Additively manufactured Haynes 282: effect of unimodal vs. bimodal γʹ- microstructure on mechanical properties

Abstract This study examines the effects of lower-than-nominal heat treatment (HT) temperatures and cooling rates —possible during the treatment of larger components— on microstructure and tensile properties Haynes 282 manufactured via laser powder bed fusion (L-PBF) additive manufacturing process. Two main HT schedules, i.e., conventional treatment and its lower temperature variants were performed. The microstructural evolution at each step of the HTs was tracked and compared. It was shown that solution temperature of a wide range (1062–1146 °C) could moderately remove the as-solidified dendritic microstructure resulting in similar distribution of grain boundary (GB) carbides. In addition, the lower temperature double aging process resulted in a bimodal γ′-precipitates consisting of both nano-sized secondary γʹ- and large primary (>∼100 nm) γ′-precipitates, while the conventional aging gave rise to a unimodal γ′-precipitates with precipitates of diameter ∼60 nm. Owing to the bimodal γ′-precipitates and a similar GB carbide distribution, the low temperature HTs resulted in comparable tensile properties to the conventional HT despite having much larger γ′-precipitates. The results imply that moderate HT temperature deviations due to excessive component size, such as lower temperatures and slower heating/cooling rates, does not negatively impact the mechanical properties of L-PBF Haynes 282.