Influence of Cr/Mo ratio on Microstructure and Mechanical Properties of the Ni-based Superalloys Fabricated by Laser Additive Manufacturing

Abstract From the perspective of mechanical properties and weldability, four Ni-based superalloys with varying Cr/Mo ratio were designed using cluster model, and fabricated by laser additive manufacturing and subsequent solution treatment and aging. The influence of Cr/Mo ratio on microstructure, hardness, and tensile properties of the alloys in both as-deposited and post heat-treated states were investigated. The results show that the microstructure of all as-deposited alloys is featured by γ dendrites with fewer interdendritic phases. With the decrease of Cr/Mo ratio, the interdendritic phases evolve from lath and eutectic Laves phases to blocky P phases. The P phase can deteriorate the ductility, while the hardness and tensile strength monotonously increase due to enhanced solid solution strengthening. Post heat treatment results in dissolution of TCP phases and uniform precipitation of γ′′ phases, which enhances remarkably the hardness and tensile strength of as-deposited alloys, but slightly decreases the ductility. At nearly the same level of ductility (23.4-25.8%), the post heat-treated Ni56.3Cr15.2 Mo3.52Fe18.8 Al1.56Nb3.13Ti1.56 alloy with the Cr/Mo ratio of 13:3 shows the highest hardness (470 HV) and tensile strength (1063 MPa) among the studied alloys.