The changes of microstructures after the exhaustion of dislocation glide ability but before cracking, as well as microcrack initiation by them, were studied in detail byin-situ transmission electron microscopy (TEM) f...The changes of microstructures after the exhaustion of dislocation glide ability but before cracking, as well as microcrack initiation by them, were studied in detail byin-situ transmission electron microscopy (TEM) for pure copper, aluminum and iron. Thinning occurred in the thicker regions through dislocation gliding in the three metals. After that, {111} 〈112〉 twinning or tensile cracking took place in thinned zones in fcc metals. In the case of twinning, new microcracks were initiated along another {111} plane by the high stress concentration near the growing tip of the twin, while in iron (bcc), many nanocracks were initiated in the thinned areas just ahead of the crack front, resulting in misorientation microstructure from which microcracks or microvoids were developed.展开更多
The research activities of the calculation of the elastic constants of metal are mainly focused on the elastic constants of crystal at the micro level. To the calculation of the macroscopic elastic constants of metal,...The research activities of the calculation of the elastic constants of metal are mainly focused on the elastic constants of crystal at the micro level. To the calculation of the macroscopic elastic constants of metal, although molecular dynamics method and quasicontinuum method can be used, but there are shortcomings in them, such as a large amount of computation and that the spatial scale of the study model is limited. Therefore, with a pure metal thin plate composed of a single layer of microscopic particles as research object, a new mechanical model is established after the interactions between microscopic particles of the thin plate are applied on the continuum mechanics model of the thin plate. According to this model, the calculation formulas for the microscopic elastic constants, which are the elastic constants of any triangle region in the model, are obtained. After the concept of the ideal micro structure is presented, the calculation formulas for the macroscopic elastic constants, the elastic modulus and the Poisson’s ratio of pure metal are obtained, where the Poisson＇s ratio is the constant that is equal to 1？3. As an example, the elastic constants and the elastic modulus of pure copper are solved, where c11 is 175.811 GPa, c12 is 58.604 GPa, c33 is 58.604 GPa and E is 156.277 GPa, the rationality and the correctness of the model are verified. The model presented fully embodies the discreteness of the microstructure of solid, is a development to the continuum model, and is more suitable to reality, more simplified and more new to the study of the macroscopic elastic constants of pure metal.展开更多
Purification is a primary application of zone melting, in which the improvement of efficiency, production yield and minimum achievable impurity level are always the research focus due to the increasing demand for high...Purification is a primary application of zone melting, in which the improvement of efficiency, production yield and minimum achievable impurity level are always the research focus due to the increasing demand for high purity metals. This paper has systematically outlined the whole development of related research on zone refining of metals including basic theories, variants of zone refining, parametric optimization, numerical models, and high purity analytical methods. The collection of this information could be of good value to improve the refining efficiency and the production of high purity metals by zone refining.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 59471048, 59725104, 19891180).
文摘The changes of microstructures after the exhaustion of dislocation glide ability but before cracking, as well as microcrack initiation by them, were studied in detail byin-situ transmission electron microscopy (TEM) for pure copper, aluminum and iron. Thinning occurred in the thicker regions through dislocation gliding in the three metals. After that, {111} 〈112〉 twinning or tensile cracking took place in thinned zones in fcc metals. In the case of twinning, new microcracks were initiated along another {111} plane by the high stress concentration near the growing tip of the twin, while in iron (bcc), many nanocracks were initiated in the thinned areas just ahead of the crack front, resulting in misorientation microstructure from which microcracks or microvoids were developed.
文摘The research activities of the calculation of the elastic constants of metal are mainly focused on the elastic constants of crystal at the micro level. To the calculation of the macroscopic elastic constants of metal, although molecular dynamics method and quasicontinuum method can be used, but there are shortcomings in them, such as a large amount of computation and that the spatial scale of the study model is limited. Therefore, with a pure metal thin plate composed of a single layer of microscopic particles as research object, a new mechanical model is established after the interactions between microscopic particles of the thin plate are applied on the continuum mechanics model of the thin plate. According to this model, the calculation formulas for the microscopic elastic constants, which are the elastic constants of any triangle region in the model, are obtained. After the concept of the ideal micro structure is presented, the calculation formulas for the macroscopic elastic constants, the elastic modulus and the Poisson’s ratio of pure metal are obtained, where the Poisson＇s ratio is the constant that is equal to 1？3. As an example, the elastic constants and the elastic modulus of pure copper are solved, where c11 is 175.811 GPa, c12 is 58.604 GPa, c33 is 58.604 GPa and E is 156.277 GPa, the rationality and the correctness of the model are verified. The model presented fully embodies the discreteness of the microstructure of solid, is a development to the continuum model, and is more suitable to reality, more simplified and more new to the study of the macroscopic elastic constants of pure metal.
文摘Purification is a primary application of zone melting, in which the improvement of efficiency, production yield and minimum achievable impurity level are always the research focus due to the increasing demand for high purity metals. This paper has systematically outlined the whole development of related research on zone refining of metals including basic theories, variants of zone refining, parametric optimization, numerical models, and high purity analytical methods. The collection of this information could be of good value to improve the refining efficiency and the production of high purity metals by zone refining.
