Deformation behavior, twinning propensity model, and twinnability map for laser powder bed fused austenitic steel homogenized by hot isostatic pressing

Abstract

Hot isostatic pressing (HIP) has emerged as a highly effective and extensively adopted technique for eliminating intrinsic flaws, mitigating residual stress, and addressing microstructural anisotropy in laser powder bed fused (L-PBF) metallic materials. However, the deformation behavior, strengthening mechanism, and associated mechanistic models of HIPed l-PBF austenitic steel remain largely unclear. Through multiple microstructural characterizations, this study determined that the primary deformation mechanism of HIPed l-PBF austenitic steel involved the emission of twinning partials from either the annealing twin boundaries or high-angle grain boundaries (HAGBs) with the decoration of extra dislocations and prismatic inclusions. A twinning propensity model was formulated based on the identified deformation mechanisms, revealing that the critical angle (θτ-crit) for twinning partial emissions ranged from 25.64° to 28.46° By incorporating the mathematical relationship describing the force equilibrium state between trailing and twinning partials, a twinnability map considering both the crystallographic orientation and stress state (magnitude and direction) was established to guide the twinning control for desired mechanical properties. Finally, the accuracy of the twinning model and twinnability map was effectively confirmed using the microstructural results, whereas the limitations of the twinning model and twinnability map were reasonably examined through micro-defect and texture analysis. The results of this study provided a significant theoretical framework for understanding the twinning behavior of high-performance and homogeneous l-PBF metallic materials.