NANOSTRUCTURED HARD MATERIAL COMPOSITES BY MOLECULAR ENGINEERING .1. SYNTHESIS FROM SOLUBLE TUNGSTATE SALTS

A key issue, in the development of very fine grades, is to produce mat erials with high uniformity. The aqueous chemistry of tungsten offers several possibilities for the synthesis of homogenous molecular precur sors containing W and Co mixed on the atomic scale. Powders containing (NH4)(8)[H2Co2W11O40] have been prepared starting from sodium tungsta te or ammonium metatungstate. Nanophase powders of W-Co and WC-Co powd ers were obtained after reduction at 750 degrees C under H-2 and carbu risation at 1000 degrees C under H-2/CH4. Hard materials with submicro n microstructures were obtained after sintering at 1410 degrees C. (C) 1997 Acta Metallurgica Inc.