Abstract
In this paper, the fracture toughness of the thermo-mechanically affected zone (TMAZ) and the weld zone (WZ) of the TC17 titanium alloy linear friction welding joint was studied. The relationship between microstructure and fracture toughness of the joint, as well as the morphologies of the joint microstructure and fracture were investigated. The results indicate that after heat treatment, there was no significant difference in hardness between the WZ and the TMAZ of the joint, which was about 420 HV. However, the microstructures of the different zones of the joint were significantly different. The TMAZ was composed of coarse grains having an internal basket-shaped α phase with an uneven grain size, while the WZ was composed of relatively uniform fine grains and contained a sheet-like α phase. The fracture toughness of the TMAZ was found to be higher than that of the WZ, indicating that the microstructure of the joint had a significant impact on the fracture toughness. In addition, the fracture resistance of the TMAZ with coarser grains and uneven microstructure was better than that of the WZ with fine grains and uniform microstructure.
Highlights
TC17 (Ti–5Al–2Sn–2Zr–4Mo–4Cr) is a dual-phase (α + β) titanium alloy that is rich in β-stabilizing elements
The working temperature of TC17 titanium alloy can reach up to 450 ◦ C, so it has been used in the manufacturing of aeroengine fans and compressor discs and in the forging of large-section pieces [1,2,3,4]
The microstructure around the joint had a significant variation compared to the base metal (BM)
Summary
TC17 (Ti–5Al–2Sn–2Zr–4Mo–4Cr) is a dual-phase (α + β) titanium alloy that is rich in β-stabilizing elements. In linear friction welding joint of TC4 titanium alloy, the microstructure is α” martensite in the weld zone (WZ), and the thermo-mechanically affected zone (TMAZ) is a deformed primary α phase and a deformed α + β structure, in addition to a small amount of martensite [13,14,15,16]. The WZ of Ni-based superalloy linear friction welding joint has fine grains, and its TMAZ is composed of a deformed grain structure that contains a large number of twinning crystals [18,19,20,21]. The fracture toughness of each typical zone of the TC17 titanium alloy linear friction welding joint, usually used in blisks, was measured and analyzed using the fracture mechanics method, providing technical knowledge for the engineering application of the linear friction welding technology
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