Phase Diagrams: The Beginning of Wisdom

Abstract

This work presents a primer on ''How to Read and Apply Phase Diagrams'' in the current environment of powerful thermodynamic software packages. Advanced aspects in that context are also covered. 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 stateof-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. Thermodynamic solidification simulation using the Scheil approximation in comparison to the equilibrium case is covered in context of multicomponent multiphase solidification and exemplified for Mg-Al-Zn alloys. The generic approach is directly applicable for all inorganic materials, but exemplified in this concise work for a small selection of metallic systems to highlight the interdependences among the phase diagrams. The embedded application examples for real material systems and various materials processes also emphasize the use of phase diagrams for the path from initial off-equilibrium state towards equilibrium.

PHASE DIAGRAMS AND THEIR APPLICATIONS TO Mg ALLOYS

“…There are two main reasons: (i) the need to address multicomponent systems for "real" materials, and (ii) the additional benefits of quantitative prediction of phase formation of a selected multicomponent alloy under equilibrium and special off-equilibrium processing conditions. Many of such applications are exemplified in a recent work [3], which is also a primer on "How to Read and Apply Phase Diagrams" in the current environment of powerful software packages.…”

“…That phase is modeled by intermixing of Ce and La on the first sublattice of the single phase (Ce, La) 1 Mg 3 . In the entire Mg database with 25 components, PanMg (www.computherm.com), the phase RMg 3 with crystal structure cF16-BiF 3 is modeled as (Ce,Gd,La,Nd,Y) 1 (Li,Mg,Zn) 3 . The major constituents are highlighted by bold font whereas Y, Li, and Zn are minor constituents indicating that these elements exhibit limited solubility only in the phase RMg 3 .…”

“…A more detailed discussion of the Scheil approximation in the context of numerical "Scheil algorithms" is given in ref. [3].…”

Material design and development: From classical thermodynamics to CALPHAD and ICME approaches

“…Current material software and research codes focusing integrated for ICME implementation. Such integration would require 30 error) to meet specific system design goals [95,96]. ICME can unite materials, manufacturing and system design into a holistic computational framework in the development of new mate and manufacturing processes as shown in Fig.…”

Calculation of 2D and 3D Phase Diagrams

“…3 In the early days, most phase diagrams were measured experimentally and limited to unary, binary and ternary systems. 4,5 Calculation of phase diagrams can be dated back to van Laar 6,7 and Meijering, 8 who calculated some simple binary and ternary phase diagrams with miscibility gaps.…”