Effect Of Nb And Cr₃C₂ On Microstructure And Wear Resistance Of Fe-base Alloy Coatings By Plasma Transferred Arc Welding

In this paper,Fe-based alloy coatings with micro/nano Nb powder and Cr₃C₂powder were prepared on Q235 surface by plasma transferred arc welding.Phase composition and microstructure of the coatings were investigated by means of optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The microhardness and wear resistance of the coatings were tested using microhardness tester and pin-on-disc wear tester.The changes of microstructure and properties of coatings were compared in order to obtain the best ratio and improve the hardness and wear resistance of the Fe-based coatings.Fe90 alloy coatings were mainly composed of?-Fe,?-Fe and Cr₇C₃.After adding Nb powder,Nb C phase appeared in the coatings.With the increasing of micro/nano Nb powder,Cr₂₃C₆ phase appeared in the coatings.The Cr₃C₂ phase was detected in the coatings after Cr₃C₂ powder were added.The microstructure of Fe90 alloy coatings was equiaxed crystal,and the coatings was mainly composed of equiaxed crystal and eutectic structure.The microstructure of coatings with micro Nb powder addition was mainly coarse equiaxed crystal.The refined dendrite with growth direction was observed in the coatings by adding nano Nb powder or micro Nb and Cr₃C₂ powder.The fine and uniform equiaxed crystal appeared with nano Nb and Cr₃C₂ powder addition.Precipitates of Nb C appeared in the coatings with Nb powder addition.The microhardness of the Fe90 alloy coatings was about 526 HV0.3.The hardness of coatings decreased after adding micro Nb powder.The microhardness increased to 750 HV0.3 by adding 1%and 3%nano Nb powder,which decreased after adding 5%nano Nb.With the increased of micro/nano Nb and Cr₃C₂ powder,the microhardness of coatings increased gradually,and the highest hardness was 775 HV0.3 and 850 HV0.3respectively.The worn surface of Fe90 alloy coatings has obvious ploughing grooves and serious peeled off,and the wear mechanism was mainly adhesive wear and abrasive wear.The wear resistance of coatings became worse after adding micro Nb powder.The wear resistance of the coatings was improved obviously by adding different mass fraction of nano Nb powder,and the wear mechanism was mainly abrasive wear.The best wear resistance of the coatings was obtained with 3%nano Nb powder addition.The wear resistance of the coatings with the addition of Cr₃C₂ powder increased with the increase amount of the powder,and the wear mechanism was mainly abrasive wear.