Molecular dynamics simulation for nanometric cutting of NiTi shape memory alloys at elevated temperatures

In nanometric cutting, the deformation mechanism is closely related to the cutting temperature. This study investigates the cutting mechanism at elevated temperatures via molecular dynamics simulation of nanometric cutting on equiatomic NiTi SMAs. Mutual transformation between martensite and austenite during the indentation and cutting process, and effects of the cutting temperature are analyzed. The results indicate that the NiTi workpiece atoms experience martensite phase transformation and reverse phase transformation during the indentation and cutting process, with different orientation of martensite facilitating the transformation. Besides, the average resistance coefficient decreases with increasing cutting temperature due to the elevated temperature lubrication effect, and the cutting forces and phase transformation in the processing area also experience a gradual reduction. Some of the dislocations inside the NiTi workpiece show plugging and tangling phenomena at temperatures of 400 and 600 K. Cutting simulations reveal that fewer dislocation slips and less residual stress occur at elevated temperatures and lead to significantly reduce of residual martensite phase after cutting. From an atomic perspective, this investigation explains the cutting mechanism of difficult-to-machine materials NiTi SMAs at elevated temperatures and gives guidance for improving its machinability.