Effect of morphology of primary a on fatigue crack propagation resistance in a near a heat resistant Titanium alloy

Abstract

DAT54 is a new near a heat resistant Ti alloy developed for disk applications in the compressor part of jet engines. DTA54 with bimodal microstructure shows a good balance of fatigue strength and creep life, and performs better than Ti-6242s up to 873 K. However, the influence of microstructure on properties, especially the effect of the morphology of primary a on fatigue crack growth resistance is not understood. In this study, samples with different types of microstructure were prepared by applying different heat treatment temperatures, and the influence of microstructure on fatigue crack growth properties at ambient temperature and 823 K was investigated. Influence of environment was also investigated by testing in vacuum and in air condition. Acicular microstructure shows lower fatigue crack growth rates in Paris’ region than the bimodal microstructures at 823 K. For the bimodal structures, aspect ratio of primary a do not have apparent influence on fatigue crack growth rates in Paris’ region, whereas fatigue threshold (DKth) seems to be affected by the morphology of primary a.

Keywords

• near a titanium alloy
• fatigue crack propagation