Fracture mechanics behavior of TiNbSn alloys as a function of alloy content, cold working and aging

Mechanical properties such as tensile strength, ductility and elastic modulus, which are directly related to fracture mechanics characteristics, can be controlled during termo-mechanical manufacture of TiNbSn alloys. Cold working the alloys reduces its ductility and elastic modulus. Aging reduces their ductility further, but increases their elastic modulus. The present study aims to evaluate the effect of Nb (35% and 42% wt.) and Sn (0% and 2.5% wt.) contents on fracture toughness and fatigue crack growth of TiNbSn alloys of both cold worked and aged at 400 degrees C. The fracture toughness K-IC was performed, and fracture analysis allowed to evaluate micromechanics changes. Crack growth rate (da/dN-Delta K) tests were also performed. Aging was beneficial to fracture threshold Delta K-th and crack growth rate of the alloys. However, aging did not interfere with fracture toughness K-IC. The increase in Nb content is beneficial to both fracture toughness and crack growth rate of the aged alloys. The addition of Sn in the aged 42% Nb alloy decreases the crack growth rate at higher Delta K. For alloys of similar elastic modulus, the size of dimples is proportional to fracture toughness.