Influence of MCrAlY coating on low-cycle fatigue behavior of a directionally solidified nickel-based superalloy in hot corrosive environment

The turbine blade in marine environments usually suffers from combined hot corrosive and cycle loading effects. MCrAlY coating was used as a protective coating to prevent corrosive degradation for practical applications. However, the coating can sometimes alter fatigue behavior, which is not reported for nickel-based superalloy. In the present study, MCrAlY coating influence on low-cycle fatigue behavior (e.g., lifetime and fatigue cracks initiation mechanism) was experimentally investigated in a hot corrosive environment for an uncoated and coated directionally solidified nickel-based superalloy. The lifetime of uncoated samples was drastically reduced due to corrosive attacks. However, the presence of the MCrAlY coating was beneficial for the lifetime of samples under low stresses. But the coating effect was nearly negligible under high stresses because of the early cracking. Moreover, the crack in coating facilitated corrosive elements to reach substrate materials and then local corrosion zone took place in substrate. The fatigue crack in the substrate nucleated from the local corrosion zone. Our results show that MCrAlY coating can be successfully used in machine parts in an aggressive environment only under relative lower fatigue loading condition.