The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scannin...The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.展开更多
The symmetrical push-pull fatigue tests in load control were carried out for prestrained polycrystalline Cu.The change in mechanical behaviour during cycling was recorded in detail and the effect of various degree of ...The symmetrical push-pull fatigue tests in load control were carried out for prestrained polycrystalline Cu.The change in mechanical behaviour during cycling was recorded in detail and the effect of various degree of prestraining on saturated behavior and dislocation structure was compared.The results show that the cyclic saturation state is still history-dependent at low stress amplitude and the dislocation structure after fatigue exhibits an “inheritance” be- havior.The level of softening was calculated at various load amplitudes and a softening threshold of about 0.43 to 0.45 of the flow stress was obtained.This is the same as that of low carbon steel.Three stages of cyclic processes and their mechanism have been described.展开更多
The prestrained metals show substantial asymmetry between tension and compression in addition to the softening under cyclic loading, thus the cyclic creep takes place at a load-control test. The soft- ening reflects t...The prestrained metals show substantial asymmetry between tension and compression in addition to the softening under cyclic loading, thus the cyclic creep takes place at a load-control test. The soft- ening reflects the decrease in density of dislocation and total internal stress, and the creep implies the asymmetry in back stress between tension and compression, The mechanical behaviour of the soft- ening is similar for materials with different slip modes, but their features of creep differ significantly. The creep of planar slip Cu-Zn alloy exhibits“explosively”, while that of wavy slip Cu and low car- bon steel occurs continuously and slowly. The explanation of creep behaviour via the internal dislo- cation structure was presented in this paper. According to asymmetw behaviour, it can be concluded that the internal processes of softehing also strongly depend on the slip mode. In addition, under high stress amplitude the opposite asymmetries take place for Cu and Cu-Zn alloy, it indicates that asymmetric back stresses developed in pretension have been eliminated even though the density and the configuration of dislocations have not reached equilibrium.展开更多
基金This work was financially supported by the Natural Science Foundation of Shaanxi Province, China (No.2004E107)
文摘The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.
文摘The symmetrical push-pull fatigue tests in load control were carried out for prestrained polycrystalline Cu.The change in mechanical behaviour during cycling was recorded in detail and the effect of various degree of prestraining on saturated behavior and dislocation structure was compared.The results show that the cyclic saturation state is still history-dependent at low stress amplitude and the dislocation structure after fatigue exhibits an “inheritance” be- havior.The level of softening was calculated at various load amplitudes and a softening threshold of about 0.43 to 0.45 of the flow stress was obtained.This is the same as that of low carbon steel.Three stages of cyclic processes and their mechanism have been described.
文摘The prestrained metals show substantial asymmetry between tension and compression in addition to the softening under cyclic loading, thus the cyclic creep takes place at a load-control test. The soft- ening reflects the decrease in density of dislocation and total internal stress, and the creep implies the asymmetry in back stress between tension and compression, The mechanical behaviour of the soft- ening is similar for materials with different slip modes, but their features of creep differ significantly. The creep of planar slip Cu-Zn alloy exhibits“explosively”, while that of wavy slip Cu and low car- bon steel occurs continuously and slowly. The explanation of creep behaviour via the internal dislo- cation structure was presented in this paper. According to asymmetw behaviour, it can be concluded that the internal processes of softehing also strongly depend on the slip mode. In addition, under high stress amplitude the opposite asymmetries take place for Cu and Cu-Zn alloy, it indicates that asymmetric back stresses developed in pretension have been eliminated even though the density and the configuration of dislocations have not reached equilibrium.
