The carbides of the Group IV A transition metals titanium, zirconium, and hafnium,and the Group V A transition metals vanadium, niobium, and tantalum are often suggested for load-bearing members for high-temperature applications. Such suggestions are usually based on the well-known properties of carbides: high melting point and high room -temperature hardness indicative of high stability and high strength.
The chief deterrent to the use of the carbides is their brittleness at temperatures below about one -half their absolute melting points. Without some plastic deformation, stress concentrations at flaws are not relieved, and premature fracture results. However, at higher temperatures, the deformation and strength characteristics of the polycrystalline carbides are not well defined and some beneficial plasticity may be present, Therefore, for a proper assessment of the high-temperature suitability of the carbides, the temperature dependencies for plasticity and strength must be determined.
The mechanism by which any plasticity occurs must also be identified.
