Low-density, High-strength Intermetallic Matrix Composites by XD (trademark) Synthesis

Book excerpt: There is an increasing need for lightweight high performance materials in today's aerospace arena. High temperature engine designs, for example, require engine materials with elevated temperature strength, creep resistance, damage tolerance, oxidation resistance, and low density. Ordered intermetallics are considered potential alternatives to superalloys because they exhibit many of these properties. A major problem with most ordered alloys is their tendency toward inherently low ductility. The reasons can be quite varied depending on the alloy system, and include poor grain-boundary cohesion, an insufficient number of available slip systems (primarily in non-cubic alloys), limited cross slip, and impurity locking of dislocations. However, intermetallics of high symmetry, such as the L12 structure, have a number of slip systems, which can provide some plasticity, at least at intermediate temperatures, thus enabling the matrix to accommodate some of the strain associated with the thermal stresses.