Three YSZ powders with different particle size distributions and an ethanol-based YSZ suspension were deposited on steel substrates using a cascaded plasma torch with a 9 mm nozzle. Coatings with dense, porous, segmented, and columnar microstructures were achieved by varying process parameters such as gun current, argon flow rate, spray distance, and suspension injection pressure. Linear relationships between in-flight particle state and process variables were observed and are shown to correlate well with coating structure and porosity.

A high efficiency single electrode (HESE) version of the popular TriplexPro Plasma Gun (Sulzer Metco, Westbury, NY) has been developed and evaluated. A single electrode gun has the advantage that in most cases it can be directly or simply retrofitted to any existing conventional plasma spray system. Three electrode cascade guns like the TriplexPro platform require a unique power supply and control configuration. The design of newly developed single electrode plasma gun was based upon the TriplexPro platform and retains many of the features that contribute to the guns high efficiency characteristics, in particular the cascaded arc configuration. A study was conducted to compare the performance of the newly developed HESE gun against a conventional single electrode design. Factors examined include: voltage stability; in flight particle characterization; coating properties for selected materials and spray spot size.

Wear and corrosion protection are the main applications for carbide cermet coatings which are most commonly applied by HVOF in the field of thermal spray technology. The TriplexPro-200 offers to produce carbide coatings economically and at an outstanding quality level. The influence of spray parameters, material composition and morphology was investigated and put into comparison to the established HVOF process. Two spray parameters for the TriplexPro-200 were used: standard setup in which the particle velocities around 200 – 280 m/s and the high-velocity setup reaching particle velocities above 550 m/s. Materials with different morphologies were tested showing influences on coating structure and residual stress. The material compositions are WC-Co and WC-CoCr as they are widely used in wear and corrosion resistance. Coatings sprayed with the standard setup of the TriplexPro-200 show coating qualities beyond single cathode APS systems and at higher deposition efficiency and feed rate. In the high velocity operation window the coatings become HVOF-like with hardness values up to 1200 HV 0.3 and very low porosity level. The measurement of the residual stress shows that compressive stress can be achieved using the TriplexPro- 200 technology.

This paper focuses on the use of hydrogen and nitrogen as secondary gases for atmospheric plasma spray using the TriplexPro-210 gun platform. The paper includes process mapping of particle state in addition to measurements of actual stress states within the coating during coating application. The feedstock powders used for this investigation include yttria stabilized zirconia, chromium oxide, nickel chromium aluminum and nickel aluminum. In addition, the paper discusses differences in application costs.

Abstract-Solution precursor plasma spray (SPPS) is a relatively new thermal spray process in which chemical precursors are injected into DC-arc plasma spray torch in place of powder. This process is able to make relatively porous (15-25% porosity) thermal barrier coatings with through-thickness cracks that enhance their thermal strain resistance. The SPPS process can also make dense titania and alumina zirconia coatings. The process can make thin and thick coatings, dense and porous coatings, structural and functional preforms, new compositions, and metastable materials. Metastable materials arise because the solution is molecularly mixed and the cooling rate in thermal spray is high. The process has the disadvantage of needing to provide energy to evaporate the solvent and of being a new process where less extensive empirical knowledge and modeling insights exist, compared to air plasma spray with powders. The microstructure process parameter relation is explored. Results from modeling studies concerning evaporation of droplets and related solute concentration gradients, modeling studies of aerodynamic break-up and experimental studies of non-aero-based droplet break-up and of the effects of solution concentration will be described. These studies will be related to experimental results for making dense coatings.

The Solution Precursor Plasma Spray process allows the creation of coatings directly from chemical precursors, thus avoiding the task of making sprayable powders. To date, our research has been based on injecting chemical precursors into a DC plasma torch. The process has proven to be useful in making vertically cracked thermal barrier coatings and has shown special advantages for making thick thermal barrier coatings (up to 4 mm). More recently, the process has been modified to produce dense, crack free coatings. This development was enabled by an improved understanding of the process, including making a coating almost exclusively from ultra-fine splats and avoiding the formation of vertical cracks. A crack free, dense alumina-yttria stabilized zirconia coating has been produced which is 98% dense and has an average Vickers hardness (300 gf) of 1177.