A comparison of the mechanisms of fatigue-crack propagation behavior in a Zr-based bulk amorphous metal in air and an aqueous chloride solution

Bulk amorphous alloys, such as the Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at.%) alloy, have received much interest lately, particularly for their commercial application in golf club heads. This study seeks to investigate the fatigue behavior of this Zr-based amorphous metal in the presence of air and sodium chloride solution, with the specific goal of identifying mechanisms of environmentally assisted fatigue-crack growth in these environments. Results from experiments, including fatigue testing in air and sodium chloride, fatigue under potential control, and static load testing in sodium chloride, suggest that quite distinct mechanisms of fatigue-crack propagation are active in air and sodium chloride solution. Specifically, the fatigue-crack growth rates observed under static and cyclic loading in sodium chloride likely depend on an anodic process, which results in a brittle mode of failure. Conversely in air, fatigue-crack propagation is associated with alternating blunting and re-sharpening of the crack tip, as evidenced by the presence of classic fatigue striations.