THE CHARACTERIZATION OF SILVER COATING ON THE SURFACE OF TIN BRONZE BY ELECTRO-SPARK DEPOSITION
Abstract
Silver, as a soft material, is used in the construction of bearings that carry high loads and high speeds, and has good lubrication characteristics, mechanical properties and corrosion resistance. There are many methods of forming a suitable coating, but the process of applying Ag coating to the surface of a tin-bronze bearing sleeve using electrospark deposition (ESD) technology to improve operating conditions has not been sufficiently described. In the article the investigated coating is obtained on a tin bronze substrate, which was formed as a result of ESD with the use of silver as a soft antifriction material. The morphology, composition and properties of the coating were studied. The Ag coating on the surface of tin bronze that was formed by alternately electro-spark deposition applying the soft material of silver. The analysis of deposition on mass transfer, roughness, thickness, surface morphology, elemental composition and tribological properties of the Ag coating were investigated by electronic scales, 3D optical profilometers, scanning electron microscopy (SEM), energy dispersion spectrum (EDS) and tribometer. The results show that the soft material coating of silver is dense, uniformly distributed and metallurgical fusion with the substrate. The coating of silver was deposited on the surface of tin bronze by electro-spark deposition. The optimal process parameter was obtained as follows: the voltage is 60V, the duty cycle is 25%, the efficiency is 1min/cm2. Under the optimal process parameters, the mass transfer is 25.0mg, the surface roughness of the Ag coating is 15.46μm and the thickness is 15μm. In particular, the layer obtained under the optimal process parameters reduces surface micro-cracks and has a relative smooth and dense surface with good integrity. The Ag coating have a good metallurgical bonding with the substrate, and the microstructure of the deposition is compact. Due to the rapid heating and cooling of the substrate surface by ESD technology, the grains in the deposition layer are very dense, refined, uniformly distributed. The tribological properties of the coating in dry friction show that the lower resistance is exhibited by the Ag coating deposited using the soft antifriction material. The surface friction coefficient is stable after running-in, and becomes stable throughout the test and the minimum friction coefficient of the Ag coating is about 0.31 after running-in stage. The wear mechanism of the Ag coating is dominated by plastic deformation, abrasive wear and slight polishing. Plastic deformation and abrasive wear dominated on the relatively soft Ag coating. Silver and copper have very good wettability, which is conducive to improving the metallurgical bonding performance between metals during ESD. However, the performance of silver as antifriction material coating needs to be further improved.
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