Sprayed coatings spray-welding

In recent years, the spraying process has been adapted for hard facing, using the chromium-nickel-boron alloys which have become known as Colmonoy. More recently still, the cobalt-base Stellite alloys have also been used. These materials in powder form are sprayed on to the surface in the usual way. The deposit is afterwards heat treated by a torch, so that fusion takes place. The process is often known as spray-welding. Such coatings are primarily used for hard facing under wear conditions, but as the Anal surface is nickel-chromium or cobalt-chromium they exhibit very high anticorrosive properties. 

Protection by Sprayed Metal Coatings, The Welding Institute, London (1968)... 

Borisov, Y.S., Borisova, A-L., Tunik, A.Y., Karpets, M.V., Vojnarovich, S.G., Kislitsa, A.N.Kuzmich-Yanchuk, E.K. (2008) Effect of microplasma spray conditions on structure, phase composition and texture of hydroxyapatite coatings. Paton Welding /., 4, 10-15. 

A group of coating or welding processes in which finely divided metallic or non-metallic materials are deposited in a molten or semi-molten condition to form a coating. The coating material may be in the form of powder, ceramic rod, wire, or molten materials. See also flame spraying and plasma spraying. 

T. Yoshikawa, Spray Coating and Weld Overlay in Circulating Eluidized Bed Boiler (CFB) and Waste-to-Energy (WTF) Boilers, Proceedings of International Symposium on High Temperature Oxidation and Corrosion/2005 (Nara, Japan), 2005, p 27... 

Ziac foil coated with a conductive, pressure-sensitive adhesive is used for repair of other ziac coatings or for imparting corrosion resistance at field sites. The 0.08-mm ziac tape or sheet has a 0.025-mm coaductive adhesive. The laminate is cut to size and pressed tightly to activate the adhesive. Conductive tape can be wrapped around pipe, especially around welds or connections. The corrosion resistance of this material is iatermediate between galvanized or thermally sprayed coatings and zinc-filled paints (21,50). 

Chromium carbide is important in powder preparations designed for thermal spray apphcations of corrosion and wear-resistant coatings on tool and machine parts. Lower carbon carbides of chromium are important in hardfacing tods and electrodes for weld-apphed ovedays on machine wear surfaces. However, these carbides are usually formed in situ from Cr and C in the rod and not added as preformed carbides. The properties of Ci2C2 are hsted in Table 2. 

Aluminium coatings exposed as sprayed show remarkable protective properties and in many cases the only evidence of age is the appearance of small hard nodules of aluminium oxide, and these do not appear to be deleterious. However, the dead white of the sprayed surface soon becomes discoloured by dirt and so a paint covering is usual. A chromate inhibitor is not essential and two coats of a simple vinyl-based sealing paint have given remarkable results in the tests of the American Welding Society over periods of 12 and 15 years. 

Corrosion Tests of Flame Sprayed Coated Steel-19 Year Report, American Welding Society. Miami (1974)... 

Bailey, J. C. and Porter, F. C., Sprayed Metal Coatings for the Protection of Structural Steel-A Fresh Appraisal, Const. Steel, 12-19, Feb (1972) (Reprinted by American Welding Society)... 

Endoh, M., Influence of Surface Roughness of Mild Steel Substrate on Adhesive Strength of Zinc Sprayed Coatings . Proc. 8th Int. Thermal Spray. Conf., American Welding Society, pp. 492-502 (1976)... 

Porter, F. C. and Walden, G. K., Inspection of sprayed zinc coalings, 2nd Conf. Institute of Welding Spraying and Plastic Coating Div. London, Reprint/ZDA, London (1967)... 

Steel with up to 0 075 mm thick aluminium coatings can be gas-cut by both hand and machine methods, and welded, without removal of the aluminium. No fume problems arise in welding aluminium-coated material in practice, however, it is usual to leave the edges bare and to spray the joint with aluminium after welding. 

Tests by Clark for the Corrosion Sub-committee of the American Welding Society were carried out at severe marine and industrial sites. After four years, the greatest protection to steel was given by sprayed aluminium coatings combined with aluminium vinyl paint in the following environments id) sea air, ib) sea-water immersion, (c) alternate sea-water immersion and exposure to air (tidal conditions) and id) industrial atmospheres contaminated with sulphur compounds. 

In addition to the Alloy 625 of the autoclave itself, the materials or material junctures examined were nickel (Ni) 201, platinum, platinum to Hastelloy C-276 weld in Zone 3, the YSZ supports, and arc-plasma sprayed YSZ on zirconium (thermal cycling only). The nickel, YSZ supports, and YSZ coating on zirconium exhibited poor performance (high corrosion, fracture, and delamination, respectively) in Zone 1 and Zone 2. Platinum was deemed to be satisfactory in Zones 1 and 3 but exhibited corrosive attack, including pitting and the formation of a platinum-sulfur compound, at the grain boundaries in Zone 2. The platinum/Hastelloy C-276 weld was determined to be satisfactory in Zone 3. 

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