Preparation And Properties Of Al₂O₃Coatings For High Temperature Oxidation Resistance By Sol-gel Process

In order to reduce the waste caused by metal material oxidation, oxidation resistance properties of metals in high temperature service conditions should be improved, making metal materials under high temperature both have certain mechanical strength and good oxidation resistance. The preparation of inorganic ceramic coating on metal surface was regarded as a good approach.The Al2O3sol was prepared from aluminium isopropoxide as precursor. Using the orthogonal experiment to find the best parameter of producing clear, stable and viscous sol. The dried sol was analyzed by SEM, XRD and DSC. Then Al2O3coatings were overlaid on316L austenite via dip-coating method. After drying and calcination at800℃in vacuum, coatings of different numbers of layers was studied by SEM and AFM for morphology. The high temperature oxidation resistance of the coatings were characterized by the mass gain of unit area under air atmosphere at800℃.So as to compare the degree of oxidation between coated and blank samples, optical digital microscope was applied in observation of morphology after oxidation. Furthermore, ZrO2coatings were introduced as intermediate layers to enhance the overall performance of Al2O3coatings.The results showed that, the best parameter combination for preparing Al2O3sol was: hydrolysis temperature90℃, hydrolysis time4h, Al (iso-OC3H7)3:H2O mole ratio for1:100, pH value for2.The quantity of secondary particles increased as the number of layers of the coatings grew. Protection effect of Al2O3coatings on substrate under high temperature was very significant, among all the samples, A3showed the best performance compared to others no matter in persistent of high temperature oxidation resistance or thermal shock resistance. ZrO2intermediate layers prevented the formation of secondary particles somehow, the maximum height of the particles reduced about40%. Although the persistent of high temperature oxidation resistance or thermal shock resistance had no obvious improvement, the composite coating at high temperature was much more uniform and stable.