The smaller path to material hardness.

The smaller path to material hardness

Miners, oil drillers and others who cut, drill or saw through rock and other hard substances use tools even harder than the materials they penetrate. Most of those tools are based on Co-WC, a composite of cobalt metal and tungsten carbide ceramic. The Co-WC industry has grown over about 40 years to gross $3 billion to $4 billion per year, notes materials scientist Bernard H. Kear of Rutgers University in Piscataway, N.J.

Kear now reports that he and his colleagues at the recently formed Nanodyne Inc. have developed a radically new method for making Co-WC and other composites. Their technique, he says, should lead to longer-lasting, easier-to-make components that could save many millions of dollars by reducing energy consumption during manufacturing and by boosting efficiency in industries using such tools.

The traditional method for making Co-WC powder involves crushing, mixing, grinding, milling and consolidating tungsten carbide and cobalt powders before sintering the compacted hybrid powder into the final component. "Yet merely by reducing the scale of your microstructure, you can get a systematic improvement in properties [such as hardness and wear resistance]," Kear says.

The standard, mechanical method reaches its particle-shrinking limit at diameters of about 1 micron, whereas Kear's chemical processing method makes particles in the 200-nanometer range or a crucial several times smaller. By mixing carefully chosen pairs of cobalt- and tungsten-bearing chemicals in water, the researchers make a solution containing a prechosen bimetallic ingredient. Pumping the solution through a small nozzle produces a quick-drying aerosol that leaves behind aggregates of "nanophase" tungsten-cobalt particles. The final step occurs within a "fluid bed reactor," in which a stream of carbon-containing gas reacts with the particles as it whips them into a carbide-forming sandstorm.