Effects of oxygen, water vapor, argon, air and exposure history on fracture strength of Ti–48Al–2Nb–2Cr notched tensile specimens

Thin plate notched tensile specimens with 0.14 mm radius 45° notches were deformed in tension with step-wise load increments in 2–3 torr gas environments in-situ in an environmental scanning electron microscope and in air. The load was applied in small increments near the fracture load, resulting in average net area stressing rates near 10 kPa s−1. Fracture occurred at net area stresses near 200 MPa, for all conditions. Contrary to experiments in vacuum, 16 out of 17 specimens in gas environments fractured suddenly without stable crack growth being observed. Specimens in which the grip slipped before fracture were unloaded, exposed to air and reloaded to failure. Specimens deformed with various loading and aging histories in air were evaluated to determine how air can attack TiAl that is slightly damaged. Specimens with prior net area stress history above 100 MPa and exposed to air had a higher probability of failing at lower stress levels. The effects of loading history on damage nucleation and environmental degradation is discussed with the potential to use this effect to help identify stress and/or strain criteria for damage nucleation.