Isothermal Oxidation Behaviour of Ni–Cr–Ta–Al–Co–Mo Alloy at 900oC and 1000oC

The oxidation behaviour of Ni12.59Cr6.74Ta4.04AI5.16Co1.35Mo6.29W superalloy at 900℃and 1000℃in air has been investigated by means of measuring the kinetics curves of the oxidation and analysis method of TGA,XRD and SEM(EDAX).Results show that the initial oxidation rate is large, and the rate of mass gaining decreases gradually with time extending,the oxidation kinetics obeys parabolic law.After oxidized at 900℃and 1000℃,three oxide layers form in the alloy including the outer consists of Cr_2O_3,AI_2O_3,a few(Ni,Co) Cr_2O_4 and CrTaO_4 phases,middle consists of AI_2O_3 phase,and internal oxidizing layers is identified as AI_2O_3 phase.In the oxidizing process of the alloy,the phase containing Ta-richer may restrain diffusing outward of the element Al in the matrix,which restrains the growth up of the oxide scales to decrease the oxidizing rate of the alloy.