A TECHNIQUE FOR EXTRUSION FORMING OF BRITTLE AND REFRACTORY COMPOSITIONS

Abstract

Recently, a number of compounds of transition-group metals with carbon, nitrogen, boron, and silicon have been found to exhibit high values of the important superconducting parameters, critical temperature and critical magnetic field strength. As a group, these compounds are characterized by high melting points and extreme brittleness, and hence require special fabricating techniques. A brief description is given of an extrusion method in use at the authors’ laboratory.

A powdered material, either metallic or not, is coated with polystyrene in such a manner and proportion that the mixture as a whole takes on the characteristics of a typical thermoplastic. The preparation may then be subjected to the forming methods commonly employed with plastics, such as moulding, extruding, and hot forming. Brittle materials may thus be obtained in the form of rod, ribbon, or wire. These products are next subjected to a programmed heating cycle in an appropriate atmosphere, during the course of which the polystyrene is volatilized, and sintering of the powdered material takes place with retention of the original shape. Under favourable conditions, sintering may proceed to a point where near-theoretical densities are attained.

Among the materials processed by this method are the carbides of tantalum and niobium, carbo-nitrides of niobium, tungsten carbide/cobalt mixtures, and aluminium oxide.

Notes

* Manuscript received 10 June, 1965.