Effect of temperature on near-surface microstructural evolution in nanocrystalline metal under shear stress

Molecular dynamics simulations were used to investigate the temperature effect in the microstructural evolution of nanocrystalline Al-Mg-Si alloy under different pressures and velocities. A deformation mechanism map is proposed through quantitative characterization of the microstructural evolution. This map provides a "phase diagram" illustrating the elastic-plastic transition, stacking faults (SFs), grain refinement, and shear layer formation under different temperatures and loads. Changes in temperature alter SFs motion and microstructural integrity. SFs appear in the form of single trace line (300 K) and multiple parallel lines (77 K), respectively. Compared to 300 K, the rotation and slip motion of grains in the sample are restricted at 77 K, making it difficult for the microstructure to rearrange. Under external loading, the degree of grain refinement is greater at 77 K (up to 13.2% refinement) compared to the refinement at 300 K (maximum similar to 8.3%). This leads to the generation of a greater number of grain boundaries (GBs) and SFs. Additionally, there is a significant variation in the special GBs (represented by 23) with a relatively high overall content. A sudden drop in integrity occurs at a pressure of 10(5) atm. And the deformation at the highest velocity recovers to almost the same low level as at the lowest velocity.