The Preparation of a Molybdenum Based High Temperature Refractory Alloy by Powder Processing Route

Abstract

Molybdenum-based TZC alloy having nominal composition of Mo–1.2 Ti–0.3 Zr–0.1 C (wt%) possesses several attractive features for high temperature structural applications. These include high melting point, high tensile and creep strength, high resistance to heat and corrosion, good thermal diffusivity and satisfactory welding properties. However, synthesis of TZC alloy with micro-alloying additions of Ti, Zr and C by conventional high vacuum melt-casting route is a challenging task to achieve homogeneous alloy composition in view of segregation of alloying components. Hence, in the present investigation, an alternative approach to prepare homogenous TZC alloy was adopted by a powder processing route, namely, mechanical alloying (MA) at room temperature. As, Mo is a major ingredient (~98.25%) in TZC alloy, hence, this component was prepared in the laboratory to satisfy the requirement for indigenous development of the alloy. Apart from pure elements used for the alloy preparation, carbon requirement of the alloy was fulfilled from toluene medium used during milling. MA powder that was obtained exhibited fine grained microstructure with nano sized grains available in the range of 10-20 nm having polyhedral shapes. A high rate of densification, close to theoretical density, was achieved during sintering of MA powder between the temperature ranges of 1500-1700°C. XRD analysis confirmed the formation of carbides phases and the composition of the sintered alloy nearly matched the desired alloy composition. Transmission electron microscopy (TEM) studies have revealed the uniform distribution of carbides in the MA alloy having round shapes.