Abstract
Phase-field modeling coupled with calculation of phase diagram (CALPHAD) database was utilized to perform a series of two-dimensional phase-field simulations of microstructure evolution in the γ + γ′/γ + γ′ Ni–Al–Cr mode bond coat/substrate systems. With the aid of phase-field simulated microstructure evolution, the relationship between the interdiffusion microstructure and the cohesiveness/aluminum protective property with different alloy compositions and bond coat thicknesses was fully discussed. A semi-quantitative tie-line selection criteria for alloy composition of the bond coat/substrate system with the identical elements, i.e., that the equilibrium Al concentrations of γ′ and γ phases in the bond coat should be similar to those in substrate, while the phase fraction of γ′ in the bond coat tends to be higher than that in the substrate, was then proposed to reduce the formation of polycrystalline structure and thermal shock from the temperature gradient.
Highlights
Thermal barrier coatings (TBCs) with a thickness of 100–500 μm [1], consisting of a metallic bond coat, intervening thermal grown oxide (TGO) layer, and outside ceramic topcoat, are extensively used in turbine blades to improve the high temperature resistance
Spallation and crackling of the TGO scale occurs. Another problem caused by the bond coat/substrate interdiffusion is the polycrystalline structure around the interdiffusion zone, which may aggravate crack propagation and intergranular fractures
Different types of interdiffusion microstructure will form due to the variation of alloy compositions of interdiffusion will The formthickness due to ofthe alloy in theDifferent bond coattypes and substrate for a givenmicrostructure bond coat thickness
Summary
Thermal barrier coatings (TBCs) with a thickness of 100–500 μm [1], consisting of a metallic bond coat, intervening thermal grown oxide (TGO) layer, and outside ceramic topcoat, are extensively used in turbine blades to improve the high temperature resistance. The quantitative description of the microstructure evolution in bond coat/substrate systems during service is the prerequisite for optimization of alloy composition, thickness, and service temperature, and later design of novel γ + γ0 two-phase bond coats. Employed the multi-phase-field (MPF) model to perform two-dimensional phase-field simulations of the microstructure evolution in four types of representative Ni–Al–Cr bond coat/substrate systems with different phases (including β, γ and γ0 phases). As a continuous work of our previous publication [42], a similar strategy, i.e., phase-field modeling coupled with CALPHAD-type databases, is to be utilized in the current work to perform phase-field simulation of microstructure evolution in Ni–Al–Cr mode bond coat/substrate systems, with a focus on the effect of alloy composition, bond coat thickness, and temperature gradient. By establishing the relation between the interdiffusion microstructure and the cohesiveness, the aluminum protective property with different alloy compositions and bond coat thicknesses, a trial to design the bond coat composition and thickness is to be performed, as is the major task of this paper
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