Extrusion and selected engineering properties of Mo-Si-B intermetallics

In this study, an extrusion process has been developed to produce defect free, high-density rods of Mo-Si-B material. An initial powder composition (53.5 vol.%, 91 wt.%) of 66 vol.% Mo5Si3Bx (T1)-16 vol.% MdB-18 vol.% MoSi2 was mixed with a paraffin-wax based binder (46.5 vol.%, 9 wt.%) and extruded using a twin-screw extruder. Following binder removal by a combination process of wicking and thermal degradation, the material was sintered at 1800 degreesC. The bulk density of the sintered material was 90-92% of theoretical. Thorough binder removal was evidenced by low impurity levels. 258+/-6 ppm carbon and 772+/-10 ppm oxygen. The material demonstrated excellent high temperature oxidation resistance. The calculated parabolic rate constant is 1.1 x 10(-2) mg(2)/cm(4)/h at 1600 degreesC. The extruded material was also successfully tested as a resistance heating element. These materials show promise for the development of heating elements with enhanced performance compared to current MoSi2-based heating elements. (C) 2000 Published by Elsevier Science Ltd.