| Nanostructured materials possess excellent properties in mechanics,calorifics and tribological. Nano-powders are the base of application ofnanostructured material, and nanostructured coating is one of the appliednanostructured materials. The study on the preparation of nano-powdershas been engaged all over the world for two decades, but there is still oneof technology difficulties in gaining nano-powders with excellentdispersion, spherical shape and high productivity. On the other hand, thestudy in preparation and properties of nanostructured coating by thermalspraying is on the way. Though the research in this field is limited, itshows excellent foreground in its application. This dissertation encirclesthe two points mentioned above. The ZrO2 nano-powders with excellentdispersing, spherical shape and narrow particle size distribution havebeen prepared via the coupling route of w/o emulsion with methyl oxalatehomogenous precipitation. At the same time, nanostructured zirconiacoating has been prepared by atmosphere plasma spraying. Consideringthe landscape orientation comparison study of nanostructured zirconiacoating and microstructured zirconia coating in the majority of theprevailing studies, the author longitudinally compared the preparationmethods and properties of nanostructured zirconia coating. The effects ofplasma spraying technologic parameters on phase composition,microstructure and thermal shock property of nanostructured zirconiacoating were examined. In addition, mechanics properties,thermophysical properties and tribological properties of nanostructuredzirconia coating were also studied.(1)The emulsion system containing high water phase was used forthe first time, in which system cheap xylol was used as the oil phase,span-80 as the surfactant, and aqueous solution containing Zr(NO3)4,Y(NO3)3 and methyl oxalate as the water phase. During the process ofheating water, methyl oxalate hydrolysis occurs to come into beingprecipitator, and precipitate become spherical shape grains in the waterdroplets of emulsion. Through this method, the ZrO2 nano-powders containing 3.5% Y2O3 with excellent dispersion, spherical shape andnarrow particle size distribution have been prepared via the couplingroute of w/o emulsion with methyl oxalate homogenous precipitation.The principle of the coupling route of emulsion with homogenousprecipitation to attain spherical shape particle was analyzed. At the sametime, in order to attain ideal powder, considering the effect factors ofemulsion and homogenous precipitation, the author selected BET of ZrO2precursor powders as review target of orthogonal test, and usedorthogonal test to optimize preparation process. The optimum technicalconditions were obtained as follows: The volume percentage of waterphase in emulsion is 20; the mol ratio of methyl oxalate and Zr (NO3)4 is2:1; the reaction temperature is 50℃; the reaction time is 3h; and G is 7.(2)The phase volume fractions of nano-powders were calculated.Tetragonal phase is 0.78 and cubic phase 0.22. Forthermore, the phasecrystal lattice constants were calculated, that is ac is 0.514357nm, at is0.51067nm, ct is 0.51799nm and ct/at is 1.01433. At the same time, inorder to explain in theory the prepared powders possessing excellentspherical shape, the theoretical density was calculated.(3)Nanoscale zirconia powders, which are suitable for plasmaspraying, were reconstituted by spraying and drying before the plasmaspraying. The properties of the powder were reviewed. Basing onexploring experiments, the effect factors and levels of plasma sprayingwere confirmed and tetragonal table was planed. According to thetechnical parameters of tetragonal table, nanostructured zirconia coatingswere deposited by atmosphere plasma spraying. The author selectedthermal shock life of ZrO2 coating as review target of orthogonal test, andused orthogonal test to optimize technical parameters. The optimumtechnical conditions were obtained as follows: Power is 45kw, sprayingdistance is 120mm, the ratio of powder feeding is 25g/min, the flowvelocity of argon is 40slpm and current is 580A. In addition, the effect ofspraying technical parameters on microstructure and thermal shockproperty of ZrO2 coatings was systematically studied.(4)The phase volume fractions of nanostructured coating werecalculated. Tetragonal phase is 0.91 and cubic phase is 0.09. In addition, the phase crystal lattice constants were obtained by calculation: act is0.51079nm, acc is 0.51460nm, cct is 0.51762nm and cct/act is 1.01337.Through comparing these values of nano-powder and nanostructuredcoating, the principle of phase transformation during the process ofplasma spraying was studied. Y2O3 theoretic contents of nano-powder andnanostructured coating were calculated according to the phase crystallattice constants, and the phase composition of nano-powder andnanostructured coating were confirmed by comparing Y2O3 theoreticcontent and real content.(5)On the base of successfully gaining nanostructured zirconiacoatings via optimize spraying technical parameters, the coatings weresealed holes or heat-treated in vacuum. The thermal shock property andhigh temperature oxidation property of as-coatings were examinedthrough analytical comparison. Experimental results indicate that sealinghole or heat-treating in vacuum go against thermal shock life and hightemperature oxidation property of the coating. What's more, the phasestructure and surface configuration of the coating were analyzed, and thethermal shock failure principle and oxidation principle of coating wereexplained basing on experiment results. At last, thermal diffusivities ofnanostructured zirconia coatings and coatings after treating weremeasured and analyzed contrastively, and thermal diffuseness principlewas analyzed.(6)Adopting the optimize spraying technical parameters, S1 coatingand B1 coating were prepared by plasma spraying with two kinds ofreconstituting and drying powders. Microhardness, adhesion strength andresist crack spread force of as-spraying coatings were studiedcontrastively, and results indicate that microhardnesses of S1 coating andB1 coating go with Weibull distribution, and microhardness, adhesionstrength and resist crack spread force of S1 coating excel those of B1coating. Cross-section microhardnesses of two coatings excel theirsurface microhardnesses.(7)The wear properties of S1 coating and B1 coating were examined.The experimental results show that the frictional coefficients of twocoatings reduce with load rising, the frictional coefficient of S1 coating against stainless steel in low load condition is lower than that of B1coating against stainless steel. But in high load condition, the frictionalcoefficients against stainless steel of two coatings tend to accord. Duringfriction process, wear properties of S1 coating excel that of B1 coating.At the same time, the wear principles of two coatings against stainlesssteel in different loads were studied.
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