In this study, microstructural characterization is conducted on WC-17Co coatings produced via High Velocity Oxygen Fuel (HVOF), High Velocity Air Fuel (HVAF), and Cold Spraying (CS). All coatings prepared were observed to be of good quality and with relatively low porosity content. SEM study showed important microstructural features and grain morphologies of each coating. While composition of feedstock material was approximately similar, elemental composition using EDS showed higher Co content and lower WC in the CS deposited coating. XRD experiment identified formation of more complex oxides and tungsten phases in coatings deposited technologies involving melting of powders such as HVOF and HVAF. These phases consisted mainly of cobalt oxides and brittle phases such as W 3 Co 3 C or W 2 C caused by decarburization of the tungsten carbide particles. Hardness of all coating samples were examined and CS deposited coating exhibited considerably lower hardness compared to the other two coating samples instead of having significantly lower porosity content. It could be contributed to dissociation and physical loss of hard carbide phase during high velocity impact of particles in CS process. It is in good agreement with detection of higher amount of cobalt in CS deposited coating material. It is strongly believed that results obtained from this study can be used for future investigation in thermo-mechanical properties of WC-Co coatings.

During heat treatment of Cr 3 C 2 -NiCr thermal spray coatings, regions of carbide dissolution have been observed to precipitate very small grains that grow into finely structured carbide networks. This study investigates the potential of developing tailored submicron carbide composites based on that process. The approach taken is to spray a conventional Cr 3 C 2 -NiCr powder under high-power plasma conditions to generate a supersaturated solid solution of Ni-Cr-C from which carbides could be precipitated via heat treatment. Preliminary trials assessed the effect of a broad range of plasma parameters to determine what conditions generate the greatest carbide dissolution with the lowest carbon loss. Follow-up trials investigated the most promising parameters in more detail to determine the effect of spray distance, with and without shrouding, on carbon loss and carbide dissolution. This paper presents the results from one of these trials in which an Ar-H 2 plasma was sprayed with a low-velocity nozzle. Gas shrouding had a minimal effect on carbide dissolution but was effective in reducing air entrainment in the plasma and the degree of decarburization.

Near net shape coating is a trend in thermal spraying being aimed at for several years to lower costs through shortened spray time and reduced after treatment work. Because of better microstructure compared to conventional coatings, the thickness is often also reduced. To characterise the quality of those thin layer systems the standardized tensile adhesive test is not suitable, as the adhesion outweighs the cohesion by far due to reduced quantities of coating defects. To characterize the coatings behaviour under tensile stress, three-point bending tests were performed. As especially thin cermet coatings do not show abrupt catastrophic failure in bending tests, ultrasonic signals being emitted from cracks propagating through the coatings were taken during the tests. Three coating systems (Cr 2 O 3 , Cr 3 C 2 -NiCr and WCCoCr) were investigated in this work using fine grained feedstock powders with three different size distributions per system. The tests showed the negative influence of stress moments in case of the oxide ceramic and the embrittlement of the cermets, especially the Cr 3 C 2 -NiCr, with increasing spraying temperature regime due to increased formation of solid solutions and decarburization. It can be said, that the analysis of acoustic emission during bending tests gives valuable information about how to achieve thin wear and corrosive protecting coatings being qualified for high operational demands.

For the promising erosion and oxidation resistance of carbide cermet coating, Cr39Ni7C cermet coatings were deposited by Diamond Jet spray process using a commercial Sulzer Metco 5241 powder in this study. The microstructure, phase composition and high temperature oxidation behavior of the deposited coatings were investigated. The speed and temperature of in-flight particles were measured by DPV-2000. The results revealed that the speed of in-flight particles decreased from 229 m/s to 150 m/s with the increasing of spraying distance from 100 mm to 300 mm, whereas the average temperature of in-flight particles increased from 1926 to 2245 K. The decarburization of Cr 3 C 2 increased with the increasing of fuel gas flow from 30 FMR to 40 FMR for higher heat enthalpy of flame. Due to the formation of Cr 2 O 3 on/in the coatings at high temperature, the sprayed coatings had good oxidation resistance at 1073 K in air atmosphere. For the lower porosity of the coating deposited under the spraying distance of 150 mm, its oxidation resistance was better than that sprayed under the spraying distance of 200 mm.

A significant group of steel-making process parts is exposed to high contact pressure, shock abrasive wear and elevated temperature. High productivity repair techniques are necessary because of the large size of the parts. Analysis of coating metallographic investigations, wear and corrosion test results, full-scale tests shows that restoration of base share of these parts is possible by High Velocity Oxygen Fuel / High Velocity Air Fuel (HVOF/HVAF) process. Comparison of manufacture's data has showed that HVAF excels HVOF alternatives noticeably at productivity. At the same time production costs are 2-2.5 times less. With regard to typical steel-making process parts some investigations results and examples of HVAF restoration at Joint Stock Company "Mashprom" are represented.

This paper evaluates the effect of adding graphite and amorphous carbon to WC-10Co-4Cr powders during HVOF spraying. The carbon-based materials are added in order to protect the WC phase from decarburization during the spraying process. The powders were made by ball milling and spray drying and the resulting layers are characterized by means of SEM, X-ray diffraction, microhardness, and wear testing. Paper includes a German-language abstract.

WC-based coatings have found extensive application in industries requiring wear resistance. WC-12% Co coatings were applied with a variety of high speed combustion spray guns (including HVAF) with various spray parameters. This paper aims to investigate the influence of the particle velocity, the particle temperature and the spray atmosphere on the decarburisation reactions and phase changes that take place during spraying. XRD and SEM used BSE image processing to characterize and quantify these responses. A comparison between temperature and speed measurements as well as the XRD results showed that the decarburisation is influenced not only by the temperature but also by the residence time and the entrainment of oxygen. Paper includes a German-language abstract.

Experimental apparatus simulating a horizontal belt caster has been constructed for the study of thin strip casting of steels and light metal alloys. In this apparatus, the solidifying metal is deposited onto a moving substrate. The substrate was flame sprayed with various commercial coatings while its speed and the thicknesses of strip produced matched industrial values. The main objective of the present work was to determine the influence of various operational variables on local cooling rates and final microstructures. To this end, experiments were carried out to study the effects of various types of coating, roughness of the substrate, initial superheat, and strip thickness on heat fluxes. An interesting feature of this equipment is that the strip is subjected to different rates of cooling at the lower and upper surfaces, allowing two different rates of solidification to be studied simultaneously.

High velocity oxy-fuel (HVOF) experiments were carried out with Diamond Jet (DJ) 2600 and 2700, P-5000, Jet Kote and Top Gun to investigate the influence of the spray system and of the spray parameters on microstructure and properties of Cr3C2-NiCr coatings. The results show that with all applied HVOF systems Cr3C2-NiCr coatings of high density, high bond strength and high wear resistance can be produced. However, microstructure and properties of the coatings mainly depend on the degree of oxidation and carbon loss of the material during the spray process. Due to the relatively low heating of the spray material the decarburization of CrsCa-NiCr was found to be very low using the HVOF systems DJ 2600, DJ 2700 and JP-5000. Additionally favored by the increased particle velocities coatings sprayed with the Diamond Jet systems and the JP- 5000 exceed coatings produced with the traditional HVOF systems with regard to hardness, wear resistance and bond strength.