Fabrication And Characteristic Of Ceramic Coatings On Stainless Steel Substrates

With the development of high-tech industries, metallic materials used are needed to possess some excellent capabilities of high-temperature resistance, corrosion resistance, wearlessness and heat-strike resisitance, while the conventional metallic materials can not meet these demands anymore. However, the surface coating technology is such an effective method to improve the properties of metallic materials that many countries are trying to research and apply the technology and the corresponding coating processing method. And then, the preparation of ceramic coatings on the metallic materials has become a new hot spot.In this study, sol-gel and slurry methods were used to prepare ceramic coatings on 1Cr18Ni9 stainless steel substrates, which can improve the high temperature oxidation resistance and thermal shock resistance of the stainless steel.Mullite coatings were produced on stainless steel substrates by sol-gel method, and then the influences of flux agent B2O3 and heating temperatures on apparent morphology of coatings were investigated respectively. XRD, TG-DTA and SEM were used to characterize and analyzed the composition and microstructure of mullite coatings, and the capability of high temperature oxidation resistance and hardness were also estimated. Testing results indicated that the mullite coating was uniform and dense, moreover it can be closely bonded with the stainless steel substrates when heating at 850℃and mass ratio of B2O3-mullite gel is attained to 0.5. The hardness of the coatings was about 5 times of the stainless steel. Oxidation weight gain was just 0.076 mg/cm2 after oxidated at 850℃for 30 h, the mullite coating has excellent capabilities of oxidation resistance, as well as, high temperature stability. Result of the thermal shock resistance test demonstrated that the mullite coatings possess the fairly high adhesive strength with substates with a capability of bearing 30 times thermal lash at 800℃.A series of SiO2-based, MgO-based and B2O3-based ceramic coatings were respectively prepared on the 1Cr18Ni9 stainless steel by slurry method. The influence of techniques and the composition on the ceramic coatings were analyzed in detail. The optical microscope and X-ray diffraction (XRD) were performed to analyze the structure and apparent morphology. The thermo-chemical reaction of the coating was studied by TG-DTA, and then the properties of hardness, thermal shock resistance and high temperature oxidation resistance were tested. The results showed that the structure of SiO2-based coatings was amorphous state,.while there was some new ceramic phases CaMgSi2O6 and Mg2Al4Si5O18 formed in the MgO-based coatings. Hardness of SiO2-based coating which SiO2 content reached 48 wt% was about three times of substrate. After 17 times of thermal shock, the coatings still intact, so that the thermal shock resistance of ceramic coatings was excellent. High temperature oxidation at 700℃showed that:MgO-based coating with 48 wt% MgO has well ability of oxidation resistance, of which weight-gain just reached at 0.021 mg/cm2 after oxidized for 16 h. The weight-gain of soaking and immersion oil of boron-based coatings were 0.56 mg/cm2 and 0.88 mg/cm2 respectively. At the same time, the boron coatings has good corrosion-resistance which the coatings were still intact after immersed in 6 wt% H2SO4 and 10 wt% NaCl for 5 days.