Periodic Plastic Deformation Behavior of Ti-6Al-4V Titanium Alloy Based on Strain Controlling Mode

Ti-6Al-4V titanium alloy is a dual-phase material; the discontinuous microstructure has an important influence on its fatigue properties. Studies have shown that the fatigue cracks are more likely to occur in stress and strain concentration areas during service of the material. In order to study the periodic plastic deformation behavior of Ti-6Al-4V titanium alloy, a finite element model based on strain controlling mode is established. The distribution of the equivalent plastic strain and its evolutions with the cycle index are studied. The results show that after cyclic loading with different periods, considerable equivalent plastic strain is observed in the microstructure of Ti-6Al-4V alloy. With the increases in the cycle index, the equivalent plastic strain becomes more significant, finally forming equivalent plastic strain bands, which are 45° to the loading direction. The equivalent plastic strain in the primary alpha phase close to transformed beta matrix is greater than that of other regions; this region is prone to plastic damage. So the primary alpha phase is the region where the fatigue cracks are easy to initiate when titanium alloy undergoes cyclic loading. The maximum equivalent plastic strain ratio between primary alpha phase and transformed beta matrix increases with the increase in the cycle index. This is unfavorable for stable service of titanium alloy.