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 for structural aircraft materials because Ti-62222S shows both characteristics of α type alloys with excellent high temperature strength and creep resistance, and α + β type alloys with high fracture toughness and high strength. The intermetallics, Ti₃Al, and silicides, precipitated in Ti-62222S during aging treatments decrease the strength and fracture toughness. However, the effect of each intermetallics on fracture characteristics of Ti-62222S is not yet clearly understood. Therefore, the fracture characteristics of Ti-62222S with only Ti₃Al or only silicides precipitated by aging treatment were investigated with relating the matrix microstructure. 0.2% proof stress, tensile strength and elongation of the as-received material 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 treatment are better than those of the material with only silicides precipitated by aging treatment, while elongation of the material with only silicides is better than that of the material with only Ti₃Al. Static fracture toughness of the material with only silicides is better than that of the material with only Ti₃Al. The intergranular fracture appears in the material with only Ti₃Al. Coarsening of Widmanstaetten α structure and increasing ductility of β phase during aging is considered to be effective for increasing static fracture toughness.