Abstract The novel High Velocity Combustion Wire Process (HVCW), which has a higher particle velocity compared to some other conventional spray processes, appears to be an alternative to improve the quality and corrosion resistance of the layers. In this paper, various electrochemical measurement methods are used to compare the electrochemical and corrosion behavior of thermal spray coatings based on Fe and Ni. For this purpose, the corresponding layers are produced not only by means of the HVCW process, but also by flame spraying, arc spraying, and high-speed flame spraying. The microstructure of these layers is investigated in order to understand the corrosion mechanisms of the layers sprayed under different manufacturing conditions. Paper includes a German-language abstract.

Abstract As a rule, the main processes of friction surface destruction are contact fatigue damage, micro-contact grabbing wearing, abrasive, and oxide wearing. The considered mechanism of the mentioned processes proves that to reduce their intensity and harden friction surfaces it is effective to form surfaces of composite materials; containing Ni, Cr, Si, and Mn; hard structural inclusions (for example, a carbide phase); and a hard lubricant (for example, as molybdenum disulfide, calcium fluoride, and graphite). This paper presents studies on powders for thermal spraying of wear protection layers. The focus is on studies of the influence of the shape, size, and structure of mixed powders made of nickel and iron with dry lubricants, such as molybdenum disulfide and calcium fluoride, which are analyzed using SEM and metallographic methods. The examinations are supplemented by X-ray diffractometry. Paper includes a German-language abstract.

Abstract 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.

Abstract FeAl iron-aluminide based materials with the ordered B2 structure are excellent candidates for use in high temperature applications because of the combination of good mechanical properties, low density, low cost and availability of raw materials, and improved oxidation resistance. The aim of this article is to produce an ultra-fine grained FeAl coating by HVOF thermal spraying of milled powders and characterize the fine scale features of its microstructure. Comparison is made with a more conventional coating obtained by projection of powders obtained by atomization. Starting powders and coatings were investigated using X-ray diffraction and transmission electron microscopy. It was observed that the coating obtained from milled powders had a microstructure essentially characterised by a nanometer grain size and the presence of a disordered FeAl phase.

Abstract Amorphization induced by sliding wear and consequent wear resistance have been investigated in relation with the microstructure of Fe-Cr-B alloy spray coatings. The Fe-Cr-B spray coated layer exhibited much higher wear resistance and significantly lower friction coefficient in comparison with that of low carbon steel substrate thanks to the amorphous surface film formed during the dry sliding wear. Electron microscopy on the cross-section of the coated layer exhibited intra-particle segregation associated with rod-shape Cr rich (Cr,Fe)xB particles in the matrix of Fe-Cr solid solution phase. From the observations using TEM and EDS, Fe-Cr solid solution phase with super-saturated B and Si content was confirmed to be the phase which mainly contribute to the crystalline-to-amorphous transition induced by sliding wear. The formation of oxide inclusions seems to impede the crystalline-to-amorphous transition by lowering the solute content in Fe-Cr solid solution phase. Keywords : microstructure, wear-resistance, Fe-Cr-B alloy, amorphization, detonation gun

Abstract Electric arc sprayed coatings with a disperse lubricating phase have potential for use in a variety of industrial applications as bearing materials including low friction coatings for drill string joints in the oil industry to reduce casing wear and lower drilling torque. This paper describes the optimisation of electric arc spray parameters for Fe-0.06wt.%C that will subsequently be used as a self-lubricating coating matrix. The effect of electric arc spray parameters on the microstructure of a Fe-0.06wt.%C matrix has been characterised in terms of deposition rate, temperature during manufacture, porosity and microhardness. It has been shown that the local coating temperature during directly affects the final coating porosity, grain size, grain morphology and microhardness. The most effective parameter in controlling coating temperature was the coating deposition rate. The Fe0.06wt.% C coating microstructure was primary equiaxed ferrite with a dispersion of spherodised Fe3C particles formed from the in-situ tempering of the as-sprayed martensite or bainite during spraying. A fuller analytical treatment of these phenomena is given elsewhere (13). Fe-0.06wt.%C powder particles microstructure was primarily bainitic or martensitic. A small number of Fe-0.06wt.%C powder particles showed a dendritic phase which has been proposed as retained austenite because of austenite stabilisation by fine grains and the N2 atmosphere, or an unidentified nitride layer.

