1991 Volume 55 Issue 7 Pages 756-764
Microfracture processes of Ti-6Al-4v alloys with various acicular α structures were investigated by acoustic emission (AE) source location, source characterization and fractography.
The specimen with a coarse acicular α structure showed higher fracture toughness than with a fine acicular α structure.
AE source characterization showed that two types of microcracks were generated before the final unstable fracture. One was a smaller microcrack with a higher propagation velocity, and the other was a larger microcrack with a lower propagation velocity.
In the fracture process, the microcracks of the former type were generated around the fatigue pre-crack front in the early stage of loading. The main crack extension occurred when the microcracks of the former type coalesced. The latter corresponded to the coalescence of the former.
In the specimen with a coarse acicular α structure, microcracks distributed widely out of the fatigue pre-crack plane and the main crack extension was hindered or distorted by phase boundaries.
It was concluded that both the distribution of microcracks and the resistance of acicular α structure to the coalescence of microcracks had a significant influence on the fracture toughness of this alloy.
