EFFECTS OF PRECIPITATED INTERMETALLICS ON FRACTURE CHARACTERISTICS OF Ti-6Al-2Sn-2Zr-2Mo-2Cr-Si

摘要

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, Ti_3Al and silicides, precipitated in Ti-62222S during aging treatments decrease the strength and fracture toughness. However, the effect of each intermetallic on fracture characteristics of Ti-62222S is not yet clearly understood. Therefore, the fracture characteristics of Ti-62222S with only Ti_3Al 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 Ti_3Al precipitated by aging treatment are better than those of the material with only silicides precipitated by aging treatment. Static fracture toughness of the material with only silicides is better than that of the material with only Ti_3Al. The intergranular fracture appears in the material with only Ti_3Al. Coarsening of Widmanstaetten α structure and increasing ductility of β phase during aging is considered to be effective for increasing static fracture toughness.