Fracture toughness and low cycle fatigue behaviour in boron modified Timetal 834 titanium alloy

The effect of addition of 0.2 wt.% B to Timetal 834 alloy on the fracture toughness at room temperature and low cycle fatigue (LCF) behaviour at room temperature and 600 degrees C was studied in the thermomechanically processed condition after subjecting it to a standard heat treatment. The fracture toughness of the boron modified alloy was found to be only marginally lower than that of the base alloy in both L-T and T-L orientations. Both the B modified Timetal 834 alloy and the base alloy exhibited cyclic softening throughout their fatigue life at a total strain amplitude of 1.0% for LCF tests at room temperature and 600 degrees C. The fatigue life of the B modified Timetal 834 alloy was also found to be nearly same as that of the base alloy at both room temperature and 600 degrees C. The observed behaviour was attributed to the fact that the microstructure of the matrix alloy remains unaffected by the addition of 0.2 wt.% B in the thermomechanically processed and heat treated condition except for the presence of about 0.015 volume fraction of TiB whiskers and this results in similar deformation and fracture mechanisms in the base and boron modified Timetal 834 alloys. (C) 2011 Elsevier B.V. All rights reserved.