In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize ph...In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.展开更多
Compressive and tensile pre-strains at room temperature were induced in the second generation single crystal superalloy CMSX-4 fully heat treated.Both compressive and tensile pre-strain generated shear bands in the si...Compressive and tensile pre-strains at room temperature were induced in the second generation single crystal superalloy CMSX-4 fully heat treated.Both compressive and tensile pre-strain generated shear bands in the single crystal CMSX-4.Thermal exposure for 10 h at 950 ℃ on the pre-strained single crystal CMSX-4 developed preferential coarsening of γ＇ particles along the shear bands.γ＇ particles on the shear band gradually invaded γ channel.Finally,the γ channels along the shear band disappeared.TCP-like particles appeared at the expense of γ channel disappearance.However,thermal exposure for 10 h of the normal single crystal CMSX-4 did not develop TCP precipitation or preferential coarsening of γ＇ particles.Thermal exposure for 100 h of pre-strained CMSX-4 developed preferential coarsening of γ＇ and TCP phase particles along the shear bands as well as coarsening of γ＇ particles in the matrix.展开更多
文摘In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.
文摘Compressive and tensile pre-strains at room temperature were induced in the second generation single crystal superalloy CMSX-4 fully heat treated.Both compressive and tensile pre-strain generated shear bands in the single crystal CMSX-4.Thermal exposure for 10 h at 950 ℃ on the pre-strained single crystal CMSX-4 developed preferential coarsening of γ＇ particles along the shear bands.γ＇ particles on the shear band gradually invaded γ channel.Finally,the γ channels along the shear band disappeared.TCP-like particles appeared at the expense of γ channel disappearance.However,thermal exposure for 10 h of the normal single crystal CMSX-4 did not develop TCP precipitation or preferential coarsening of γ＇ particles.Thermal exposure for 100 h of pre-strained CMSX-4 developed preferential coarsening of γ＇ and TCP phase particles along the shear bands as well as coarsening of γ＇ particles in the matrix.
