9 - Creep of Intermetallics

Abstract

The term “intermetallics” is used to designate the intermetallic phases and compounds which result from the combination of various metals, and which form a large class of materials. Intermetallics often have high melting temperatures (usually higher than 1000 C), due partly to the strong bonding between unlike atoms, which is a mixture between metallic, ionic and covalent to different extents. The presence of these strong bonds also results in high creep resistance. Another factor that contributes to the superior strength of intermetallics at elevated temperature is the high degree of long-range order, which results in low diffusivity; the number of atoms per unit cell is large in a material with longrange order. Therefore in alloys in which dislocation climb is rate-controlling, a decrease in the diffusion rate would result in a drop in the creep-rate and therefore in an increase of the creep resistance. Creep resistance is a critical property in materials used for high-temperature structural applications. Some intermetallics may have the potential to replace nickel superalloys in parts such as the rotating blades of gas turbines or jet engines due to their higher melting temperatures, high oxidation and corrosion resistance, high creep resistance, and, in some cases, lower density. This chapter reviews the current understanding of creep of intermetallics placing special emphasis on investigations published over the last decade and related to the compounds with potential for structural applications such as titanium aluminides, iron aluminides, and nickel aluminides.