| Cast iron is widely used in the field of construction machinery.There are many casting processes to prepare cast iron.Meanwhile,it serves in harsh environment.Under long-term heavy load,fatigue and impact load,the surface of the casting is easy to crack,which will finally lead to cease to be effective of equipment without maintenance in time.The original defects formed in the casting process will also form cracks and propagate in serving.The re-casting of the damaged cast iron in furnace not only costs high but also pollutes the environment.Plasma cladding technology,as a green re-manufacturing technology,can realize the re-manufacturing and repair of workpieces.Therefore,repair and re-manufacturing of cast iron parts through plasma cladding not only have great engineering application values but also can turn waste into treasure and achieve green development.In this work,Fe-Al-C alloy cladding layer was prepared through plasma cladding and its microstructure and properties are investigated.Firstly,the single-pass cladding process parameters are optimized and the influences of the cooling methods on the coating's microstructure and precipitated graphite morphology are studied.Subsequently,a multi-pass cladding method was adopted to investigate its influence on the coating's microstructure,properties as well as friction and wear properties.The influence of annealing on the graphite morphology and distribution of the cladded Fe-Al-C layer were discussed.The effect of WC addition content into Fe-Al-Co on the microstructure and friction and wear properties of the cladding layer was studied.The optimized processing parameters of single-pass Fe-Al-C alloy coating are current at 65A,cladding speed at 2mm/min,powder feeding speed at 12rad/min and dilution rate at 19.6%.When the cladding current was increased to 140A,there was no graphite precipitated in the coating at a high undercooling,and its hardness was between 800-900HV.With the increase of the cooling rate,the dilution rate of the cladding layer decreased and the diffusion of carbon atom slowed down.The graphite in the middle and top part of the cladding layer had a curved and long shape under air cooling conditions and a clumpy shape under forced air cooling and CO2 cooling conditions.While,the graphite morphology at the bottom of the coating had little change.Under multi-pass cladding conditions,a spherical graphite transition zone appeared at interfaces between the coating and the cast iron,and carbides distributed in the austenite dendrites inside the coating with a skeleton shape.When the multi-pass cladding current was 45A,the coating had the highest micohardness of 402HV.The cladding layer had the minimum friction coefficient of 0.45 and lest wear amount of 5.4 mg when the cladding current was 50A,which had the best wear resistance.During the heat treatment,the cementite in the coating decomposed and the carbon atoms diffused and precipitated in the form of graphite.After the heat treatment at 900? and 980?,the martensite,austenite and cementite disappeared,and the matrix structure transformed to ferrite.The maximum diffusion coefficient at 980? was 17.4?m2/s.The graphite precipitated after heat treatment in the form of small clumps in the coating.The precipitation of graphite at 700? for 60 min was 6.52±0.54%,and the maximum precipitation at 980? for 60 min was 10.84±0.89%.In the FcAlC/WC-Co composite coating,fishbone-like Fe3W3C precipitated forming an anti-wear framework,and uninelted WC particles dispersed cvenly at the bottom of the coating.The coating mainly composed of ?-Fe,?-Fe,WC and Fe3W3C.When the added WC-Co content was 20%,the FeAlC/WC-Co composite coating had the lowest friction coefficient of 0.45,the lest wear amount of 1.3mg,which was 6 times that of the cast iron.The coating had the best friction and wear performance with wear morphologies mainly of abrasive wear,shallow furrows and less adhesion. |
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