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
The influence of Re addition and withdrawal rate on the solidification behavior of the first generation single crystal superalloy AM3 was investigated by directional solidification and quenching experiments.The primar...The influence of Re addition and withdrawal rate on the solidification behavior of the first generation single crystal superalloy AM3 was investigated by directional solidification and quenching experiments.The primary dendrite arm spacing and eutectic volume fraction were measured from directionally solidified superalloy AM3 with different Re contents.It is found that the primary dendrite arm spacing is determined by the withdrawal rate,and Re does not influence on the value.The eutectic fraction increases with increasing Re addition.Partition coeffcients of alloying elements were investigated with energy-dispersive X-ray spectrometry（EDS） analysis.The data was submitted to a statistical treatment to establish the solidification path,and the partition coeficients were measured by fitting the curve with a modified Scheil formula.It is shown that the addition of Re results in bigger microsegregation of alloying elements in directionally solidified AM3 superalloy.展开更多
Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-l...Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-like phase precipitated in the interdendritic region of as-cast specimen during thermal exposure.The phase,which has bcc structure,was enriched with Cr.Thermo-calc also predicted precipitation of a bcc phase at around 950℃.The Cr-rich bcc phase was considered asα-Cr and formed due to the segregation of Cr under the as-cast condition.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The influence of Re addition and withdrawal rate on the solidification behavior of the first generation single crystal superalloy AM3 was investigated by directional solidification and quenching experiments.The primary dendrite arm spacing and eutectic volume fraction were measured from directionally solidified superalloy AM3 with different Re contents.It is found that the primary dendrite arm spacing is determined by the withdrawal rate,and Re does not influence on the value.The eutectic fraction increases with increasing Re addition.Partition coeffcients of alloying elements were investigated with energy-dispersive X-ray spectrometry（EDS） analysis.The data was submitted to a statistical treatment to establish the solidification path,and the partition coeficients were measured by fitting the curve with a modified Scheil formula.It is shown that the addition of Re results in bigger microsegregation of alloying elements in directionally solidified AM3 superalloy.
文摘Microstructural stability of a nickel base single crystal alloy DD8 has been investigated.Standard heat treated specimen showed good microstructural stability at 950℃.While under the as-cast condition,a kind of rod-like phase precipitated in the interdendritic region of as-cast specimen during thermal exposure.The phase,which has bcc structure,was enriched with Cr.Thermo-calc also predicted precipitation of a bcc phase at around 950℃.The Cr-rich bcc phase was considered asα-Cr and formed due to the segregation of Cr under the as-cast condition.
