Effect of recrystallisation on the residual stress pattern and fatigue behaviour of titanium alloy IMI-685

The residual stress pattern following recrystallisation of shot-peened layers of the near α-titanium alloy IMI-685 was determined by the method of drilling holes. The residual stresses were found to be tensile in nature. Recrystallisation produced a dual microstructure consisting of equiaxed or fine plates of α in the surface while retaining acicular-α in the interior. A constant stress amplitude axial fatigue test on peened and recrystallised samples indicated an increase in fatigue life compared to unpeened (UP) but similarly heat-treated samples. However, the same showed a drastic decrease in fatigue life of 80% compared to peened/unpeened samples without any heat-treatment. The decrease in fatigue life could be attributed to the combined effect of the tensile residual stresses and silicide precipitation in the material.