Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied ...Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.展开更多
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...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.展开更多
The MoSi2 coating on C103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffus...The MoSi2 coating on C103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffusion obeying parabolic rule during pack cementation process. It is found that the composite structural coating is composed of three inferior layers as follows. The main layer is composed of MoSi2, the two phases’ transitional layer consists of NbSi2 and a few Nb5Si3 and the diffuse layer is composed of Nb5Si3. The dense amorphous glass layer formed on the surface at high temperature oxidation circumstance can effectively prevent the diffusion of oxygen into coating.展开更多
A silicide coating was prepared on the surface of the Nb521 alloy by the complex pack cemented method. The oxidation resistance properties of the present coating were examined by the static oxidation tests at 1 700 ℃...A silicide coating was prepared on the surface of the Nb521 alloy by the complex pack cemented method. The oxidation resistance properties of the present coating were examined by the static oxidation tests at 1 700 ℃ in air. The compositions and the microstructures of the coating before and after test were characterised and analysed through scanning electron microscopy(SEM),X-ray diffraction analysis(XRD),energy dispersive X-ray spectrometry(EDS) and electron probe microanalysis(EPMA),respectively. The present silicide coating can provide an effective protection for the Nb alloy for 25 h at 1 700 ℃ in air. The results show that the oxidation kinetics of the present silicide coating is parabolic. The diffusion of Si leads to the phase transformation and evolution during the oxidation.展开更多
The forming process of silicide coatings on pure Mo and Mo-base alloys, obtained by the gas- phase deposition method. has been studied by examining the microstructure of coatings and the relationship between coating t...The forming process of silicide coatings on pure Mo and Mo-base alloys, obtained by the gas- phase deposition method. has been studied by examining the microstructure of coatings and the relationship between coating thickness and process parameters. It was shown that the growth of coatings was diffusion-controlled, the diffusion of silicon to be coated into Mo or Mo-base alloys was mainly responsible for the formation of silicide. The relationship between initial silicide thickness and oxidation resistance was also investigated, and the equation of service life of the coatings at high temperature in air is presented.展开更多
Pure silicide coating and Y-Ce modified silicide coating were prepared on Ti-6Al-4V alloy by pack-cementation process. The structures as well as the isothermal oxidation behaviors of the coatings were comparatively st...Pure silicide coating and Y-Ce modified silicide coating were prepared on Ti-6Al-4V alloy by pack-cementation process. The structures as well as the isothermal oxidation behaviors of the coatings were comparatively studied. The results showed that both pure silicide coating and Y-Ce modified silicide coating prepared at 1080℃ for 4 h were composed of a TiSi2 outer layer, a TiSi middle layer and a Ti5Si4 inner layer. The oxidation tests showed that the Y-Ce modified silicide coating possessed much better oxidation resistance than the pure silicide coating at 1000℃, implying the beneficial effects of Y and Ce on the oxidation resistance of the coating.展开更多
基金Projects(51371145,51431003,U1435201,51401166)supported by the National Natural Science Foundation of ChinaProject(B080401)supported by the Programme of Introducing Talents of Discipline to Universities,China
文摘Zr-Y jointly modified silicide coatings were prepared on an Nb-Ti-Si-Cr based ultrahigh temperature alloy by pack cementation process. The wear behaviors of both the base alloy and coatings were comparatively studied at room temperature and 800 ℃ using SiC balls as the counterpart. The Zr-Y jointly modified silicide coating is mainly composed of a thick （Nb,X）Si2 outer layer and a thin （Ti,Nb）5Si4 inner layer. The coatings possess much higher microhardness than the base alloy. The wear rates of both the base alloy and coatings increase with increasing the sliding loads. However, the coatings have much lower wear rates than the base alloy under the same sliding conditions. The coatings have superior anti-friction property, and can provide effective protection for the base alloy at both room temperature and 800 ℃ in air.
基金financially supported by the National Natural Science Foundation of China(No.51431003)the Joint Funds of the National Natural Science Foundation of China(No.U1435201)
文摘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.
文摘The MoSi2 coating on C103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffusion obeying parabolic rule during pack cementation process. It is found that the composite structural coating is composed of three inferior layers as follows. The main layer is composed of MoSi2, the two phases’ transitional layer consists of NbSi2 and a few Nb5Si3 and the diffuse layer is composed of Nb5Si3. The dense amorphous glass layer formed on the surface at high temperature oxidation circumstance can effectively prevent the diffusion of oxygen into coating.
基金Supported by the Science and Technology Program of Hunan(05JT1065)
文摘A silicide coating was prepared on the surface of the Nb521 alloy by the complex pack cemented method. The oxidation resistance properties of the present coating were examined by the static oxidation tests at 1 700 ℃ in air. The compositions and the microstructures of the coating before and after test were characterised and analysed through scanning electron microscopy(SEM),X-ray diffraction analysis(XRD),energy dispersive X-ray spectrometry(EDS) and electron probe microanalysis(EPMA),respectively. The present silicide coating can provide an effective protection for the Nb alloy for 25 h at 1 700 ℃ in air. The results show that the oxidation kinetics of the present silicide coating is parabolic. The diffusion of Si leads to the phase transformation and evolution during the oxidation.
文摘The forming process of silicide coatings on pure Mo and Mo-base alloys, obtained by the gas- phase deposition method. has been studied by examining the microstructure of coatings and the relationship between coating thickness and process parameters. It was shown that the growth of coatings was diffusion-controlled, the diffusion of silicon to be coated into Mo or Mo-base alloys was mainly responsible for the formation of silicide. The relationship between initial silicide thickness and oxidation resistance was also investigated, and the equation of service life of the coatings at high temperature in air is presented.
基金Project supported by the Shanxi Science and Technology Research and Development Program(2013KJXX-08)
文摘Pure silicide coating and Y-Ce modified silicide coating were prepared on Ti-6Al-4V alloy by pack-cementation process. The structures as well as the isothermal oxidation behaviors of the coatings were comparatively studied. The results showed that both pure silicide coating and Y-Ce modified silicide coating prepared at 1080℃ for 4 h were composed of a TiSi2 outer layer, a TiSi middle layer and a Ti5Si4 inner layer. The oxidation tests showed that the Y-Ce modified silicide coating possessed much better oxidation resistance than the pure silicide coating at 1000℃, implying the beneficial effects of Y and Ce on the oxidation resistance of the coating.
