Relationships between arc plasma jet properties and plasma/liquid interaction mechanisms for the deposition of nanostructured ceramic coatings

Abstract

Ceramic nanostructured coatings with intermediate thicknesses between 10 and 100 µm exhibit improved thermal and mechanical properties for thermal barrier coatings or wear resistant coatings. Such coatings comply with the technical requirements of aeronautical and automotive applications. This implies to develop deposition processes with high throughput and deposition rates promoting the formation of nanostructured coatings. The use of a liquid phase as a carrier medium of nanoparticles or of solution precursors has been shown to be of major interest when being injected within a thermal plasma jet. The as-sprayed materials can form ceramic nanostructured coatings provided the liquid injection encompassing the physicochemical properties of liquid and its injection method copes with the plasma properties. Especially the repeatability of the interaction phenomena between the liquid phase and the arc jet has a key role in the efficiency deposition so that some research efforts are devoted to stabilize the arc while a liquid jet is continuously injected within the plasma. Alternatively a pulsed arc plasma jet can be generated and associated with a time-phased injection of droplets. This paper presents the different issues related to the arc plasma properties produced by direct plasma torches including the arc instabilities and their influence on plasma/liquid interaction mechanisms leading to the formation of nanomaterials. A focus is made on pulsed plasma spraying associated with a synchronized injection of microsized droplets by means of an inkjet printing method.