High-Temperature Oxidation Behavior of Plasma-Sprayed CoCrAlTaY-30Al2O3 Cermet Coating at 1050 °C

Abstract

Cermet coatings with ceramic and metal characteristics will play an increasingly important role in extending the service life of critical components in harsh service environments. In this paper, CoCrAlTaY-30Al2O3 (wt.%) cermet coating was prepared by air plasma spraying technique. The effect of powder feeding rate on the microstructure and mechanical properties of the coating and its high-temperature oxidation behavior was investigated. The results showed that the CoCrAlTaY-30Al2O3 spraying powder mainly consisted of Al5Co2, α-Al2O3, Co, Cr7C3, and TaC in five phases. The microstructure of cermet coating was uniform and its porosity was relatively low. The coating was mainly composed of Al5Co2, Cr, and Al2O3 phases, and the change of powder feeding rate had no obvious effect on the phase composition of the coating. When the powder feeding rate was 32 g/min, the minimum porosity of the coating was (3.68 ± 0.86)%, and the maximum Vickers hardness and binding strength were (664.9 ± 55.9) HV0.3 and (78.6 ± 6.6) MPa, respectively. The oxidation rate constant kp1 of the coating at 1050 °C was 0.066 mg2∙cm−4∙h−1, and the fitted curve R2 value was 0.99547. In the oxidization initial stages, the alloy elements Co, Al, and Cr in the cermet coating were rapidly oxidized to form CoO, Al2O3, and Cr2O3. Then Al2O3 and Cr2O3 reacted with CoO to form Co(Al,Cr)2O4 spinel oxides. The θ-Al2O3 phase was formed after initial oxidation while the θ-Al2O3 phase was completely transformed into α-Al2O3 after 200 h. The oxide film mainly contained Co(Cr,Al)2O4, Cr2O3, and α-Al2O3 phases.