An exploration of the cold gas-dynamic spray method for several materials systems

Abstract

This paper reports activities of a consortium of companies formed under the aegis of the National Center for Manufacturing Sciences (NCMS) to explore a cold gas-dynamic spray method (CGSM) developed in Russia by Alkhimov, Papyrin and coworkers. In this spray process metal powder particles develop into a coating as a result of ballistic impingement on a suitable substrate. In some instances, surface preparation of the substrate using such traditional methods as grit blasting is unnecessary. The spray nozzle used in this process has been designed so as to permit introduction of powder particles into a preheated gas stream which is then rendered supersonic by expansion through a converging-diverging throat, with accompanying temperature reduction. Thus, the temperature of the gas stream is always below the melting point of the particulate material, providing coatings developed primarily from particles in the solid state. The fundamentals of CGSM are reviewed and results from several material combinations explored in the first phase of the research program are presented. Experimental coatings including copper on alumina ceramic, steel on cast aluminum, and a chromium carbide composite on titanium were produced. Typical microstructures, porosity, adhesion, and physical characteristics of these coatings are discussed.