Effect of heat treatment temperatures on microstructure and mechanical property of linear friction welded joints of titanium alloys TC17(α+β)/TC17(β)

The heat treatment experiments were carried on titanium alloys (TC17 (α+β) + TC17 (β)) linear friction welded joint. Optical microscope (OM), scanning electron microscope (SEM) and microhardness instrument were used to investigate the effects of different heat treatment temperatures on the microstructure and mechanical properties of welded joints. The results show that recrystallization occurs at the weld zone (as weld). Metastable β phase structure is formed at the weld interface of as-welded joint. The microhardness of as-welded joint is lower than base metal and high cycle fatigue strength of as-welded joints is 345 MPa. Because welding speed is rapid, a large number of primary α phase is retained in thermal mechanically affected zone (TMAZ) of TC17 (α+β). After post-weld heat treatment, the metastable β phase structure is decomposed and dispersed (α+β) phase is separated out at the welded joints. With the increase of the heat treatment temperature, small secondary α phase is grown up and phases are partly spheroidized. After heat treatment, because metastable β phase structure is decomposed, the micro-hardness is greatly increased at the weld zone and TMAZ, and fatigue strength is increased by an average of 65 MPa at the welded joints. With the increase of the heat treatment temperature, the fracture toughness is improved at the TMAZ of welded joints