The invariant laws of the amorphization processes by mechanical alloying

Abstract

Abstract Several Ti-, Zr-, Hf- and Nb-based alloys were synthesized using differing milling regimes. Metastable phases, either crystalline or amorphous, develop from the parent elements according to a general sigmoid-shaped behaviour ruled by an interface-controlled kinetic mechanism. The extent of the alloying reactions was related to the operating variables, experimentally determined in the course of the process. Although the transformation rates depended on the milling intensity, that is on the impact energy times the impact frequency, it was found that the reaction yield, defined by the ratio of the transformed fraction to the specific energy dose, is an invariant quantity characteristic of each system. The specific energy dose defines the mechanical work done on the system per mass unit of the reactants. A rationale for the observed behaviours was provided by the energy needed to reach a given level of the reactant dispersion. Ruling the total extent of the grain boundary area, and the overall kinetics of the alloying process, the work expended in the microstructure refinement was found to be another invariant property of the treated mixtures. The reaction yield is the reference parameter to compare milling trials on an absolute basis, so providing an opportunity towards a quantitative understanding of the mechanical alloying processes.