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Title: A summary of 'solid state amorphisation'
Author: Highmore, R. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1989
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Abstract:
In chapter 1 I provide an introduction to solid state amorphisation, explain how the subject has developed and describe different means of making metallic glasses in the solid state. In chapter 2 I comment upon models for atomic transport in metallic glasses and suggest how these might allow the diffusional asymmetry which is felt to be essential for formation of amorphous alloys by interdiffusion. I discuss the origins of the thermodynamic driving force for amorphisation and compute semi-quantitative diagrams of free energy as functions of composition. I compare the predictions of these diagrams with data obtained using calorimetry. I describe relationships between eutectics, in either equilibrium or metastable binary phase diagrams, and formation of metallic glasses by melt quenching or solid state reaction. I suggest how these phase diagrams might evolve as the stability of the liquid alloy relative to the mixture of crystalline elements is varied. I propose that there may exist a novel transformation, an inverse eutectic transition. I conclude the chapter by discussing lattice instability models of solid state amorphisation. In chapter 3 I discuss factors which may determine the kinetics of amorphous phase growth. I comment upon nucleation at a Ni/Zr interface, and in particular how one might reconcile the experimental consensus that there is a barrier to nucleation of an amorphous phase with the prediction of classical nucleation theory that no such barrier should exist. I suggest a model in which strained solid solutions are formed as precursors to the amorphous phase. I examine how the amorphous alloy is able to attain a certain critical thickness, after which a crystalline compound forms and grows instead. I suggest that the crystalline compound is suppressed because sub-critical clusters of that phase are consumed by the growing amorphous layer, and that this is made possible by two factors: diffusional asymmetry in the amorphous alloy, and long transient times for nucleation of crystalline compounds at temperatures below the glass transition temperature. I derive approximate expressions for the critical rate of thickening of the amorphous layer (above which suppression is possible) and for the maximum thickness which the amorphous layer can attain before the crystalline phase nucleates. I draw analogies between this model for amorphisation and the situation which is envisaged for formation of glasses by rapid quenching of the melt. I suggest describing thin film reactions by constructing analogues of TTT plots. I write about the usefulness of solid state reaction as a means of manufacturing metallic glasses, review the possible role which gaseous impurities play an amorphisation, and suggest simple means of predicting the likelihoods of binary systems forming metallic glasses by solid state reaction. In chapter 4 I describe the methods which I used to gain the experimental results presented in chapters 5, 6 and 7. In chapter 5 I describe how I used d.c. magnetron sputtering to grow Ni/Zr multilayers. I relate experiments in which the magnetron powers and thermalisation used to deposit the multilayers were varied, one at a time, and explain how changing these parameters affected the degree of mixing at Ni/Zr interfaces, the roughnesses of interfaces, and the textures and stress states of the elemental layers. I interpret the results in terms of the energy input to atoms on the instantaneous surface of a growing film. In chapter 6 I explain how I used differential scanning calorimetry (DSC) and x-ray diffraction to follow amorphisation and subsequent crystallisation in Co/Zr and Ni/Zr multilayers. I derive a model for DSC traces caused by diffusion-controlled layer growth reactions in which there is an Arrhenius dependence of the interdiffusion coefficient and a constant pre-exponential factor and activation energy. I use this model to derive interdiffusion coefficients from experimental DSC traces, and to compute simulated DSC traces. I describe attempts to observe homogeneous amorphisation in thin films and bulk samples of Cr-Ti. In chapter 7 I recount work in which I used differential scanning calorimetry to gain quantitative information concerning the kinetics and thermodynamics of oxygen intercalation and desorption in superconducting Y1Ba2Cu3O7-x. In chapter 8 I summarise the dissertation and suggest ideas for future work.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.604042  DOI: Not available
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