Phase Transformations in Metals and Alloys

David A. Porter, Kenneth E. Easterling, Mohamed Y. Sherif

• Editore: CRC Press
• Anno: 2021
• ISBN:
  9781000467826
• Edizione: 4
• Argomento: Physical Sciences
• Categoria: Thermodynamics

Revised to reflect recent developments in the field, Phase Transformation in Metals and Alloys, Fourth Edition, continues to be the most authoritative and approachable resource on the subject. It supplies a comprehensive overview of specific types of phase transformations, supplemented by practical case studies of engineering alloys. The book's unique presentation links a basic understanding of theory with application in a gradually progressive yet exciting manner. Based on the authors' teaching notes, the text takes a pedagogical approach and provides examples for applications and problems that can be readily used for exercises.

NEW IN THE FOURTH EDITION

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• 40% of the figures and 30% of the text

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• Insights provided by numerical modelling techniques such as ab initio, phase field, cellular automaton, and molecular dynamics

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• Insights from the application of advanced experimental techniques, such as high-energy X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, combined with electron backscattered diffraction

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• New treatment of ternary phase diagrams and solubility products

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• The concept of paraequilibrium in systems containing highly mobile interstitial elements

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• Thermodynamics of grain boundaries and the influence of segregation on grain boundary diffusion

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• Reference to software tools for solving diffusion problems in multicomponent systems

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• Introduction to concepts related to coincident site lattices and methods for determining the dislocation content of grain boundaries and interfaces

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• Updated treatment of coherency and interface structure including the important fcc–bcc interfaces

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• Treatment of metallic glasses expanded to cover critical cooling rate

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• Austin–Rickets equation introduced as an alternative to the Avrami equation in the case of precipitation kinetics

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• Discussion of the effects of overlap in nucleation, growth and coarsening

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• Discussion of pearlite and bainite transformations updated

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• Entirely new and extensive treatment of diffusionless martensitic transformations covering athermal and thermally activated martensite in ferrous systems as well as shape memory, superelasticity and rubber-like behavior in ordered nonferrous alloys

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• New practical applications covering spinodal alloys, fir-tree structures in aluminum castings, Al–Cu–Li aerospace alloys, superelastic and shape memory alloys, quenched and partitioned steels, advanced high-strength steels and martensitic stainless steels

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• Each chapter now concludes with a summary of the main points

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• References to scientific publications and suggestions for further reading updated to reflect experimental and computational advances

Aimed at students studying metallurgy and materials science and engineering, the Fourth Edition retains the previous editions' popular easy-to-follow style and excellent mix of basic and advanced information, making it ideal for those who are new to the field.

A new solutions manual and PowerPoint figure slides are available to adopting professors.

1 Thermodynamics and Phase Diagrams

DOI: 10.1201/9781003011804-1

This chapter deals with some of the basic thermodynamic concepts that are required for a more fundamental appreciation of phase diagrams and phase transformations. It is assumed that the student is already acquainted with elementary thermodynamics and only a summary of the most important results as regards phase transformations will be given here. Fuller treatments can be found in the books listed in the bibliography at the end of this chapter.

The main use of thermodynamics in physical metallurgy is in the prediction of equilibrium conditions in an alloy. In considering phase transformations we are always concerned with changes towards equilibrium, and thermodynamics is therefore a very powerful tool; it can allow the calculation of the driving force for the transformation, and the conditions that exist locally at interfaces before equilibrium is reached throughout the system.

1.1 EQUILIBRIUM

It is useful to begin this chapter on thermodynamics by defining a few of the terms that will be frequently used. In the study of phase transformations, we will be dealing with the changes that can occur within a given system, e.g., an alloy that can exist as a mixture of one or more phases. A phase can be defined as a portion of the system whose properties and composition are homogeneous and which is physically distinct from other parts of the system. The components of a given system are the different elements or chemical compounds which make up the system, and the composition of a phase or the system can be described by giving the relative amounts of each component.

The study of phase transformations, as the name suggests, is concerned with how one or more phases in an alloy (the system) change into a new phase or mixture of phases. The reason why a transformation occurs at all is because the initial state of the alloy is unstable relative to the final state. But how is phase stability measured? The answer to this question is provided by thermodynamics. For transformations that occur at constant temperature and pressure, the relative stability of a system is determined by its Gibbs free energy $\left(G\right)$.

The Gibbs free energy of a system is defined by the equation

$$G=H-TS$$(1.1)

where H is the enthalpy, T is the absolute temperature and S is the entropy of the system. Enthalpy is a measure of the heat content of the system and is given by

$$H=E+PV$$(1.2)

where E is the internal energy of the system, P is the pressure and V is the volume. The internal energy arises from the total kinetic and potential energies of the atoms within the system. Kinetic energy can arise from atomic vibration in solids or liquids and from translational and rotational energies for the atoms and molecules within a liquid or gas; whereas potential energy arises from the interactions, or bonds, between the atoms within the system. If a transformation or reaction occurs, the heat that is absorbed or evolved will depend on the change in the internal energy of the system. However, it will also depend on changes in the volume of the system and the term PV takes this into account, so that at constant pressure the heat absorbed or evolved is given by the change in H. When dealing with condensed phases, i.e., solids and liquids, the PV term is usually very small in comparison t...