Simulation of reaction-diffusion phenomena occurring between Ir coating and Ni-Al alloy substrate using phase-field model

It is very important to understand the development of the microstructure in the interdiffusion zone between coatings and superalloy substrates for designing bond coat materials. In this study, the reaction-diffusion phenomena in the Ir-coating/Ni -Al binary substrate system are simulated using the phase-field model. The thermodynamic database developed based on the CALPHAD method is directly incorporated in the simulation. The effect of coating thickness on the growth of the secondary precipitated β-phase is discussed. In the case of a semi-infinite system, the thickness of the β-phase increases proportionally with the square root of time. In the case of a thin (1 μm thick) coating, inconstant β-phase growth is observed. It is suggested that the phase growth is related to the change in the β-phase fraction, which is derived from a thermodynamic line calculation from the substrate composition to pure Ir.