Crack initiation and short crack propagation of friction stir welded TC17 alloy joint.

• TMAZ consists of needle-like α precipitates and elongated α p within β grains. • Fine β grains in SZ contribute to the highest strength in the 3rd layer. • Cracks tend to nucleate from HAGBs and {1 1 2} 〈1 1 1〉 slip deformation of β structure. • Fatigue cracks initiate from the 2nd layer of SZ below 210 MPa. • Crack growth exhibits a higher crack growth rate in HAZ than SZ. Heterogeneities of microstructure, tensile and fatigue behavior of FSWed titanium alloy joint were in-situ studied by utilizing replica, DIC and electron back-scattered diffraction methods. Banded TMAZ consisting of needle-like α precipitates and elongated α p within DRXed β grains bridges the HAZ and SZ. Fine β grains in SZ contribute to the highest tensile strength in the 3rd layer. Fatigue cracks prefer to nucleate from HAGBs and {1 1 2} 〈1 1 1〉 slip deformation of β structure in the 2nd layer of SZ below 210 MPa and 3rd layer of HAZ otherwise. Transgranular crack propagation along the {1 1 2} planes exhibits a higher crack growth rate in HAZ than SZ. [ABSTRACT FROM AUTHOR]