Studies of Tungsten Composites Containing Fibered or Reacted Additives

Abstract

Twenty-one sintered tungsten and tungsten-plus-additive billets were prepared in order to evaluate the feasibility of producing fiber-bearing composites by the elongation of materials in situ (in a tungsten matrix) during extrusion and to study reactions between the additives and the matrix with the objective of producing high-strength materials. Eight compounds, including oxides, borides, nitrides, and carbides, ranging in melting point from 4370–7030°F were successfully elongated in tungsten by extrusion at 4200°F. All composites with less than 10 vol. % additive exhibited improvements in stress-rupture strength. Composites with highly elongated additives ranged from 4 to 18 times better in stress-rupture life at 3000°F than the unreinforced pure tungsten matrix. The stress-rupture lives of several composites with more reactive additives and only moderate fibering increased to 25 to 50 times that of tungsten at 3000°F. The strengthening was presumed to be caused by reactions between the additives and the matrix. No judgment could be made from the study as to what extent the in situ fibering contributed to the increased strength. Because of inherent advantages, the in situ fibering method appears to have great potential for producing strong fibered composite materials and for producing fibers from strong, hard, and brittle refractory compounds and other relatively nondeformable materials.