| Compared with coarse-grain materials,nanocrystalline(nc)materials have superior hardness senior yield strengths and higher wear resistance owe to their unique microstructure,so a lot of attention had been paid to study in the past 20 years.A quantity of researchers find a fact that voids initiation and growth must be operative.It is generally believed that the unique microstructure and plastic deformation mechanism of nc materials make for different from the conventional coarse grained materials.Based on fully understanding in the cavitation nucleation and development of nc materials.We have set up models of nanovoids initiation and growth to study the plastic deformation in nc materials.The main researches content are summarized as follows:(1)We have reviewed the research processes,concluded the influence of voids initiation and growth,summarized the deformation mechanism of nc.(2)A theoretical model has been established to research the accumulation of dislocation on triple junction,grain boundary diffusion energy,microvoids initiation in deformed nc materials on the basis of energy conservation.(3)The influence of micro-voids nucleation on the triple junction caused by grain boundary sliding,grain boundary diffusion,loads and grain boundary length were counted.The calculation results show that voids were nucleated easier with big applied load and large grain boundary,but the high temperature and the grain boundary diffusion inhibited the initiation of microvoids.(4)A model was built to analyze the effects of surface energiers,stress,yield strength and grain size on the growth process of the cavitation.The results show that compared with the grain boundary energy,the surface energy has a great of influence on the void development.However,the hydrostatic stress has a certain effect on the growth of the hole.Under the certain external stress,before the hole coalescence the growth rate of the hole decreased with the microvoid larger and larger. |
PDF Full Text Request