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To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb–Si-based alloy substrate,the coating was oxidized at 1250°C for 5,10,20,50,or 100 h.The interfacial diffusion between the(Nb,X)(Si,Ge)_2(X = Ti,Cr,Hf) coating and the Nb–Si based alloy was also examined.The transitional layer is composed of(Ti,Nb)_5(Si,Ge)_4 and a small amount of(Nb,X)_5(Si,Ge)_3.With increasing oxidation time,the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate,which obeys a parabolic rate law.The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm×h~(-1/2).Moreover,the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.
To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb-Si-based alloy substrate, the coating was oxidized at 1250 ° C for 5,10,20,50, or 100 h. The interfacial diffusion between the (Nb, (Si, Ge) _2 (X = Ti, Cr, Hf) coating and the Nb-Si based alloy was also examined. The transitional layer is composed of (Ti, Nb) _5 (Si, Ge) _4 and a small amount of (Nb, X) _5 (Si, Ge) _3.With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law.The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm × h ~ (-1/2) .Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from the experimental concentration profiles.