Laser powder bed fusion of a Ni3Al-based intermetallic alloy with tailored microstructure and superior mechanical performance

Ni3Al-based alloys are excellent candidates for the structural materials used for turbine engines due to their excellent high-temperature properties. This study aims at laser powder bed fusion and post-hot isostatic pressing (HIP) treatment of Ni3Al-based IC-221 M alloy with a high gamma ' volume fraction. The as-built samples exhibits unavoidable solidification cracking and ductility dip cracking, and the laser parameter optimization can reduce the crack density to 1.34 mm/mm(2). Transmission electron microscope (TEM) analysis reveals ultra-fine nanoscale gamma ' phases in the as-built samples due to the high cooling rate during rapid solidification. After HIP treatment, a fully dense structure without cracking defects is achieved, which exhibits an equiaxed structure with grain size similar to 120-180 mu m and irregularly shaped gamma ' precipitates similar to 1-3 mu m with a prominently high fraction of 86%. The room-temperature tensile test of as-built samples shows a high ultimate tensile strength (sigma(UTS)) of 1039.7 MPa and low fracture elongation of 6.4%. After HIP treatment, a significant improvement in ductility (15.7%) and a slight loss of strength (sigma(UTS) of 831.7 MPa) are obtained by eliminating the crack defects. Both the as-built and HIP samples exhibit retained high sigma(UTS) values of 589.8 MPa and 786.2 MPa, respectively, at 900 degrees C. The HIP samples exhibita slight decrease in ductility to similar to 12.9%, indicating excellent high-temperature mechanical performance. Moreover, the abnormal increase in strength and decrease in ductility suggest the critical role of a high gamma ' fraction in cracking formation. The intrinsic heat treatment during repeating thermal cycles can induce brittleness and trigger cracking initiation in the heat-affected zone with notable deteriorating ductility. The results indicate that the combination of LPBF and HIP can effectively reduce the crack density and enhance the mechanical properties of Ni3Al-based alloy, making it a promising material for high-temperature applications.