R.F. Induction Plasma Spraying

Abstract

Radio Frequency (r.f.) Induction plasma spraying, or as more commonly known as Vacuum Induction Plasma Spraying (VIPS), has attracted increasing attention over the past three decades. While it is not a technology that is posed to replace any of the other thermal spray processes, it is commercially used in niche applications such as to perform cladding in the fiber optics industry, or X-ray target manufacturing, where the high purity and density of the deposit obtained are of critical importance. VIPS is characterized by the electrodeless nature of the discharge, which allows for high purity and greater flexibility with regard to the chemistry of the plasma gas, and the ease of axial injection of the powder into the center of the plasma jet. In this context, one of the fastest growing applications of induction plasma spraying is in the area of powder treatment for powder densification, purification, and/or spheroidization. The r.f. induction plasma torch is first presented with the basic concepts, its design and resulting temperature, fluid flow, and concentration fields. Then the discharge and the plasma–particle interactions modeling are discussed and typical results presented. At last vacuum induction plasma spraying (VIPS) with the torch operating conditions, the reactive, the suspension, and the supersonic spraying are described.