Molecular Dynamics Simulations Of Deformation Mechanism Of {1011} Twin In Magnesium

The microstructures of metal,such as:grain boundary,coherent twin boundary,incoherent twin boundary,are often used as the main means of strengthening metals.Traditional strengthening methods will reduce the plasticity of materials.Because of the special interaction between twin boundary and dislocation,nanotwin will improve the strength of materials when the feature size of twin is at the nanometer level.And it will not reduce the plasticity of materials.There are two common kinds of twin in magnesium:{1012} and {10(?)1} twin.Molecular dynamics simulations are applied in this paper to investigate the mechanisms of {10(?)1} twinning and the deformation mechanisms of {10(?)1} nanotwinned magnesium under nanoindentation.The main results are as follows:(1)The mechanisms of {10(?)1} twinning is analyzed in this paper:it is realized by the continuous emission of 2/9[1012]pyramidal partial dislocations.And there are shuffle accompanied with 2/9[1012]pyramidal partial dislocations emission.Detailed analysis on the vector of dislocation and the magnitude of shuffles is given.The results show that this is a shear-dominated twinning mechanism with a shear amount of 1.0672,which is much larger than the shearing of two other twin dislocation mechanisms(0.1736,0.1338).In addition,this paper also analyzes the effects of temperature and strain rate on this mechanism.The increase of temperature has a tendency to promote the formation of twin,but with the increases of strain rate,the promoting effect of temperature will decrease.The increase of strain rate is beneficial to the appearance of this mechanism.(2)The plastic deformation mechanism of {10(?)1} nanotwinned magnesium under nanoindentation is:In the early stage,it is dominated by the continuous emission of the 1/3[1010]basal partial dislocation,and then the phase transition will occur.When the basal partial dislocations meet the twin boundary,it will interact with the twin boundary,and the 2/9[1012]pyramidal partial dislocations will be left on the other side of twin boundary.Moreover,Lattice Reorientation will appear at the end of the deformation.With the increase of orientation angle,the plastic deformation mechanism transforms into the continuous emission of 1/3[1010]basal partial dislocations accompanied with Lattice Reorientation.The increase of the size of the indenter will reduce the area of Lattice Reorientation.The increase of the size of the indenter will reduce the Lattice Reorientation,so the hardness of the material will decrease.The loading rate has no significant effect on the hardness of the material.But it will cause the {10(?)1} twinning in nanotwinned magnesium,resulting of the increase of the hardness of the material.