Modification of powders by atmospheric pressure plasma and embedding into nickel coatings

Abstract

The aim of this work was to achieve improved dispersibility of hydrophobic dry lubricants in aqueous media through plasma activation. As a result, the use of wet-chemical environmentally questionable substances – for example, certain surfactants – to ensure the dispersibility of such particles can be avoided. These plasma-activated particles can be further embedded in electroless nickel (Ni) coatings to improve wear behaviour. Thus, the hydrophobic polymeric powders polyimide and polyetheretherketone and the ceramic powder hexagonal boron nitride (BN) were activated with atmospheric pressure plasma using a diffuse coplanar dielectric barrier discharge system. The generation of polar chemical bonds on the powder surface resulted in an improved dispersibility of the powders in aqueous media. This led to a higher deposit volume of the particles in electroless nickel dispersion coatings. The modified bonding conditions at the powder surfaces were analysed with infrared and X-ray photoelectron spectroscopy. Optical microscopy and scanning electron microscopy investigations showed the deposit of the activated dispersed phase in the coatings. Furthermore, the wear behaviour of the coating was tested by using the Taber abraser test. The plasma activation led to surface modifications – namely, linkage of polar groups at the powder surfaces – and therefore to improved dispersibility. The deposition of the particles in the electroless nickel coatings was possible with all three materials, and the wear resistance of the coatings was improved.