parameters. Density value higher than 95% was obtained from this experimental study.

This study investigated the microstructural characteristics and mechanical properties of Inconel 718 (IN718) fabricated using laser powder bed fusion and focused on developing post-heating methods to enhance the mechanical properties. Three different heat treatments with various times and temperature ranges were examined, followed by standard aging. Samples were fabricated in horizontal and vertical orientations. Digital light microscopy, scanning electron microscopy, X-ray diffraction, hardness, and fatigue tests were performed to characterize the microstructure and mechanical properties of IN718. The findings revealed that heat treatment at 980 °C enhanced the hardness, tensile strength, and fatigue life, whereas a further increase in the heat treatment temperature led to an increase in grain size and undesired precipitates. In addition, the work utilized a pre-heated substrate to decrease thermal gradients, provide better control over cooling, and regulate the mechanical properties of the material. A heated bed with a temperature of 250 °C to 500 °C resulted in better mechanical properties compared to as-built samples and higher ductility compared to post-process heat-treated samples. This comprehensive study showed that optimizing the in-situ heating temperature has the potential to eliminate the need for post-process heat treatment for high-cycle fatigue performance. It also allows for a greater understanding of the fabrication and modification of the post-process heat treatment and in-situ heating to optimize the mechanical properties of additively manufactured IN718. • In-situ heating reduced Laves phase and promoted δ-phase formation, improving the microstructure which can enhance high-temperature performance. • Post-process heat treatment also promoted γ′ and γ″ strengthening phases, significantly increasing hardness and strength. • Combined effect of in-situ heating and post-process treatments produced refined microstructure and improved mechanical and fatigue properties. • Grain structure evolved from columnar to equiaxed grains due to thermal gradients induced by in-situ heating. • Optimizing in-situ heating parameters is crucial to balance strength, ductility and surface roughness in AM of IN718.

This work investigates the effect of Hot Isostatic Pressing (HIP) on FeMnAlNi and FeMnAlNiCr shape memory alloys (SMAs) fabricated by Laser Powder Bed Fusion (LPBF). Specimens with and without in-situ laser remelting were HIP-treated at 1150 °C and 150 MPa for 4 h, thereby eliminating most internal porosity and increasing the relative density from ~ 97% to 99.98%. This densification substantially improved ductility, with the Cr-free alloy reaching elongations up to 24%, while the strength and hardness decreased. The addition of ~ 4 at% Cr mitigated these softening effects, enabling higher retention of strength and hardness after HIP. Notably, a remelted Cr-containing sample achieved an excellent property balance with post-HIP indentation-derived equivalent ultimate tensile strength of ~ 1085 MPa, hardness nearly 295 HV, and a modest modulus increase to 161.8 GPa. In contrast, the Cr-free alloy exhibited a larger drop in strength but greater gains in ductility, underscoring a composition-dependent trade-off between strength and plasticity. Nanoindentation testing confirmed these trends, showing reduced nano-hardness and elastic recovery after HIP in both alloys. While Cr additions preserved more of the reversible transformation capacity, pop-out events observed during unloading suggest localized transformation-related deformation during indentation, and that HIP homogenization likely does not suppress pseudoelasticity. Overall, this study bridges a research gap in combining Cr alloying with post-HIP treatment. The results highlight the synergistic role of LPBF parameter control, Cr alloying, and HIP treatment in tailoring Fe-SMAs with near-full density, high strength retention, and reliable ductility.