Primary Creep of a Near γ-TiAl Intermetallic

Abstract

The primary creep behaviour at 760°C and stresses of 172 MPa and 240 MPa is presented for a binary Ti-48at%Al intermetallic heat treated to the duplex and two fully lamellar microstructures. The results indicate that at both stresses the fully lamellar microstructures exhibit better primary creep resistance than the duplex structure. Reducing the lamellar interface spacing causes a further increase in the primary creep resistance. After primary creep deformation, dislocation loops emanating from lamellar interfaces and bowed dislocation segments spanning the γ lamellae exist. This is interpreted to indicate that the primary creep behaviour is dependent on the emission of dislocations from lamellar interfaces and the combined glide and climb of dislocations in the γ lamellae. Reverse anelastic strain follows near total stress reductions during primary creep. The anelastic strain is the result of reverse glide of bowed dislocations that span γ lamellae, annihilation of dislocations and the development of a γ subgrain structure.