Development of MoSi2-SiC Component for Satellite Launch Vehicle

Intermetallic base MoSi2-SiC composite, an excellent high temperature oxidation-resistant material meant for the aerospace structural applications between 1600°C and 1700°C under oxidizing environment, has been developed successfully using powder metallurgy techniques. Mechanically milled (MM) MoSi2 powder, blended with SiC particulate was consolidated by vacuum hot pressing, yielded about 98.5% theoretical density. The composite has been characterized for physical, mechanical, and thermal properties. Properties were found satisfactory. Machining of semis to intricate shape was possible through electro-discharge machining (EDM) process. Plasma arc jet test (PAJT) under argon and argon + oxygen environment has proved its excellent high temperature oxidation resistance properties as it could sustain high heat flux up to 250？W/cm2 under oxidizing environment. The component realized has full potential to be used in critical aerospace application. This paper highlights the details of experimental work carried out and its characteristic properties attained. 1. Introduction Molybdenum disilicide (MoSi2) is an intermetallic with tetragonal unit cell arrangement (Figure 1) and has strong potential for high temperature structural applications in aerospace industries due to its high melting point (2030°C) and ability to undergo plastic deformation above 1200°C. Molybdenum disilicide possesses outstanding oxidation resistance up to 1700°C due to the formation of an impervious film of SiO2 on the surface which prevents further oxidation. Being electrically conductive, it could be machined by electro-discharge machine (EDM) to desired shapes [1–3]. Apart from wide use as heating element, it is also used in power generation components, heat exchanger, filters, turbine blades, vanes, combustion nozzles, turbocharger rotors, valves, and so forth [4]. However, its room temperature fracture toughness is poor compared to other high temperature metallic systems. Other mechanical properties such as yield strength and creep strength gradually decrease above 1100°C. Hence, reinforcement of the matrix with thermally stable ceramic particles or whiskers which can significantly improve the fracture toughness at room temperature as well as high temperature properties is recommended [5–7]. It is chemically compatible with a number of ceramic constituents such as SiC, Si3N4, TiC, TiSi2, ZrO2, Al2O3, and so forth, which could be judicially selected as reinforcement for particular use and temperature regime [8, 9]. Figure 1: Schematic sketch of atomic arrangement of tetragonal unit