Fc. Dary et Tm. Pollock, EFFECTS OF HIGH-TEMPERATURE AIR AND VACUUM EXPOSURES ON THE ROOM-TEMPERATURE TENSILE BEHAVIOR OF THE (O-22AL-23NB(B2) TITANIUM ALUMINIDE TI), Materials science & engineering. A, Structural materials: properties, microstructure and processing, 208(2), 1996, pp. 188-202
A new class of titanium alloys, based on the orthorhombic Ti2AlNb phas
e, have received considerable attention recently as a potential matrix
candidate for foil-fiber-foil processed intermetallic matrix composit
es. Ln the present study, the microstructure and room temperature defo
rmation of one such an orthorhombic titanium aluminide alloy, Ti-22Al-
23Nb (atomic per cent), were investigated. The O + B2 microstructure o
f the as-processed sheets was found to be quite inhomogeneous with res
pect to the O phase precipitation. The thermal and environmental respo
nses of the sheet microstructure were investigated at 760 degrees C fo
r 100 h in air and vacuum. The microstructure was stable but emerged a
s being very sensitive to oxygen exposure even in a vacuum environment
. The effects of high temperature exposure on room temperature deforma
tion were studied by heat treating tensile samples prior to testing at
760 degrees C for 100 h in air and vacuum. The room temperature ducti
lity and strength were very sensitive to the variations in size and ar
rangement of the O phase, resulting from processing, and to the presen
ce of surface oxides and oxygen-enriched surface layers, resulting fro
m pre-exposure treatment and specimen surface preparation. This study
has clearly shown that improved resistance to oxygen exposure represen
ts a challenge in the development of this type of alloy for use at tem
peratures near 760 degrees C.