SELF-FLUXING ALLOY POWDERS FOR EXTREME CONDITIONS AND APPLICATIONS

Self-fluxing powders based on nickel are hard alloy materials having a wide application for hardening and reconditioning surfaces of rapid-wearing parts working in aggressive media and wear conditions. This hard alloy powder is similar in chemical composition to those of the granulated spheroidized alloy powders. The self-fluxing powder is slightly different with a lower content of oxygen and other impurities, although classified according to composition. These coatings have complex structures, which consist of minutely dispersed super hard phases of carbides, borides and carboborides with micro-hardness up to 40.10³ MPa, uniformly distributed in a hard metallic matrix based on solid solutions and complex nickel-based eutectic.

These hard coatings are chemically resistant to different active media. On the basis of research works, it was ascertained that, within the range of specific pressure 1.5 x 10⁶ – 7 x 10⁶ Pa and sliding velocity up to 8m/s, it is possible to recommend nickel-based self-fluxing powder materials for friction pairs in water and in solutions of NaOH and CH₃COOH of 10 – 50% concentration. The wear resistance of this type of hard coating in frictional contact with steel (friction of boundary lubrication) is 4 – 9 times higher than the wear resistance of steel in steel – steel pairs and steel p iron pairs under specific loads of 1.5 x 10⁶ – 10 x 10⁶ Pa and sliding velocities of 8 – 54 m/min; within this range, the amount of wear of steels working in pairs with hard coatings is reduced by a factor of 1.5 – 2.5 times. The friction coefficient in pairs of hard coating – steel with initial surface roughness of Ra = 0.16 – 0.3  is 1.8 – 2.2 times lower than in pairs of steel – steel, but with constant surface roughness, the amount of wear is 2 – 10 times reduced.

These hard coatings are high wear and corrosion resistant, capable of withstanding impact and hard conditions under abrasive wear at temperatures up to 600^oC. They are cost effectively used for reconditioning and hardening valves, camshafts, blades, fans, rotors, shafts and sleeves of hydraulic pumps, parts of agricultural machines etc. At this juncture, it is worth knowing that, there are several contributing factors that have combined to determine the results of high wear, corrosion and temperature resistance of these hard alloy coatings. The knowledge of these multiple factors will definitely help to predict the determinant result of a single failure resistance mechanism (wear and its competing failure resistance mechanism) with the help of technological inheritance model that integrates the factors. This single failure resistance mechanism of a particular component can be used to determine maximum achievable wear, corrosion and temperature resistance for extreme industrial conditions.  

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