Effect of microstructure on fracture characteristics of Ti-6Al-2Sn-2Mo-2Zr-2Cr-Si alloy

Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-62222S) is highly expected to be widely used f or structural aircraft materials because Ti-62222S shows both characteristi cs of a type alloys with excellent high temperature strength and creep resi stance, and alpha+beta type alloys with high fracture toughness and high st rength. The intermetallics, Ti3Al, and silicides, precipitated in Ti-62222S during aping treatments decrease the strength and fracture toughness. Howe ver, the effect of each intermetallics on fracture characteristics of Ti-62 222S is not yet clearly understood. Therefore, the fracture characteristics of Ti-62222S with only Ti3Al or only silicides precipitated by aging treat ment were investigated with relating the matrix microstructure. 0.2% proof stress, tensile strength and elongation of the as-received mater ial are much better than those of the aged materials. 0.2% proof stress and tensile strength of the material with only Ti3Al precipitated by aging tre atment are better than those of the material with only silicides precipitat ed by aging treatment, while elongation of the material with only silicides is better than that of the material with only Ti3Al. Static fracture tough ness of the material with only silicides is better than that of the materia l with only Ti3Al. The intergranular fracture appears in the material with only Ti3Al. Coarsening of Widmanstatten alpha structure and increasing duct ility of beta phase during aging is considered to be effective for increasi ng static fracture toughness.