A Novel Single Cathode Plasma Column Design for Process Stability and Long Term Component Life

It is well known that arc instability in DC plasma gun has serious implications on component life as well as deposition quality. This paper investigates a novel single cathode plasma column design consisting of a patented arc constrictor and its impact on process stability, versatility and component life. The design aims to minimize the re-strike of arc, increase the arc length enabling high voltage and low amp operation as well as the use of ternary gas combination to increase the enthalpy. The arc unsteadiness and dynamic behavior are investigated through the fluctuations of electrical signals combined with tools, such as fast Fourier transform (FFT) and correlation analysis. Further, the particle velocity and temperatures have been characterized by commercial diagnostics systems to demonstrate the influence of arc stability on their evolution. The current–voltage characteristics of the plasma jet show an increasing tendency. The takeover mode appears to be the typical fluctuation behavior of the plasma jet in this design. Further, the design allows the gun to operate at very high plasma velocities reaching the characteristics of an HVOF jet. The particle temperature, velocity and deposition efficiency in high velocity mode is also presented. The significance of the design is demonstrated through long term cathode and anode life as well as cost of operation.