Cyclic softening of Zr_(55)Al_(10)Ni_5Cu_(30) bulk amorphous alloy

摘要

In the last decade, Zr-based [1, 2] amorphous alloy systems exhibiting a wide supercooled liquid region combined with a distinct glass transition have attracted considerable interest, for these types of alloys allow the production of large-scale bulk amorphous specimens by the conventional casting process at low cooling rates of 1-10 k/s. The bulk amorphous alloys make it possible to conduct mechanical testing under a much wider range of conditions compared with earlier as-quenched metallic glasses. Recently, several studies of mechanical properties of bulk amorphous alloys, including fracture toughness and fatigue-crack propagation, have been done [3-8], In contrast to oxide glasses, bulk amorphous alloys can exhibit fracture toughness as high as ～55 MPam, and also show fatigue-crack growth properties comparable to those of high-strength steels and aluminum alloys. Conversely, fatigue life-limes are much shorter in the amorphous alloy as compared with the steels and exhibit a far lower dependence on the applied stress range. The low fatigue strengths have been considered to be due to the inhomogeneous slip distribution, and no microstructure stabilizes the crack growth for these amorphous alloys. However, in the partially or fully crystallized condition, the bulk amorphous alloys become brittle and display a severe drop in fracture toughness [3, 8].