| Stainless steel has been widely used in many fields.But in the practical life,ithas the some disadvantages about low hardness,high friction coefficient and poor wear resistance.These disadvantages often caused early failure of some mechanical parts,which impacted on life and reliability of industrial parts.Cobalt-based alloys have good properties by laser cladding,especially high temperature resistance and friction and wear resistance.Coating of Stellite12 can be prepared on the 304 stainless steel substrate by laser cladding to improve the substrate surface properties.Stellite12 powder was subjected to coaxial powder feeding method andStellite12/Ti/B4C composite powder was subjected to pre-pulverizing method,and coating was synthetized on a 304 stainless steel substrate by laser cladding.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffractometry(XRD)were used to observe and analyze the microstructure and phase composition of the coating,respectively.The hardness,wear resistance and high temperature oxidation resistance of the coating were studied.The Stellite12/Ti/B4C composite coating and the substrate were subjected to high temperature oxidation test at 800? for 50 h.The room temperature friction and wear behavior and high temperature oxidation resistance of the coating and the substrate were analyzed.The oxide film composition of the oxidized surface of the sample was analyzed by EDS and XRD.Revealing the room temperature wear mechanism of the coating and the high temperature oxidation mechanism,and obtaining the strengthening effect of the Stellite12/Ti/B4C cladding coating.The results show that:Pure Stellite uses a coaxial powder feeding method andpre-fabrication method to prepare a good coating for metallurgical bonding between the coating and the substrate by laser cladding.The macroscopic appearance of the coating has a metallic luster and no defects such as pore splashing.Coaxial powder feeding optimization of process parameters result that parameters with the power of 2500w,scanning speed of 400mm/min and powder feeding rate of 49.56g/min lead the coating with low dilution rate and good morphology.The phase of the pure Stellite coating is mainly equal to the face-centered cubic?-Co and Cr7C3,and the coating phase of adding2%and 4%Ti/B4C mainly includes?-Co,Cr23C6 and Ti C,etc.,adding 6%.The coating phase with 8%Ti/B4C mainly includes?-Co,Co2Ti and Ti C.The in-situ Ti C submicron particle phase is synthesized with the addition of Ti/B4C.The remaining B4C acts as a heterogeneous nucleation mode,forming a submicron structure Ti C/B4C strengthening phase,and the particle size is gradually reduced.The results simultaneously indicate that the particles of Ti/B4C obviously lead to the refined microstructures by using the measurement of secondary dendrite arm spacing(SDAS)of the coating.The Stellite12 composite coating improves the hardness of the 304 stainless steelmatrix and the hardness of the coating increasingly is improved with the addition of Ti/B4C and the maximum value is 656 HV,the average hardness is 624 HV with 8%Ti/B4C,which is three times as large as the 304 stainless steel substrate.The wear resistance of 304stainless steel substrate was improved by laser cladding Stellite12 composite coating,and the wear resistance of Stellite12 increased with the Ti/B4C.Through sliding friction and wear experiments,the average friction coefficients of 304 stainless steel matrix,Stellite+0%Ti/B4C,Stellite+4%Ti/B4C and Stellite+8%Ti/B4C were 0.62,0.55,0.47 and0.41,respectively.The wear morphology of pure Stellite coating is mainly in the form of furrow,and the adhesive wear is better than that of 304 stainless steel matrix.After adding4%Ti/B4C the wear resistance of the coating was enhanced due to the formation of hard phase Ti C and partially incompletely melted B4C,resulting in a abrasive wear.After adding 8%Ti/B4C,the coating has a smooth wear profile,resulting in a slight furrow and abrasive wear.when the addition of 8%Ti/B4C,the wear resistance of the Stellite12 coating is optimized.After the substrate and the cladding coating were high temperature oxidized at800? for 50 h,result that the pure Stellite 12 coating was mainly composed of?-Co,Cr 2O 3,(Co Fe 2)O 4 phase,the phases of the coating were?-Co,Cr2O3,(Co Fe2)O4 and Ti O2with the addition of Ti/B4C.The pure Stellite12 coating has a good resistance to high temperature oxidation on the base 304 stainless steel,and the Ti/B4C is added to improve the high temperature oxidation resistance of the cladding coating,when the addition of6%Ti/B4C,the cladding coating has the best resistance to high temperature oxidation. |
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