Interdiffusion and segregation in materials including high entropy alloys
Many materials depend on interdiffusion for their formation. In service, the components of many materials segregate as a result of the high temperatures and large driving forces present. This can lead to a degradation of designed properties. In this research program we have been investigating all aspects of interdiffusion and segregation processes in technologically important materials.
Segregation of atomic species to surfaces and grain boundaries is of special interest in the Centre. At present, we are examining cation segregation processes in the solid electrolytes: yttria-stabilized zirconia and magnesium and strontium doped lanthanum gallate as well as interdiffusion in a number of multicomponent alloys including austenitic stainless steel.
Recently we have been awarded research funding for work on the diffusion kinetics in high entropy alloys (HEAs). HEAs are a special class of multicomponent alloys with roughly equi-atomic elements. With between 5 and 13 components they have extraordinary properties including high levels of creep, oxidation and corrosion resistance at high temperatures, outstanding wear resistance, exceptionally high temperature strength, high hardness, superior thermal and chemical stability and outstanding magnetic properties
Thermodynamics tells us that because of the high configurational entropy, HEAs are stable at high temperatures but probably not at lower temperatures. Nonetheless, the high temperature state remains metastable at lower temperatures because of the sluggish kinetics of mass transport. Mass transport is thus the key which determines the longevity of HEAs by determining the kinetics of unmixing, intermetallic compound formation, grain growth and creep. The aims of this part of the Project are to:
- Focus on HEAs with an intensive development of a new atomistic theory that has input from experimental thermodynamic data and density functional theory. This theory will have the capacity to predict mass transport behaviour such as unmixing, intermetallic formation, grain growth and creep in HEAs.
- Extensively develop and extend their phenomenological mass transport formalism to target the very rapid acquisition of experimental mass transport data in extreme multicomponent (5 or more) alloy systems.
- Concurrently engage in an integrated experimental program for mass transport data acquisition in key HEA systems and theory validation.