Micro-scale thermodynamic model of microstructure and stress evolution in parts via selective laser melting

Abstract

The thermodynamic state changes during selective laser melting (SLM) processing dominate the microstructure and mechanical properties of the built parts. Improper operational parameters often lead to uneven microscopic morphology, microcracks, distortions, and other failures. The key to controlling the microstructure of the forming metal lies in an in-depth understanding of the micro-scale thermodynamics of this process. A micro-scale thermodynamic model was developed herein to predict the microstructure and internal stress evolution in parts fabricated by SLM with two typical scanning strategies. The modified two-temperature (TTM) model was employed to discover the dominant interface thermodynamic phenomenon in unitary path scanning and the novel symmetrical multi-path scanning capable of reliving residual stress and homogenizing microstructure. The real-time identifying method of temperature, microstructure, and stress could be further applied to closed-loop control of the SLM process.

Effects of Thermal Cycling on Residual Stress in Parts via Selective Laser Melting

“…The impact of laser scanning parameters on stress distribution is significantly nonlinear due to the intricate geometric constraints and heat dissipation conditions. The heat dissipation conditions in the regions with the high stress of sample 1-2 differ greatly, namely efficient heat conduction of the interface between the bottom powder layer and deposited layer [41], the worst heat dissipation condition in the middle, and the most prominent external contact area at the top. These results suggest that the stress magnitude induced by the multi-layer thermal cycling in samples 1-2 was relieved due to high energy density.…”