The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron m...The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show the tensile strength and yield strength of DZ68 alloy increase slightly with increasing temperature, so that at 760°C its reach maxima value: 1214 and 1019 MPa, respectively. When the experimental temperature is higher than 760°C, the tensile and yield strengths decrease evidently and the ductility increases remarkably. The fractograph of fracture surface for the tensile specimen at room temperature shows a dimple-ductile fracture mode. The fractograph from 760 to 850°C shows a slide fracture mode. The fractograph from 900 to 1000°C exhibits a creep rupture mode with uneven deformation.展开更多
Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereut...Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.展开更多
The chemical reaction and dissolution processes of RE_2 O_3 in REF_3-LiF(RE = La and Nd) molten salts were studied by X-ray diffraction, differential thermal analysis and chemical analysis. Firstly, RE_2 O_3 disperses...The chemical reaction and dissolution processes of RE_2 O_3 in REF_3-LiF(RE = La and Nd) molten salts were studied by X-ray diffraction, differential thermal analysis and chemical analysis. Firstly, RE_2 O_3 disperses in molten salts and reacts with REF_3 and LiF, which lead to the generation of a new phase REOF, resulting in the dissociation or formation of complex ions by part of REOF, and the sedimentation of excessive REOF at the bottom. The RE contents in molten salts were used to determine the solubility of RE_2 O_3. The results show that with 20 mol%-40 mol% of REF_3, the solubility ranges from 1.79 to 3.05 g RE_2 O_3 per100 g electrolyte and the corresponding mole concentration is 0.33%-0.87%. RE_2 O_3 solubility increases with increasing temperature and REF_3 concentration. The natural logarithm of the RE_2 O_3 solubility is plotted against 1/T and can be interpreted by linear relationship. The fitting parameters can be used to estimate the solubility of RE_2 O_3 with minimized experimental efforts and difficult experiment conditions.展开更多
The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) met...The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) method.Electrical conductivity values of LaF3-LiF and NdF3-LiF molten salts within the studied ranges are 4.11-9.39 and 3.62-9.51 S/cm,respectively.The composition and temperature dependences of electrical conductivity and the factor of RE2 O3 on electrical conductivity were investigated.The electrical conductivity nonlinearly decreases with the increasing mole percent of REF3 for the changing of structural ion in molten salts.A good linear relationship between the natural logarithm of electrical conductivity(lnκ) and the reciprocal of the absolute temperature(T-1) can be interpreted by the trend that electrical conductivity linearly increases with increasing temperature.Although it is an important factor of RE2 O3 on electrical conductivity,the influence of RE2 O3 on conductivity is small for the very limited solubility of RE2 O3 in REF3-LiF molten salts.The results of this work supplement the present electrical conductivity data of rare earth fluoride electrolyte.展开更多
The bastnaesite was defluorinated by steam roasting process,and fluorine was removed in the form of hydrogen fluoride to realize the separation from rare earth.The effects of particle size of raw material,roasting tem...The bastnaesite was defluorinated by steam roasting process,and fluorine was removed in the form of hydrogen fluoride to realize the separation from rare earth.The effects of particle size of raw material,roasting temperature and time on defluorination rate of bastnaesite were studied.The suitable conditions of steam roasting process are that the particle size of raw material is less than 74μm,the roasting temperature is 1000℃and the roasting time is 4 h.The defluorination rate of bastnaesite is close to 100%under above these conditions.When the temperature rises to 1000℃,the voids on the surface of the particles increase obviously,and there is a developed network of voids,which indicates that the fluorine oxides in bastnaesite react fully with the saturated water vapor at this stage,and a large amount of fluorine escapes in the form of hydrogen fluoride from the surface and inside of the mineral.X-ray diffraction results show that there are only rare-earth oxides in the form of Ce_(0.33)La_(0.33)Ca_(0.33)O_(1.5)and Ce_(7)O_(12)in the slag.The results of energy spectra and chemical analysis show that the fluorine in the baking sand was basically completely removed.展开更多
文摘The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show the tensile strength and yield strength of DZ68 alloy increase slightly with increasing temperature, so that at 760°C its reach maxima value: 1214 and 1019 MPa, respectively. When the experimental temperature is higher than 760°C, the tensile and yield strengths decrease evidently and the ductility increases remarkably. The fractograph of fracture surface for the tensile specimen at room temperature shows a dimple-ductile fracture mode. The fractograph from 760 to 850°C shows a slide fracture mode. The fractograph from 900 to 1000°C exhibits a creep rupture mode with uneven deformation.
