Material instability under localized severe plastic deformation during high speed turning of titanium alloy Ti-6.5AL-2Zr-1Mo-1V

High temperature, large strain and fast strain rate resulting from the severe plastic deformation will cause local material instability, then physical and chemical reactions such as phase transition, grain redistribution and fracture may occur during this process. This paper presents an in-depth investigation about the material instability and corresponding microstructures during the serrated chip formation of titanium alloy Ti-6.5AL-2Zr-1Mo-1 V by high speed turning. Firstly, intense deformation during high speed cutting was verified. Phase transition under different loading conditions including temperature, strain and strain rate were also explored, followed by the domination of equiaxed α-phase due to suitably localized severe plastic deformation and sufficient cooling. Secondly, criterion for initiation of fracture of material was introduced and applied to chip breaking. Finally, particle redistribution phenomenon was analyzed accordingly and the so-called severe plastic flow was further verified.