Mechanisms of elevated temperature fatigue crack growth in Zr–Ti–Cu–Ni–Be bulk metallic glass

Abstract Zr-based bulk metallic glasses (BMGs) are surprisingly susceptible to cyclic fatigue processes. In the present study, the sub- T g elevated temperature fatigue crack growth behavior was examined. The fatigue threshold, Δ K TH , was found to increase from ∼1.1 to ∼1.4 MPa m 1/2 as testing temperature was increased from 100 to 220 °C. Low levels of fatigue crack closure were apparent and not associated with threshold behavior. Regular arrays of micron-sized elongated ridges formed parallel to the crack growth direction in the near-threshold fatigue crack-growth regime at elevated temperatures. A model for ridge formation based upon the planar stability of a Mode I crack was proposed. Ridge wavelengths and amplitudes were accurately predicted with respect to changes in applied stress intensity and temperature, and ridge angles were calculated on the basis of a Mohr–Coulomb yield criterion.