Micron Scale Magnesium Single Crystal Plastic Deformation Mechanism By Dislocation Dynamics

Micro-Electro-Mechanical Systems(MEMS)have an important role in modern electronics,enabling a variety of functions such as sensing,control and actuation.As the scale of MEMS parts is on the same order of magnitude as the grain size,good plastic forming capability of the part material at the micron scale is required,taking into account size effects and discontinuities.Dislocations,as one of the main carriers of plastic deformation,play a crucial role in the evolution of the material’s plastic deformation.In this paper,discrete dislocation dynamics is used to calculate the variation of yield stress in magnesium single crystals at different temperatures,different strain rates and different initial dislocation densities.The evolution of dislocations is simulated and key information on the type,number and position of dislocations is obtained.The internal mechanism of plastic deformation of magnesium crystals was investigated by analysing the changes in dislocation configuration during the deformation of magnesium single crystals.The results show that strain rate hardening and forest dislocation hardening compete with each other during the deformation of magnesium crystals.As the initial dislocation density increases,the yield strength of magnesium crystals shows a tendency to first decrease and then increase.In order to distinguish between the two trends,the concept of critical dislocation density is proposed.When the initial dislocation density is less than the critical dislocation density,the magnesium crystal strength decreases with the increase of the initial dislocation density,when the initial dislocation density is greater than the critical dislocation density,the magnesium crystal strength increases with the increase of the initial dislocation density.The relationship between the critical dislocation density and strain rate is linear at room temperature and non-linear at high temperature.The results of simulations of magnesium crystals at different temperatures show that the temperature sensitivity of each slip system differs during deformation.The temperature sensitivity of the basal slip system is weak,the number of basal dislocation openings hardly changes with increasing temperature.The temperature sensitivity of the columnar and tapered slip systems is stronger because the critical shear stress of the columnar and tapered slip systems decreases with increasing temperature.The critical dislocation density of magnesium crystals tends to increase and then decrease with temperature.