Nano-scale microstructural evolution and mechanical property enhancement mechanism during crack inhibition in nickel-based superalloys fabricated by laser powder bed fusion

Abstract

Haynes 230, a nickel-based superalloy with a high melting point, is prone to forming microcracks during laser powder bed fusion (LPBF). The correlation between microstructure evolution during crack inhibition and deformation behavior remains unclear. This study compares the microstructure and fracture behavior in both the as-deposited and hot isostatic pressing (HIP) states. After HIP, microcracks closed with the formation of nanoprecipitates at the closure sites, accompanied by increases in both grain and nanoprecipitate sizes, which were limited by pressure. M₂₃C₆ precipitates transformed into M₆C, reducing lattice mismatch. The deformation mechanism in the as-deposited state was dislocation slip, which transitioned to deformation twinning and stacking faults (SFs) after crack inhibition. Importantly, strength and ductility improved synergistically. Strength was enhanced by the combined effects of crack closure and nanoprecipitates hindering dislocation slip, while ductility improved due to crack closure, the formation of nanoprecipitate-induced nanotwins, and the transition in deformation mechanisms. This study elucidates the precipitate transition mechanisms and their role in enhancing mechanical properties.