Microstructure and Phase Composition of Titanium Coatings Plasma Sprayed with a Shroud

Abstract

Excellent corrosion resistance has made titanium a preferred material for use in industry with harsh environments. Protective titanium coatings combined with cheap bulk materials are expected to enable sufficient corrosion protection and lower the cost. Plasma spray processing of titanium feedstock becomes a challenging topic of research as titanium powder particles have to experience high temperatures in the flight during the thermal spraying process in an open air environment. In this paper, plasma spraying of titanium has been carried out by using a shroud in order to shield molten particles from reacting with surrounding environment. Microstructure analyses on the titanium coatings were performed by using SEM, EDS and XRD. The results show that the shroud attachment is capable of withstanding high plasma temperatures; the as-sprayed shrouded titanium coating exhibits a similar phase composition as the pure titanium powder, and an enhanced microstructure with a lower porosity for the titanium coating plasma-sprayed with a shrouding system is observed.

Oxide Free Wire Arc Sprayed Coatings—An Avenue to Enhanced Adhesive Tensile Strength

“…Usually, a ring gas nozzle is attached to the spray gun [7,25,26], and a reduction in the oxide content and porosity of the coating can be realized. To ensure that process gases and overspray can flow out, a spray gap must be kept open between the shroud and the substrate surface, and thus, oxidation cannot be completely prevented [25,27]. Furthermore, the splat surfaces are exposed to the ambient atmosphere after each coating overrun, resulting in passivation of the splat surfaces.…”

Effect of Shroud in Plasma Spraying on Chemical Composition and Thickness of Titanium Coatings

“…A SG-100 plasma gun from Praxair surface technologies, Indianapolis, IN, USA, together with a shroud attachment [24,25], was then used to plasma spray the pure titanium powder, as shown in Figure 2. The plasma gun with the shroud attachment was mounted on a 6-axis robot.…”

Microstructural Characterization of Shrouded Plasma-Sprayed Titanium Coatings

“…The powder particle size and distribution was determined using a laser diffraction method (Malvern Mastersizer 2000, Malvern Instruments Ltd., UK), which relies on the fact that the diffraction angle is inversely proportional to the particle size. A shroud attachment was designed for the plasma spraying of titanium coatings [10]. A SG-100 plasma gun (Praxair surface technologies, Danbury, CT, USA) with the shroud attachment was then used to do the plasma spray work with the HDH titanium powders, as shown in Figure 1.…”

“…Coating technology has been developed to fulfill the industrial demands. This technology allows combining cheap structural materials with a thin layer of high value material [8][9][10]. Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface.…”

“…Within the thermal spray area, low pressure plasma spray (LPPS) or vacuum plasma spray (VPS) has been the promising technique used for titanium deposition thanks to its inert atmosphere and ability to form dense coatings with low porosity and oxygen content [4]. Corrosion resistance similar to that of bulk Ti has been reported if proper spraying parameters, including the size of the feedstock powder, are optimized [10]. However, this process has limitations in terms of the size of the components and is rather expensive.…”