Oxidation Behaviors in High Entropy Alloys

These examples show the application of oxidation when using the TCS High Entropy Alloys Database (TCHEA). Including oxygen (O) in the simulations allows for the study of oxidation behaviors of HEAs at various compositions, temperatures, and oxygen activities.

The element oxygen (O) and relevant oxide phases are included in the database starting with version 8.0 (TCHEA8).

Oxidation of AlxCoCrFeNi

This is an example of the oxidation of AlxCoCrFeNi HEAs at 1273 K. The plot shows that with the increase of Al, the microstructure of the base HEA Alx(CoCrFeNi) shifts from a single FCC to dual B2+FCC, where the inner oxidation product corundum shifts from Cr2O3- to Al2O3-dominant.

At high Al, for example 9 and 12 at%, Al2O3 corundum is stable at very low oxygen activity. There is various multicomponent spinel phases that result as inner oxidation products. When Al is increased, the spinel phase contains more Cr but less Fe. Also, halite forms at low Al alloys. Overall, it predicts improved oxidation-resistance with the increase of Al, which agrees well with the experimental observation of [2021Dab].

The oxidation of AlxCoCrFeNi HEAs at 1273 K.

Figure 1: The oxidation of AlxCoCrFeNi HEAs at 1273 K.

Oxidation Resistant Refractory HEA Protected by Rutile Oxide

The microstructure of the alloy Al17.6Cr25.2Mo20.3Nb15.2Si2.9Ta13.4Ti5.4 (at%) consists of three phases (BCC + Sigma + Laves). The main oxidation products are rutile (CrTaO4 dissolving Al, Cr, Ti, etc.) and corundum (Al2O3 and Cr2O3). The MoO3-dominant liquid around x(O)=0.7 indicates the porous oxide scale. Most important, the continuous rutile oxide scale attributes to the high oxidation-resistance of this RHEA, which agrees well with the experimental observation of Lo et al. [2019Lo].

An example of the oxidation resistant refractory HEA alloy Al17.6Cr25.2Mo20.3Nb15.2Si2.9Ta13.4Ti5.4 (at%) with the main oxidation products of rutile and corundum.

Figure 2: An example of the oxidation resistant refractory HEA alloy Al17.6Cr25.2Mo20.3Nb15.2Si2.9Ta13.4Ti5.4 (at%) with the main oxidation products of rutile and corundum.

References

[2019Lo] K.-C. Lo, Y.-J. Chang, H. Murakami, J.-W. Yeh, A.-C. Yeh, An oxidation resistant refractory high entropy alloy protected by CrTaO4-based oxide. Sci. Rep. 9, 7266 (2019).

[2021Dab] J. Dąbrowa, G. Cieślak, M. Stygar, M. Zajusz, M. Jawańska, A. Gil, J. Jedliński, K. Mroczka, K. Matsuda, T. Kulik, M. Danielewski, Oxidation Behavior of Alx(CoCrFeNi)100-x High-Entropy Alloys Under Thermal-Cycling Conditions. Oxid. Met. 96, 307–321 (2021).