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.

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.

Triplex is a second generation plasma gun technology that offers multiple benefits in term of rates of application and deposit efficiencies. This paper focuses on Triplex technology as it relates to daily operational aspects of a typical thermal spray facility. Today, Triplex is the only plasma technology that features "fixed" parameter operation for extended run times which has significant impact at multiple levels within the spray shop. Data presented will compare Triplex to first generation plasma technology with regards to quality, training, simplification, and process repeatability.

Development of coatings using the TriplexPro 200 plasma gun has provided an ideal means for implementing process maps due to the large operating window in terms of particle velocity and particle temperature, as well as the flexibility to use multiple plasma gasses to tailor the coating process. Process mapping enables tracking of coating characteristics, such as hardness, and relating those characteristics to the conditions of the particle that are induced upon the particle by the process parameters. Work performed to date has provided new insights into conditions of the powder particle that result in specific characteristics in the coating. An example is the ability to determine the critical particle energy state that affects coating stress. This work affords an understanding of general theory behind coating characteristics that result from the conditions of the particle. This paper describes the parameter impact in controlling coating stresses and determining optimum particle conditions to produce a desired, or set of desired, coating characteristics.

Process mapping is an ideal method for tracking coating characteristics in the thermal spray process. With the increased utilization of in-flight particle diagnostic tools in recent years it is now possible to quickly and effectively characterize inflight powder particle properties. With industries' increasing understanding of the relationship of these properties and coating characteristics, it is now possible to rapidly understand the implications of in-process changes with respect to coating performance. This paper is an exploratory exercise that describes the utilization of process mapping of in-flight particle velocity and temperature characteristics to optimize tungsten carbide (WC) coatings sprayed with a High Velocity Plasma torch (HVP). Key performance factors of WC coatings include high inherent hardness, low porosity and neutral to compressive stress conditions. The combination of these factors all contribute to the coatings' overall success in it's intended application and elude to its toughness, wear resistance, corrosion resistance and general ability to protect the required components. Presently, the High Velocity Oxygen Fuel (HVOF) and High Velocity Liquid Fuel (HVLF) combustion processes are the favored method of applying dependable and commercially viable WC coatings that meet all of these criteria.

Various methods of calculating coating costs and process performance have been used throughout the development of thermal spray processes; each tending to be unique to each process or coating method. Comparison of the effective performance of each process, in relation to each other, is hampered and difficult to compare on an equal basis. A more generic and global method is presented, based on deriving a unified process efficiency formula that takes into account all energy inputs and energy outputs of a process in the same energy units. Applying the coating process specifics such as deposit efficiency can then be used to determine a unitized process cost in terms of energy required and subsequently coating cost. This method permits direct comparison of process efficiency for each process and specific coating conditions, promoting the advancement of more efficient and controlled thermal spray processes. Example of the results are the surprisingly low process efficiencies, less than 5%, for processes that use higher energy levels, and the highest efficiency recorded by arc wire at nearly 30%.

The use of computational fluid dynamics (CFD) to model the operation of thermal spray processes has gained interest in the thermal spray community, able to provide an understanding as to how a process functions, and better yet how to make a process work better. Advancements to the science of modeling now permits the ability to create a comprehensive model of a plasma gun that not only simulates the dynamics of the gas but also the mechanics of arcs (plasma), thermodynamics, and entrained particulates to form a nearly complete model of a working thermal spray process. Work presented includes the methods and procedures used to validate the model to a Sulzer Metco TriplexPro 200 plasma gun and exploration of the operating regime to give an in depth and insightful look into the physics behind the operation of a triple arc cascaded plasma gun.

Utilization of a comprehensive validated computer model of a thermal spray process enables an ability to improve, optimize, and fine tune the performance of that thermal spray process. A validated model of the Sulzer Metco TriplexPro 200 plasma gun has been used to improve the performance of the actual gun in terms of enhancing gas flow dynamics, thermal management, and overall performance in terms of a robust design. Internal changes to the gun geometry using the model have extended the life of the hardware beyond any current plasma gun. In addition the model has permitted the investigation of the fundamental operation of the gun, specific to the behavior and path of the arcs, as well as the ability to operate the plasma gun, under simulation, in operating regimes that currently cannot be supported by the physical hardware. The model has been run at gas pressures above 14 bar and/or voltages above 300V that currently cannot be obtained with the physical hardware due to equipment limitations to evaluate the potential to extend the operating window of the Sulzer Metco TriplexPro 200 gun beyond current levels in terms of particle velocity and temperature. The end result is an improved process tool for applying thermal spray coatings from high temperature ceramics to relatively colder and faster carbides and alloys.

