A high-strength Ni–Cr–W based superalloy prepared by laser powder bed fusion: printability, microstructure and tensile properties

Abstract

The Ni–Cr–W based Haynes 230 alloy, is considered to have important applications in the hot-end components of aerospace engines due to its excellent high-temperature properties and oxidation resistance. However, Haynes 230 alloy presents a high hot-cracking tendency during the laser powder bed fusion (LPBF) process. In this study, a novel composition optimized Ni–Cr–W superalloy based on Haynes 230 alloy was fabricated by the LPBF method. The metallurgical defects, microstructure and tensile properties at room temperature (RT) of the LPBF Ni–Cr–W based superalloy printed under different volume energy densities (VEDs) were systematically researched. The results show that the novel Ni–Cr–W superalloy presents excellent processability, and a near-fully dense specimen without any metallurgical defects was obtained under optimal VED of 83.33 J/mm3. However, solidification cracks also occurred in the samples with higher VEDs (exceeding 100 J/mm3). The main reason is the increase of thermal stress and liquid-feeding resistance as VED increases. The rapid scanning speed and steep temperature gradient during the LPBF lead to the occurrence of the multi-scale heterogeneous microstructures, including the epitaxial columnar grains with a mixing of {100} and {110} crystallographic alignment along the building direction (BD) and cellular substructures entangled with high-density dislocation. The cellular substructure strengthening and solution strengthening are the dominant factors for the excellent ultimate tensile strength (1100 MPa), yield strength (850 MPa), and ductility (29.3%) of the LPBF alloy at RT. With the increase of VED, the yield strength of the LPBF alloy decreases. The main reason is the reduction of cellular substructure strengthening. The ultimate tensile strength of the LPBF alloy at 1000 °C reaches 200 MPa, which is superior to that of the LPBF Haynes 230.