Abstract
The effect of microstructure on fracture toughness of near α titanium alloy Ti-6Al-2Sn-4Zr-2Mo was investigated by Acoustic Emission three dimensional location, Acoustic Emission source characterization and fractography method. The fracture toughness of alloy with acicular α structure was superior to that of alloy with equiaxed α structure at the same yield strength level. It was considered that the result was based on the number of large amplitude Acoustic Emission events prior to KIC and on the deflection of the crack path. The large amplitude Acoustic Emission events coresponded to microcracks of 50-80μm which nucleated at the pre-fatigue crack tip along crack front in both structures. Macroscopic crack growth occured where these microcracks coalesced in the direction to specimen thickness. These microcracks lower the stress concentration at the crack tip. Thus it was concluded that microcrackings enhanced the fracture toughness of titanium alloy with acicular α structure.
