| Based on the hot research topic——repair of blade of aero enjine, remanufacturing of blade wasachieved by the technology of laser cladding. For the reasons that nano rare and nano ceramic ownmany superior properties and the laser cladding technology makes the alloy melt and solidify rapidly,Ti-Al cladding coating reinforced by nano particles was prepared on aluminum alloy by the method ofsquash presetting. Nano powders were added to microparticles in the form of suspension with highdispersion. Research about the morphology, microstructure and hardness of the cladding coatingswere carried out and the mechanism of nano particles to cladding coatings was studied, which werebenefit for the extensive use of coatings.The major work done and the results obtained are as follows:Firstly, by investigating various dispersion behaviors of nanometer SiC particles in deionizedwater,1:1water-ethanol mixture and pure ethanol, it was confirmed that the most suitable dispersionsolvent for preparing nanometer SiC suspension was pure ethanol. The best mass fraction ofnanometer SiC powder added was3%of the solution which was ensured by analysis of dispersionbehavior with different amount in pure ethanol. In comparison of dispersion behavior of ultrasonicand ball milling, suspension with high dispersion was obtained by the method of ultrasonic when theultrasonic time was up to30min, while there was less influence on preparing nano SiC suspension bymethod of ball milling.Secondly, based on the finite element software——ANSYS，temperature simulation wasconducted for the process of laser cladding which was accompanied with high energy and rapidcooling. A reasonable3-D thermo finite element model (FEM) was built with the consideration offactors including heat source mode, material property, latent heat of phase change, boundaryconditions and etc. Temperature fields for the process of laser cladding for compound micropowderand single phase micropowder were studied. As a result, the morphology of weld pool and distributionof temperature in the process of scanning were gained and discussed. The influence law of laser power,scanning speed and diameter of spot on temperature field were discussed with the maximumtemperature of the spot as evaluation index.Thirdly, based on the method of squash presetting, Ti-Al composite powder which was coatedevenly by mechanical ball milling method was pressed on the surface of7050aluminum alloy treatedwith sand blast. When laser power was1.5kW，scanning speed was150mm/min and defocusing amount was50mm, continuous and complete cladding coating was achieved with an orthogonalexperiment. Cross-sectional morphology was observed, which presented that there was none pore andcracks. The grain morphology of cladded coating was mainly cellular dendrites and hardness ofcoating reached up to160.4HV.Finally, mechanism of nano particles to caldding coating and theoretical analysis of process ofgrain growth of coating were expounded. With analysis of morphology and microstructure of lasercladded coating reinforced by nano SiC，nano La2O3and both of them, growth of grain for Ti-Alcladded coating was refined, and none pore and cracks appeared. Specially, dilution rate of biphasereinforced Ti-Al coating was very low and the coating with well-closed formation formed bettermetallurgial bonding with basis material with coarse grain. With the measurement and comparison ofmicrohardness of nano reinforced cladded coatings, it was result in that nano particles prevented thegrain from growth which is benefit to refine grain to improve the hardness of cladded coating. Besides,addition of nano ceramic made the hardness of coating raise substantially compared with basismaterial while the hardness of biphase reinforced Ti-Al cladding coating decreased for the reason thatthe coating was overheated. |
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