Friction and Wear Properties of T6 Treatment And As-Plated Duplex NiP/NiB Coatings on Az91d Magnesium Alloy

Abstract

Electroless nickel coatings can be preferred in wear resistant applications like firearms with good lubricity properties. In this study, a widely-used magnesium alloy, AZ91D both as-cast and precipitation-hardened conditions were coated with nickel phosphorus/nickel boron duplex coatings by the electroless deposition method. Solution treatment (W) of the alloy was carried out at 415 °C for 22 h in carbon powder followed by water quenched at 25 °C. Aging treatment (T6) of the solution-treated samples was performed at 216 °C for 6 h. The microstructures, elemental distributions and phase analysis of the obtained coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) analysis. According to the XRD analysis, the obtained coatings have an amorphous character and subsequent to this, a crystallization process to the sample is carried out at 350 °C. The friction and wear properties of the coating are studied by means of ball-on-disc experiments at room temperature under 10N applied loads at 0.1 m/s sliding speed using alumina balls as counterparts. The friction coefficient of the sample was compared with each other from friction coefficient-distance graphics. The wear rates were determined by measuring the depth of the track with an 3D-optical microscope (3D-OM). Characterization of the wear tracks was performed by SEM and EDS.