Thermal cycling on microstructure and mechanical properties of laser powder bed fusion manufactured IN738LC alloy

This study investigated the impact of thermal cycling effects on the microstructure and mechanical properties of IN738LC alloy manufactured by laser powder bed fusion, considering different volumetric energy densities (VEDs) and interlayer times (ILTs) as part of the experimental parameters. The results show that low VED and long ILT samples displayed superior quality, with an average grain size of 10.97 μm and relatively low strain accumulation level. In contrast, samples with high VED and long ILT exhibit increased cracking and porosity, the average grain size is 14.63 μm and present higher strain accumulation degree. The nano-primary MC phase within the alloy transformed into a spherical secondary MC phase inside the grain and a polygonal secondary MC phase on the grain boundary. In the low VED and long ILT, the mean equivalent diameter (MED) of MC carbide within the grain and on the grain boundary was 63 and 140 nm, respectively, the tensile strength was 1072 ± 21 MPa. By contrast, for the high VED and long ILT, the MED of MC carbide in the grain and on the grain boundary were 47 and 105 nm, respectively, and the tensile strength was 794 ± 31 MPa. The tensile strength of high VED and long ILT decreased by 26% compared with low VED and long ILT.