Navy researchers have filed a patent on a new way to synthesize a composite material from a metal matrix and reinforcing particles. The technique significantly increases the wear resistance of a metalís surface. Called "Sedimentation Casting," the technique results in a high concentration of particulates at a flat surface of the final product. Using this method, the researchers have cast bronze components with abrasion-resistant tungsten carbide (WC) and titanium carbide (TiC) particles in the wear area. The researchers create the composite by dispersing silicon carbide particles in the metal matrix while it undergoes inductive heating to a molten state. They agitate the melt to encourage optimal dispersion throughout the matrix, then allow it to cool at room temperature. After it solidifies, the mixture is re-melted, allowing the particles to settle along the bottom surface.
Sedimentation Casting technique is an outgrowth of the centrifugal casting process patented in 1992 by the same research team. In centrifugal casting, centrifugal force sends the heavier molten metal, say, bronze, to the cylinderís outer surface, while the lighter ceramic particulates, TiC, migrate to the inside and form a wear-resistant surface. The Navy funded development of centrifugal casting process to eliminate the asbestos -- a carcinogen -- used in traditional winch break systems. Ships at sea require frequent replenishment of everything from groceries to ammunition. The job is usually done using hauling winches that automatically control line tension in rolling seas. In the past, the winches relied on air clutches with asbestos brake shoes. New centrifugally cast clutch drums with titanium carbide particles embedded in an aluminum bronze matrix improves winch performance, reduces clutch maintenance costs, and eliminates the asbestos. The new Sedimentation Casting technique will be used to create watertight, wear resistant seals aboard ships. Both the Sedimentation and Centrifugal casting techniques were developed by researchers at Port Hueneme and the Naval Surface Warfare Center, Carderock Division.