Combined effects of heat treatment and TiB2 content on the high-temperature tensile performance of TiB2-modified Ni-based GH3230 alloy processed by laser powder bed fusion

Laser powder bed fusion (LPBF) is widely used to manufacture advanced nickel-based superalloys for aero-engine components. LPBF-formed GH3230 nickel-based superalloy, however, suffers cracking and high residual stresses. This study systematically investigated the effects of different contents of submicron TiB2 particles on crack suppression and post-heat treatment for residual stress relief and improved microstructure anisotropy. The introduction of both 0.5 wt% and 1 wt% TiB2 achieved complete crack suppression in the LPBF-manufactured GH3230 specimens. As-built specimens with 0.5 wt% and 1 wt% TiB2 exhibited a supersaturated solid-solution microstructure, with the solid elements (Cr, Mo and W) almost fully dissolved in the matrix and only a limited number of Mo and Cr enriched carbides precipitated at the grain boundaries. Electron backscattered diffraction (EBSD) characterization demonstrated that a large number of deformed grains remained in the as-built specimens. After heat treatment, the residual stresses were released and the number of deformed grains significantly reduced. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) char-acterization demonstrated the disappearance of the dense dislocation network in the as-built specimens after heat treatment, accompanied by the precipitation of a large number of W-rich M6C carbides. This paper also discusses elevated-temperature (900 degrees C) mechanical properties. The ultimate tensile strength (UTS) values of the as-built GH3230 with 0.5 wt% (GH-0.5) and 1 wt% TiB2 (GH-1) specimens were 255 and 290 MPa, respectively. Compared to the as-built materials, the UTS values decreased by 40 and 53.5 MPa, respectively, after heat treatment. The paper also discusses the effect weight of the second-phase, solid-solution and dislocation-strengthening mechanisms on the elevated-temperature mechanical properties. The findings indicate that the added 1 wt% TiB2 particles and the solid-solution elements contributed about 106.2 MPa and 111.5 MPa stress, respectively, in the heat-treated GH-1 specimen. The precipitated M6C carbides after heat treatment, however, were not found to significantly improve the high temperature strength. This work is expected to provide a reference for industrial applications to improve the LPBF formability of nickel-based superalloys and to acquire attractive microstructures.