| 304 stainless steel has good density and specific heat capacity.It has very good stability and safety both in processing and in use.It can adapt to the external environment well and is not prone to rust,so it is commonly used materials for thermal power unit components in coal-fired power generation.However,304 stainless steel exhibits poor wear resistance and oxidation resistance in high temperature environments.In order to improve the high temperature performance of 304 stainless steel,this paper uses synchronous powder feeding laser cladding modification technology to prepare FeCrAlNbNi alloy coating on the surface of 304 stainless steel.The structure and properties of the coating under different process parameters are studied,and on this basis,the high temperature wear resistance of the coating at 200?,400?,and 600? and the high temperature oxidation performance at 900? are further studied.Focusing on the analysis of the high temperature wear mechanism and high temperature oxidation mechanism of the coating.The main research contents and results are as follows:(1)The effect of laser power on the structure and properties of FeCrAlNbNi coatings was studied.The results showed that the FeCrAlNbNi coatings prepared by different laser powers are all composed of Fe2AlCr,Fe3Al,FeAl,Al3Nb,Cr2Nb phases and Fe(Cr)solid solution phases,and with the increase of laser power,Fe2AlCr,Fe3Al,FeAl phases and Fe(Cr)solid solution content gradually increases.The coatings prepared with different laser powers are composed of snowflake-like dendrites and non-snow-like regions.With the gradual increase of laser power,snowflake-like dendrites gradually increase.The hardness of FeCrAlNbNi coatings prepared with different powers is mainly concentrated in the range of 602.4HV0.2-707.2HV0.2,which is about 3.34-3.93 times that of the substrate(180HV0.2).When the laser power is 1600W,the coating hardness is the best,and the average hardness is about 681.4HV0.2.When the laser power is 1600W,the self-corrosion current density of the coating is the smallest,which is one order of magnitude lower than that of the substrate,and the corrosion resistance of the coating is the best.The wear coefficient and wear profile area of the coating are smaller than that of the substrate,and have the same changing trend as the laser power increases:first decrease and then increase.When the laser power is 1600W,the coating has the smallest wear coefficient(0.536)It has the best abrasion resistance,and the surface morphology is mainly shallow and thin furrows,and the wear mechanism is abrasive wear.(2)The effect of scanning speed on the structure and properties of FeCrAlNbNi coating was studied.The results showed that the coatings prepared at different scanning speeds were all composed of Fe2AlCr,Fe3Al,FeAl,Al3Nb,Cr2Nb phases and Fe(Cr)solid solution.The microstructure of the coating is dominated by snowflake-shaped dendrites,and the size of the snowflake-shaped dendrites gradually increases with the increase of the scanning speed.The hardness of the coating prepared at different scanning speeds is higher than that of the substrate.When the speed is 7mm/s,the hardness of the coating is relatively stable,and the average microhardness is the highest.When the scanning speed is 7mm/s,the coating has a smaller self-corrosion current density than the substrate,indicating that the FeCrAlNbNi coating has better corrosion resistance at this time.The friction coefficient and wear section contour area of the coating are lower than that of the substrate,indicating that the coating has better wear resistance.When the scanning speed is 7mm/s,the wear depth and wear width are the minimum,and the wear surface is distributed with fine furrows and a few wear particles.The wear mechanism is abrasive wear,and the wear resistance is the best.(3)The wear resistance of FeCrAlNbNi coating at 200?,400?and 600? was studied.The results show that the wear resistance of the coating is better than that of the substrate at different high temperatures.The friction and wear coefficient and wear volume of the coating increased first and then decreased with the increase of temperature.The maximum friction coefficient(0.83)and wear volume(0.1905mm3)of the coating were obtained at 400?,while the minimum friction coefficient(0.49)and wear volume(0.0119mm3)were obtained at 600?.At 200?,finer furrows and smaller wear particles appear on the wear surface of the coating,and the wear mechanism is abrasive wear.At 400?,the furrow of the worn surface becomes larger and loose layered fragments appear.The wear mechanism is mainly abrasive wear,adhesive wear and oxidative wear.At 600?,a large number of lamellar fragments appear on the wear surface,and Al2O3 lies below the fragments.The wear mechanism is mainly oxidized wear and adhesive wear.(4)The high temperature oxidation performance of FeCrAlNbNi coating at 900? was studied.The study found that the mass gains of the coating and the substrate were 1.31 mg/cm2 and 4.235 mg/cm2 when oxidized at 900? for 100 h.The weight gain of the substrate is close to the linear law,while the weight gain of the coating is closer to the cubic law.The oxidation rate of the coating is about one-half of the substrate,and the coating has better high temperature oxidation.After the coating is oxidized for different time,?-Al2O3 is formed,and the content of ?-Al2O3 gradually increases with the increase of oxidation time.In the early stage of oxidation,a less dense Al2O3 oxide layer was formed on the surface of the coating.As the oxidation progressed,Al elements passed through the oxide layer to form aggregated Al2O3 on the surface.In the middle of oxidation,the Al2O3 oxide layer gradually becomes dense,and the aggregated Al2O3 begins to scatter.In the late stage of oxidation,a stable,dense and continuous Al2O3 layer was formed on the surface of the coating with a thickness of about 1.2 ?m,indicating that the FeCrAlNbNi coating has excellent high temperature protection performance. |
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