Alloy Phase Diagrams
More than two decades have passed since the previous edition of ASM Handbook, Volume 3, Alloy Phase Diagrams was published in 1992. During that time, improvements in experimental techniques and materials quality have increased the accuracy of experimental results, allowing better resolution of “fine details” and filling the remaining gaps of existing systems and resolution of phase fields for phases of marginal stability. An even more significant advance is the increased sophistication and reliability of computer modeling techniques for phase diagram calculations. “Optimizations” of binary, ternary, and higher-order systems are now commonplace, and the results are considered sufficiently trustworthy to compliment or even act as substitutes for experimentally determined data. These new calculation techniques can determine phase equilibria that could not be determined experimentally in a practical manner. The result has been numerous revisions of previously accepted phase diagrams, and predicted phase diagrams for newly assessed systems. The more recent advent of phase diagram calculations based on first principles may turn out to be the next revolution in the field.
In revising Volume 3, the decision was made to provide a better explanation of phase diagrams and their significance. This was done primarily by including several chapters of F.C. Campbell's Phase Diagrams: Understanding the Basics (ASM International, Materials Park, OH, 2012). The added material on ternary phase diagrams is of particular importance. Other explanatory material from the previous edition has been retained.
In displaying phase diagrams for this edition, it was again necessary to answer the question of whether to use atomic percent (or mole percent) scales to represent component concentration—nearly all phase diagrams currently published use atomic percent. However, most engineers still use weight percent to express alloy composition, and ASM International is at heart an organization dedicated to serving its membership. As a result, all the diagrams reproduced here use a weight percent scale. This required extensive redrawing of numerous published diagrams.
The binary section of the 1992 edition of the ASM Handbook was constructed by its editors by selecting 1053 phase diagrams from 2159 phase diagrams collected in Binary Alloy Phase Diagrams, Second Edition by editors T.B. Massalski, H. Okamoto, P.R. Subramanian, and L. Kacprzak, ASM International, Materials Park, OH, 1990. Most of these systems have been retained in this new edition, with the exception of 30 systems based on Eu, Np, and Os, which have found little practical application. A few others have been added, based on frequency of citation in the ASM Alloy Phase Diagram Database (P. Villars, editor-in-chief; H. Okamoto and K. Cenzual, section editors, ASM International, Materials Park, OH, 2006). ASM International since 1992 has published two collections of binary phase diagrams (H. Okamoto, Desk Handbook: Phase Diagrams for Binary Alloys, ASM International, Materials Park, OH, 2000; H. Okamoto, Desk Handbook: Phase Diagrams for Binary Alloys (2nd Ed.), ASM International, Materials Park, OH, 2010). The revised diagrams produced for these collections are a significant portion of the total 1095 binary diagrams in this Volume.
The number of ternary systems (115) and ternary diagrams (406) in this Volume is a considerable expansion over the number published in the 1992 edition. The choice of new systems is again based primarily on citation frequency from the ASM Alloy Phase Diagram Database. While some of these systems have been extensively investigated, in several cases the age and scarcity of the available information compared poorly with the level of interest, suggesting a new way of prioritizing future ternary-system research!
We are indebted to two colleagues and subject matter experts, Dr. Hiroshi Ohtani, Tohoku University; and Dr. Seiji Miura, Hokkaido University; who graciously agreed to review page proofs of the Volume's binary phase diagrams.
ASM International staff who deserve thanks are Amy Nolan, Content Developer; Vicki Burt, Content Developer; Steve Lampman, Senior Content Developer; Karen Marken, Senior Managing Editor; Patty Conti, Production Coordinator; Diane Whitelaw, Production Coordinator; Kate Fornadel, Senior Production Coordinator; Madrid Tramble, Manager of Production; and Scott Henry, Director, Content and Knowledge-Based Solutions.
As always, reader feedback on the phase diagram selections and other material presented in this Volume will be valuable the next time a revised edition is produced. We hope the readers of this edition will gain a better understanding of phase diagram construction and alloy system interactions, while having a valuable resource available to aid in their research and engineering pursuits.