| The magnesium alloy is one kind of ideal modern industrialstructural materials with excellent thermal and electrical conductivity, it hasbeen widely used and the demand for such material increased year by year.However, the applications of the magnesium alloy have been limited by itspoor corrosion resistance and wear resistance in many fields. It has beenshown that the Ti-Al-N film which is one kind of hard thin film can reducethe interfacial friction and wear, and effectively improve the surface hardnessand toughness as well as corrosion resistance. As the phenomenon of wearand corrosion always start from material surface, the Ti-Al-N film coated onthe surface of magnesium alloy by surface treating technique can enhance thewear and corrosion resistance performance and preserve the properties ofmagnesium alloy. In the current work, the Ti-Al-N films have been coated onsurface of magnesium alloy by the self-designed MIB-700multifunction ionbeam sputtering equipment using the magnetron sputtering composite ionimplantation method, and the phase composition, surface morphology,adhesion, wear and corrosion resistance performance of the Ti-Al-N filmshave been studied.I. Parameter optimization in the DC magnetron sputtering processParameter optimization in the magnetron sputtering is very significantfor the combination of magnetron sputtering and ion implantation technology.The effect of gas pressure, power and time on the thickness of thin films hasbeen investigated. The results are as follow: the film thickness increases withincreased sputtering power; the film thickness is proportional to thesputtering time and a linear relationship between the film thickness andsputtering time can be found within a certain range of film thickness; anapproximate parabolic relationship can be seen between the film thicknessand working gas pressure, that is, increased gas pressure can enhance the filmthickness when the gas pressure is low, while the film thickness decreases rapidly with increased gas pressure as it exceeds a critical value. Afteranalysis of the experimental data, the optimized parameters for magnetronsputtering Ti and Al are respectively listed as:150w,0.5Pa,5~180minutesand120W,1.5Pa,5~180minutes.II. The composite preparation of Ti-Al-N film on surface of magnesiumalloyThrough a depth understanding of the composite surface treatment andion implantation technology, the Ti-Al-N multilayer films with theadvantages of more dense tissue and uniform fine crystal grain as well assmall residual stress were coated on the surface of magnesium alloy by usinga multi-periodic composite processing technology. The structure and patternof the Ti-Al-N multilayer films were analyzed by atomic force microscopeand X-ray diffraction. It has been shown that the present method waseffective to coat the Ti-Al-N multilayer films on the surface of magnesiumalloy. The diffraction peak intensity of sphalerite structure (B phase) waslarge, which indicates that the solid solution strengthening effect was evidentand the quality of the film is high. It can be found that the surface of6cyclesfilm without cracking is smooth and there are serious cracks on the surface of8cycles film. Thus, more cycle doesn’t mean higher quality of the film. It hasbeen found that the residual stress of the multilayer films was smallercompared with TiN films. The results by atomic force microscope show thatthe6cycles Ti-Al-N films were smooth and dense, the averaged surfaceroughness Ra is10.692nm. Adhesion tests show that the binding force wasinadequate, and thus the process needs to be improved.III. Process improvement of Ti-Al-N filmSeveral solutions for the inadequate adhesion problem of Ti-Al-N filmby ion bean composite processing have been proposed, and the feasibility ofthe various options has been discussed. The pre-plated pure Ti transitionlayer has been adopted to improve the adhesion. The adhesion, frictional wearproperties and corrosion resistance performance have been tested on theTi-Al-N film, multi-layer TiN thin film and single-layer TiN film as well asuntreated magnesium alloy. The results indicate that:1. Pure Ti buffer layer can effectively improve the adhesion of all film. The adhesion of Ti-Al-Nfilms with pure Ti buffer layer was best.2. Pure Ti buffer layer can improvethe friction coefficient and significantly reduce the wear of all films.3. Tibuffer layer can significantly improved self-rot potential and corrosioncurrent density of the all films. |
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