Properties and structure of niobium carbide heating elements

Conclusions In operation at 1900°C in a carbon-free atmosphere at a residual pressure of 10^–2-2· 10^–3 Pa a heating element of composition NbC + Nb₂C + Nb experiences a steady loss of carbon at a rate of 0.5–1 m/h from its surface, with the formation of a metallic phase. Heating elements of this composition may be recommended for service in vacuum resistance furnaces at temperatures of up to 1900°C, where they can be expected to have a useful life of the order of 1000 h. Niobium monocarbide heating elements operating at 2100–2500°C in a carbon-containing atmosphere under a pressure of 10^–2-2·10^–3 Pa experience no change in phase composition or shape and only minor changes in structure, and possess good thermal fatigue resistance. They can thus be employed in vacuum electric furnaces under these conditions. Long experience (more than two years) with the operation of a laboratory vacuum electric furnace with a niobium carbide heating element in the temperature range 1000–1500°C has demonstrated that the use of niobium carbide heating elements widens scope for new electro-thermal equipment.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 92–97, March, 1982.