Investigation on microstructure and microhardness of linear friction welded joints of dissimilar titanium alloys

On the basis of previous welding experiments,the dissimilar titanium alloys TC4/TC17 were welded by linear friction welding and the interface temperature was measured.The joint microstructure and microhardness was analyzed and tested by optical microscope,scanning electronic microscope and microhardness tester,respectively.The results showed that the interface temperature during welding exceeds 1 200℃,above β-transformation temperature.Recrystallization happens in the weld zone in the cooling process after welding,which forms a refined needle-like structure.The recrystallized structure of the mixture zone is equiaxed and even spheroidized.In the TMAZ of TC4,the microstructure consists of the elongated α phase and the broken β phase.In the TC17 TMAZ,the α and β phases was elongated and fined.The microhardness results showed that strain-hardening occured in TC4 TMAZ,while TC17 TMAZ was softened near the weld zone and strain-hardening was obvious near the base metal.