The Influence of Size, Geometry, and Temperature on Deformation Mechanisms in Laser-Powder Bed Fusion Alloys

Abstract

This study presents a comprehensive experimental investigation into the effects of size, geometry, and temperature on the mechanical behavior and deformation mechanisms of additively manufactured (AM) metal alloys produced via laser powder bed fusion (L-PBF). The work focuses on four major alloy systems, Ti-6Al-4V, Haynes 214, Haynes 282, and GRX-810, to elucidate how geometric scaling and temperature jointly influence strength, ductility, and the underlying microstructural processes governing deformation and failure in L-PBF metals. Through a combination of quasi-static mechanical testing, surface topography analysis, X-ray computed tomography (XCT), and electron microscopy (SEM/EBSD/EDS), the influence of intrinsic microstructural features such as porosity, grain morphology, and crystallographic texture on mechanical response was systematically characterized across multiple sample sizes and temperature regimes. In the first segment of this work, the mechanical response of L-PBF Ti-6Al-4V was investigated as a function of specimen thickness, geometry, and test temperature. These findings underscore the importance of accurately capturing surface topography and cross-sectional area variations in thin-wall structures to ensure reliable stress calculations and model calibration. Results revealed that thin-wall flat samples exhibited enhanced elongation but reduced strain hardening at room temperature, with this trend reversing at 250 °C and 450 °C. Round samples showed no change in ductility at ambient temperature; however, they experienced more pronounced ductility losses compared to flat samples as the sample diameter decreased. The increase in strain hardening with temperature, independent of geometry or sample size, is presumed to be attributed to the reduction in the critical resolved shear stress (CRSS) of basal slip systems, which promotes increased dislocation entanglement. The second phase of this study extended the investigation to the high-temperature L-PBF nickel-based superalloy Haynes 214. Here, strong size dependence was observed in the plastic flow behavior, particularly through the activation of the Portevin–Le Châtelier (PLC) effect and dynamic strain aging (DSA) at 650 °C. Thinner specimens exhibited increased serration frequency and reduced critical strain for onset, reflecting the sensitivity of DSA to grain boundary volume and solute diffusion kinetics. A pronounced ductility loss was observed between 600 °C and 870 °C, associated with the transition from transgranular plasticity to intergranular grain-boundary cracking driven by carbide segregation and oxidation. Above 870 °C, partial recovery of ductility occurred due to the onset of Orowan bypass mechanisms and the partial dissolution of the strengthening γ′ phase. Building upon these findings, the final stage of this work investigated temperature-dependent deformation behavior in two additional high-temperature L-PBF superalloys: Haynes 282 and GRX-810. Comparative analysis revealed that L-PBF Haynes 282 maintains higher tensile strength and work-hardening capacity than L-PBF Haynes 214 and L-PBF GRX-810 as temperatures increase up to 870 °C, owing to its leaner and thermally stable γ′ fraction. At 1093°C, L-PBF GRX-810 demonstrated superior high-temperature strength and ductility retention due to the stabilizing effect of its yttria-based oxide dispersoids and late-stage deformation twinning, respectively. Despite higher bulk defect densities, including voids and microcracks, GRX-810 exhibited minimal degradation in mechanical properties, indicating that the observed porosity had negligible influence on quasi-static performance. Across all alloys, the severity of the PLC effect was found to increase as sample size decreases at 650°C testing temperatures. The collective findings of this work highlight that the influence of size and geometry on mechanical performance cannot be universally generalized across AM alloys but must instead be understood within the context of specific microstructures, thermal histories, and alloys. The results provide a robust experimental foundation for advancing microstructure-sensitive constitutive models, including physics-informed and machine-learning–assisted crystal plasticity frameworks. Ultimately, this work enhances the fundamental understanding of how thin-wall AM structures deform and fail across a wide temperature range, guiding the optimization of L-PBF process parameters, alloy design strategies, and component qualification protocols for high-performance applications in aerospace, propulsion, and energy systems.