COMPARISON OF ORTHORHOMBIC AND ALPHA-2 TITANIUM ALUMINIDES AS MATRICES FOR CONTINUOUS SIC-REINFORCED COMPOSITES

The attributes of an orthorhombic Ti aluminide alloy, Ti-21Al-22Nb (at . pct), and an alpha-two Ti aluminide alloy, Ti-24Al-11 Nb (at. pct), for use as a matrix with continuous SiC (SCS-6) fiber reinforcement ha ve been compared. Foil-fiber-foil processing was used to produce both unreinforced (''neat'') and unidirectional ''SCS-6'' reinforced panels . Microstructure of the Ti-24Al-11 Nb matrix consisted of ordered Ti3A l (alpha2) + disordered beta (beta), while the Ti-21Al-22Nb matrix con tained three phases: alpha2, ordered beta (beta0), and ordered orthorh ombic (O). Fiber/matrix interface reaction zone growth kinetics at 982 -degrees-C were examined for each composite system. Although both syst ems exhibited similar interface reaction products (i.e., mixed Ti carb ides, silicides, and Ti-Al carbides), growth kinetics in the alpha2 beta matrix composite were much more rapid than in the O + beta0 + alp ha2 matrix composite. Additionally, interfacial reaction in the alpha2 + beta composite resulted in a relatively large brittle matrix zone, depleted of beta phase, which was not present in the O + beta0 + alpha 2 matrix composite. Mechanical property measurements included room and elevated temperature tensile, thermal stability, thermal fatigue, the rmomechanical fatigue (TMF), and creep. The three-phase orthorhombic-b ased alloy outperformed the alpha2 + beta alloy in all of these mechan ical behavioral areas, on both an absolute and a specific (i.e., densi ty corrected) basis.