Chapter 1 - General Introduction

Abstract

This chapter provides a general introduction of the book that deals particularly with changes in the phase structure of metals and alloys when the external constraints are varied. In a complete discussion of the theory of phase changes, the phase change, and transformation mechanism, two questions must be considered. To answer the first question the chapter investigates the properties of different arrangements of a given assembly of atoms or molecules and thus attempts to find the equilibrium configuration. The second fundamental question focuses on how a transformation occurs. Any phase transformation requires a rearrangement of the atomic structure of the assembly. The methods of classical thermodynamics are now of more limited application, since phase transformations are “natural changes.” The appropriate theories are essentially kinetic theories, and some model of the atomic processes involved is implicit in any treatment. An assembly of atoms or molecules that has attained equilibrium under specified external constraints consists of one or more homogeneous and physically distinct regions. The regions of each type may be distinguished by a common set of parameters defining such intrinsic properties as density, composition, etc., and they constitute a phase of the assembly.