Effects of microstructural modification on fatigue crack growth resistanceof Ti-15V-3Al-3Sn-3Cr

The recent development of multi-step aging treatments and thermo-mechanical processes to improve fracture toughness of optimum strength Ti-15V-3Al-3Sn -3Cr has increased the range of aerospace applications for this cold-formab le alloy. This investigation describes the impact on fatigue performance of the microstructural changes induced by these new processes. Beta solution treated material exhibited a transition in fatigue crack growth rates, dram atically slowing when a critical plasticity dimension produced by the appli ed stress intensity was exceeded. In material exhibiting transgranular frac ture, crack propagation was not significantly altered by changes in alpha m orphology (including precipitate size, aspect ratio and distribution) resul ting from multi-step heat treatment. Changes in grain and precipitate orien tation due to warm or cold rolling prior to aging increased fatigue propaga tion rate when tested in L-T and T-L orientations. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.