In the present work,paraffin phase change material is used as quenchant for the heat treatment of 42CrMo4 alloy and compared with water,air,and CuO doped paraffin.The samples were prepared based on ASTM E 8M-98 standa...In the present work,paraffin phase change material is used as quenchant for the heat treatment of 42CrMo4 alloy and compared with water,air,and CuO doped paraffin.The samples were prepared based on ASTM E 8M-98 standard for tensile test and then heated up to 830°C,kept for 4 h in an electric resistance furnace and then quenched in the mentioned media.Elastic modulus,yield strength,ultimate tensile strength,elongation,and modulus of toughness were determined according to the obtained stress?strain curves.Moreover,the hardness and microstructural evolution were investigated after the heat treatment at different media.The samples quenched in paraffin and CuO-doped paraffin are higher in ultimate tensile strength(1439 and 1306 MPa,respectively)than those quenched in water(1190 MPa)and air(1010 MPa).The highest hardness,with a value of HV 552,belonged to the sample quenched in CuO-doped paraffin.The microstructural studies revealed that the non-tempered steel had a ferrite/pearlite microstructure,while by quenching in water,paraffin and CuO-doped paraffin,ferrite/martensite microstructures were achieved.It is also observed that using the air as quenchant resulted in a three-phase bainite/martensite/ferrite microstructure.展开更多
A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, fo...A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The synthetic conditions were optimized by orthogonal experiment. The results indicate that the fast quenching treatment can avoid the overgrowth of single crystal and improve its availability ratio of active material. The sintering temperature has the greatest effect on the electrochemical performance of sample. Next is the molar ratio of Li to Fe and the sintering time, respectively. The samples prepared in the optimized technical condition has the highest reversible discharge specific capacity of 149.8 mA·h/g.展开更多
Directly quenched Nd9.5Fe81Zr3B6.5 nanocomposite permanent magnets were prepared under different melt treatment conditions, i.e., the melt temperature was varied prior to ejection onto the quenching wheel. The effect ...Directly quenched Nd9.5Fe81Zr3B6.5 nanocomposite permanent magnets were prepared under different melt treatment conditions, i.e., the melt temperature was varied prior to ejection onto the quenching wheel. The effect of quenching temperature on the microstructure and magnetic properties of the alloys was studied by X-ray diffractometry, transmission electron microscopy and magnetization measurements. It is found that a finer and more uniform microstructure can be obtained directly from the melt quenched at lower temperature. With increasing initial quenching temperature, the optimal quenching speed decreases and the microstructure of the ribbons becomes coarser and more irregular. As a result, the magnetic properties of the alloys are deteriorated. It is believed that the break of the pre-existing Nd2Fe14B clusters and decrease in number of the developing nuclei of Nd2Fe14B phase with increase in quenching temperature may be the causes for the change of the microstructure and the magnetic properties of the ribbons.展开更多
Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(ave...Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(average thickness of 4 nm) within nanograins. The unique nanotwinned microstructure offers high hardness, wear resistance, fracture toughness, and thermal stability which are essential for advanced cBN tool materials. Thus, a circular micro tool of nt-cBN was fabricated using femtosecond laser contour machining followed by focused ion beam precision milling. Thereafter turning tests were performed on hardened steel using the studied micro tool. To evaluate the cutting performance, the machined surface quality and subsurface damage of the hardened steel were characterized. The wear mechanism of the nt-cBN micro tool was also investigated. It is found that the fabricated nt-cBN micro tool can generate high quality surface with surface roughness less than 7 nm and nanograin subsurface of about 500 nm deep. In addition, abrasive wear is found to be the dominant wear mechanism of the nt-cBN micro tool in turning hardened steel. These results indicate that nt-cBN has outstanding potential for ultra-precision cutting hardened steel.展开更多
Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been ...Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain,it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.展开更多
文摘In the present work,paraffin phase change material is used as quenchant for the heat treatment of 42CrMo4 alloy and compared with water,air,and CuO doped paraffin.The samples were prepared based on ASTM E 8M-98 standard for tensile test and then heated up to 830°C,kept for 4 h in an electric resistance furnace and then quenched in the mentioned media.Elastic modulus,yield strength,ultimate tensile strength,elongation,and modulus of toughness were determined according to the obtained stress?strain curves.Moreover,the hardness and microstructural evolution were investigated after the heat treatment at different media.The samples quenched in paraffin and CuO-doped paraffin are higher in ultimate tensile strength(1439 and 1306 MPa,respectively)than those quenched in water(1190 MPa)and air(1010 MPa).The highest hardness,with a value of HV 552,belonged to the sample quenched in CuO-doped paraffin.The microstructural studies revealed that the non-tempered steel had a ferrite/pearlite microstructure,while by quenching in water,paraffin and CuO-doped paraffin,ferrite/martensite microstructures were achieved.It is also observed that using the air as quenchant resulted in a three-phase bainite/martensite/ferrite microstructure.
基金Project(50604018) supported by the National Natural Science Foundation of China
文摘A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The synthetic conditions were optimized by orthogonal experiment. The results indicate that the fast quenching treatment can avoid the overgrowth of single crystal and improve its availability ratio of active material. The sintering temperature has the greatest effect on the electrochemical performance of sample. Next is the molar ratio of Li to Fe and the sintering time, respectively. The samples prepared in the optimized technical condition has the highest reversible discharge specific capacity of 149.8 mA·h/g.
基金Projects(51201109,51001076)supported by the National Natural Science Foundation of ChinaProject(T201108)supported by Shenzhen Key Laboratory of Special Functional Materials(Shenzhen University),China
文摘Directly quenched Nd9.5Fe81Zr3B6.5 nanocomposite permanent magnets were prepared under different melt treatment conditions, i.e., the melt temperature was varied prior to ejection onto the quenching wheel. The effect of quenching temperature on the microstructure and magnetic properties of the alloys was studied by X-ray diffractometry, transmission electron microscopy and magnetization measurements. It is found that a finer and more uniform microstructure can be obtained directly from the melt quenched at lower temperature. With increasing initial quenching temperature, the optimal quenching speed decreases and the microstructure of the ribbons becomes coarser and more irregular. As a result, the magnetic properties of the alloys are deteriorated. It is believed that the break of the pre-existing Nd2Fe14B clusters and decrease in number of the developing nuclei of Nd2Fe14B phase with increase in quenching temperature may be the causes for the change of the microstructure and the magnetic properties of the ribbons.
基金supported by the National Natural Science Foundation of China(Grant Nos.51205343,51332005&51421091)Hebei Provincial Science Foundation of China(Grant No.E2016203372)
文摘Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(average thickness of 4 nm) within nanograins. The unique nanotwinned microstructure offers high hardness, wear resistance, fracture toughness, and thermal stability which are essential for advanced cBN tool materials. Thus, a circular micro tool of nt-cBN was fabricated using femtosecond laser contour machining followed by focused ion beam precision milling. Thereafter turning tests were performed on hardened steel using the studied micro tool. To evaluate the cutting performance, the machined surface quality and subsurface damage of the hardened steel were characterized. The wear mechanism of the nt-cBN micro tool was also investigated. It is found that the fabricated nt-cBN micro tool can generate high quality surface with surface roughness less than 7 nm and nanograin subsurface of about 500 nm deep. In addition, abrasive wear is found to be the dominant wear mechanism of the nt-cBN micro tool in turning hardened steel. These results indicate that nt-cBN has outstanding potential for ultra-precision cutting hardened steel.
基金supported by the National Natural Science Foundation of China(Grant No.11272313)
文摘Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain,it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.
