Effect of oxygen on the crack growth behavior of V–4Cr–4Ti at 600°C

Exploratory experiments were performed to evaluate the effect of oxygen on the crack growth response of V–4Cr–4Ti at 600°C under constant load. Tests were run in gettered argon, argon containing 2000 ppm oxygen, and laboratory air using fatigue pre-cracked compact-tension (CT) specimens. Crack growth was measured primarily by post-test fracture surface examination, but also by in-test compliance measurements. Crack growth rates measured in air and gettered argon were about 2–3 × 10−3 mm/h at a stress intensity factor of about 40 MPa m. The crack growth rate in argon with 2000 ppm oxygen was about 7 × 10−2 mm/h at the same stress intensity level. The crack growth rates were very sensitive to the stress intensity factor. Over a limited range of stress intensity values the crack growth rate in argon plus 2000 ppm oxygen appears to be power-law dependent on stress intensity with an exponent of about 8.9. The fracture mode in air and gettered argon was transgranular cleavage with 20–30% intergranular fracture. In the oxygenated argon environment crack growth occurred predominantly by transgranular cleavage.