Effect of heat treatments on the microstructure and mechanical properties of IN738LC prepared by electron beam powder bed fusion

Abstract

The heat treatment of non-weldable nickel-based superalloy prepared by electron beam powder bed fusion (EB-PBF) is vital for the properties of parts. The current study aims to use a heat treatment method to increase the properties of the as-built EB-PBF IN738LC and explore the applicability and necessity of standard heat treatment designed for cast IN738 on the EB-PBF counterpart. Different heat treatment (HT) methods, such as standard heat treatment (SHT), hot isostatic pressing (HIP), and HIP+SHT, have been performed. The microstructures before and after HT are scrutinized focusing on the evolution of the precipitates. Tensile tests were carried out to evaluate the effect of the heat treatment. The grain morphology can be altered by a HIP process but not the SHT process. The HIP process induces more carbides to be precipitated; the carbide changes from MC to M 23 C 6 during the SHT process, and the γ’ phase changes from the cuboidal shape in the as-built state to the spherical shape in SHT processes. The refined grain and disappearance of pores are the reasons for the increased elongation ratios of HIP samples. Combining the HIP and SHT processes helps refine the grain and improve the mechanical properties. • The elongated grains in EBSM IN738LC are different from the equiaxed grains in cast IN738LC. • The different heat-treated process of EBSM IN738LC samples were compared for the first time. • The refined grain and disappearance of pores are the reasons for the increased elongation ratios of HIP samples. • Combining the HIP and SHT processes helps refine the grain and increase the mechanical properties (YS, UTS, and total elongation ratios).