Research on Deep Hardening Titanium Alloy for Large Airframe Structural Members. Volume I.

摘要

This is the final technical report of a contract to develop a titanium alloy capable of being hardened in section sizes significantly greater than currently available while retaining adequate toughness and tensile ductility. Work was carried out in three successive phases: Phase I in which the hardening potential at the center of a six inch section was defined for sixty alloy compositions; Phase II in which the detailed evaluation of tensile properties and fracture toughness data of aged samples led to development of characteristic alloy trend lines for the ten most promising alloys; and finally, Phase III in which three alloys - alloy 334 (10Mo-6Cr-2.5Al), 227 (7Mo-4Cr-2.5Al) and 253 (10Mo-8V-2.5Al) - were scaled up as 500 lb. ingots. After a study of various thermomechanical processes, the three alloys were converted to 6-inch diameter billet, duplex solution annealed and aged, and full mechanical properties evaluated. Transverse center properties of alloy 334 attained contract goals while equivalent properties for the other two alloys were very promising. Generally the alloy represents an advance in state-of-the-art deep hardenable titanium alloys. They show little edge to center variation in properties, in contrast to commercial and semi-commercial present alpha-beta alloys which are characterized by large edge to center difference. This property differential is to particular concern in considering fracture toughness since the effective fracture toughness in a heavy section is only as high as the lowest value occurring in the material.