Abstract Fe-Cr(-Mo) alloy coatings were thermal sprayed by different processes of LPPS, HVOF and HPS. The as-sprayed coating by LPPS is perfectly amorphous and coatings by other processes contain partly crystalline phases. The amorphous phases crystallize at 773 K or more and shows a high hardness of about 1000 to 1400 DPN just after crystallization. The anodic polarization curves of the coatings shift from active to passive state in 1N H2SO4 and 1N HCl solutions. The coatings obtained by LPPS indicate the lowest active and passive current densities and possess the best corrosion resistance. The corrosion resistance of the coatings obtained by other processes are better than a SUS316L stainless steel coating. The LPPS coating of Fe-Cr-C-P alloy is not attacked on immersion test in 6% FeCl3·6H2O solution containing 0.05N HCl at the corrosion potential, while large pit corrosion is developed in a SUS316L stainless steel sheet.

Abstract This paper examines the stress state of plasma-sprayed amorphous coatings of Fe-B with additions of Ni, Cr, and Mo. Internal stresses depend on the type of plasma gas used, the thickness and composition of the coating, and the material and temperature of the substrate. In this study, additional cooling of the substrate was found to be the most efficient way to reduce internal stresses. Amorphous coatings were also found to improve fatigue strength by as much as 25-30%, which is attributed to the formation of compressive stresses in the coating layers adjoining the substrate.

Abstract Thermally sprayed Fe-based coatings can be applied in conditions ranging from almost solid to complete molten droplets. While spraying under atmospheric conditions, the oxygen content in the coating varies depending on the spray parameters and the portion of molten phases in the droplets. Using vacuum-plasma technology, Fe-based alloys can be sprayed with a significant amount of molten phase without oxidation. This capability can also be used for alloying Fe-based sprays with nitrogen as is done during reactive vacuum plasma spraying. Such alloying promotes the formation of dispersed vanadium-nitride which greatly improves corrosion and wear resistance.

Abstract A composite was obtained by spraying ferromagnetic powder with a plasma arc torch onto an aluminum substrate. The influences of spraying conditions (substrate temperature, plasma gas composition, powder granulometry) on the efficiency of the induction heating by the composite are investigated.

Abstract This work evaluates the potential of using new competitive powders of Fe/TiC system for plasma spraying of wear resistant coatings. To improve coating properties, Cr and Ni were added to the iron matrix. The results of complex investigations of plasma coatings from such materials are presented.

Abstract The thermal spray process melts powder at very high temperatures and propels the molten material to the substrate to produce a coherent deposit. This heating produces a certain amount of vaporization of the feedstock. Upon exiting the plasma plume the fast cooling conditions lead to condensation of the vapor. An electrical low pressure impactor was used to monitor the concentration of ultra-fine particles at various radial and axial distances. Metal, namely iron powder, showed very high concentration levels which increase with distance. Ultra-fine particles from ZrO 2 -8Y 2 O 3 reached a peak concentration at 6 cm. Use of an air barrier during spraying decreases the population of ultra-fine particles facilitating the production of a stronger coating.

Abstract Addition of CaSi 2 in steel melt leads to a decrease of oxygen content, an increase of the melt flow capability, an improvement of a metal ductility and weldability. For an estimation of CaSi2 and Si additions effect in conditions of thermal spraying composite powders were produced. A base material of these powders particles is nickel, nichrom and iron. CaSi 2 and Si are additional components of the powders (3-12 wt. %). Plasma coatings produced with using of these powders exhibit high density and adhesion. The coatings structure has a high grade of microcrystallinity with a decreasing size of lamels. Oxides content in the coatings decreases with an increasing of CaSi 2 and Si content in the composite powders, moreover this effect is more essential in case of CaSi2 addition. Addition of CaSi 2 and Si to Ni-base coatings increases a microhardness from 1900-2000 MPa to 2200-2850 MPa. In case of NiCr-base coatings this increasing is from 1800-2100 MPa to 2400-3500 MPa.

Abstract In thermal spraying, Fe-based alloys are often applied for relatively thick and inexpensive coatings. The main advantage of the Fe-based alloy coatings is their high ductility as compared to ceramic and hardmetal coatings. Other advantages such as high toughness, easy machineability and satisfactory corrosion resistance are characteristic of Fe-based alloys. The wear resistance is not outstanding, but nevertheless acceptable for a large number of applications. A further improvement of the wear resistance can be achieved by reinforcing the Fe-based alloy coatings, e.g. by addition of nitrogen to the spraying powder.