Thermal and mechanical stability of a Ni 55Cr 5Nb 40 metallic glass

Abstract

Differential scanning calorimetry (DSC), temperature dependence of ductility and hardness and stress relaxation measurements have been employed to study the thermal and mechanical stability of a Ni 55Cr 5Nb 40 glass. The results are compared with the data reported [1. L.E. Collins, N.J. Grant and J.B. Vander Sande, J. Mater. Sci. 18, 804 (1983); 2. L.E. Collins and N.J. Grant, Mater. Sci. Engng 61, 137 (1983)] for the binary Ni 60Nb 40 glass to ascertain the effects of Cr addition. It is observed that crystallization temperature and activation energy for crystallization of Ni 55Cr 5Nb 40 glass are considerably less than that of the binary alloy. An annealing embrittlement phenomena is observed in the ternary glass similar to that reported in Ni 60Nb 40, however, ductile-brittle transition temperature is reduced drastically on the addition of Cr. Hardness increases on annealing and follows a behaviour similar to that of embrittlement. Kinetic studies of annealing embrittlement and stress relaxation yield a spectrum of activation energies for structural relaxation. These values are significantly smaller than for the Ni 60Nb 40 glass. It is concluded that the addition of Cr reduces the thermal as well as the mechanical stability of the Ni 60Nb 40 glass.