Very High Cycle Fatigue Properties of a Coated Nickel-Based Single Crystal Superalloy

Very High Cycle FatigueVery high cycle fatigue (VHCF) properties of thermally sprayed MCrAlY coated samples of CMSX-4 at high temperatureHigh temperature were studied. Nine fatigueFatigue tests up to failure were performed at 1000 °C, 20 kHz, and R = –1 on coated samples. These samples showed lower fatigueFatigue life when compared with the bare reference. Fatal crack initiationCrack initiation systematically occurred at the interdiffusion zone (IDZ) between the coatingCoating and the CMSX-4 substrate or at a casting pore in the vicinity of the IDZ. Failed samples showed a high density of secondary surface cracks. In order to better understand the mechanism leading to surface crackingCracking, one interrupted test was performed. It is shown that cracks nucleated from the very first fatigueFatigue cycles and propagated through the coatingCoating almost instantly. Surface cracks then spent most of the fatigueFatigue lifetime sitting at the IDZ/substrate interface. The fatal as well as the surface crack initiationCrack initiation mechanisms are discussed to better understand the durability in these VHCF conditions.