GB1031678A - Improvements in or relating to cermets - Google Patents

Abstract

<PICT:1031678/C6-C7/1> <PICT:1031678/C6-C7/2> A cermet having particles of ceramic material dispersed in a continuous metal matrix is made by placing in a die alternate layers of ceramic particles, one particle in depth, and layers of metal matrix material and subsequently pressing the contents of the die to form a compact which is then sintered at an elevated temperature. In one embodiment (Fig. 2), a nuclear fuel cermet is made by rolling VO2 particles 1 in an adhesive such as resin and then in stainless steel powder so as to produce a coating 3 of the latter, alternate layers of the coated particles and thin stainless steel sheets 4 being placed in a die 5 and pressed to form a compact which is sintered at 1000 DEG C., and then hot rolled at 1000 DEG to 1200 DEG C. Each of the layers of coated particles may be covered by a layer of stainless steel powder after being placed in the die and before being covered by the next stainless steel strip in the assembly. Alternatively (Fig. 7), UO2 particles 1 are dropped on to strips 3, of a combustible material such as cellulose or of stainless steel, coated with a layer 4 of adhesive such as sulphur-free rubber solution, the particle coated strips 3 being placed in a die 5 alternately with layers of stainless steel powder 6. The contents of the die 5 are cold compacted under pressure to form a compact which is sintered at 1000 DEG C. and then hot rolled at 1000 DEG to 1200 DEG C. The hot rolling is carried out in directions parallel to the layers of particles, e.g. in the direction of the arrow Y and at right angles to this direction and in the same plane, to draw the particles apart which in the finished product are separated by stainless steel. In order to obtain a desired degree of separation and a desired patter of distribution of the particles, each strip 3 may (Fig. 4, not shown) be coated with discrete spots 7 of adhesive so that when loose particles 1 are dropped on to such a strip, one particle 1 will adhere to each spot 7. In alternative methods of coating the strips 3 with ceramic fissile particles the strips 3 are coated with particles 1 in parallel lines either by first coating the strips with parallel lines 8 of adhesive (Fig. 5, not shown) and then shaking particles 1 on to the strips, or by transversely corrugating adhesive coated strips 3 (Fig. 6, not shown), shaking particles 1 on to the strips, and subsequently removing the corrugations by applying longitudinal tension or by rolling the strips. The compacts formed from such strips are hot rolled only in a direction parallel to the lines of particles. In any of the above methods, the particles may be coated with stainless steel powder and these particles may be dropped through a plasma flame to fuse the powder coatings into solid metal coatings.