CREEP CHARACTERIZATION OF A DUPLEX TI-AL BASE ALLOY AT 700-DEGREES-C AND 750-DEGREES-C

The constant load creep behaviour of a two phase Ti-46Al-2W-0.5Si allo y was investigated at 700 and 750 degrees C, under stresses ranging fr om 225 to 370 MPa. The initial microstructure was found to be duplex, consisting of equiaxed primary gamma grains and of lamellar gamma + al pha(2) colonies. The minimum creep rate dependence on applied stress w as studied by means of the conventional power law equation; the stress exponent was found to vary between five (low stress regime, climb con trolled creep) and ten (high stress regime). The transition between th e two regimes occurs at stresses close to 300 MPa. The stress exponent , the apparent activation energy as well as the pre-exponential consta nt are comparable, at least in the low stress regime, with those obser ved in a Ti-48.7Al-2.2W alloy produced by powder metallurgy. (C) 1997 Elsevier Science S.A.