MECHANOCHEMICAL ALLOYING OF AL-SI-HBN COMPOSITE POWDERS FOR APPLICATION OF SEALING PLASMA COATINGS

Abstract

In this study, powders were synthesized by the method of mechanochemical alloying of aluminum with a chemical composition similar to that of the Oerlikon Metco composite powder (Metco 320NS). The composite powder was based on two types of industrial aluminum powders obtained by atomization of molten primary aluminum, differing in their morphology – spherical and elongated. The aim of this study was to produce mechanochemical alloyed Al powder using a planetary ball mill with a composition of silicon (8 %), boron nitride (20 %) for the production of powder coatings applied by plasma spraying. The effect of the powder processing method on the chemical composition, powder morphology, and coating microhardness was evaluated. The characteristics of the powders were achieved by mixing them in a ball mill for 2 hours in an alcohol environment. A prerequisite for alloying was the use of sealed drums equipped with inert gas supply nozzles. The alloying was carried out in an argon environment to prevent moisture and oxygen from entering the active surface of the powders. After alloying, the powders were also removed from the drum in a protective environment to avoid oxidation. The ratio of mass of ball: mass of powder = 5 : 1–10 : 1, and the diameter of steel balls: 8–12 mm. To prepare the pellets for plasma sputtering, a 5 % gasoline solution of synthetic rubber was added to the resulting mixture. After mixing with the plasticizer, the mixture was granulated by rubbing it through a sieve with a 50 μm mesh. To remove residual moisture, the granular powders were dried in a vacuum drying oven at 70 °C for 3 h. The deposition of the Al-Si-BN composite powder by plasma spraying was achieved by using the laminar plasma jet generation mode, which helped to reduce the oxidation of powder particles during flight. The formed coatings had a thickness of up to 500 μm and a microhardness of 0.3 to 0.41 GPa.