Preparation And Tribological Properties Of Ta-Ag Alloys Films

The technology of solid lubrication has advanced rapidly in the past four decades,primarily in response to the needs of the aerospace and automobile industries.Therefore,the successful use of materials and coatings as solid lubricants requires understanding their material and tribological properties and knowing which solid lubricant formulation is best for a chosen application.Ta-Ag alloys were typical immiscible alloys which the phase structure of sputtered Ta-Ag films was related to the elemental composition.The phase structures and tribological properties of Ta-Ag immiscible alloy films depend on the elemental composition and processing parameters.The Ta-Ag films with the thickness of 5-6 μ m were deposited on carbon steel by DC magnetron sputtering under the ambient temperature.Their microstructures were adjusted by controlling working pressures(0.2-0.6Pa)and sputtering powers of silver target(10W-25W).The morphologies and microstructures of the Ta-Ag films were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)attached with EDS.The nano-crystalline α Ta phase(bcc)was obtained under lower working pressure and higher sputtering power of Ag.With the increase of the sputtering power of Ag,the contents of Ag in the films increased lineally,which corresponds to the reduction of the hardness and elastic modulus for Ta-Ag films.A low friction coefficient of about 0.2 were presented for the Ta-Ag film deposited at the working pressure of 0.4Pa when rubbing against Si3N4 ball at RT,200℃ and 700 ℃.The high contents of silver in the deposited films and higher contents of oxygen on the frictional surface contributed to low friction at RT and 700 ℃,respectively.The tribo-chemical reaction products at high temperatures are closely related to the microstructure and compositions of films.