A new carbothermic reaction process is described for the thermochemical processing of nanophase WC-Co powders. The process permits shorter reaction times, reduced temperatures, and finer microstructures compared to conventional processing methods.The process builds on our experience with spray conversion processing but involves 1) chemical vapor infiltration reaction of the carbon infiltrant using a carbon source gas at a carbon activity greater than or equal to 1.0 with the particle substrate to form WC-CO; and 2) removal of any excess (unreacted) carbon by controlled gasification using a gas with carbon activity less than 1.0. A feature of the carbothermic reaction process is its adaptability to conventional WC-Co processing technology, as well as to spray conversion processing technology.The resulting power particles consist of a network of fine grains, (less than 100 nm) of WC and Co with interconnected fine porosity. Powder particles suitable for subsequent handling and consolidation are readily produced with diameters greater than 10 microns.