Effect of high preheating on the microstructure and mechanical properties of high gamma prime Ni-based superalloy manufactured by laser powder bed fusion

Abstract

Laser powder bed fusion (L-PBF) is an additive manufacturing method with potential applications in the aerospace industry. Currently, IN738LC has been a challenging engineering material to work with as it is inherently brittle due to its high γ′ volume fraction. In this study, crack-free IN738LC was manufactured on a customized L-PBF system capable of preheating to 700 °C. A wide processing parameter range (58–83 J/mm3) could be selected to achieve solid bulk fabrication with a density of 99.95%. The microstructure and mechanical behavior difference between preheating at 200 °C and 700 °C were assessed. In addition to achieving cracking suppression, the high preheating temperature resulted in a strong textured columnar microstructure with finely dispersed carbide particles along the grain boundaries of as-built parts, and superior room temperature ultimate tensile strength of 1612 MPa associated with good ductility of 18% was achieved. Work hardening rate evolution that differed from 200 °C preheating was thought to cause abnormal anisotropic tensile behavior. The influence of preheating on the melt pool morphology, the development of fluid dynamics, and the thermal behavior were discussed according to simulations with the discrete element model (DEM) and volume of fluid (VOF) method.