Novel synthesis of thermal spray grade silicon carbide (SiC) feedstock powder is necessary to allow deposition of this material using atmospheric plasma spraying (APS) method. SiC particles with average size of 1.0 µm are treated using co-precipitation techniques to deliver yttrium aluminum garnet (YAG) binder from its solution precursor as a nano-film onto SiC particles surface. The YAG nano-film will protect SiC core from direct interaction with plasma jet thus hindering their decomposition as well as providing matrix phase within the SiC particles vicinities. The modified SiC particles are sintered and crushed and then sieved to separate 25-45 µm and 45-90 µm size powders, which are then plasma sprayed to deposit SiC coatings of about 300 µm in thickness. Both the feedstock and the coatings were analyzed and compared with regards to their phase composition and microstructures.

This study investigates the effects of operating environment and temperature on the friction behavior of self-mated WC-CoCr coatings in sliding contact. Nickel superalloy substrates were coated with 86WC-10Co-4Cr powder using a warm spray gun. Coating cross-sections and surfaces were examined by SEM, XRD, EDX, and x-ray photoelectron spectroscopy (XPS). Tribological tests were conducted on a high-load tribometer at various temperatures in air, nitrogen gas, and distilled water. Test samples were examined by SEM and XPS, revealing wear patterns and elemental compositions while providing insights on oxide formation.

In this work, wire arc spraying is used to produce coatings in which oil-filled capsules are incorporated in the metal matrix. The coatings were deposited on carbon steel substrates using commercially available Zn-Al and FeNiCr alloy wires. The capsules were injected almost radially toward the substrate using an independent slurry feeder. No signs of degradation were observed during spraying and the coatings were able to keep a low coefficient of friction. Wear tracks produced by the steel ball used for friction testing were examined and volume loss was determined based on wear track profiles.

Gate valves used in oil and gas production undergo stringent qualification before going into service. During qualification there is no external lubrication, leaving contact surfaces susceptible to friction evolution and wear. The work presented in this paper was carried out to better understand the changes that can occur during qualification and where and when the limit for mild wear and stable friction is reached. Ni-Cr alloy gate valve components were coated with WC-CoCr by HVOF spraying and dry sliding wear tests were conducted in nitrogen and in air. The coatings were then evaluated by means of SEM, EDX, and XRD analysis, nanoindentation and surface roughness measurements, and compression tests on micropillars milled out by FIB. Similar tests and analyses were performed on gate valves returned from the field. Examination of the valves that had been in service revealed the presence of oxygen rich layers on polished surfaces due to opening and closing of the gate. Such layers were also observed in coating samples following tribological testing. Initial surface roughness was found to play a role in the development of the oxygen rich layers as well as friction evolution.

Thermal spraying of pure SiC is difficult due to decomposition issues at elevated temperatures. However, the development of suspension plasma spray opens a new path to investigate the deposition of this material since the liquid carrier can hinder this phenomenon. The present work investigates a new route for producing SiC submicron structured coating by suspension plasma spraying (SPS). Classical SiC manufacturing routes using suspension (i.e: spray drying, tape casting) are studied regarding their feasibility to be used on suspension plasma spraying. Aqueous-based suspensions containing 10 wt.% SiC powder (0.60 µm) along with sintering additives are dispersed and stabilized. Both suspensions are sprayed on martensitic stainless steel substrate (AISI 440C) to achieve finely structured and dense coatings. Digital image analysis, X-ray diffraction and scanning electron microscopy are utilized to characterize the coating microstructures. Their dependency on suspension characteristics and spray operation parameters are discussed with respect to the final coating performance.

Problems with corrosion resistance in hydraulic cylinders used in marine environments contribute to many failures. Thermal spraying has proven to be a reliable method for replacing electroplated coatings in aircraft, but performance in high corrosive environments is still a drawback. In the present work, a new sealing method to densify WC-CoCr HVOF coatings is tested, which appears to be applicable to hydraulic cylinders in marine environments. The method is based on the use of nanoparticle solutions that penetrate and fill pores and cracks to seal the coatings. Two such solutions are tested and compared to as-sprayed coatings. Open-circuit potential and tribocorrosion measurements in 3.4% NaCl show that sealed coatings are more resistant to corrosion and wear than as-sprayed layers.

The Cr 3 C 2 -NiCr coatings were sprayed on an AA 7050-T7 alloy by HVOF Thermal Spray Process using AMPERIT 586.054 powder. The substrate was refrigerated during the sample preparation using liquid nitrogen in a device specially designed for this purpose. The spray conditions were also performed increasing the carrier gas flow or the oxygen flow. The XRD and SEM studies showed well-bounded coating/substrate interface, pores, metallic matrix, chromium oxides, carbides, and carbides dissolution into the matrix. The structure comparison between the samples showed a denser structure due to the increase in the carrier gas velocity and the highest carbide dissolution due to the high temperature achieved during the spray process. All samples showed similar wear abrasive behavior, and all of them showed wear rates 7 times higher than the aluminum alloy. All samples also showed corrosion resistance much higher than the AA7050 alloy in NaCl solution.

Due to its oxidation resistance, HVOF thermal sprayed Cr 3 C 2 -NiCr coatings have been widely used for wear resistance at elevated temperatures up to 850ºC. During HVOF spraying deposition, compositional degradation occurs through dissolution of the carbide phase into the metal matrix. The occurrence of carbide dissolution and the high working temperatures affects on the final properties of the coating. The aim of this work is to study the effect on the structure and wear properties at elevated temperatures of Cr 3 C 2 - NiCr coatings using hydrogen as a fuel gas against propylene. The structural characterization was done by SEM-EDS, XRD, and Scanning White Light Interferometry (SWLI). Wear properties at room and high temperatures have been evaluated by Ball-on-Disk (ASTM G99-90). Oxidation resistance of all coatings was carried out using a calorimetric technique Abstract only; no full-text paper available.