Effect Of NbC On Microstructure And Wear Resistance Of Fe-based Alloy Coatings By Plasma Transferred Arc Welding

In this paper,the Fe-based alloy with 0.0%,1.0%,3.0%and 5.0%（in weight percentage）micro-NbC or nano-NbC coatings were deposited on Q235 low carbon steel by plasma transferred arc welding.The effects of different content of micro-NbC or nano-NbC on the microstructure and wear resistance of Fe-based alloy spray-welded layer were investigated.Microstructure and phases composition of the coatings were investigated by means of X-ray diffraction instrument（XRD）,optical microscope（OM）,scanning electron microscope（SEM）and energy dispersion spectroscopy（EDS）.Microhardness were examined by microhardness tester.The wear resistance of the spray coating was tested by friction wear tester and step meter,and the wear morphology was observed by SEM.The results showed that the mainly phases ofα-Fe,γ-Fe and（Cr,Fe）₇C₃ existed in the Fe-based alloy coatings.The peak intensity ofγ-Fe phase decreased with the increase of micro-NbC or nano-NbC content from 1.0%to 3.0%.The peak intensity of theγ-Fe increased by adding 5.0%micro-NbC but decreased by adding 5%nano-NbC.The peak intensity of the NbC phase increased as the micro-NbC or nano-NbC content increased.The microstructure of equiaxed dendrites and eutectic existed in the Fe-based alloy spray-welded layer.The addition of micro-NbC or nano-NbC changes the grain size and growth morphology,and the morphology of the eutectic structure is also changed.The gradually refined microstructure of the coatings was observed by adding1.0%and 3.0%micro-NbC or nano-NbC.And the dendritic appeared in the coatings by adding 5.0%micro-NbC or nano-NbC.The refined eutectic structure was also obtained with the addition of micro-NbC or nano-NbC,and which was lamellar.The microhardness of the Fe-based alloy coatings increased gradiently from substrate to the top surface,which was improved by adding micro-NbC particles,and the which increased with increase amount of micro-NbC or nano-NbC addition.The wear mechanism of Fe-based alloy coatings was fatigue spalling.The inhibited fatigue spalling and improved wear resistance of the spray coatings was obtained by adding micro-NbC or nano-NbC particles to a certain amount.The best wear resistance was achieved by adding 3.0%micro-NbC or 5.0%nano-NbC,the wear mechanism were the mixed wear of fatigue spalling and abrasive wear and only abrasive wear,respectively.