Stress-Induced Formation of μ-TCP Phase During the Early-Stage Interdiffusion Process in the NiCrAlY/NiAlCoCrW Model Coating/Superalloy System at Ambient Temperature

In this paper, two model NiCrAlY/NiAlCoCrW coating/superalloy diffusion couples, cp0 and cp15, were prepared and subjected to annealing at 1173 K for 40 h under no stress and a uniaxial compressive stress of 15 MPa, respectively. No microstructural evolution occurred in cp0, while apparent interdiffusion zones and especially a number of TCP phases developed across the interface in cp15. The TCP precipitates, majorly consisting of Ni, Cr, Co and W, were identified as μ phase. Moreover, μ-TCP phase precipitated as small granular particles along the interface perpendicular to the loading axis, while as large needle-like ones on both coating and superalloy sides parallel to the loading direction. The formation of μ-TCP phase with complex morphologies at such early stage of interdiffusion process due to the coupled effect of compressive stress and ambient temperature may seriously reduce the creep lifetime of the coatings/superalloy system.