Cyclic oxidation behavior of a cobalt aluminide coating on Co-base superalloy AMS 5608

Aluminization has been employed on alloys to form dense and adhesive Al2O3 surface layers to prolong their service life at high temperature. A cobalt-base superalloy AMS 5608 was used to deposit a cobalt aluminide layer at 950 °C for 9 h by a pack cementation process. The cyclic oxidation tests on aluminized alloys and the untreated substrate were conducted at 1100 °C for 196 h. It is found that the cobalt aluminide phase (around 60 μm in thickness) is achieved. A continuous Cr–W rich intermetallic layer is formed in the interdiffusion zone. After cyclic oxidation test, a dense and protective Al2O3 surface layer is produced on the aluminized alloy and phase transformation reactions occur in the aluminide layer and interdiffusion zone. It is observed that the aluminizing process has greatly enhanced the cyclic oxidation resistance of the Co-base superalloy at 1100 °C. However, the inward diffusion of Al and formation of cracks and pores in the interdiffusion zone cause detrimental effects on the cyclic oxidation resistance of the superalloy for long-term exposure.