| Centrifugal compressor plays an important role in the national economic development fields.With the promotion of the green and circular economy development strategy,remanufacturing damaged impeller containing high additional value is getting more and more attention,which is one of the effective ways to solve the problem of natural resource scarcity and achieve energy conservation and emission reduction.Remanufacturing impeller services in equivalent environment as the primary product,so erosion wear is the main reason for the failure of remanufacturing impeller.Hence,it is significant to research on the repairing the impeller and the erosion wear mechanism in order to ensure the safety of workers as well as the engineering and company.value.Therefore,supported by the National Basic Research Program of China(973 Program),this thesis has studied the Tungsten Inert Gas welding(TIG)and laser cladding repair technique with the same chemical composition of alloy with repair base metal.The structure and physical properties of cladding layer were studied,and the differences in texture and property were also analyzed.Due to the lack of researching on micro-size particles impacting on cladding layer,erosion characteristics were studied systematically.Within the problem of erosion models with bad portability,base on elastoplastic theory,erosion rate calculation model which could predict maximum erosion angle were built.Finally,in order to learn about the influence law and mechanism that erosion wear process have on the surface geometry morphology,metallographic structure and property of the subsurface,the variation rules and formation mechanism of the surface characteristics such as erosion depth,surface roughness,surface metallographic structure,microhardness and residual stress were analyzed systematically.Coating layer with the same composition as the FV520B steel was deposited on the base material by the laser cladding and tungsten inert gas(TIG)cladding,then TIG cladding were tempered at 470? and 615?,respectively.The results showed that,laser cladding with compact and symmetrical microstructure has the highest hardness;TIG cladding with tempering has the similar microstructure compared with base material.fracture under tension for different cladding layer occurred at different places,where is the weak link.The influences of impact time,impact angle,impact velocity and particle diameter on the erosion characteristics were studied systematically.There is the peak value for the cladding layers,and with increasing the plasticity,the erosion peak will move towards the low angles.At low impact angles,the erosion is dominated by micro-cutting,and the harder the microscopic structure of material is,the stronger erosion-resisting becomes.At higher impact angle,deformation dominates the erosion surface,and materials bias stack the end of the grooves,which will be cut down or broken off by subsequent particles.Close to the positive erosion,materials will be hardened and peeled off after repeated deformation.Based on the elastoplastic theory,particle impacting target model was built firstly.In this model,the analytical expressions of velocity after impact and the maximum erosion angle were obtained.With Bitter theory,the erosion rate calculation model was finally established which parameters including the yield strength,elastic modulus,mass density,and particle size,and so on.Comparative analysis showed that the predictions were in good agreement with the results of single factor experiments.According to research on the erosion surface,some results show that The surface roughness increases initially then decreases,and the surface has poor quality at the middle impact angle.The better the ductility of material is,the stronger the erosion hardening becomes,and degree of erosion hardening is highest at the impact angle of 90°.Both residual extend stress and residual compressive stress which caused by erosion are maximal for the laser cladding layer with highest hardness. |
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