An experimental study of the spheroidization efficiency of induction plasma processes was completed. The main objective being to obtain models which could be subsequently used for the prediction of the spheroidization efficiency for various powders and plasma operating conditions. Silica, alumina, chromium oxide and zirconia powders were treated during the experimentation. For the plasma treatment of the powders the installation used had a maximum available power of 50 kW with an operating frequency of 3 MHz. Operating conditions were varied such to minimize side reactions and the evaporation of powders. The resulting powders did show the presence of cavities and a slight change in the mean diameters. The maximum energy efficiency based semi-empirical model did predict the spheroidization efficiency of the particles beyond a defined critical point known as the maximum energy efficiency point. For the model, the maximum energy efficiency is distinct for the individual powders but remain within a defined range which is reflected in the small variations in the Z constant.

WC-Co based cermets are extensively used in wear applications due to their hardness and toughness. Recent work has demonstrated the potential for using nanoscale constituents to improve the wear properties of these materials. In the present study, two WC-Co powders containing a nanosized WC phase were used to produce coatings by HVOF thermal spraying. These powders had similar properties except for the volume percent binder present: WC-8C0 and WC-12Co. The thermal spraying conditions were varied in order to identify their effect on the microstructure, properties and phase composition of the sprayed coatings. The as-sprayed coatings possess porosity values ranging between 1% and 2% and microhardness values (HV100) from 1150 to 1550, which are quite similar to values obtained for conventionally sized WC-based coatings. For all the coatings, phase analysis indicated significant degradation of the WC phase to produce W2C, W, CO3W3C and Co6W3C. For some spray conditions, even WO3 phase was found in the coatings. The JP-5000 HVOF system produces coatings with lower porosity, similar microhardness values and, more importantly, with lower WC degradation than the coatings produced with the DJ-2700.

Layers of high-purity copper and iron produced by cold gas-dynamic spraying have been thermally processed to induce recrystallization and grain growth. In the case of copper deposits, the as-sprayed structure could be "pinned" by arrays of Cu2O particles present on the surfaces of the feedstock powder, however copper powders of higher purity and sphericity yielded sprayed structures which could be annealed to induce recrystallization and grain growth. The higher purity copper compacts exhibited a morphological change in fracture from a brittle, intraparticle mode in the as-deposited condition, to a ductile, "cup-and-cone" morphology in the annealed condition. For compacts produced from water atomized iron, annealing at sub-critical temperatures produced recrystallization and grain growth as found with copper, and thermal processing in the austenitic region resulted in altogether new and coarser grain structures upon cooling. Ease of thermal processing of cold-sprayed materials may offer additional processing routes for engineered surfaces and functional devices produced in this manner.

For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal and a fluorinated ethylene-propylene copolymer-based material. The volume content of this Teflon-based material in the feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel system to produce coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary carbon-graphite disks identified an optimum level of Teflon-based material in the feedstock formulation required to produce coatings exhibiting minimum wear. This optimum level was in the range of 7-17% by volume and depended on the composition of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a factor of approximately two) were obtained for the best-performing compositions, as compared to couples m which the coating contained no solid lubricant.

In this paper a process based on both Thermal Plasma Chemical Vapor Deposition (TPCVD) and Suspension Plasma Spraying (SPS) is applied on r.f. induction thermal plasma for α/β-SiC ceramic synthesis and deposition. The starting materials are low-cost liquid disilanes. The resulting coatings are investigated by means of SEM and XRD. Results on the influence of the processing parameters (i.e. pressure, spray distance, substrate temperature, plasma gas nature and composition, precursor composition, atomization parameters) on the coating phase and microstructure are shown. Control of the microstructure (or nanostructure) as well as of the phase content, namely the ratio α/β can be achieved. A processing route presenting the elementary steps of SiC TPCVD is also proposed.

Ceria (CeO2) based electrolytes have been considered for use in solid oxide fuel cells (SOFC) for more than 20 years. There are however some limitations to this usage that this study has tried to address, indeed the study objective has been that of synthesizing and thermal spraying thin layers (50 - 100 µm) of doped CeO2 by the technique of suspension plasma spraying, using radio frequency (RF) plasma technology. Various dopant combinations and concentrations have been selected for this work in order to increase the useful partial oxygen pressure range for satisfactory ionic conductivity development, thereby increasing the anionic conductivity and preventing CeO2 reduction in fuel cell service. Ceria possesses the fluorite crystal structure at low temperatures but does not have enough oxygen vacancies to be a good ionic conductor. In ceria the cerium have 4+ oxidation state within the fluorite structure, and by substituting a certain amount of Ce4+ ions by trivalent dopant ions, oxygen vacancies are induced into the structure. Recent studies have demonstrated that at low temperatures doped ceria seems to be a better electrolyte than doped zirconia. Also, it seems that dopants with ionic radii close to Ce4+ ions give rise to better ionic conductivities. The doped ceria conductivity increases with the dopant concentration because more oxygen vacancies are created, but at higher concentrations vacancy ordering occurs which results in decreased ionic conductivity.

The growing need for new materials and material combinations with superior properties for severe service applications has led to the development of near net-shape forming techniques for certain materials, such as superalloys, refractory metals (Ta, W, and Mo) and highly reactive metals (Ti and its alloys). Vacuum plasma spray (VPS) was used to produce dense Ti-6Al-4V deposits for mechanical properties evaluation. Spherical Ti-6Al-4V powder, produced by Plasma Atomization (PA), a novel patented powder fabrication technique, was used as the starting powder. Plasma atomized Ti-6Al-4V powder characteristics include: high purity, tight particle size range, highly spherical with no attached satellites, and excellent flowability. The resulting as-sprayed Ti-6Al-4V deposits were dense and low in oxygen content. Thermal treatment was conducted after spraying in order to improve the structure and the properties of the spray formed material. The mechanical properties of the material, including tensile strength, elongation and hardness, in both the as-sprayed and the heat treated conditions were compared. The mechanical properties of these preliminary VPS Ti-6Al-4V specimens indicate that the combination of high purity starting powder and controlled environment deposition can be used to produce dense spray formed Ti-6Al-4V structures with properties comparable to those of cast or sintered powder metallurgy parts.

