Effect of temperature gradient on microstructure evolution in Ni–Al–Cr bond coat/substrate systems: A phase-field study

• Effect of temperature gradient on Ni–Al–Cr TBCs was investigated.
• Quantitative phase-field simulation was investigated by using MICRESS.
• Reasonable CALPHAD databases were coupled via TQ interface.
• The γ/γ′ interfacial energy was estimated by using the Kaptay's method.
• The temperature gradient promotes diffusion of both Al and Cr.

Two-dimensional (2-D) phase-field simulations were employed in the present work to investigate the effect of temperature gradient on the microstructure evolution in various Ni–Al–Cr bond coat/substrate systems (i.e., β/γ + γ′, γ + β/γ + γ′, γ′ + β/γ + γ′ and γ + γ′/γ + γ′) with the aid of MICRESS (MICRostructure Evolution Simulation Software). Reliable CALPHAD (CALculation of PHAse Diagram) thermodynamic and atomic mobility databases were coupled via TQ interface. The γ/γ′ interfacial energy was estimated by using the Kaptay's method. The present phase-field simulations indicate that component Al migrates towards substrate, while component Cr towards bond coat during the interdiffusion process. The temperature gradient promotes diffusion of both Al and Cr, which greatly accelerates the failure of various bond coat/substrate systems caused by the rapid depletion of Al concentration in bond coat. Furthermore, the formation of γ′ polycrystalline structure around bond coat/substrate interface as well as in the substrate is also observed, which may result in the generation of intergranular fracture and crack propagation.