Supersonic Laser Deposition of Metals

Abstract

Cold spray (CS) is a relatively new materials deposition technique discovered in last thirty years and has been rapidly developing during past two decades, owing to many unique features. In the CS process, deleterious effects such as high temperature oxidation, evaporation, melting, residual stresses and other common problems inherent to traditional thermal spraying (such as flame spraying, arc spraying, plasma spraying, etc.) can be minimized or eliminated. Certainly, preheating of the deposited particles and substrate can favor the adhesion of the coating to the substrate, in particular, when depositing hard materials. Therefore, it would be desirable that introducing additional heat sources into CS can thermally soften the deposited particles and/or substrate. Laser, as one of the most ideal heat sources for material processing due to its unique advantages such as high energy density, chemically clean and flexible operation, has been coupled with CS. This combined process is termed as supersonic laser deposition (SLD). This novel coating fabrication technique has been employed to deposit both soft materials, for example, copper, and hard materials such as Stellite alloys, Ni60 alloy, etc. The experimental results have demonstrated that SLD surpasses CS to produce a dense coating with good interfacial bonding between particles and between particles and substrate for both soft and hard materials. The coatings prepared via SLD are compared with those by cold spray or laser cladding, showing that SLD can minimize oxidation of deposited materials, so the prepared coatings contain much fewer defects, simultaneously, and display strong interface bonding by both mechanical interlocking and metallurgical diffusion mechanisms. This novel deposition technique utilizing laser provides the coating industry an effective means to deposit hard materials which are temperature-sensitive.