Micro and nano-indentation of MoSi2

Abstract

Molybdenum disilicide based materials are candidate for high temperature structural applications, such as a furnace heating element and an electrical conductor in silicon intergrated circuit design or parts of engines [1]. MoSi2 exhibits a high melting point (2030 ◦C), excellent high temperature oxidation resistance, and posseses many convenient properties such as high stiffness, high thermal conductivity, relatively low density, and high strength at elevated temperatures. However, a major difficulty in application of these materials is the lack of adequate ductility and fracture toughness below 1000 ◦C. Only toward the higher temperatures (between 1000 and 1400 ◦C), with the onset of dislocation climb and diffusional creep processes, does MoSi2 exhibit significant plasticity in compression, bending, and tension in both single crystals and polycrystalline materials [2, 3]. During the last decade many approaches had been applied to reduce the brittle-to-ductile transition temperature (BDTT) of these materials, to overcome the limitation of dislocation mobility and dislocation density, and to enhance the capability for plastic flow and increase the fracture toughness. The main approaches for ductility enhancement are solid solution alloying, second phase microstructure control, ductile phase toughening, and high temperature prestrain [4]. The crystal structure of MoSi2 is tetragonal (C11b type), space group 14/mmm. The lattice parameters are a = 0.3205 nm and c = 0.7845 nm with c/a = 2.45 (Fig. 1). MoSi2 is also reported to have hexagonal C40 structure above 1900 ◦C [5]. There exists an absence of knowledge concerning the relative mobility of edge and screw dislocations and information about different dislocation types 〈100〉, 〈110〉, 1/2〈111〉, and 1/2〈331〉, their glide planes; furthermore the operative slip systems as a function of temperature, strain rate, and crystallographic orientation are only partially understood. Studies of the slip systems by means of hardness indentation for MoSi2 single crystal has found that the primary and secondary slip systems were {100} 〈001〉 and {110} 〈001〉, respectively [4]. Berkowitz et al. [6] reported that {110} is the slip plane in MoSi2 single crystal deformed between 625 and 1125 ◦C under compressive load along three different directions. They con-