Chromium carbide coating

Chromium carbide Coating for wear and corrosion resistance. 

Cr3C2 powder is prepared by the reaction of chromium oxide (Cr203) with carbon up to 16(KK]) in hydrogen if the temperature is kq>t below 1300, Cr7C3 is obtained. An oxygen free-carbide can be obtained by the carburization of the chromium metal. Chromium carbide coatings are d osited by CVD, reactive evaporation, and sputtering (see Chs. 14 and 15). 

Furman, V.V., Gaiduchenko, G.K., Vlastuk, R.Z. and Oeimontovich, V.B., Structure and properties of electrophoretic chromium carbide coatings with a eutectic composition nickel-boron binder, Sov. Powder Metall. S Met. Ceram. 22 942-45 (1983). 

Thermal spray processes can be used to give coatings of chromium carbide or nickel chromium for erosion resistance, copper nickel indium for fretting resistance, tungsten carbide cobalt for wear and abrasion resistance, and even aluminum siHcon polyester mixtures for abradabiHty. 

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. 

Fig ure 5-25. Rotor disk shown from the exhaust end. Blade trailing edges are coated with chromium carbide. 

Most cast irons, except those fully decarburised during malleabilising, give coatings of the chromium carbide type. In view of the great variations in composition of cast irons, reproducibility of results can be achieved only by careful control of specification. High phosphorus and sulphur contents are detrimental to the formation of non-porous coatings. 

A wide range of applications for hard, wear-resistant coatings of electroless nickel containing silicon carbide particles have been discussed by Weissenberger . The solution is basically for nickel-phosphorus coatings, but contains an addition of 5-15 g/1 silicon carbide. Hiibner and Ostermann have published a comparison between electroless nickel-silicon carbide, electrodeposited nickel-silicon carbide, and hard chromium engineering coatings. 

Coating life in moist atmospheres is also influenced by the effects of moisture on the substrate-coating interface, and marked improvements in life have been claimed by the use of moisture-protective pre-treatments of the substrate. Niederhauser et al ° studied a wide range of metals and titanium nitride, titanium carbide and chromium carbide as pre-treatments. The material was sputter-deposited on a steel substrate, and then sulphided by introducing hydrogen sulphide into the sputtering chamber in order to improve molybdenum disulphide adhesion. They found a marked improvement in life, particularly with a rhodium or palladium interlayer, but the actual degree of improvement is confused because they also used co-sputtered PTFE, and this is discussed further in Section 10.6. 

Ceramic materials are also utilized in nuclear reactor components. Applications include insulation of pressure vessels with linings fabricated from silica and alumina-base ceramic bricks or fiber insulation pressure vessels made of prestressed concrete structures that enclose the entire reactor and secondary system wear-resistant surfaces produced by means of coatings such as chromium oxide or chromium carbide and shielding applications, which include materials such as concrete, graphite, and leaded glass ... 

The use of chemical vapor deposition (CVD) and physical vapor deposition (PVD) for forming coatings of carbides, boride, nitrides, and oxides has increased. The CVD method has been developed the furthest for the deposition of TiC, titanium nitride (TiN), chromium carbide (CrC), WC, and aluminum trioxide (AI2O3) (Simon and Thoma 1985). 

With the adoption of the seal concepts proposed by the seals task force, all seals are accessible for removal and replacement when the turbomachine is removed. The seals will utilize a softer material than those interfacing surfaces which are not intended to be replaced over their 60 year design life. The hardness of these latter surfaces will be attained with suitable coatings, of which chromium-carbide is one candidate. A second sealing location on these surfaces is incorporated in the design as a backup should the first location become inadvertently... 

Titankute + C6, Chromium carbide, PVD coating, Richter Precision Inc. 

Chromium carbide by thermal spray or CVD is extremely resistant to corrosion and resists atmospheric oxygen up to 900"C. It is used to coat steel and as an intermediate coating for combined corrosion and wear-resistance... 

Next in importance is chromium carbide also used in the coating of steam turbines. Mixtures of WC, TiC, and Cr3C2 are used to a lesser d ee. 

Tungsten carbide coatings were also considered in addition to chromium oxide There is little to choose between tuem in respect of calculated flash temperatures. 

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