W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method...W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method required a long time of high temperature sintering is very likely to cause low density and abnormal grain size growth.Therefore,90W-10Cu refractory alloys were successfully prepared by hot oscillatory pressing(HOP)under diff erent sintering time in this work.Then the infl uence of sintering time on the microstructure,grain size,density,Vickers hardness,room-tensile property,and electrical conductivity of the W–Cu refractory alloy was systematically invested.The results showed that during the short sintering time(30–90 min),the density,Vickers hardness,tensile strength,and electrical conductivity of the W–Cu refractory alloy increased signifi cantly to 98.7%,163.29 HV 30,507.3 MPa,and 14.2%International Annealed Copper Standard with the sintering time increasing,respectively,while its grain size showed no obvious change.When the sintering time further increased to 120 min,the density was basically consistent with the sintering time of 90 min.Nevertheless,the prolonged high temperature sintering resulted in the grain growth of the samples,which caused the deterioration of the Vickers hardness,room-tensile strength,and conductivity properties of the W–Cu refractory alloy.At the same sintering time,the density,Vickers hardness,and electrical conductivity of the HOP sintered W–Cu refractory alloy were signifi cantly higher than those of the HP sintered sample.It was indicated that high density,fi ne-grain,and excellent properties W–Cu refractory alloys could be prepared by hot oscillatory pressing under appropriate sintering time.展开更多
The mineral composition of the sinter affects the quality of cold-bonded briquettes(CBB),which are prepared from returned sinter fines and serve as a cleaner blast furnace charge.Pulverization rate,compressive strengt...The mineral composition of the sinter affects the quality of cold-bonded briquettes(CBB),which are prepared from returned sinter fines and serve as a cleaner blast furnace charge.Pulverization rate,compressive strength,reduction disintegration index(RDI)and compressive strength after reduction experiment were tested to analyze the experimental parameters of CBB under the influence of different basicities and sintering time.The results show that when the basicity of CBB is increased from 0.5 to 1.5,the pulverization rate increases,and performance indexes such as compressive strength,RDI,and compressive strength exhibit a decreasing trend.When the basicity is increased from 1.5 to 3.0,all the aforementioned performance indexes are improved.When the sintering time is extended from 0 to 8 h,the properties mentioned above are improved.The results of X-ray diffraction,microstructure,and thermodynamic calculations confirm that the hematite in the mineral composition of CBB tends to convert into calcium ferrite,which leads to the increased compressive strength of CBB.The reasonable basicity and sintering time during sinter preparation not only form the desired mineral composition but also improve the properties of the CBB.展开更多
Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties we...Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties were significantly influenced by the size of introduced seed grains, and introducing larger seed grains is more advantageous to the modification of microstructure and the improvement of varistor properties. The varistor properties were considerably improved with a moderately increased sintering temperature or time, whereas degraded apparently when the sintering temperature or time was excessively increased. Compared with the sintering time, the sintering temperature plays a more critical role in determining the varistor properties. By introducing pre fabricated ZnO seed grains into the original powders, low voltage ZnO varistor ceramics possessing the desired electrical properties have been produced with a sintering temperature of about 1 210 ℃ and a sintering temperature of 2～2.5 h. [展开更多
The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on...The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on two factors： the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.展开更多
基金supported by National Natural Science Foundation of China(51904277)the Open Fund of Sichuan Province Engineering Technology Research Center of Powder Metallurgy,Chengdu University(SC-FMYJ2023-02)+4 种基金Opening Foundation of Key Laboratory of Advanced Manufacture Technology for Automobile Parts,Ministry of Education(2022 KLMT05)the Open Fund of Hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering at Wuhan University of Science and Technology(MTMEOF2022B02)Fund of Key Laboratory of Advanced Materials of Ministry of Education(ADV22-20)Training Program for Young Backbone Teachers in Colleges and University of Henan Province(2020GGJS171)Fund of Zhengzhou University of Aeronautics Graduate Education Innovation Program of China(2022CX57).
文摘W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method required a long time of high temperature sintering is very likely to cause low density and abnormal grain size growth.Therefore,90W-10Cu refractory alloys were successfully prepared by hot oscillatory pressing(HOP)under diff erent sintering time in this work.Then the infl uence of sintering time on the microstructure,grain size,density,Vickers hardness,room-tensile property,and electrical conductivity of the W–Cu refractory alloy was systematically invested.The results showed that during the short sintering time(30–90 min),the density,Vickers hardness,tensile strength,and electrical conductivity of the W–Cu refractory alloy increased signifi cantly to 98.7%,163.29 HV 30,507.3 MPa,and 14.2%International Annealed Copper Standard with the sintering time increasing,respectively,while its grain size showed no obvious change.When the sintering time further increased to 120 min,the density was basically consistent with the sintering time of 90 min.Nevertheless,the prolonged high temperature sintering resulted in the grain growth of the samples,which caused the deterioration of the Vickers hardness,room-tensile strength,and conductivity properties of the W–Cu refractory alloy.At the same sintering time,the density,Vickers hardness,and electrical conductivity of the HOP sintered W–Cu refractory alloy were signifi cantly higher than those of the HP sintered sample.It was indicated that high density,fi ne-grain,and excellent properties W–Cu refractory alloys could be prepared by hot oscillatory pressing under appropriate sintering time.
基金supported by Distinguished Professor(Tracking Plan)of Oriental Scholars of Shanghai Universities(Grant No.GZ2020013)National 111 Project(The Program of Introducing Talents of Discipline to University)(Grant No.Dl7002)+1 种基金Independent Research Project of State Key Laboratory of Advanced Special Steel Shanghai Key Laboratory of Advanced Ferrometallurgy and Shanghai University(Grant No.SKLASS 2022-Z011)Additionally,the authors are appreciative of the funding from the Academy of Finland with Grant No.349833.
文摘The mineral composition of the sinter affects the quality of cold-bonded briquettes(CBB),which are prepared from returned sinter fines and serve as a cleaner blast furnace charge.Pulverization rate,compressive strength,reduction disintegration index(RDI)and compressive strength after reduction experiment were tested to analyze the experimental parameters of CBB under the influence of different basicities and sintering time.The results show that when the basicity of CBB is increased from 0.5 to 1.5,the pulverization rate increases,and performance indexes such as compressive strength,RDI,and compressive strength exhibit a decreasing trend.When the basicity is increased from 1.5 to 3.0,all the aforementioned performance indexes are improved.When the sintering time is extended from 0 to 8 h,the properties mentioned above are improved.The results of X-ray diffraction,microstructure,and thermodynamic calculations confirm that the hematite in the mineral composition of CBB tends to convert into calcium ferrite,which leads to the increased compressive strength of CBB.The reasonable basicity and sintering time during sinter preparation not only form the desired mineral composition but also improve the properties of the CBB.
文摘Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties were significantly influenced by the size of introduced seed grains, and introducing larger seed grains is more advantageous to the modification of microstructure and the improvement of varistor properties. The varistor properties were considerably improved with a moderately increased sintering temperature or time, whereas degraded apparently when the sintering temperature or time was excessively increased. Compared with the sintering time, the sintering temperature plays a more critical role in determining the varistor properties. By introducing pre fabricated ZnO seed grains into the original powders, low voltage ZnO varistor ceramics possessing the desired electrical properties have been produced with a sintering temperature of about 1 210 ℃ and a sintering temperature of 2～2.5 h. [
文摘The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on two factors： the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.
