| Remanufacturing is an important way to solve the problems of resource shortage and realize energy-saving and emission-reduction.It is an effective way to achieve"size recovery" and "recovery performance" for high-value damaged parts by additive repair technology.The working condition of centrifugal compressor is very bad.Blade of impeller as the key part of centrifugal compressor is impacted by gas-solid two-phase flow which caused erosion wear.Thinning damage is one of the important forms for impeller.So,it is of great significance to carry out the research on the blade repairing the blade and the anti-erosion performance in order to lengthen the residual life span and improve the engineering value.Thermal spraying technique has many advantages,such as fast deposition rate,variety of materials sources and small heat-affected zone.It has unique advantages in repairing large area for thinning damage of thin-walled parts such as blades.Hence,NiCr-Cr3C2/NiCrAl coating was prepared by atmospheric plasma thermal spraying technique.Also NiCr-Cr3C2/NiCrAl coatings with different NiCr content were prepared.The effects of NiCr content on microstructure,mechanical properties,friction coefficient and wear properties of coatings were studied.Due to the lack of studying on high-speed micro-particles impacting on thermal spraying coating,the erosion wear law and mechanism of NiCr-Cr3C2/NiCrAl coating with different NiCr contents under the multiple factors were studied.Finally,the erosion depth and surface quality of NiCr-Cr3C2/NiCrAl coatings with different NiCr contents were studied by using optical microscope and white light interferometerNiCr-Cr3C2 coatings with different path distances were prepared by APS.All the coatings present layered structure,which were composed of gray blocky particles and light gray fillers.It had dense structure and pore,microcracks and other defects.No elements diffusion was found between coating and coating or substrate and coating.So the coating bonding model was mainly mechanical bonding.Also the results showed that the bonding strength,microhardness and coating thickness of coating decreased first and then increased under the premise of a certain amount of powder per unit area.The maximum bonding strength,microhardness and coating thickness were 42.43MPa,829HV and 410 ?m,respectively,at a distance of 6mm and twice spraying.NiCr-Cr3C2/NiCrAl coatings with different NiCr contents were prepared by double channel powder feeder.With the increase of the content of NiCr,the white strips inside the coating gradually increased and the layered structure were presented.All the coating had Cr3C2?Cr7C3?Cr23C6?Cr2O3?(Ni,Cr)and other phases except 100wt%NiCr coating.The carbide phase decreased gradually,and the(Ni.Cr)alloy phase increased gradually with the increase of the NiCr contents.The hardness of the coating decreased from 829HV to 265HV.When the NiCr content was 40%,60%and 80%,the hardness fluctuated greatly due to layered structure.The friction coefficient of coating decreased gradually with the adding of NiCr,while the depth of wear pits increased.So the anti-wear performance of NiCr-Cr3C2/NiCrAl coating decreased gradually.The oxidative wear,abrasive wear and fatigue wear were the mainly failure modes.The influences of impact angles,erosion particle size,erosion velocities and NiCr contents on erosion resistance of NiCr-Cr3C2/NiCrAl coating were studied by using erosion wear tester.It was found that the erosion rate of NiCr-Cr3C2/NiCrAl coating increases first and then decreases with the increase of impact angles.With the increase of NiCr contents,the erosion rate of the coating increased at low angles,while the erosion rate at high angles showed the opposite trend.Erosion morphology of the coating changed from semi-circle to V shape with the increase of impact angles.At low impact angles,the wear mechanism of NiCr-Cr3C2/NiCrAl coating was micro-cutting,and the erosion rate decreased with the increase of hardness.At medium or high angles,fatigue spalling or fracture were the mainly wear mechanism which would cut down or remove the materials from the coating surface.The anti-erosion properties will be weak with the increase of hardness. |
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