Ultrafine Composite Synthesis by Laser-Reactions and Rapid Condensation

Abstract

ABSTRACTA new approach in ultrafine composite synthesis involves rapid condensation of metallic and non-metallic species, produced by laser-induced evaporation. A heated tungsten filament is simultaneously employed for codeposition of W via chemical transport mechanisms. This process occurs in a reducing environment of hydrogen gas, where evaporated species were produced by a laser-induced plume. Composite layers were formed on a Ni alloy substrate surface, at a rate of about 1Pm/sec. The matrix of the composite films was either Al or W, and the dispersed phase was amorphous silica fibers. The diameter of the fibers was between 25nm and 120nm, depending on the interaction times. Various analytical techniques have been employed to characterize the as-synthesized layers. Experimental evidences do not support the Vapor-Liquid-Solid model for fiber growth. An alternative fiber growth mechanism is proposed.