M. Gao – High-Entropy Alloys (2016)

Автор: M. Gao
Название книги: High-Entropy Alloys
Формат: PDF
Жанр: Физика
Страницы: 524
Качество: Изначально компьютерное, E-book

This book provides a systematic and comprehensive description of high-entropy alloys (HEAs). The authors summarize key properties of HEAs from the perspective of both fundamental understanding and applications, which are supported by in-depth analyses. The book also contains computational modeling in tackling HEAs, which help elucidate the formation mechanisms and properties of HEAs from various length and time scales.

Scientific curiosity has driven Professors Jien-Wei Yeh and Brian Cantor to
investigate multicomponent solid solution alloys in equal or near-equal molar
ratios since 1995 and 1981, respectively. Both unconnectedly published their
research in scientific journals in 2004. These unique alloys, in sharp contrast
to traditional alloys based on one or two principal elements, have one striking
characteristic: the unusually high entropy of mixing. Thus Prof. Yeh named
these new alloys as high-entropy alloys (HEAs), and they soon have attracted
the ever-rising interest from academia and industries all over the world. The
history, definition, and progress of HEAs are introduced in Chap. 1, while their
promising potential applications and perspectives are outlined in Chap. 15.
Since the first six journal papers published in 2004, there have been tremendous
progress and development in both the fundamental understanding and applications
of HEAs. This book is written in order to capture in time what have been understood,
what attractive properties have been reported, and what challenges still
remain pertaining to HEAs. In particular, this book attempts to tackle these questions:
What kinds of physical and metallurgical aspects contribute to those superior
material properties that are unique to HEAs? What are the entropy sources of
HEAs? How can we accelerate the design and development of single-phase
HEAs and high-performance multiphase HEAs? What are the proper modeling
techniques available to mimic the disordered structures of HEAs at the atomic
level, and how can they in turn help people understand the formation and properties
of HEAs?
The 15 chapters cover very wide spectra of HEAs, ranging from manufacturing
and processing, to advanced characterization, to mechanical and functional properties
and from physical metallurgy to computational modeling on different time
and length scales. This book mainly presents our own research work, including a
great amount of unpublished results, but it also contains a minor amount of review
of peers’ work in order to be comprehensive. As a result, the review portion is not
meant to be complete or impartial. The chapters are written by authors of varying
backgrounds in experiments and/or modeling, who decide their preference in the writing style and chapter contents. The intended readers of this book are students
from colleges and graduate schools and research professionals from academia and
industries.
Establishing the effective criteria to distinguish single-phase HEAs from
multiphase HEAs and bulk metallic glasses (BMGs) has been an intense research
topic. To date a number of empirical parameters have been proposed for this
purpose, and they include enthalpies of mixing of liquid and solid solution phases,
atomic size difference, electronegativity difference, valence electron concentration,
Ω-parameter, ϕ-parameter, lattice topological instability, and the root mean square
residual strain. Alternatively, one can design HEAs using the computational thermodynamic
approach (i.e., CALPHAD (acronym of CALculation of PHAse Diagrams)),
experimental phase diagram inspection, ab initio molecular dynamics
(AIMD) simulations, Monte Carlo simulations, and density functional theory
(DFT) calculations. These theoretical efforts are all addressed in Chaps. 2 and 8,
9, 10, 11, 12 and 13, and hundreds of model-predicted single-phase HEAs with the
face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal closepacked
(HCP) structures are provided in Chap. 11.
Detailed descriptions on the physical metallurgy of HEAs, which plays a center
role in understanding their processing/structure/properties’ relationships, are
presented in Chap. 3. The impact on thermodynamics, kinetics, phase transformations,
and properties from high entropy is evident, and the lattice distortion effect is
regarded to be critical to the claimed properties unique to HEAs. Chapter 4 overviews
advanced microstructure characterization tools, such as high-resolution
scanning transmission electron microscopy (STEM), analytical transmission electron
microscopy (TEM), three-dimensional atom probe, and neutron and synchrotron
scattering for characterizing HEAs. Then fabrication routes via liquid, solid,
and gas states are illustrated in Chap. 5, including ingot metallurgy, powder
metallurgy, coating, rapid solidification, mechanical alloying, single-crystal preparation
using the Bridgman method, laser cladding, and thin-film sputtering.
Mechanical properties of HEAs, which include tension, compression, hardness,
wear, fracture, fatigue, and creep behavior, are reviewed in Chap. 6 in a comprehensive
manner. Compositional, temperature, and temporal dependences of their
mechanical behavior where available are also reviewed. Functional properties are
reviewed in Chap. 7, including electrical, magnetic, electrochemical, and hydrogen
storage properties of HEAs. As a special category of HEAs, the research progress in
high-entropy BMGs is presented in Chap. 13, covering compositions, glass-forming
ability, mechanical properties, and atomic structures and diffusion constants
predicted from AIMD simulations. Chapter 14 describes the processing, microstructure,
and properties of thick or thin HEA films on substrates for protection,
function-enhancement, and/or decoration purposes.
It is worth mentioning that this book contains substantial amounts of pioneering
unpublished computer modeling work, as presented in Chaps. 8–13. Chapter 8 first
describes DFT calculations of phase stability of HEAs at zero temperature using the
cluster expansion method, molecular dynamics simulations, and Monte Carlo
simulations and then applies them to predict phase transformations in three quaternary refractory BCC HEAs and, more importantly, their entropy sources. The
applications of the coherent potential approximation (CPA) to HEAs are reviewed
in Chap. 9, and the thermodynamic, magnetic, electronic, and elastic properties of
selected HEAs are presented. Chapter 10 details the construction of special quasirandom
structure (SQS) and their applications to determine structural stability,
lattice vibrational property, electronic structure, elasticity, and stacking fault
energy in quaternary and quinary FCC, BCC, and HCP HEAs. Both the positive
and negative vibrational entropies of mixing are illustrated for selected FCC and
BCC HEAs, respectively. The development and applications of CALPHAD thermodynamic
databases for HEAs are detailed in Chap. 12, and the thermodynamic
properties (entropy, enthalpy, and Gibbs energy) of FCC and BCC HEA systems
are presented as a function of temperature and composition. The calculated entropies
of mixing in selected FCC and BCC HEAs are consistent with the DFT
calculations presented in Chaps. 8 and 10. Comparisons in the phase stability and
solidification from model predictions with experiments are also highlighted.
We are very grateful for the following scientists who kindly reviewed one or
more chapters of this book: Dan Dorescu, Sheng Guo, Shengmin Guo, Derek Hass,
Jeffrey A. Hawk, Ursula Kattner, Laszlo J. Kecskes, Rajiv Mishra, Oleg Senkov,
Zhi Tang, Fuyang Tian, Levente Vitos, Weihua Wang, Mike Widom, Quan Yang,
Fan Zhang, and Margaret Ziomek-Moroz.
Finally we would like to thank all contributors for their effort and patience.