1 - Structural intermetallics and intermetallic-matrix composites: An introduction

Abstract

The position of intermetallics in binary phase diagrams is either in the form of line compounds or with an intermediate composition range not extending to pure metals. The research on ordered binary or multicomponent intermetallic alloys with multiphase microstructures has been driven by the need to develop materials capable of withstanding high temperatures and extreme environments with reduction in weight. At temperatures exceeding 1000°C, maximum protection against oxidation is achieved with the formation of impervious and stable scale of Al2O3 or SiO2 in aluminide- or silicide-based intermetallics, respectively. Therefore, aluminides based on Ni, Ti, and Fe and silicides based on Mo and Nb with selected compositions have drawn significant attention for their ability to retain strength at elevated temperatures and the possibility of improving oxidation resistance by addition of suitable alloying elements or reinforcements. Furthermore, metal-matrix composites with intermetallic phases as reinforcements are of interest for enhanced specific strength, toughness, and stiffness due to metallic bonding at the metal-intermetallic interfaces. The major challenges lie in optimizing compositions for the enhancement of toughness at the ambient temperature without adversely affecting high-temperature strength and oxidation resistance and in fabricating defect-free near-net-shaped products through economically viable processes. A brief overview of structure and properties of selected aluminides and silicides, which have formed the basis for further development, is being presented along with an introduction to the subsequent chapters focused on selected intermetallics, processing methodologies, and properties.