1992 Volume 78 Issue 3 Pages 493-499
Effect of bi-modal microstructure on fracture toughness of beta type Ti-15V-3Cr-3Sn-3Al alloy was systematically examined. Bi-modal microstructure that was obtained through combination of aging at high and low temperatures after solution treatment is composed of coarse and fine alpha precipitates and beta matrix. This bi-modal microstructure improves fracture toughness-strength balance compared with microstructure produced by aging at single temperature after solution treatment. Comparing at the same strength level, increase of volume fraction of the coarse alpha precipitated by aging at 873 K in the bi-modal microstructure gives higher fracture toughness, however, it reduces attainable strength. Homogeneous distribution of coarse alpha precipitates obtained by pre-aging at 573 K before aging at high temperature tends to reduce the superiority of the bi-modal microstructure in fracture toughness. This superiority is provided by the formation of voids and microcracks in the coarse alpha precipitates and rugged crack propagation due to the uneven microstructure.
