Preparation And Tribological Properties Of MAO Ceramic Film On Surface Of Ti6Al4V Alloy

Titanium alloy is vulnerable to failure brought by its poor wear resistance, so this is a threatening risk to the security of components in practical application. MAO technology (micro-arc oxidation) can be applied to fabricate wear resistant ceramic films on titanium alloy, therefore it has aroused great concern on this studies. The preparation of MAO film is a complicated process which is affected by multiple parameters, but the reaction mechanism has not been throughly revealed. The investigation to the impact of parameters on the formation and trobological performance of the ceramic film is valuable either theoretically or practically.In this paper, constant current mode was adopted to prepare MAO films on Ti6A14V alloys in Na2SiO3+Na2WO4solution. The characteristics of film growth, micro-structure, phase components, thickness, friction and wear resistance of the ceramic film were investigated by XRD, SEM, metallographic microscope, and pin-on-disk tribometer. Two kinds of mixture electrolyte based on Na2SiO3+Na2WO4solution were made by adding Na3PO4and NaAlO2 respectively, in the end, the effect of solution system on performance of ceramic film was studied. The main results are listed as follows:1) Voltage curve can always be divided into three stages under different current density, pulse frequency and solution system condition, corresponding to the spark discharge stage, transition of spark to micro-arc discharge stage, and micro-arc discharge stage.2) The film roughness increased with the increase of current density and oxidation time and reduced with the increase of pulse frequency. The ceramic film is mainly composed of rutile and anatase TiO2, and titanium had the strongest diffraction peak. As the parameters increased, the film thickness increased. The transition of phase components followed the same rule:substrate titanium phase diffraction peak intensity was significantly reduced, anatase TiO2diffraction peak intensity decreased, rutile TiO2peaks intensity increased. When the current density was low, the film growth rate increased with the increasing of current density, however when the current density increased to a certain value, the film growth rate was significantly reduced. At the early stage of micro-arc oxidation (5-20min), film growth rate increased with the extension of oxidation time, but the film growth rate reduced in the latter stage of oxidation (after20min)3) Surface morphology of ceramic films prepared in the three solution systems were similar. The film in Na2SiO3+Na2WO4had larger micro-pore and surface sediment, and is mainly composed of rutile and anatase TiO2, and titanium had the strongest diffraction peak. With the addition of Na3PO4and NaAlO2respectively, the micro-pore number increased and the size of pore expanded, smaller micro-pore was recognized in the micro-pore, and much more sediment existed on the surface. The surface roughness and thickness of the film increased with the addition, and the rutile TiO2peaks intensity also increased, while the anatase TiO2diffraction peak intensity decreased. Moreover, with the addition of NaAlO2, the spinel Al2TiO5could be found in the film.4) Under constant current mode, with the increased of current density and oxidation time, the run-in period in sliding friction test prolonged, and the coefficient of friction had greater fluctuation. With the increased of frequency, the run-in period became shorter, average friction coefficient of stable stage decreased, fluctuations in the friction coefficient became smaller. When the current density was low, average friction coefficient phasing stabe stage increases with the increasing of current density, wear volume was slightly increased. As the current density increased to a certain value, average friction coefficient decreased with the increasing of current density, abrasion loss was increased obviously. When oxidation time increased from10min to20min, abrasion loss was nearly doubled; from20min to30min, wear extent was slightly increased. Frequency had almost no effect to the abrasion loss.5) Adding Na3PO4and NaAlO2to the Na2SiO3+Na2WO4solution respectively, the run-in period of sliding friction test were reduced, and abrasion loss were similarly increased. With the addition of Na3PO4, fluctuations of the friction coefficient and average friction coefficient were reduced; with the addition of NaAlO2, friction coefficient had greater fluctuation and average friction coefficient were reduced.