Study of the Kinetics of the Order-Disorder Transformation in the Alloy MnNi₃

Citation

Loh, Eugene Yu-Cheng (1954) Study of the Kinetics of the Order-Disorder Transformation in the Alloy MnNi₃. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/D45V-WR30. https://resolver.caltech.edu/CaltechETD:etd-01082004-103918

Abstract

MnNi3 is one of many alloys, which, in equilibrium have disordered (random) and ordered atomic arrangements at temperatures above and below the so-called transition temperature respectively. Specimens of MnNi3, previously quenched from a temperature at which the structure is disordered, were heated at different constant temperatures below the transition temperature. The magnetization and resistance of these specimens were measured after different intervals of time at these temperatures for the purpose of obtaining data for a study of the kinetics of the isothermal ordering process. The mechanism of the isothermal ordering process of MnNi3 can be interpreted as first local ordering and then the growth of ordered domains. This mechanism is the same as that qualitatively described by Sykes in 1935 for AuCu3. The mechanism of the local ordering, however, is viewed in the present work as the sharpening of the Gaussian distribution curve of local composition within the alloy. Previous studies on the kinetics of ordering in MnNi3, AuCu, CoPt and AuCu3 are also reviewed and analyzed; and three different types of ordering mechanisms are proposed.

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