(376aq) Phase Thermodynamics and Ab Initio Simulations to Optimize Oxidation Resistance of High Entropy Alloys in Additive Manufacturing

Materials used in vehicle engines, space shuttles, etc. are often exposed to extreme oxidation conditions with temperature over 1000K. This application requires improved materials with increased oxidation resistance. One approach is to use additive manufacturing to build oxidation-resistant coatings on traditional alloy engine parts. Hence, there is a need to search for materials that have a combination of specialized mechanical properties (amenable to additive manufacturing) and thermal/chemical properties (high oxidation resistance and melting point). High entropy alloys (HEA), which contain four or more constituent elements, are one possible class of materials to address this challenge. For example, equimolar Mo-W-Al-Cr-Ti has high oxidation resistance [1], while equimolar Nb-Mo-Ta-W and V-Nb-Mo-Ta have high yield stress of 1058 MPa and 1246 MPa respectively [2]. However, the HEA search space is far too large for exhaustive experimental search methods to discover alloys with desired properties. In this work we show how thermodynamic methods like Calculated Phase Diagrams (CALPHAD) and ab initio calculations from Density Functional Theory (DFT) can correlate with oxidation resistance and additive manufacturing ability of high entropy alloys. Even these theoretical methods are too slow to directly search the entire composition space. We further demonstrate the use of machine learning to guide these calculations and accelerate the underlying ab initio methods.

References:

1. Gorr, B., Azim, M., Christ, H. J., Mueller, T., Schliephake, D., & Heilmaier, M. (2015). Phase equilibria, microstructure, and high temperature oxidation resistance of novel refractory high-entropy alloys. Journal of Alloys and Compounds, 624, 270-278.
2. Senkov, O. N., Wilks, G. B., Scott, J. M., & Miracle, D. B. (2011). Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys. Intermetallics, 19(5), 698-706.