On the dislocation storage capacity of additively manufactured Hastelloy X: In situ synchrotron diffraction study

Abstract

Considering the results obtained from different types of synchrotron diffraction experiments, this research investigation presents deeper insights about the effects of heat treatment on characterization of microstructure and mechanical properties of laser powder bed fusion (L-PBF) processed Hastelloy X (HX). HX is a candidate material for variety of applications ranging from petroleum and chemical industries, high temperature gas cooled reactors and gas turbine engines. L-PBF processed samples of HX were subjected to three aging treatments at 650 °C, 760 °C and 870 °C after solutionizing them at 1175 °C. Examination of Debye-Scherrer rings and orientation imaging maps (OIM) of electron back scattered diffraction (EBSD) experiments revealed the randomization of grains in heat treated microstructures of HX. Synchrotron diffraction patterns and transmission electron microscopy observations confirmed the presence of laves phase and carbides (M₆C and M₂₃C₆) in as-built HX (AB-HX). Increase in precipitation of M₂₃C₆ carbides with increase in aging treatment from 650 °C to 870 °C was revealed by line profiles of synchrotron diffraction patterns and EBSD phase maps. Tensile deformation behavior in four different metallurgical conditions of HX viz. AB-HX, solution treated (ST), solution treated and aged conditions was characterized by evaluating the evolving dislocation density carrying out in situ synchrotron diffraction experiments. The diffraction data corresponding to the first six {hkl} reflections were considered for evaluating the dislocation density using modified Warren-Averback methodology. Analysis of work hardening behavior, as probed by dislocation density measurements, indicated increase in dislocation storage capacity with increase in aging treatment from 650 °C to 870 °C. Variations in tensile properties were analyzed in light of the dislocation density measurements and EBSD results to gain more insight into the deformation mechanisms operating in different heat-treated conditions.