The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was...The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was measured by four-point method. The results show that a diffusion layer has formed around the boundaries between the filaments and bronze matrix after 15 h heat treatment. The diffusion layer thickness keeps stable after heat treatment duration of 50~75 h. The stable and solid Nb 3 Sn layer is obtained in the sample after 100 h heat treatment. Excessive heat treatment would induce superconductivity degeneration because of superconductor grain coarsening. The characteristics of the element diffusion process were discussed. The diffusion of tin atom is the governing factor in diffusion. In this study, Nb_3_Sn superconductors with good superconducting property were fabricated successfully at 670 °C after 100h heat treatment.展开更多
Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning elect...Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine.The results indicated that during isothermal annealing at 750°C,the tensile strength of pearlitic ductile cast iron was increased to a peak value at 0.5h,and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time.Moreover,the diffusion coefficient of carbon atoms could be approximately calculated as 0.56μm2/s that could be regarded as the shortrange diffusion.As the holding time was short（0.5h）,diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape.In addition,the ductile cast iron with tensile strength of 740MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 0.5h.Two principal factors should be taken into account.First,the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%.Second,the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix,enhancing the tensile strength to 740 MPa.展开更多
基金supported by the National Natural Science Foundation of China(No.50925726)
文摘The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was measured by four-point method. The results show that a diffusion layer has formed around the boundaries between the filaments and bronze matrix after 15 h heat treatment. The diffusion layer thickness keeps stable after heat treatment duration of 50~75 h. The stable and solid Nb 3 Sn layer is obtained in the sample after 100 h heat treatment. Excessive heat treatment would induce superconductivity degeneration because of superconductor grain coarsening. The characteristics of the element diffusion process were discussed. The diffusion of tin atom is the governing factor in diffusion. In this study, Nb_3_Sn superconductors with good superconducting property were fabricated successfully at 670 °C after 100h heat treatment.
基金supported by the Program for Innovative Research Team in University of Liaoning Province(Grant No.LT2015020)National Natural Science Foundation of China(Grant No.51274142)
文摘Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine.The results indicated that during isothermal annealing at 750°C,the tensile strength of pearlitic ductile cast iron was increased to a peak value at 0.5h,and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time.Moreover,the diffusion coefficient of carbon atoms could be approximately calculated as 0.56μm2/s that could be regarded as the shortrange diffusion.As the holding time was short（0.5h）,diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape.In addition,the ductile cast iron with tensile strength of 740MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 0.5h.Two principal factors should be taken into account.First,the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%.Second,the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix,enhancing the tensile strength to 740 MPa.
