A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure a...A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure and reactive products between CBN grains and filler layer,is observed by optical microscope and scanning electron microscope （SEM）. Resistant-to-wear experiments of the brazed grains are performed. Results show that the nano-TiC powders evenly distribute in the filler layer so that the resultants grow compactly and uniformly on the surface of CBN grain. This indicates that the chemical bond is established between CBN grains and nano-TiC modified filler. Accordingly,the bonding strength of the grains is ensured. The CBN grains are worn smoothly without grain pull-out.展开更多
Effects of dopant size on the magnetic properties and corrosion behavior of hot-deformed NdFeB with the intergranular additions of nano-TiC were investigated using X-ray diffraction(XRD),X-ray photoelectron spectromet...Effects of dopant size on the magnetic properties and corrosion behavior of hot-deformed NdFeB with the intergranular additions of nano-TiC were investigated using X-ray diffraction(XRD),X-ray photoelectron spectrometer(XPS),scanning electron microscopy(SEM),electrochemical and magnetic measurement technologies.Additions of 50 nm-TiC,unlike 30 nm- and 40 nm-TiC,are found to increase the magnetic energy product and comprehensive magnetic properties,due in main to the improvement of magnet orientation by more strip-shaped Nd-rich phases.Nano-TiC dopants especially with a size of40 nm can increase the electrochemical corrosion resistance of magnets.It is attributed to the hindrance of additives on the reaction channel formation and their barrier effect on the oxidations of Nd and Fe.For 40 nm-TiC doped magnet,the charge transfer resistance in electric double layer structure reaches 15000 Ω·cm^(2) that is one order of magnitude higher than other cases,which is responsible for the lowe st corrosion current density and accordingly the best anti-corrosion properties.展开更多
In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical p...In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.展开更多
基金Supported by the National Basic Research Program of China ("973" Program) (2009CB724403)the Program for New Century Excellent Talents in University from Ministry of Education of China (NCET-07-0435)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University (IRT0837)the Innovative and Ex-cellent Foundation for Doctoral Dissertation of Nanjing University of Aeronautics and Astronautics (BCXJ10-08)~~
文摘A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure and reactive products between CBN grains and filler layer,is observed by optical microscope and scanning electron microscope （SEM）. Resistant-to-wear experiments of the brazed grains are performed. Results show that the nano-TiC powders evenly distribute in the filler layer so that the resultants grow compactly and uniformly on the surface of CBN grain. This indicates that the chemical bond is established between CBN grains and nano-TiC modified filler. Accordingly,the bonding strength of the grains is ensured. The CBN grains are worn smoothly without grain pull-out.
基金Project supported by the National Natural Science Foundation of China(52174346)Natural Science Foundation of Shandong Province of China(ZR2021ME031)。
文摘Effects of dopant size on the magnetic properties and corrosion behavior of hot-deformed NdFeB with the intergranular additions of nano-TiC were investigated using X-ray diffraction(XRD),X-ray photoelectron spectrometer(XPS),scanning electron microscopy(SEM),electrochemical and magnetic measurement technologies.Additions of 50 nm-TiC,unlike 30 nm- and 40 nm-TiC,are found to increase the magnetic energy product and comprehensive magnetic properties,due in main to the improvement of magnet orientation by more strip-shaped Nd-rich phases.Nano-TiC dopants especially with a size of40 nm can increase the electrochemical corrosion resistance of magnets.It is attributed to the hindrance of additives on the reaction channel formation and their barrier effect on the oxidations of Nd and Fe.For 40 nm-TiC doped magnet,the charge transfer resistance in electric double layer structure reaches 15000 Ω·cm^(2) that is one order of magnitude higher than other cases,which is responsible for the lowe st corrosion current density and accordingly the best anti-corrosion properties.
基金support from China Scholarship Council(No.202107000038)the Na-tional Natural Science Foundation of China(52004227).
文摘In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.