Wire flame sprayed molybdenum is a wide used procedure for manufacturing of wear resistance coatings. The properties of thermal sprayed coatings depend mainly on the kinetic and thermal energy of sprayed particles, i.e., a higher particle velocity causes an increase of coating quality. The now available high velocity spray system from Praxair which is used within this work is capable to realise the aim of high particle velocities. The coating properties presented in this work are analysed in comparison to conventional wire and powder plasma spray processes. HVWFS molybdenum coatings show lower porosity, higher adhesion and cohesion and better wear properties. To explain the results, particle size distribution, oxygen/carbon content and structure are analysed. Hardening mechanisms of coatings and their adhesion/cohesion properties are discussed based on light microscopy, SEM, XRD and TEM investigations.

Among candidate materials for plasma spraying titanates ATiO3, where A is an element from the alkaline earth group (11), were not systematically tested until today. This paper reports on plasma spraying of synthetic perovskite CaTiO3 and geikielite-perovskite system MgTiO3-CaTiO3. Perovskite CaTiO3 is well known as dielectric material and a basic component of complex dielectric ceramics. Since it is relatively chemically simple and inexpensive material it has been selected for the basic preliminary studies. Mixture of geikielite-perovskite MgTiO3-CaTiO3, with Mg:Ca ratio equal to 94:6, was chosen because its permittivity is independent of temperature. Plasma spraying was done with the water stabilized plasma gun WSP. Plasma spraying conditions were optimized using single splat observation for various substrates and varying substrate temperature. Standard experimental techniques were used for studying of microstructures, chemical and phase compositions and porosity of as-sprayed and annealed deposits. Mechanical properties such as Young’s modulus and microhardness were measured.

Electromagnetic acceleration plasma generators, which are called Magneto-Plasma-Dynamic (MPD) arcjet generators, can produce higher-velocity, higher-temperature and higher-density plasmas than those of conventional thermal plasma torches, because MPD arcjet plasma is efficiently accelerated by electromagnetic body forces in MW-class input power operation. These properties are effective for deposition of rigid coatings adhering strongly to substrate surfaces. In the present study, we newly developed an ablation type MPD arcjet generator for titanium nitride (TiN) reactive spray coatings. The coatings were deposited onto steel substrate. The phase structure and the composition of the coatings were analyzed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their Vickers hardness were measured. These analyses showed that the MPD spray process could successfully form dense and uniform titanium nitride coatings. The properties of the titanium nitride coatings were highly sensitive to the titanium cathode diameter and discharge current.

The metallic interior surfaces with cylindrical symmetry have been processed by knocking them with centrifuged balls. The first author has designed the used processing tool and it has been carried out under his instructions. There have been processed cast iron and carbon steel samples, using 80 different combinations for the process parameters: axial advance S, tangential rotation speed of the processed piece V, and the impact force F between the balls and the processed surface. Using the measured values of roughness Ra, Vickers microhardness HV and of the depths of cold-hardening h, we have achieved and used an optimizing computer program for the qualitative parameters of the cold-hardening process, i.e. Ra, HV and h. Also, we found optimal solutions for the processing regime. The study establishes the ability to increase the mechanical characteristics of the turned out metallic surfaces, thus taking out any further mechanical, thermal and/or chemical superficial processing. The results of the current study allow a correct choice of the processing regimes for different materials with similar bulk properties.

Total quality management requires definite process control as well as online diagnostics, if applied in industrial surface refinement by thermal spraying. A concept for integrated online diagnostics for the high velocity oxygen fuel (HVOF) flame spray process is presented using Siemens S7-300 programmable logic controller and PC-based Siemens WinCC (Windows Control Center) visualization software. The standard functionality of the WinCC programming environment can be extended by C-scripts. The integrated database allows to protocol the relevant process parameters periodically for total quality assurance. Also particle flux imaging software tools can be implemented to adjust online process parameters and for process diagnostic purposes. The Siemens bus system hierarchy thereby provides high speed communication skills for field bus level data exchange and for supervising system components, e.g. CCD-cameras. The interconnection between S7-300 PLC, 6-axis-robot and a novel WinCC software tool enables definite automatic changes of recipes during the coating process to generate functionally graded coatings.

In order to properly characterize the entire deposition process, evaluation of the coating, including a reliable metallographic preparation technique which reveals the true microstructure, must be performed. Often, recommended metallographic sample preparation methods for thermally sprayed coatings are generic and are not tailored to specific materials. They are time-consuming and, in some cases, may provide inaccurate details (pull-outs, smearing, etc). This could lead to a wrong interpretation of the coating quality. The aim of the investigation was to develop new metallographic sample preparation procedures tailored to different types of coatings (metallic, ceramic, multilayer and composites), in order to reveal a more representative microstructure. A comparative study of different preparation procedures for the examination of various as-sprayed coatings is presented using an optical microscope. The coatings were deposited by atmospheric and vacuum plasma spray (APS and VPS) and high velocity oxygen fuel (HVOF) processes. A separate approach is recommended for choosing the right metallographic preparation procedure for ceramic, metallic, or composite coatings. Applied load and positioning of the mounted sample during preparation are identified as key factors in developing proper procedures. The microhardness of the coating must be considered when determining the applied load. Interesting practical trends in preparation procedures that may lead to superior coating representation and, in some instances, cost and time savings are presented.