Introduction of phase diagram

Hongqun Dong 2010.10.14

Introduction of phase diagram

outline Introduction

Application of the phase diagram

The method to build a phase diagram experiments CALPHAD approach

Challenge

Introduction A phase diagram is a type of chart used to show conditions at which

thermodynamically distinct phases can occur at equilibrium.

Common components of a phase diagram are lines of equilibrium or phase boundaries, which refer to lines that mark conditions under which multiple phases can coexist at equilibrium. Phase transitions occur along lines of equilibrium.

Application Phase diagrams are the foundation in performing basic materials research

in such fields as solidification, crystal growth, joining, solid-state reaction, phase transformation, oxidation, etc.

On the other hand, a phase diagram also serves as a road map for materials design and process optimization since it is the starting point in the manipulation of processing variables to achieve the desired microstructures.

examples

The composition and melting temperature of the traditional SnPb solder can be directly obtained from the phase diagram

examples

The upper temperature of homogenization treatment can be gained, besides, it can also show the solidification process of a certain alloy.

x1

Determine the phase diagram Metallurgy—needs a lot of alloying samples

Diffusion couple (two-phase couple, multi-components couple)—often used to determine the multi-component systems

measuring tools: EPMA, SEM, XRD (occasionally)

equilibrium

CALculation of PHAse Diagrams— CALPHAD: common software Thermo-Calc (founder: B. Sundman) Pandat (founder: Y.A. Chang) Lukas program (founder: H.L. Lukas) ChemSage (founder: G. Eriksson) FACT (founder: W.T. Thompson) MTDATA (founder: A.T. Dinsdale)

General progress of CALPHAD approach

Rule to build the phase diagram

AA BB

Some models For solution phase (LIQUID, FCC, BCC, HCP…..)

ideal substitutional solution model substitutional-regular solution model associated model quisi-chemical model

For IMCs stoichiometry compounds (Neumann-Kopp rule) Compounds with the homogeneity range (sublattice model) Order-phase of the end member (depends)

Refs. H.L. Lukas, S.G. Fries and B. Sundman, Computational thermodynamics, Cambridge University Press, NY, 2007

Challenge

The fundamental experimental experiments are indispensable;

The accuracy of the outcomes deeply depend on the initial parameters inputted by users