Low pressure plasma spraying (LPPS) is well established as coating process for the deposition of TBC systems for industrial gas turbines as well as aero applications under industrial standards. With the extension to LPPS Thin Film process, the operating conditions can vary in a wide range from only a few mbar up to typically 200 mbar which imposes different characteristics of the corresponding spray conditions and resulting coating properties. The flexibility of this process allows for subsequent coating of different layers for bond and top coat of a complex TBC system by using only a single TS technology. This simplifies the operational needs for industrial production and offers the potential of increased technological and economical benefits. Depending on the process conditions a broad variety of different TBC layers, multi-layer systems including bond coats & diffusion barriers, dense, porous or graded YSZ layers as well as EB-PVD like layers with columnar microstructure, can be realized using the LPPS-TF technology. Proper adjustment of spraying conditions and suited material selection allows controlling the grade of “columnarity” of the layer. Thermal cycling as well as GE erosion tests have been used to characterize and benchmark the coating quality. Transfer of such coatings onto real turbine blade has demonstrated that all substrate areas could be coated with a columnar TBC structure up to a thickness of about 250 microns. This offers the possibility either to develop coatings with optimized performance or of comparable quality at reduced production costs when compared to established vapour deposition techniques like EB-PVD. This paper presents an overview on the development of various TBC systems such as multi-layers or columnar structures by using the LPPS Thin Film technology.

In the thermal spray industry there remains a constant demand for more stable, controllable and economical processing devices. Most thermal spray applicators apply a wide range of materials especially those who are allied with the turbine markets. Each material coating specification requires a relatively specific range of velocity and temperature transferred to the powder particle to achieve the required material properties on the part. The plasma gun has become a dominant process tool in the turbine industry due to the wide range of parameters that are achievable with the basic tool. In addition, there are today a large number of individual plasma guns that are each known to provide excellent results with some, but not all coating requirements. In many cases the optimum gun running condition can never be achieved due to the interdependence of arc behavior and gas conditions. The turbine industry is currently largely populated with guns that are based on the technology as it was developed in the 1960’s. These guns are characterized by poor voltage stability with a large quasi periodic oscillation in the 3-5 kHz range as described by Bisson [1], with poor performance and life under more extreme operating conditions. A key element of any plasma gun is the nozzle geometry. The cascaded gun types as typified by the Triplex offer a unique opportunity to study and document a wide range of operational parameters, especially at extreme operating conditions.

For the effective development and optimization of plasma torches and plasma processes a knowledge of the spatial distribution of plasma properties within the generated plasma jets is useful. Information about some of these properties also in case of arbitrary distribution can be achieved by computer tomography (CT) using radiation emitted by the plasma jet. The stationarity of the plasma jet is a necessary condition for the CT technique described in this paper. By CT in principle the radiation from a small cross-sectional disk of the plasma jet is recorded successively under different directions perpendicular to the torch axis. From the recorded data the spatial distribution of radiation emissivity within the jet is calculated using an algebraic recursive algorithm. The CT was applied for the investigation of a TRIPLEX II plasma jet giving the following results: The jet is characterized by a very high degree of stationarity and exhibits a definite triple symmetry, which can be described by three partial plasma jets. Measuring their positions the influence of the arc current on the TRIPLEX plasma jet rotation was determined.

Plasma spraying at low pressure conditions (LPPS) is a well established thermal spray process with a broad variety of important applications in different industrial segments. The operating conditions for LPPS processes can vary in a wide range from only a few mbar up to typically 200 mbar which imposes different characteristics of the corresponding spray conditions and resulting coating properties. Thermal spray processes have been approved being suitable for integrated fabrication of various layers for SOFC components. Depending on the process conditions, different layers used as functional coatings of SOFC components such as dense electrolyte layers as well as porous electrodes can be realized using the LPPS technology. Due to the flexibility of these processes, an optimized performance of the application on different target materials and geometries is possible with an increased technological and economical benefit compared to conventional thermal spray techniques. This paper presents an overview on the general potential and spray conditions of the LPPS process and its application for the deposition of various functional layers such as electrolyte and electrodes for SOFC components.