r LA-5962 MS Process for Improving the Low Temperature Ductility of Tungsten-Base Composites MASTER An Affirmative Action /Equal Opportunity Employer UNITED STATES TNERSV RESEARCH AND DEVELOPMENT ADMINISTRATION CONTRACT W-7405ENG. 36 Thii report wu prepar

ABSTRACT At temperatures below about 100°C, liquid-phase-sintered tungsten-base composites fail in a brittle manner because of the formation of cleavage cracks in the tungsten spheroids. Improving the ductility, then, would require some alloying addition or treatment which would improve the ductility of these spheroids, or some method of changing the stress distribution, such as putting the surface in compression, which would reduce stress concentrations and thereby require a higher load to initiate fracture. The ductilizing process used here consists of coating the composite with a ductile metal followed by heat treating at a high enough temperature to insure sufficient diffusion so that the coat and base become integral. The ductile coat is now the 'piece' surface, and the initiation of cleavage cracks requires much greater stresses. Coats of copper, nickel, gold,and cobalt have been used successfully. A possible added advantage is that the surface properties can now be controlled if certain reflective properties or corrosion resistance are needed. Also soldering or low temperature brazing operations are feasible,allowing the construction or assembly of intricate shapes which could not be accomplished previously