Date: Thursday, May 31st
Presenter: Dr. Michael Gao, National Energy Technology Laboratory, Albany, OR
In contrast to conventional alloys that are based on one principal element such as steels and aluminum alloys, HEAs contain multiple principal elements, often five or more in equimolar or near-equimolar ratios. Intuitively one would expect possible formation of complex microstructures that consist of several or many intermetallic compound phases in HEAs. But, the presence of multi-principal elements that are carefully chosen actually leads to very simple solid-solution microstructures, such as the face-centered-cubic (FCC) and body-centered-cubic (BCC) structures. The basic principle behind HEAs is that the HEA phase is relatively stabilized by the significantly higher entropy of mixing compared to intermetallic phases. What is most fascinating is that HEAs often have excellent materials properties, such as exceptionally high strength, reasonable ductility with appreciable work-hardening and plasticity, excellent corrosion resistance and oxidation resistance, great wear resistance, and outstanding diffusion-barrier performance, especially at elevated and high temperatures.
The AlxCoCrCuFeNi HEAs are known for their high strength and good wear resistance at elevated temperatures. The mechanical properties critically depend on especially aluminium contents and annealing temperatures, both of which dictate the microstructures and subsequent phase transformations involving A1, A2, and B2 phases. Experiments on the microstructure evolution, tension and compression strength, wear, corrosion, and oxidation have been documented in the literature. To gain fundamental understanding on HEA formation and their properties, the high-entropy AlxCoCrCuFeNi alloys are studied using ab initio molecular dynamics simulations and neutron scattering experiments. In this talk, introduction to HEAs will be given, and research progress in theoretical modelling and experimental study of this class HEAs will be presented.