Oxidation Behaviour of Refractory (HfCo)(100-x)(NbMo)(x) High-Entropy Alloys with a bcc+B2 Structure

Herein, the oxidation behaviour of refractory (HfCo)(100-x)(NbMo)(x) (x = 0; 10; 25; 40; 75; 100 (at.%)) high-entropy alloys with a bcc+B2 structure subjected to cyclic oxidation at 1000 degrees C was studied. The single-phase B2-ordered HfCo alloy demonstrated the best spallation resistance and retained a pristine form after 100 h. The oxidation kinetics of the HfCo alloy was near-parabolic, accompanied by the formation of external HfO2 or CoO layers after 1 or 100 h, respectively. Additions of (NbMo)(x) deteriorated the spallation resistance (x = 25 at.%) or led to complete disintegration (x > 25 at.%). Among the (NbMo)-containing alloys, the (HfCo)(90)(NbMo)(10) alloy with the dual phase bcc+B2 structure showed the most promising oxidation resistance. This alloy withstood cyclic oxidation up to 15 h with a mass gain close to the HfCo alloy and survived 100 h without changes in geometry of the specimen. Unlike the HfCo alloy, in the (HfCo)(90)(NbMo)(10) alloy, the external CoO layer was found already after 1 h. The effect of chemical and phase compositions on the formation of certain oxides was discussed. Comparison with the other refractory high-entropy alloys was also presented.

Automated summary

The oxidation behavior of refractory (HfCo)(100-x)(NbMo)(x) (x = 0; 10; 25; 40; 75; 100 at.%) high-entropy alloys with a bcc+B2 structure subjected to cyclic oxidation at 1000 degrees C was studied. The addition of (NbMo)(x) deteriorated the spallation resistance and led to complete disintegration. Among the (NbMo)-containing alloys, the (HfCo)(90)(NbMo)(10) alloy with the dual phase bcc+B2 structure showed the most promising oxidation resistance.