Microstructure evolution-based design of thermal post-treatments for EBM-built Alloy 718

Journal article, 2021

Alloy 718 samples were fabricated by electron beam melting (EBM) additive
manufacturing process. The work focused on systematic investigation of
response of the material to various thermal post-treatments, involving hot isostatic
pressing (HIPing), solution treatment (ST) and two-step aging, to tailor
post-treatment procedure for EBM-built Alloy 718. Results showed that HIPing
at lowered temperature can be used for attaining desired defect closure while
preserving grain size. Subjecting the material to ST, with or without prior
HIPing, mainly caused precipitation of d phase at the grain boundaries with
prior HIPing decreasing the extent of d phase precipitation. Moreover, results
suggest that the utility of ST, with prior HIPing, could be dictated by the need to
achieve a certain d phase content, as the typically targeted homogenization after
ST had already been achieved through HIPing. Detailed investigation of
microstructural evolution during subsequent aging with and without prior
HIPing showed that a significantly shortened aging treatment (‘4 ? 1’ h),
compared to the ‘standard’ long treatment (‘8 ? 8’ h) traditionally developed
for conventionally produced Alloy 718, might be realizable. These results can
have significant techno-economic implications in designing tailored post-treatments
for EBM-built Alloy 718.