Effects of temperature and strain rate on tensile properties and dynamic strain aging behaviour of LPBF Hastelloy X

This study compares the tensile response of laser powder bed fusion (LPBF) fabricated Hastelloy X (HX) coupons with those of conventionally manufactured HX over the temperature range of 22-800°C and strain rate of 10−4-10−2 s−1. Comparable ultimate tensile strength and higher yield strengths were observed for LPBF HX. The stress-strain response of LPBF HX showed pronounced evidence of dynamic strain aging (DSA) during tensile testing at temperatures from 300°C to 600°C and also limited evidence of DSA at 200° and 700°C. The transition from type-A/B to type-C DSA for LPBF HX happens at lower temperatures than that for conventionally manufactured HX. Furthermore, the activation energy for DSA is 66 kJ/mol for LPBF HX, which is lower than the reported 80-130 kJ/mol for conventionally manufactured HX. The observed differences in the tensile and DSA responses of the two variants of HX were attributed to the differences in their dislocation microstructure, observed through scanning transmission electron microscopy.