Impact of Gd minor alloying on the crystallization kinetics of Pd40Ni40P20 bulk metallic glass

Khademorezaian S.; da Silva Pinto M.; Zhou H.; Peterlechner M.; Wilde G.

Abstract

Minor alloying of metallic glasses is understood as a possible way to tune its properties and provides a study framework to the origin of their effects. Here, crystallization kinetics of Pd40Ni40P20 and minor-alloyed samples (Pd40Ni40P20)99Gd1 were studied using isothermal and isochronal calorimetry and the results were analyzed using the Johnson-Mehl-Avrami-Kolmogorov model. The addition of 1 at. % Gd into the primary alloy results in a substantial alteration of the crystallization kinetics. The Avrami exponent obtained directly from the calorimetric measurements varies from 2.5 for the ternary alloy to almost 4 for the minor-alloyed sample, indicating a change of the crystallization mechanism from a diffusion-controlled crystallization process with a constant nucleation rate and a gradually decreasing three-dimensional growth rate, to a transformation with a constant nucleation rate and a constant three-dimensional growth rate. TEM (transmission electron microscopy) microstructural analysis of the crystallized state indicates the formation of Pd-Gd-P areas, which might accelerate crystallization kinetics.