Stress corrosion cracking and fracture behaviors of gaseous-hydrogenated Titanium alloy Ti-6321 during slow strain rate tests

The stress corrosion cracking (SCC) behavior of gaseous-hydrogenated near-alpha titanium alloy Ti-6321 in the range of 20 ∼ 210 wppm (ppm by weight) was investigated using slow strain rate test (SSRT). Optical Microscopy (OM), Scanning Electron Microscopy (SEM), as well as Transmission Electron Microscopy (TEM), were utilized to observe the microstructures of raw materials, fracture surfaces, cross-sectional areas of fracture surfaces, and the microstructures after deformation; Electron Backscattered Diffraction (EBSD) method was used to analyze the grain orientations so as to analyze the fracture behavior. The results showed that the Ti-6321 alloy revealed no SCC susceptibility in this range, and the material exhibited softening effect when hydrogen content was 65wppm and a hardening effect when hydrogen content exceeded 65wppm. With the increase of hydrogen concentration, the elongation increased because the mobility of dislocations and the nucleation of twins were simultaneously enhanced by hydrogen. In addition, microvoids’ growth and nucleation were inhibited by hydrogen in the matrix.