The structures,mechanical properties and electronic structures of M metals(M=Ti,V,Cr,Mn and Fe)dopedβ-Si_(3)N_(4) were investigated by First-principles calculations within CASTEP.The calculated lattice parameters of...The structures,mechanical properties and electronic structures of M metals(M=Ti,V,Cr,Mn and Fe)dopedβ-Si_(3)N_(4) were investigated by First-principles calculations within CASTEP.The calculated lattice parameters ofβ-Si_(3)N_(4) were consistent with previous date.The cohesive energy and formation enthalpy show that initialβ-Si_(3)N_(4) has the highest structural stability.The calculated elastic constant and the Voigt-Reuss-Hill approximation indicate that elastic moduli ofβ-Si_(3)N_(4) are slightly reduced by M doping.Based on Poisson’s and Pugh’s ratio,β-Si_(3)N_(4) is a ductile material and the toughness ofβ-Si_(3)N_(4) increases with M doping,and Fe doping exhibited the best toughness.The results of density of states,charge distributions and overlapping populations indicate thatβ-Si_(3)N_(4) has the strong covalent and ionic bond strength between N and Si.展开更多
The microstructure of both {10(?)1} and {10(?)0} (directions perpendicular to the {10(?)1} and {10(?)0} planes) α-Si_3N_4 whiskers were investi- gated by high resolution electron microscopy (HREM).On one side of the ...The microstructure of both {10(?)1} and {10(?)0} (directions perpendicular to the {10(?)1} and {10(?)0} planes) α-Si_3N_4 whiskers were investi- gated by high resolution electron microscopy (HREM).On one side of the {10(?)1} α-Si_3N_4 whiskers many planar defects were ob- served,two kinds of micrograins on one side of the {10(?)0} whiskers were found.In one type,sepa- rated α-Si_3N_4 (28 H) micrograins had the same orientation with respect to the matrix whisker;in the other type,connected polymicrograins consisted of both α-and β-Si_3N_4 (14H).展开更多
The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an incremen...The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an increment in strength and microhardness may be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker and Si_3N_4/Al interface were observed by meas of HRTEM.The relation between interracial structure and composite properties was discussed.展开更多
Using newly developed Cu58Ni12Ti30 alloy as brazing filler metal, this paper has carried out the joining wxperiments of Si3N4 and the joint shength tests at room temperature.The joint brazed at 1,293K for 10 min exhib...Using newly developed Cu58Ni12Ti30 alloy as brazing filler metal, this paper has carried out the joining wxperiments of Si3N4 and the joint shength tests at room temperature.The joint brazed at 1,293K for 10 min exhibited the maximum strength value of 157.2 MPa.The microstructures of the joint cross-section were observed and the elements area distributions on the interface were examined by means of scanning electron microscope with X-ray wave-dispersion spectrometer.The phases formed in the joint were determined by X-ray diffraction analysis method.The results showed that during the brazing process the active element Ti diffused to the interfaces and reacted with Si3N4,resulted in forming the reaction products TiN NiTiSi, and Ti4Si3(or TiSi)on the interfaces.Some effects on the trend to produce these compounds were attempted to explain from α thermodynalic point of view.展开更多
Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competi...Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competitive candidate for technological applications in harsh conditions(e.g.,drill head and abrasives).Here,we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposite derived from single-phase amorphous silicon(Si)-hafnium(Hf)-nitrogen(N)precursor.The synthesis of the-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposite is performed at~20 GPa and ca.1500 ℃ in a large volume multi anvil press.The structural evolution of the amorphous precursor and its crystallization to-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction(ED-XRD)measurements at~19.5 GPa in the temperature range of ca.1000-1900℃.The fracture toughness(K_(IC))of the two-phase nanocomposite amounts~6/6.9 MPa·m^(1/2) and is about 2 times that of single-phaseγ-Si_(3)N_(4),while its hardness of ca.30 GPa remains high.This work provides a reliable and feasible route for the synthesis of advanced hard and tough-Si_(3)N_(4)-based nanocomposites with excellent thermal stabililty.展开更多
文摘The structures,mechanical properties and electronic structures of M metals(M=Ti,V,Cr,Mn and Fe)dopedβ-Si_(3)N_(4) were investigated by First-principles calculations within CASTEP.The calculated lattice parameters ofβ-Si_(3)N_(4) were consistent with previous date.The cohesive energy and formation enthalpy show that initialβ-Si_(3)N_(4) has the highest structural stability.The calculated elastic constant and the Voigt-Reuss-Hill approximation indicate that elastic moduli ofβ-Si_(3)N_(4) are slightly reduced by M doping.Based on Poisson’s and Pugh’s ratio,β-Si_(3)N_(4) is a ductile material and the toughness ofβ-Si_(3)N_(4) increases with M doping,and Fe doping exhibited the best toughness.The results of density of states,charge distributions and overlapping populations indicate thatβ-Si_(3)N_(4) has the strong covalent and ionic bond strength between N and Si.
