Selection of good glass former compositions in Ni–Ti system using a combination of topological instability and thermodynamic criteria

Abstract

A combination of two criteria, which have been recently reported in the literature to predict compositions with high glass-forming ability, has been applied in the present work for the Ni–Ti system. The first criterion is an extension of the topological instability ‘λ criterion’, used here to indicate (and avoid) the composition fields associated with the crystallization of the first phase (solid solution or intermetallic compound) to appear during crystallization. The second, the thermodynamic criterion, is based on the calculation of a parameter (γ∗) that relates the enthalpies of all the competing phases including the amorphous one. A combination of these two criteria for the binary Ni–Ti system indicated the existence of only a narrow composition interval for glass formation. Alloy compositions in this interval were prepared by melt-spinning and the glass-forming ability (GFA) of the as-cast ribbons was evaluated by X-ray diffraction and differential scanning calorimetry. The results indicated that the two criteria are complementary, since compositions with high GFA are expected to have a high γ∗ parameter and also correspond to intervals where the λ parameter is greater than 0.1.