Hydrogen-induced subcritical crack growth in Ti-6Al-4V alloy

[[abstract]]To study the subcritical crack growth (SCG) behavior of Ti-6Al-4V alloy with 47 ppm internal hydrogen, sustained load tests were performed on fatigue precracked specimens in 202 kPa Ar, 101 kPa H-2 and 505 kPa H-2 at 20, 45, 70 and 95 degrees C. The log crack velocity versus stress intensity factor curves had typical three-stage characteristics. The stage II crack growth velocity, (da/dt)(II) did not change significantly with temperature. Evidence for hydrogen-induced strain localization was found in the specimens tested in Ar and H-2 environments. From the SCG curves and fractographic findings, a fracture mode transition was found at 505 kPa H-2. As the applied initial stress intensity factor, K-ini, was between 40 and 50 MPa m(1/2), 41 55 MPa m(1/2), 70 < K-th < 76 MPa m(1/2), and (da/dt)(II) about 10(-8) mist the fracture surface showed some isolated fiat regions with micro-ridges. The transition of fracture mode is believed to be related to the relative size of plastic zone and the hydrogen affecting zone. (C) 1998 Elsevier Science.[[fileno]]2060108010042[[department]]工程與系統科學