Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation ...Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.展开更多
We study the moving and interaction of the compact-like pulses in the system of an anharmonic lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the l...We study the moving and interaction of the compact-like pulses in the system of an anharmonic lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the localization of the compact-like pulse is related to the nonlinear coupling parameter Cnl and the potential barrier height V0 of the double well potential. The velocity of the moving compact-like pulse is determined by the linear coupling parameter Cl, the localization parameter q (the nonlinear coupling parameter Cnl) and the potential barrier height Vo.Numerical experiments demonstrate that appropriate Cl is not detrimental to a stable moving of the compact-like pulse.However, the head on interaction of two compact-like pulses in the lattice system with comparatively small Cl leads to the appearance of a discrete stationary localized mode and small amplitude nonlinear oscillation background, while moderate Cl results in the emergence of two moving deformed pulses with damping amplitude and decay velocity and radiating oscillations, and biggish Cl brings on the appearing of four deformed kinks with radiating oscillations and different moving velocities.展开更多
Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements. It was found that in both cases the flow stresses increase with decreasing film thickness. The flow stresses in the epit...Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements. It was found that in both cases the flow stresses increase with decreasing film thickness. The flow stresses in the epitaxial Al films are in agreement with a dislocation-based model, while the same model strongly underestimates the flow stresses of textured Al films. In-situ transmission electron microscopy studies indicate that dislocations channeling through epitaxial Al films on single-crystalline (0001) α-AI2O3 substrates frequently deposit dislocation segments adjacent to the interface. Furthermore, the AI/α-AI2O3 interface acted as a dislocation source. In this case, the interface is between two crystalline lattices. In contrast, the interface of textured Al films on oxidized silicon substrates is between the crystalline Al and the amorphous SiOx interlayer. It is speculated that the different nature of the interfaces changes dislocation mechanisms and thus influences the flow stresses.展开更多
Micrometer NbC_x-C three-dimensional netted fibers were synthesized by thecarbothermal method under 0.1 MPa of N_2 ambient atmosphere at a relatively low temperature. Rawmaterials were commercial powders of Nb_2O_5 (9...Micrometer NbC_x-C three-dimensional netted fibers were synthesized by thecarbothermal method under 0.1 MPa of N_2 ambient atmosphere at a relatively low temperature. Rawmaterials were commercial powders of Nb_2O_5 (99.95 percent), reactive carbon (99.99 percent), NaCl(99.95 percent) and sucrose (99.94 percent). The relationship of the fabrication processing with thecomposition, crystal structure and morphology of fibers was investigated. The formation mechanismwas also proposed and discussed.展开更多
基金The authors wish to thank the Royal Society, UK, and the Chinese Academy of Sciences for sponsoring a joint project-Grant No.761. The nitridation of the SiC fiber (Sigma SM1240) was carried out at QM, University of London, UK. Supply of the SiC fiber by
文摘Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can form more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix. The effect of nitridation on the tensile strength of the fiber was investigated in this work. Nitridation could degrade the tensile strength of the SiC fiber if the treating temperature and time are not optimized. The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are responsible for the degradation in strength. The strength can be maintained by further optimization of the treating temperature and time. Therefore, stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical applications.
文摘We study the moving and interaction of the compact-like pulses in the system of an anharmonic lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the localization of the compact-like pulse is related to the nonlinear coupling parameter Cnl and the potential barrier height V0 of the double well potential. The velocity of the moving compact-like pulse is determined by the linear coupling parameter Cl, the localization parameter q (the nonlinear coupling parameter Cnl) and the potential barrier height Vo.Numerical experiments demonstrate that appropriate Cl is not detrimental to a stable moving of the compact-like pulse.However, the head on interaction of two compact-like pulses in the lattice system with comparatively small Cl leads to the appearance of a discrete stationary localized mode and small amplitude nonlinear oscillation background, while moderate Cl results in the emergence of two moving deformed pulses with damping amplitude and decay velocity and radiating oscillations, and biggish Cl brings on the appearing of four deformed kinks with radiating oscillations and different moving velocities.
文摘Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements. It was found that in both cases the flow stresses increase with decreasing film thickness. The flow stresses in the epitaxial Al films are in agreement with a dislocation-based model, while the same model strongly underestimates the flow stresses of textured Al films. In-situ transmission electron microscopy studies indicate that dislocations channeling through epitaxial Al films on single-crystalline (0001) α-AI2O3 substrates frequently deposit dislocation segments adjacent to the interface. Furthermore, the AI/α-AI2O3 interface acted as a dislocation source. In this case, the interface is between two crystalline lattices. In contrast, the interface of textured Al films on oxidized silicon substrates is between the crystalline Al and the amorphous SiOx interlayer. It is speculated that the different nature of the interfaces changes dislocation mechanisms and thus influences the flow stresses.
基金This work was financially supported by the National Nature Science Foundation of China(No.59425007, No.59432033).
文摘Micrometer NbC_x-C three-dimensional netted fibers were synthesized by thecarbothermal method under 0.1 MPa of N_2 ambient atmosphere at a relatively low temperature. Rawmaterials were commercial powders of Nb_2O_5 (99.95 percent), reactive carbon (99.99 percent), NaCl(99.95 percent) and sucrose (99.94 percent). The relationship of the fabrication processing with thecomposition, crystal structure and morphology of fibers was investigated. The formation mechanismwas also proposed and discussed.
