Superplasticity in a bulk amorphous Pd-40Ni-20P alloy: a compression study

Compressive deformation behavior of a cast Pd40Ni40P20 bulk metallic glass in the supercooled liquid region (589-670 K) was investigated at strain rates ranging from 10(-4) to 10(-2) s(-1). The material exhibited excellent mechanical formability in the supercooled liquid region. However, in contrast to a Newtonian behavior generally observed in oxide glasses, the present alloy also showed a non-Newtonian behavior, depending upon the temperature and applied strain rate. Specifically, the alloy is like a Newtonian fluid at high temperatures, but becomes non-Newtonian at low temperatures and high strain rates. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution transmission electron microscopy. The non-Newtonian behavior is proposed to be associated with the glass instability during deformation. (C) 2002 Elsevier Science Ltd. All rights reserved.