文摘The microstructure of both {10(?)1} and {10(?)0} (directions perpendicular to the {10(?)1} and {10(?)0} planes) α-Si_3N_4 whiskers were investi- gated by high resolution electron microscopy (HREM).On one side of the {10(?)1} α-Si_3N_4 whiskers many planar defects were ob- served,two kinds of micrograins on one side of the {10(?)0} whiskers were found.In one type,sepa- rated α-Si_3N_4 (28 H) micrograins had the same orientation with respect to the matrix whisker;in the other type,connected polymicrograins consisted of both α-and β-Si_3N_4 (14H).
文摘The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa was prepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃, 1 h solutioning and 160℃,24 h aging,an increment in strength and microhardness may be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker and Si_3N_4/Al interface were observed by meas of HRTEM.The relation between interracial structure and composite properties was discussed.
文摘Using newly developed Cu58Ni12Ti30 alloy as brazing filler metal, this paper has carried out the joining wxperiments of Si3N4 and the joint shength tests at room temperature.The joint brazed at 1,293K for 10 min exhibited the maximum strength value of 157.2 MPa.The microstructures of the joint cross-section were observed and the elements area distributions on the interface were examined by means of scanning electron microscope with X-ray wave-dispersion spectrometer.The phases formed in the joint were determined by X-ray diffraction analysis method.The results showed that during the brazing process the active element Ti diffused to the interfaces and reacted with Si3N4,resulted in forming the reaction products TiN NiTiSi, and Ti4Si3(or TiSi)on the interfaces.Some effects on the trend to produce these compounds were attempted to explain from α thermodynalic point of view.
基金Part of this research was carried out at PETRA III LVP at beamline P61B(beamtime I-20200434)and P02.1Shrikant Bhat and Robert Farla acknowedge the support from the Federal Ministry of Education and Research,Germany(BMBF,Nos.05K16WC2 and 05K13WC2)+2 种基金Wei Li and Leonore Wiehl also acknowledge the travel support from DESY.Zhaoju Yu thanks the National Natural Science Foundation of China(Nos.51872246 and 52061135102)for financial supportMarc Widenmeyer and Anke Weidenkaff are grateful for the financial support by the German Ministry of Education and Research(No.03SF0618B)Wei Li acknowledges the financial support from China Scholarship Council(No.201907040060).
文摘Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competitive candidate for technological applications in harsh conditions(e.g.,drill head and abrasives).Here,we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposite derived from single-phase amorphous silicon(Si)-hafnium(Hf)-nitrogen(N)precursor.The synthesis of the-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposite is performed at~20 GPa and ca.1500 ℃ in a large volume multi anvil press.The structural evolution of the amorphous precursor and its crystallization to-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction(ED-XRD)measurements at~19.5 GPa in the temperature range of ca.1000-1900℃.The fracture toughness(K_(IC))of the two-phase nanocomposite amounts~6/6.9 MPa·m^(1/2) and is about 2 times that of single-phaseγ-Si_(3)N_(4),while its hardness of ca.30 GPa remains high.This work provides a reliable and feasible route for the synthesis of advanced hard and tough-Si_(3)N_(4)-based nanocomposites with excellent thermal stabililty.
