In this work, two kinds of binders, Ammonium Zirconium Carbonate(AZC) and Ammonium Metatungstate(AMT) hydrate, and three kinds of powders(ZrO 2, Al2O3 and Y2O3) were mixed to fabricate six kinds of face coating system...In this work, two kinds of binders, Ammonium Zirconium Carbonate(AZC) and Ammonium Metatungstate(AMT) hydrate, and three kinds of powders(ZrO 2, Al2O3 and Y2O3) were mixed to fabricate six kinds of face coating systems. The thermal behaviors of the AZC and AMT dried binders were investigated by TG-DTA, and the phase transformation of the two binders was determined by XRD. Monoclinic ZrO 2 phase was formed from AZC at 620 °C and WO3 at 700 °C, and the phase transformation was completed at lower than 1000 °C in both binders, and therefore, the sintering temperature for the molds was selected at 950 °C. The interaction between the ceramic molds with different face coatings and the Ti-48Al-2Cr-2Nb alloy during investment casting was studied. Results showed no α-case reaction in the TiA l-mold reaction, and the AMT + Y2O3 face coating appeared to be the best choice for investment casting of TiA l alloys under the experimental conditions.展开更多
The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron ...The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron microscopy（SEM） equipped with energy-dispersive spectroscope（EDS） and transmission electron microscopy（TEM）.Results show that with 3 at%Ni addition,the as-cast micro structure is mainly composed of fine lamellar colonies（~50 μm）,γ grains and Ni-ridied τ_3 phase.After heat treatment at 1380℃,the Ni-containing alloy is characterized by fine fully lamellar micro structure（~90 μm）.The heat-treated Ni-containing specimen exhibits superior room temperature tensile properties than other specimens.The tensile properties are discussed in light of the microstructure evolution and role of Ni-riched τ_3 phase.展开更多
The cast ingots of Ti-46Al-6Nb-0.25Si-0.2B and Ti-46Al-6Nb-0.5W-0.25Si-0.2B（at%） were made by induction skull melting（ISM） technique.A series of heat treatments（HTs） were conducted to research the microstructure...The cast ingots of Ti-46Al-6Nb-0.25Si-0.2B and Ti-46Al-6Nb-0.5W-0.25Si-0.2B（at%） were made by induction skull melting（ISM） technique.A series of heat treatments（HTs） were conducted to research the microstructure evolution of both alloys.Microstructure and tensile property were examined by scanning electron microscope（SEM）,X-ray diffraction（XRD）,transmission electron microscope（TEM）,and tensile testing machine.The results show that microsegregation（liquid segregation and solid segregation） is exacerbated by the addition of0.5 at%W;the addition of Nb,W in TiAl alloy makes the phase transition difficultly take place;then,the microstructures and tensile properties of both alloys are improved after certain HT processes;finally,the thicknesses of the γ/α_2 lamellae after a certain HT process are significantly affected by the number of residual γ phases before the furnace-cooling moment.展开更多
文摘通过热压缩实验研究Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe-0.1B-0.1C锻态合金在750~900℃温度范围和0.001~1 s^(-1)应变速率范围内的热变形特征。应力-应变曲线表明,流变应力随着温度的提高和应变速率的降低而降低。显微组织对热变形参数十分敏感,当应变速率保持在0.001 s^(-1)不变,温度达到790℃或者温度保持在910℃不变,应变速率不高于0.1s^(-1)时合金显微组织中出现动态再结晶晶粒。计算出加工硬化率θ,并发现动态再结晶倾向于在较高温度和较低应变速率条件下发生。得到合金的本构方程和加工硬化图,平均热激活能为242.78 k J/mol,而且只有少量失稳区在热加工图中出现,说明合金具有良好的热加工性能。当应变速率为0.1s^(-1)时,应力-应变曲线呈现一种异常的形状,连续出现两个应力峰值,这一现象可以归因于连续动态再结晶和再结晶晶粒的转动所造成的硬化现象与动态软化机制的混合作用。
基金financially supported by the National Natural Science Foundation of China(Nos.51001040 and 51371064)
文摘In this work, two kinds of binders, Ammonium Zirconium Carbonate(AZC) and Ammonium Metatungstate(AMT) hydrate, and three kinds of powders(ZrO 2, Al2O3 and Y2O3) were mixed to fabricate six kinds of face coating systems. The thermal behaviors of the AZC and AMT dried binders were investigated by TG-DTA, and the phase transformation of the two binders was determined by XRD. Monoclinic ZrO 2 phase was formed from AZC at 620 °C and WO3 at 700 °C, and the phase transformation was completed at lower than 1000 °C in both binders, and therefore, the sintering temperature for the molds was selected at 950 °C. The interaction between the ceramic molds with different face coatings and the Ti-48Al-2Cr-2Nb alloy during investment casting was studied. Results showed no α-case reaction in the TiA l-mold reaction, and the AMT + Y2O3 face coating appeared to be the best choice for investment casting of TiA l alloys under the experimental conditions.
基金financially supported by the National Natural Science Foundation of China(Nos.51001040,51371064 and 51504075)the Shanghai Aerospace Science and Technology Innovation Fund(No.SAST201428)
文摘The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron microscopy（SEM） equipped with energy-dispersive spectroscope（EDS） and transmission electron microscopy（TEM）.Results show that with 3 at%Ni addition,the as-cast micro structure is mainly composed of fine lamellar colonies（~50 μm）,γ grains and Ni-ridied τ_3 phase.After heat treatment at 1380℃,the Ni-containing alloy is characterized by fine fully lamellar micro structure（~90 μm）.The heat-treated Ni-containing specimen exhibits superior room temperature tensile properties than other specimens.The tensile properties are discussed in light of the microstructure evolution and role of Ni-riched τ_3 phase.
基金financially supported by the National Natural Science Foundation of China(Nos.51001040,51371064)the Shanghai Aerospace Science and Technology Innovation Fund(No.SAST201428)
文摘The cast ingots of Ti-46Al-6Nb-0.25Si-0.2B and Ti-46Al-6Nb-0.5W-0.25Si-0.2B（at%） were made by induction skull melting（ISM） technique.A series of heat treatments（HTs） were conducted to research the microstructure evolution of both alloys.Microstructure and tensile property were examined by scanning electron microscope（SEM）,X-ray diffraction（XRD）,transmission electron microscope（TEM）,and tensile testing machine.The results show that microsegregation（liquid segregation and solid segregation） is exacerbated by the addition of0.5 at%W;the addition of Nb,W in TiAl alloy makes the phase transition difficultly take place;then,the microstructures and tensile properties of both alloys are improved after certain HT processes;finally,the thicknesses of the γ/α_2 lamellae after a certain HT process are significantly affected by the number of residual γ phases before the furnace-cooling moment.
