| Fire-retardant coating for steel structure has been widely used because of its light weight,good decorative surface and not limited by the geometric shape of components.However,at present,the design and application of steel structure.fireproof coating in engineering all assume that the:integrity of the coating is good.In fact,the carbon layer structure of the steel structure fireproof coating is constantly changing in the high temperature environment,and the adhesion between the coating and the substrate and the mechanical properties of the coating will decrease,which will cause the damage of the coating.At present,there are few studies on the preparation of composite coatings with self-lubricating and wear resistance on the surface of 304 stainless steel by laser cladding technology.In this paper,Co powder,Cu powder and Ti3SiC2 powder were used as raw materials to design reasonable powder ratios of Co,Co+2%Ti3SiC2,Co+5%Ti3SiC2,Co+8%Ti3SiC2,Co+5%Ti3SiC2+10%Cu and Co+5%Ti3SiC2+20%Cu(mass ratio).The laser cladding experiment was carried out under the optimal laser experimental process parameters.The optimal laser experimental process parameters are as follows:laser power is 1600 W,scanning speed is 700 mm/min,powder feeding gas is 18 L/min,powder feeding rate is 15 g/min,spot diameter is 2 mm,wavelength is 514 mm,energy density is 1.415×105J/m2,multi-channel cladding spot overlap rate is 50%.The microstructure of the coating cross section was observed by MIRA3 LMH scanning electron microscope(SEM),and the element composition of the coating in different regions was detected by Oxford XMAX20 energy dispersive spectrometer(EDS).The phase of the coating was analyzed by X-ray Diffractometer(XRD)from Changsha Institute of Mining and Metallurgy,Hunan Province,and the scanning angle range was 5°～90°.Vickers microhardness tester was used to measure the cross-section hardness distribution of 304 stainless steel and coating,and the strengthening mechanism was analyzed.The friction coefficient and wear rate of 304 stainless steel and coating at room temperature and 600℃ were tested by high temperature friction and wear tester and material surface wear scar tester,respectively.The wear surface of 304 stainless steel substrate and coating was analyzed by SEM/EDS to explore its wear mechanism.The results show that the width of Co/Cu-Ti3SiC2 coating is 16 mm,and there are no obvious holes and cracks.The surface morphology of Co/Cu-Ti3SiC2 coating is good.The main phases are solid solution γ-Co,hard phase Cr7C3,TiC,Fe2C,lubrication phase Cu and Ti3SiC2.The microstructure of Co/Cu-Ti3SiC2 composite coating is similar in each region,which is composed of continuous matrix,dendritic crystal and cellular crystal.Compared with the coating without Cu addition,such as Co coating and Co+5%Ti3SiC2 coating,the microstructure of the coating with Cu addition becomes more refined.The average microhardness of Co+8%Ti3SiC2 coating is the highest,which is 497.4 HV0.5.With the increase of soft metal Cu content,the hardness of the composite coating will further decrease.At room temperature,with the increase of Ti3SiC2 content,the friction coefficient of Co-Ti3SiC2 composite coating increases first and then decreases.When the addition of Ti3SiC2 was constant,the friction coefficient of Co/Cu-Ti3SiC2 composite coating further decreased with the increase of soft metal Cu addition.The synergistic lubrication of Cu and Ti3SiC2 results in lower friction coefficient.Co+5%Ti3SiC2+20%Cu coating has the lowest friction coefficient of 0.41.At room temperature,the wear resistance of Co+5%Ti3SiC2+10%Cu coating is the best,and the wear rate is 4.93 ×10-6 mm3/Nm.At 600℃,with the increase of Ti3SiC2 content,the friction coefficient of Co-Ti3SiC2 composite coating increases first and then decreases.Compared with at room temperature,the friction coefficient of the composite coating decreased significantly,indicating that Ti3SiC2 showed good friction reduction effect at high temperature and improved the self-lubricating properties of the coating.When the addition of Ti3SiC2 was constant,the friction coefficient of Co/Cu-Ti3SiC2 composite coating increased slightly and then decreased with the increase of soft metal Cu addition.The lowest friction coefficient of Co+5%Ti3SiC2+20%Cu coating is 0.17.The Co+5%Ti3SiC2+20%Cu coating exhibits the best wear resistance at 600℃,and the wear rate is 2.4×10-5mm3/Nm.With the increase of Ti3SiC2 content,the wear rate of Co/Cu-Ti3SiC2 composite coating at high temperature gradually decreases. |
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