Role of Zr in Strengthening MoSi₂ Grain Boundaries from Density Functional Theory (DFT) Calculations

MoSi₂ is a promising intermetallic compound for ultrahigh-temperature applications due to its high melting point and excellent oxidation resistance at high temperatures (> 1000 °C) [1]. However, its application is limited due to oxygen embrittlement at the grain boundaries (GBs) under low temperatures (400-600 °C), an effect also known as “pesting” [2]. In this work, we comprehensively investigate the role of Zr in mitigating pesting in MoSi₂ using DFT calculations. We show that Zr dopants reduce the embrittling effect of interstitial oxygen at MoSi₂ GBs by donating electrons to oxygen. A more significant effect is observed when Zr is present as a secondary getter nanoparticle phase. Interstitial oxygen has a strong thermodynamic driving force to migrate from MoSi₂ to the Zr sub-surface region, and the work of separation of the Zr/MoSi₂ interface, with or without oxygen interstitials, are much higher than that of MoSi₂ GBs. Finally, we will also present an efficient screening approach to identify other potential getter elements using simple thermodynamic descriptors which can be extended to other alloy systems of interest. [1] Suzuki, Y. et al, J. Am. Ceram. Soc. 81, 3141 (1998). [2] T.C. Chou and T.G. Nieh, JOM 45, 15 (1993).