Deformation and fracture of an amorphous PdCuSi alloy in V-notch bending tests—II: Ductile-brittle transition

Abstract

The ductile-brittle transition in an amorphous Pd 78Cu 6Si 16 alloy upon isothermal annealing at 623 K is studied. Specimens with 45 V-notches in plane strain and plane stress were tested in bending. In plane-strain specimens, macroscopic changes in fracture modes were characterized by: (1) sliding off after general yielding; (2) crack initiation and unstable fracture after general yielding; (3) brittle fracture accompanied by plastic flow; (4) brittle fracture. Fibrous-cleavage transition was also found as a change in the mode of microscopic fracture in plane strain. The ductile-brittle transition in plane stress is postponed to a longer annealing time than in plane strain. The critical tensile criterion based on Hill's slip-line field does provide a self-consistent explanation of the mechanics of various macroscopic fracture phenomena in plane strain. Derived microfracture stress is found to be a structure-sensitive material parameter. A correlation between crack-opening displacement and dimple size in plane-strain and plane-stress specimens provides an experimental model for void coalescence. The micro-mechanism of fibrous fracture in an elastic-perfectly plastic solid is discussed.