Microstructure And Properties Of MoSi₂ Coating Laser Cladding On Titanium Alloy

Titanium has a low density, high strength, corrosion resistance and other characteristics. They have broad application prospects and but due to poor wear resistance of titanium alloy which greatly limits its scope of application on the project. how to improve the wear resistance of titanium is a matter of concern to many researchers. The emergence of high-power lasers for surface modification of materials provides a new and effective means of laser cladding on the metal surface. The preparation of ceramic metal matrix composite coating is to improve the wear resistance of an effective method.The main topic of laser cladding Ti-MoSi₂ powder and Ti-Mo-Si two powders obtained from the addition of titanium-based and in situ MoSi₂ composite coating titanium matrix composite coating MoSi₂ two coatings. Its microstructure content organization and other aspects of friction and wear properties were studied, discussed the strengthening phase of laser cladding parameters on the impact of the different elements in strengthening the impact phase morphology and distribution of the coating. The two methods MoSi₂ titanium-based coatings friction coefficient, wear rate and the difference between the morphology of wear on, and then study the advantages and possibilities MoSi₂ Titanium by laser cladding as a strengthening phase, and laid a foundation for the further improvement of the friction and wear properties of titanium alloys. The following is the main content and the experimental results:（1） By using of in-situ synthesis method, the ratio of Mo and Si to obtain a titanium-based MoSi₂ powder. In TC4 titanium alloy surface powder laser cladding, respectively, Ti-5%（Mo + Si）, Ti-15%（Mo + Si） and Ti-30%（Mo+Si） mixed powder（mass fraction, Mo and Si atomic ratio of 1: 2）, select the appropriate power and scanning speed and other parameters by orthogonal experiment, three different coatings obtained using optical microscopy（OM）, scanning electron microscopy（SEM） of the cladding layer of microscopic organizations to observe and study, X-ray diffraction（XRD） studies cladding phase composition, as measured by micro hardness tester hardness three cladding layer. It was found that the power of 2k W scanning speed 10 mm · s-1 to obtain fusion better, less defective cladding layer. Cladding titanium powder coating organizations to fine acicular martensite α ’phase, cladding Ti-15%（Mo+Si） coating at the interface co-precipitated white striped TiSi₂, cladding Ti-30%（Mo+Si） coating the upper appeared embedded in the coating block Mo5Si3, MoSi₂ hard phase, but increased among white crystals precipitate, XRD results showed that β phase increases. Three coating hardness cladding region are very different, cladding titanium powder coating average hardness of about 500HV0.2, cladding Ti-30%（Mo+Si） coating maximum hardness reached 1150HV0.2, is about 3.4 times that of the substrate. Comparative analysis of the reasons for differences in the organization of three coatings, Mo, Si alloy element is added impact on the organization, combined with the thermodynamic analysis to explore the mixed powder situ reaction mechanism of MoSi₂.（2） In the coating powder from adding the industrial synthesis of MoSi₂ powder was a titanium-based MoSi₂ coating using 5kW YLS-5000 fiber laser, respectively in laser cladding alloy surface TC4 Ti-5%MoSi₂, Ti-15%MoSi₂ and Ti-30%MoSi₂ powder mixture, choose the appropriate power and scanning speed and other process parameters by orthogonal experiment, three different coatings obtained using optical microscopy（OM）, scanning electron microscopy（SEM） of the cladding layer of microscopic organizations to observe and study, X-ray diffraction（XRD） studies cladding phase composition, as measured by micro hardness tester hardness three cladding layer. It was found that the power of 3k W scanning speed 10 mm · s-1 to obtain fusion better, less defective cladding layer. Since subcooling of coating delamination phenomenon, the cladding layer is mainly white crystalline particulate phase and cellular fusion predominantly white strip above the crystal and fine needle crystal, fusion line following is a fine needle like crystal. Three coating cladding region highest hardness（900 HV 1150 HV） of Ti-30% MoSi₂ powder with an average of 3.4 times the base proved MoSi₂ addition amount increases, the hardness graduall y increased. Enhanced mode are solid solution strengthening, fine grain strengthening, dispersion strengthening and so on.（3） The laser process parameters on the organization to strengthen the influence and strengthening phase trapezoidal distribution and morphology of the phase distribution compared two ways to get a coating of wear coefficient, wear rate and wear morphology and study the wear mechanism. Self-generating MoSi₂ coating main wear mechanism is abrasive wear, abrasive wear and adhesive wear coating is mixed in situ synthesis mechanism.