Akira Nozue1 and Tadatsune Okubo1
1Department of Mechanical Engineering, Faculty of Science and Technology, Sophia University, Tokyo
The purpose of the present paper is to clarify fatigue crack growth behavior in Ti-6Al-4V alloy consisting of primary α and matrix. The phase ratio of the primary α to the matrix was varied from about 65 to 20% with the solution treatment. The temperature range for this treatment was between 1148 and 1228 K. Fatigue tests were carried out in the Δ K region from the fatigue threshold to the critical fatigue fracture under constant load amplitude with CT specimens of 6 mm thickness. The crack propagated preferentially in the primary α phase compared with the matrix. On the fracture surfaces of the primary α phases, comparatively flat facets were observed in the low Δ K region and the striations were clearly observed in the high Δ K region. In addition, martensite boundary cracks existed in the matrix. It was found that the primary α fraction mainly controlled the fatigue crack growth rate in the region of the stable crack growth.
fatigue, crack propagation, microscopic striation, primary alpha phase, facet, fractography, titanium-6% aluminum-4% vanadium alloy
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