High-temperature mechanical properties and microstructure of welded joint in GH4169/IC10 dissimilar nickel-based superalloys by vacuum electron beam welding

Abstract

Jointing precipitation-reinforced GH4169 and newly-developed IC10 nickel-based superalloy through vacuum electron beam welding (VEBW) has become increasingly attractive for aeroengine's blade and disc. In this study, solution treatments (GH4169 for 980 °C/1.5 h and IC10 for 1180 °C/2 h) was chosen before welding, and different aging treatments (900 °C, 950 °C, 1000 °C, 1050 °C and 1100 °C for 6 h, respectively) were used for eliminating uneven compositions and structures of the GH4169/IC10 welded joint after VEBW method. Through optical microscopy (OM) observations, there are distinct morphological differences between the base metal (BM) and fusion zone (FZ) regions, with the BMs regions mainly being equiaxed and the FZ region mainly being dendritic grains after VEBW. Through scanning electron microscopy (SEM) observations, the carbides are mainly distributed at grain boundaries in BMs, and Ni–Cr–Nb phases are the dominant second phases in the FZs after VEBW. Moreover, the grain orientation is obviously strong in FZs with adjacent {001} orientation by electron backscattered diffraction (EBSD) characterizations. while grain orientation chiefly of BMs presents anisotropy. After heat treatments, the maximum microhardness of the welded joint was obtained after aging at 900 °C (242–258 HV), and the minimum microhardness was obtained after aging at 1050 °C (183–190 HV). Besides, among the aged welded joints, the 900 °C aged welded joint has the best high-temperature mechanical properties (tensile strength for 559 MPa and elongation for 19.3%) through high-temperature tensile tests, owing to the strengthening effect of numerous γ′ and γ′′ precipitates, nevertheless, 1050 °C aged welded joint has lower tensile strength than solution treated welded joint, mainly resulting from the numbers of δ precipitates isolating matrix. Moreover, combined with transmission electron microscopy (TEM) observations, the carbides, γ′, γ′′, and δ precipitates lead to different high-temperature tensile properties of welded joints, the transformation of γ′′ precipitates and coarsening of γ′ precipitate promote fracture crack initiation and propagation along grain boundaries.