Cyclic deformation and fatigue crack propagation of a Zr-based bulk amorphous metal

Abstract

The behavior of the cyclic deformation and fatigue crack propagation of Zr 41.25Ti 13.75Ni 10Cu 12.5Be 22.5 (in at.%) bulk amorphous metals is investigated. Both fully amorphous and partially crystallized metals are characterized in order to understand the fatigue behavior of these different microstructures. Under fully reversed load control, both amorphous metals show stable cyclic strain response until final fracture. The partially crystallized metal shows an inferior fatigue resistance in comparison with that of the fully amorphous metal. The absence of definite crystalline microstructure in the amorphous metal and a relatively small area of stable crack propagation on the fracture surface are main reasons for the stable strain response under cyclic deformation. Similar to the ductile crystalline alloys, the fatigue crack propagation of both amorphous metals obeys Paris power-law relationship at intermediate growth rates. Both fully amorphous and partially crystallized metals show a similar law of fatigue crack propagation in that their values of threshold and fatigue exponents m are comparable. The mechanisms of fatigue crack propagation in the region of near-threshold and intermediate crack growth are similar to that of ductile crystalline alloys. The crystalline phases in the partially crystallized metals can retard the crack or act as sites of crack initiation when they are oriented at a suitable direction for that of crack propagation.