Evaluation of Formation and Properties of Ag Thin Films Prepared by PVD Ion Plating
In these days, mechanical materials are requested to posess the properties of more hardness, less wear, strong corrosion protection, excellent quality and decoration in accordance with gradual progress in industries.
In order to get these properties, many kinds of material surface modification methods have been applied to the surface of bulk materials. Generally, surface coating methods are used for many reasons, including the requirements for better physical and chemical properties to improve the surface of bulk materials, in many applications, economics, materials conservation, and design flexibility. Because surface properties can be separated from the bulk properties.
Silver thin films were deposited by ion plating of Physical Vapour Deposition (PVD) since silver was known to have a low shear strength, a good transfer-film forming tendency and a good corrosion resistance etc.. The general parameters of deposition condition in ion plating technique are gas pressure, bias voltage of substrate, deposition rate and substrate temperature, etc.. Properties of the ion plating silver films have excellent tribological characteristics in vacuum environment.
In this work, the properties of deposited silver films were evaluated against deposition condition of gas pressure and bias voltage of substrate. Not only was the influence of gas pressure and bias voltage of substrate on their morphology and crystal orientation of coated films investigated by the scanning electron microscopy(SEM) and X-ray diffractor but also their properties were studied to relate with friction coefficient at vacuum ambient of physical properties and anodic polarization curves of electrochemical properties.
With an increase of gas pressure, surface film morphology changed to decrease of crystal grain size, and X-ray diffraction peaks of film became broader. The effect of increasing bias voltages was similar to that of decreasing gas pressure. Friction coefficient of silver films with vacuum ambient are decreased by smaller of crystal grain size and exposure to surface (111) plane of relatively low surface free energy with X-ray diffraction.
Also, the effects of morphology and crystal orientation of ion plated silver films on corrosion behaviors showed good corrosion resistance in 1mol HCl and 0.5mol Na2S solutions with observed smaller crystal grain size by SEM and exhibited (200) plane of higher surface free energy in preference to (111) plane by X-ray diffraction.