Preparation And Characterization Of Ceramic Coating On The Surface Of Nickel Alloy

High-temperature oxidation resistant and thermal shock resistance ceramic coating,in order to meet the application requirements, was prepared on DZ4-alloy substratesurface by using the enamel coating technology, and determinied the composition of thecoating slurry were the glass frit, Cr₂O₃, kaolin and water. The optimal conditions offiring, the effect of the Cr₂O₃doping amount, the performance of the high temperatureoxidation resistance and thermal shock resistance of the coating were studied.The slurry with the mass ratio of glass frit to Cr₂O₃is70:30was covered onDZ4-alloy substrate surface by using the dipping method, and fired in the range of1200℃to1310℃at different times for the comparison experiments to coating surfacemorphology. The ceramic coating with the dense structure, a surface gloss, no defectssuch as bubbles and pinholes was fired at1300℃with7min has resulted is the bestfiring process. The results show that the ceramic coating has a good ability ofanti-oxidation at the high temperature as7.5times to the alloy substrate from theoxidation test at1100℃in air for100h, and had good matching of its thermal expansioncoefficient with the substrate for thermal-shock tests reached20times at1200℃. Theenamel coating have good performance of the high temperature insulation for theresistance is1.28M at800℃，and apply to the thin-film sensor is prepared on thesurface of the coatingEffects of the Cr₂O₃doping amount on the performance of the coating for thecondition of firing at1300℃with7min were studied. The results show that the surfacemorphology of the sample has gradually to become good with increasing the Cr₂O₃doping amount, and then gradually deteriorating, and to achieve the better when theCr₂O₃doping amount is20wt%or30wt%. The coating with the loose structure anddefects such as voids when up to50wt%. The coating exhibits good thermal-shockresistance and high temperature oxidation resistance when the Cr₂O₃doping amount is20wt%or30wt%, and the coating surface structure was still compact also can play aprotective effect on alloy substrate after the high temperature oxidation, and had goodmatching of their thermal expansion coefficient with the substrate for thermal-shock tests respectively reached15and20times. The rest of the Cr₂O₃doping amount haveappeared varying degrees of damage. The coating lost the protective effect of the alloysubstrate becuase of the loose and voids structure after the high temperature oxidation,and the weight gain rate was up to2.987%which only1.5times as the alloy substrate,exhibited the worst of performance on thermal-shock resistance and high temperatureoxidation resistance when the Cr₂O₃doping amount is50wt%. The coating had not verygood matching of thermal expansion coefficient with the substrate for thermal-shocktests was only2times. Thus, The slurry with the mass ratio of glass frit to Cr₂O₃is from80:20to70:30can get the best performance of the ceramic coating under the processcondition of firing at1300℃with7min.