The Characterization of Soft Antifriction Coating on the Tin Bronze by Electro-spark Alloying

Abstract

Soft materials such as silver, copper and Babbitt SnSb11Cu6 were deposited on the surface of tin bronze by electro spark alloying (ESA) to form the antifriction coating. The data of the antifriction coating were tested by electronic balance, three-dimensional optical profilometer, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Vickers microhardness tester and tribometer. The mass gain, roughness, thickness, surface morphology and phase composition, cross-section and element distribution, microhardness and tribological properties of the antifriction coating were analyzed. The results show that the grain size of the antifriction coating is fine and the metallurgical bonding between the coating and the substrate is good. The surface of each substrate is composed of three layers of coating. The optimal parameters of electro spark alloying are as follows: the discharge voltages of Ag, Cu and Babbitt alloy coatings are 60 V, 60 V and 30 V respectively, the energy storage capacitance is 150 μF, 150 μF and 90 μF respectively, and the working efficiency is 3 min/cm2, 3 min/cm2 and 4 min/cm2 respectively. Under the optimized parameters, the average mass transfer efficiency is 54.4 mg/cm2, the average surface roughness is 32.3 μm, and the maximum thickness is about 160 μm. The surface friction coefficient of the soft antifriction coating is 55.6 % of that of the tin bronze substrate. The main wear mechanisms of the soft antifriction coating prepared by electro spark alloying technique are plastic deformation accompanied by slight polishing.