Study On The Micro-Mechanism Of Strain Rate Softening Plastic Instability In Alloys

Alloy materials are apt to happen strain rate softening plastic instabilityphenomenon-PLC effect at a certain temperature, and this kind of phenomenonseriously affects the application of such alloy materials.The study of microscopicmechanism of the PLC effect contributes a good link between macroscopicphenomena and microscopic mechanisms, which will provide certain help to thewidespread applications of such materials.By using the Monte Carlo method, theinteraction of dislocations and solute atoms was simulated by using the MonteCarlo method to study the internal mechanism of the alloy plastic instabilitybehavior. The influences of different external stress, temperature and the initialconcentration of solute atoms were analyzed on the evolution of the dislocationsand solute atoms, the stress of the dislocations and speed change, thetransformation of the concentration of solute atoms and the number of dislocationsthat cross the grain boundary.Based on the study of the movement characteristics ofdislocations and solute atoms under the three above conditions, the mainconclusions are as following：1. With the increase of external stress, the impediment of solute atoms todislocation motion declines after initial increment. The process of stress relaxationand solute atoms’ segregation towards dislocations at smaller external stress state isfaster than at static state’s; and it is the slowest process at bigger external stressstate；2. With the temperature increasing, the dislocations have higher energy, andthe dislocation movements exacerbate as a whole, while the solute atoms trendincreasingly difficult to form an effective pinning for the dislocations. Overall, thetemperature rises can cause the increase of the speed of dislocation movement aswell as the strain rate of the deformation of the materials at the macro；3. Dislocation rates are affected by the concentrations of the solute atoms. Thegreater the concentration of solute atoms and the drag force of dislocations by thesolute atoms, the smaller resultant force and the speed of movements of thedislocations；4. The speeds of segregation of solute atoms are related to the initial concentrations of solute atoms. The higher the initial concentration of solute atomsand the rate of segregation, the more likely it is to form a Cottrell atmosphere andthe pinning of the dislocations；5. It is also found that the segregation behaviors are basically the same forlarger and smaller solutes.