Phase Diagrams: The Beginning of Wisdom
---How to Read and Apply Phase Diagrams
Institute of Metallurgy, Clausthal University of Technology, D-38678 Clausthal-Zellerfeld, Germany
"Phase diagrams are the beginning of wisdom-not the end of it". This famous quotation coined by Sir William Hume-Rothery is a perfect guideline for any work in materials science and technology. Virtually all materials of practical interest are composed of various phases. Properly constructed phase diagrams display the phase relations at thermodynamic equilibrium state of matter. That makes them unique for a given material system. This work presents a primer on ‘‘How to Read and Apply Phase Diagrams’’ in the current environment of powerful thermodynamic software packages. It is a brief guide into using this cornerstone of knowledge in materials science and engineering and offers assistance in the proper interpretation of results obtained from state-of-the-art Calphad-type thermodynamic calculations. Starting from the very basics it explains the reading of unary, binary and ternary phase diagrams, including liquidus projections, isothermal and vertical phase diagram sections. Application examples are directly derived from these phase diagrams of Fe, Cu-Ni, Mg-Al, and Mg-Al-Zn. The use of stable and metastable phase diagrams and appropriate choices of state variables are explained for the relevant Fe-C and Fe-C-Si systems. The most useful concept of zero-phase fraction lines in phase diagram sections of multicomponent systems is made clear by coming back to the Cu-Ni and Mg-Al-Zn systems. At last, a simple rule based on Calphad calculations has been applied to facilitate design solid solution heat treatment process for Al- and Mg-alloys.
About the presenters: Dr. Song-Mao Liang, Research fellow in Prof. Schmid-Fetzer’s group in Clausthal University of Technology, Germay. His current research interests are on thermodynamics and constitution of multicomponent materials.