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Study On The Process, Microstructure And Properties Of Plasma Sprayed Alumina-based Ceramic Coatings

Posted on:2007-03-01Degree:MasterType:Thesis
Country:ChinaCandidate:L M ChenFull Text:PDF
GTID:2121360182973192Subject:Materials science
Abstract/Summary:PDF Full Text Request
The plasma spraying processing parameters of Al2O3-13wt.%TiO2 (AT13) ceramic coating on AISI1045 steel substrate were optimized by orthogonal experimental design in this paper. The microstructure and properties of plasma sprayed Al2O3, AT13 and AT13 with different contents of rare earth oxides La2O3 and CeO2, respectively, under the optimized spraying process parameters condition were comparatively investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy, normal and Weibull statistical analysis and wear tests. For the spraying distance of 80mm, the powder feed rate of 2.4kg·h-1, orthogonal experimental design method was used to study the influence of primary gas (Ar) flow rate, arc current and arc voltage on the properties of coatings. The results indicate that primary gas flow rate is the most influential factor for microstructure and properties of the coating, the optimized spray parameters are: primary gas flow rate of 45slm, arc current of 550A, arc voltage of 65V. Plasma sprayed Al2O3 coating consists of γ-Al2O3 and α-Al2O3, the AT13 coating consists of γ-Al2O3, TiO2 and a small amount of α-Al2O3. The coatings are characteristic of lamellar microstructure with porosities, microcracks and unmelted particles. The adhesion between coating and substrate is mechanical bond. The addition of TiO2 results in better integrity of AT13 coating than that of Al2O3. The microhardness distribution of Al2O3 and AT13 coatings significantly conforms with normal and Weibull distribution. Though the average microhardness of AT13 coating is lower than that of Al2O3 coating, the scatter of microhardness distribution in AT13 coating is reduced. The wear test revealed that the wear resistance of AT13 coating was better than that of Al2O3 coating, the predominant wear mechanism of coatings are spalling fatigue wear and adhesive wear. The microstructure feature of AT13 coating with the addition of rare earth oxides La2O3 and CeO2, respectively, is similar to AT13 coating. The addition of rare earth oxide improved the contact between splats in the coatings, but it leads to more unmelted Al2O3 particles. The addition of rare earth oxides La2O3 and CeO2 has less effects on the microhardness of the AT13 coating, but the statistical analysis of microhardness indentation test indicates that the scatter of microhardness distribution in the coatings with addition of rare earth oxides is reduced, the microhardness distribution also conforms with normal and Weibull distribution. The scatter of microhardness data in AT13 coatings with 6% La2O3 and 4% CeO2, respectively, is minimum. The wear test shows that the wear resistance of AT13 coating with the addition of rare earth oxide is improved. The wear mechanism is predominantly attributed to the spalling fatigue wear and adhesive wear. Compared to the AT13 coating, the fraction of the spalling area is reduced and the adhesive area is increased on the worn surface. The best wear resistance of the coatings with the addition of rare earth oxides is obtained when the contents of La2O3 and CeO2 are 6% and 12% respectively.
Keywords/Search Tags:plasma spraying, Al2O3 coating, rare earth oxide, microhardness, wear
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