Refractory complex concentrated alloys (RCCAs) exhibit promising mechanical properties for high-temperature structural applications. However, their development and practical use are hindered by extremely low ductility at room temperature, primarily caused by interstitial impurities inadvertently introduced during the RCCA processing. In collaboration with the research groups of Enrique Lavernia at Texas A&M University and Diran Apelian at UCI, we investigated the structure and properties of interstitial oxygen impurities in the MoNbTaW alloy introduced during the arc melting process. Atomic Probe Tomography and Density Functional Theory (DFT) calculations revealed localized chemical fluctuations due to oxygen segregation and oxide formation at grain boundaries. DFT calculations further demonstrated a stronger tendency for NbO and TaO formation, driven by favorable electron transfer from oxygen to Nb and Ta, as well as their low oxygen interstitial formation energies, compared to Mo and W. Our comprehensive analysis of the thermodynamics and electronic structure of oxygen absorption and grain boundary embrittlement in MoNbTaW RCCAs provides fundamental insights into the chemical driving forces behind interstitial impurity segregation. These findings are critical for the design of refractory alloys with enhanced strength and ductility.
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C. H. Belcher, D. Kamp, S. To, Y. Lu, D. Chassaing, T. Boll, B. E. MacDonald, E. M.Y. Lee, D. Apelian, and E. J. Lavernia. “The origin and control of interstitial impurities in refractory complex concentrated alloys.” Journal of Alloys and Compounds, 1010, 177520, 2025, https://doi.org/10.1016/j.jallcom.2024.177520
