Microstructural features of friction-welded Ti-6Al-4V joint have been investigated by both optical microscope and transmission electron microscope (TEM). The microstructure of the welded joint is not uniform. It can be classified into the phase transformed region(p), the deformed region(D) and the region of unchanged base metal(B). In the phase transformed region, the microstructure consists of platelike, acicular and equiaxed α phase plus β phase between them and the dislocations can be observed in some a phase particles. The equiaxed α phase mainly distributes in the near center of rod specimen. The quantity of platelike and acicular a phase and the size of the grains increase progressively along the radial direction of the rod type welded joint. In the deformed region, the grains are reoriented and the microstructure consists of the elongated or phase containing a lot of dislocations and intergranular β phase.
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