基金supported by the National Key Technology R&D Program of China(No.2009BAE80B00)
文摘Hypereutectic Al-17.5Si (wt pct) and Al-25Si (wt pct) alloys with various content of rare earth Er were prepared by conventional casting technique. The effect of Er on the microstructure and properties of the hypereutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as friction and wear tests. It was found that optimal amount of Er exists in modifying the hypereutectic Al-Si alloys. An appropriate addition of Er improved the anti-wear properties, and reduced the friction coefficient of the hypereutectic Al-Si alloys studied. The primary silicon crystals in the hypereutectic Al-Si alloys were refined with the suitable addition of Er element. The modification mechanism was also discussed in this paper.
基金supported by the National High Technology Research and Development Program(2011AA03A409)Fundamental Research Funds for the Central Universities(N110202002)
文摘The chemical reaction and dissolution processes of RE_2 O_3 in REF_3-LiF(RE = La and Nd) molten salts were studied by X-ray diffraction, differential thermal analysis and chemical analysis. Firstly, RE_2 O_3 disperses in molten salts and reacts with REF_3 and LiF, which lead to the generation of a new phase REOF, resulting in the dissociation or formation of complex ions by part of REOF, and the sedimentation of excessive REOF at the bottom. The RE contents in molten salts were used to determine the solubility of RE_2 O_3. The results show that with 20 mol%-40 mol% of REF_3, the solubility ranges from 1.79 to 3.05 g RE_2 O_3 per100 g electrolyte and the corresponding mole concentration is 0.33%-0.87%. RE_2 O_3 solubility increases with increasing temperature and REF_3 concentration. The natural logarithm of the RE_2 O_3 solubility is plotted against 1/T and can be interpreted by linear relationship. The fitting parameters can be used to estimate the solubility of RE_2 O_3 with minimized experimental efforts and difficult experiment conditions.
基金the National High Technology Research and Development Program(2011AA03A409)Fundamental Research Funds for the Central Universities(N110202002)。
文摘The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) method.Electrical conductivity values of LaF3-LiF and NdF3-LiF molten salts within the studied ranges are 4.11-9.39 and 3.62-9.51 S/cm,respectively.The composition and temperature dependences of electrical conductivity and the factor of RE2 O3 on electrical conductivity were investigated.The electrical conductivity nonlinearly decreases with the increasing mole percent of REF3 for the changing of structural ion in molten salts.A good linear relationship between the natural logarithm of electrical conductivity(lnκ) and the reciprocal of the absolute temperature(T-1) can be interpreted by the trend that electrical conductivity linearly increases with increasing temperature.Although it is an important factor of RE2 O3 on electrical conductivity,the influence of RE2 O3 on conductivity is small for the very limited solubility of RE2 O3 in REF3-LiF molten salts.The results of this work supplement the present electrical conductivity data of rare earth fluoride electrolyte.
基金Project supported by the National Key Research and Development Program of China(2020YFC1907500)the Fundamental Research Funds of the Ministry of Education of China(N2125033)。
文摘The bastnaesite was defluorinated by steam roasting process,and fluorine was removed in the form of hydrogen fluoride to realize the separation from rare earth.The effects of particle size of raw material,roasting temperature and time on defluorination rate of bastnaesite were studied.The suitable conditions of steam roasting process are that the particle size of raw material is less than 74μm,the roasting temperature is 1000℃and the roasting time is 4 h.The defluorination rate of bastnaesite is close to 100%under above these conditions.When the temperature rises to 1000℃,the voids on the surface of the particles increase obviously,and there is a developed network of voids,which indicates that the fluorine oxides in bastnaesite react fully with the saturated water vapor at this stage,and a large amount of fluorine escapes in the form of hydrogen fluoride from the surface and inside of the mineral.X-ray diffraction results show that there are only rare-earth oxides in the form of Ce_(0.33)La_(0.33)Ca_(0.33)O_(1.5)and Ce_(7)O_(12)in the slag.The results of energy spectra and chemical analysis show that the fluorine in the baking sand was basically completely removed.
