Study On Wear And Corrosion Behavior Of High Velocity Arc Spraying FeCrAl/Al Composite Coating

Q235 steel is widely used in several engineering industries because of its relatively good mechanical properties making it a common component of mechanical equipment.Q235 steel not only has good machinability but also good welding performance that make it more common than superalloys and stainless steel.However,low wear and corrosion resistance of Q235 steel,limit its applications to corrosive environments.According to this research,arc spraying is one of the practical and effective ways of improving wear and corrosion resistance.FeCrAl coatings have been widely used because of their high wear and corrosion resistance properties,high temperature oxidation and high abrasion resistance.Al coatings have good corrosion properties and high strength to weight ratio.Arc spraying of these two materials provides the possibility of a coating with improved properties.This study was conducted to investigate the microstructure,corrosion and wear behavior of FeCrAl/Al coating applied on Q235 steel substrate by High velocity arc spraying(HVAS).The process parameters and influence on the coating properties were studied and the optimum parameters for spraying FeCrAl/Al coating were obtained.The main content of the research work includes the following:(1)FeCrAl/Al was deposited onto the substrate surface by arc spraying FeCrAl and Al wires to form a composite coating.Prior to the spraying process,the substrate was prepared by chamfering the sharp corners at an angle of 45° and surface activation was done by abrasive grit blasting using steel grit.The different spraying parameters used were:voltage range between 30V-44V,current range 160A-280A,constant spray distance of 200mm and spray angle of 90°.(2)To determine the morphology of the coating structure,the surface and crosssectional images of coatings were studied by SEM.According to the surface coating morphology,the composite coating showed an improved dense splat structure with the increase in voltage and current.The coatings at lower voltage and current formed irregular splats.The cross-sectional coating morphology showed a layered-type structure that consists of interlinking layers of FeCrAl and Al.FeCrAl/Al composite coating had thicker splats of alternating FeCrAl and Al layers than the individual FeCrAl coating.Through the XRD results and analysis,it was found that the main phases of FeCrAl/Al coating constituted of A1 and FeCr,traces of AlFe intermetallic compounds and oxides of Cr₂O₃ and Al₂O₃.EDS analysis results of the composite coating suggested the increase in the Aluminum content.Average measurements taken for the coating porosity were 3.77 for FeCrAl coating and 5.34,4.97,4.29,3.46(%)for FeCrAl/Al coating with the increase in spraying voltage and current respectively.Average microhardness of FeCrAl/Al coatings was within the range of 358.48 and 513.51 HV0.1.Microhardness for the steel substrate and FeCrAl coating was 165.52 HV0.1 and 409.10 HV0.1 respectively.Due to the low hardness of the Al and high hardness of FeCr,composite coating was formed as a result of alternating layers of the hard and ductile phases.Scratch adhesion tests showed an increase in the adhesion strength of the coatings with increase in voltage and current.High voltage and current improved the splat structure thus increasing the bonding strength of the coating to the substrate.(3)The influence of spray parameters on the corrosion properties of the coatings were investigated in an electrochemical workstation.Corrosion resistance of the composite coatings exposed to 3.5 wt.%Sodium Chloride(NaCl)solution was significantly improved.The Tafel polarization tests showed a decreasing current density with the increasing current and voltage of the coatings.The lower current density shows a better corrosion resistance of the coatings.Composite coating with the highest voltage and current had the lowest current density and corrosion rate of 1.5713?A/cm² and 0.013612mm/year respectively.Formation of the passivation oxide films prevented penetration of the electrolyte into the coating microstructure.The Electrochemical Impedance Spectroscopy(EIS)measurements were also consistent with the Tafel results.The coatings showed a better corrosion behavior because of the high impedance.From the EIS measurements and Tafel polarization results,FeCrAl/Al composite coating had an improved corrosion resistance compared with FeCrAl/FeCrAl coating.FeCrAl/Al can thus be applied to coat Q235 substrates exposed to NaCl corrosive media.(4)The influence of varying loads and sliding speeds on the wear properties of the coatings was analyzed with a GCR15 steel ball surface contact method.The wear properties of the Q235 steel substrate,FeCrAl/FeCrAl and FeCrAl/Al coatings were examined.The coefficient of friction(COF)of the coatings and Q235 substrate decreased with increasing load.Wear volume loss of steel substrate and the coatings increased with increase in sliding speeds and applied load.FeCrAl/FeCrAl coating displayed the lowest wear loss rate hence the better wear resistance properties.High wear loss rate of FeCrAl/Al was due to the underlying Al layer that had low hardness hence wear rate was accelerated.The worn surfaces characterized showed that micro-cutting,plastic deformation and plowing out were the main wear mechanism of the coatings and substrate.(5)Through orthogonal test,the influence of process parameters on coating performance was studied.The effects of voltage,current and spraying distance on the coating microhardness and the width of the wear track were studied and analyzed.With the maximum microhardness and minimal wear track width as the optimization goals,the process parameters were optimized.The results show that the order of the influencing factors on the coating quality is Voltage>Current>Spray distance.The optimal parameters obtained are Voltage 44V,Current 200A and Spraying distance 150mm.