| AlN/Fe and BN/Fe coatings were prepared on Q235 steel by plasma transferred arc welding.The microstructure and phase structure of the coatings were studied by optical microscope,scanning electron microscope(SEM)and X-ray diffraction(XRD).The microhardness,wear resistance and corrosion resistance of the coatings were examined with microhardness tester,wear resistance tester and salt spray box.The main phases of the coatings were?-Fe,?-Fe and(Cr,Fe)7C3.With the increase of scanning speed,the microstructure was refined and the microhardness was improved.The phase composition was unchanged by adding AlN or BN.Equiaxed microstructure was observed without powders addition.The columnar dendrites appeared by adding AlN/BN and which was coarser with the increase amount of AlN/BN addition.The average microhardness of the coatings with BN w as lower than that of AlN composite coatings.The results shows that the average microhardness of the coatings with BN was lower than that with AlN.The the highest microhardness of 758.5 HV0.3was obtained with 1%AlN,which was 88.2 HV0.3 higher than that of Fe-based alloy coatings.The microhardness of the coatings was improved by adding small amount of AlN powder,but it decreased with excessive amount.The friction coefficient of the coatings reduced after adding AlN and the friction coefficient was 0.40?0.57.The smoothest worn surface was obtained when the AlN content was 3%,and the wear rate was 1.15×10-14 m3/N·m.The wear mechanism changed from adhesive wear to abrasive wear after AlN addition.The friction coefficient of the coatings also reduced after adding BN,and the friction coefficient was 0.42?0.52.The wear rate of the sample with 3%BN was the lowest,which was 3.71×10-14m3/N·m.At the same mass fraction,the wear resistance of AlN coating was better.In the salt spray test with a corrosion duration of 20 h,the corrosion resistance of Fe-based alloy coatings was improved by adding 5%AlN,the least spot corrosion and the smallest size were observed.But,the corrosion resistance of the coatings decreased with BN powder addition.In conclusion,the wear resistance and corrosion resistance of the coatings were improved by adding 5%AlN powder. |
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