Comparison of Fracture Toughness in Titanium Alloys IMI 550 and IMI 551

摘要

Fracture toughness tests on two high strength titanium alloys, IMI 550 and 551, showed that the higher strength alloy, IMI 551, had a much lower toughness. The alloys were very similar in microstructure and fracture mechanisms. A number of model formulations for predicting fracture toughness were compared with the experimental results. This comparison indicated a number of parameters to be important, namely yield stress, elastic modulus, plane strain fracture strain, strain hardening exponent, and microvoid (dimple) diameter. The observed increase in fracture strain, dimple diameter, and fracture toughness with decreasing strength can be rationalized by voids occuring earlier during deformation and by voids initiating at many sites inactive in the lower strength material.