Influence of grain refinement to high-temperature chemical stability of Cu-20Co-20Cr

The oxidation behavior of Cu-20Co-20Cr alloy prepared by mechanically alloying(MA) was studied at 800 ℃ in 0.1 MPa pure O2.The alloy is composed of a mixture of two phases,α phase with the largest Cu form the matrix,while β phase with the largest Cr presented in the form of nets.The oxidation kinetics curve deviates from the parabolic rate law,and the instant parabolic rate constant increases with time more rapidly than required by the parabolic rate law.The alloy formed a multi-layer oxide scale structure,where the external layer is composed of CuO,while internal layer is mainly composed of Co2O3 and Cu2O with some black island spinel oxides of Cu2Cr2O4 and Co2Cr2O6.Moreover,the content of Cr in scales increases gradually from the external layer to internal layer,but the alloy is unable to form a continuous and thin Cr2O3 oxide layer on the surface finally.The oxidation rate of MACu-20Co-20Cr alloy was significantly higher than PMCu-20Co-20Cr alloy.This shows Cu-20Co-20Cr alloy that the rate of diffusion was greatly accelerated among different elements was unable to form the selective external oxidation of reactive component Cr after the grain size is refined.