Niobium and Other High Temperature Refractory Metals for Aerospace Applications
Refractory metal alloys based on Nb, Mo, Ta, W, and Re find applications in the aerospace industries because of their high melting points and high temperature strengths. They are generally produced by powder metallurgy technique due to their very high mel
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Niobium and Other High Temperature Refractory Metals for Aerospace Applications V.V. Satya Prasad, R.G. Baligidad and Amol A. Gokhale
Abstract Refractory metal alloys based on Nb, Mo, Ta, W, and Re find applications in the aerospace industries because of their high melting points and high temperature strengths. They are generally produced by powder metallurgy technique due to their very high melting points. However, when refining is desired, melting under high vacuum becomes necessary, for which nuggets or powder based electrodes are employed. Niobium is the lightest refractory metal with density close to that of nickel, and exhibits good thermal conductivity. Niobium can be alloyed to improve high temperature strength and oxidation resistance. Applications in nuclear, aerospace, and defence sectors have been reported. The goal of current research in Nb alloys is to simultaneously achieve high strength and workability, and provide protection from oxidation for long-term operation. There is strong research interest in intermetallics also. This chapter will discuss the salient features of refractory metals and alloys in general, and Nb-based alloys in particular. Keywords Niobium Creep Applications
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Refractory alloys Processing Mechanical properties
Introduction
Future aerospace applications such as advanced turbojet and scramjet engines to be used in subsonic, supersonic, and hypersonic flights will require materials with ever increasing temperature- and load-bearing capabilities for improved performance V.V. Satya Prasad (&) R.G. Baligidad Defence Metallurgical Research Laboratory, Hyderabad 500058, India e-mail: [email protected] R.G. Baligidad e-mail: [email protected] A.A. Gokhale Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India e-mail: [email protected] © Springer Science+Business Media Singapore 2017 N. Eswara Prasad and R.J.H. Wanhill (eds.), Aerospace Materials and Material Technologies, Indian Institute of Metals Series, DOI 10.1007/978-981-10-2134-3_12
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under extreme environmental conditions. The state-of-the-art superalloys can be utilized to a maximum temperature of 1077 °C, and the need for viable materials with higher (1127–2027 °C) temperature capabilities has long been felt. Hence work is being pursued in different directions to develop materials with very high temperature capability [1, 2]. One such area is the development of ceramics and composite materials which have very good high temperature capability. However, designers frequently find that these newer materials cannot be easily fabricated into the shapes required. In other instances, users of high temperature materials are rediscovering that the applicability of advanced nonmetallic and composite materials may be limited by their relatively low thermal conductivity: alloys with good thermal conductivity require less intense air cooling in applications such as turbine hot sections. Although there are a number of metals that can be considered as refractory
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