Mechanical behaviour and oxidation resistance of structural silicides
The need for high performance materials in aerospace, automotive and industrial components operating at temperatures in the range of 1100–1500°C has led to a surge in the research and development of the refractory metal silicide based intermetallics, multiphase alloys and composites. The silicides of Mo, W, Ti, Nb and Cr are attractive for high melting points, strength retention and ductile behaviour, combined with reasonable to excellent oxidation resistance at elevated temperatures. The major limitation to the widespread use of structural silicides is their inherent brittleness and poor fracture toughness at room temperature, which may be improved further by suitable alloying or tailoring composite microstructures or use of innovative processing routes. The high temperature deformation behaviour of the structural silicides is complex, and depends on the composition and alloy content, crystal structure, character of bonding and orientation, microstructural constitution (nature of phases present and volume fraction), and grain size. Over the past decade, the basic character and role of dislocations involved in the deformation of single or polycrystalline samples at different temperatures and strain rates, including creep conditions, have been investigated in order to understand the operating mechanisms and decide on the strategies to further improve the mechanical properties. Oxidation behaviour in different structural silicides has been studied with emphasis on the constitution of the oxide scale and the kinetics of oxidation under different temperature regimes, which also involve pest disintegration at intermediate temperatures. The present study is a review with a comparative assessment of the known mechanisms of deformation, fracture and oxidation along with strategies to improve the properties to the targeted levels and some of the emerging applications of structural silicides.