WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coatingÕs properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low-and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistance.
ARTICLE INFO ABSTRACT
Keywords:Cadmium coating replacement Aluminum slurry Steel Atmospheric corrosión Aeronautical applicationsCadmium has been widely used as a coating to provide protection against galvanic corrosión for steels and for its natural lubricity on threaded applications. However, it is a toxic metal and a known carcinogenic agent, which is plated from an aqueous bath containing cyanide salts. For these reasons, the use of cadmium has been banned in Europe for most industrial applications. However, the aerospace industry is still exempt due to the stringent technical and safety requirements associated with aeronautical applications, as an acceptable replacement is yet to be found. Al slurry coatings have been developed as an alternative to replace cadmium coatings. The coatings were deposited on AISI 4340 steel and have been characterized by optical and electrón microscopy. Testing included salt fog corrosión exposure, fluid corrosión exposure (immersion), humidity resistance, coating-substrate and paint-coating adhesión, electric conductivity, galvanic corrosión, embrittlement and fatigue. The results indicated that Al slurry coatings are an excellent alternative for Cd replacement.
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