پاشش پلاسمايي و ارزيابي تربيولوژيكي پوشش كامپوزيتي نانو ساختار Cr2O3-Ag

چكيده انگليسي :

101 Plasma Spraying and Tribological Evaluation of Cr2O3 Ag Nanostructured Composite Coating Ehsan Sadri e sadri@ma iut ac ir Date of Submission 20 5 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 8415683111 Iran Degree M Sc Language FarsiSupervisor Fakhreddin Ashrafizadeh ashrafif@cc iut ac irAbstractMost of the low temperature solid lubricants have low wear resistance and high fluctuating friction coefficient athigh temperatures and in addition high temperature solid lubricants create wear debris at low temperatures Thus there is a need for such lubricant coatings that can be used at a wide range of temperatures with sufficient wearresistance Therefore in this research nanostructured composite coatings consisting of a hard Cr2O3 ceramicmatrix with silver lubricant particles were produced by atmospheric plasma spray APS process and theirproperties were evaluated First for the formation of ceramic matrix nanostructured coatings Cr2O3 nano particleswere produced by 30 hr mechanical milling in attrition mill Then a well dispersed and stable aqueous dispersionincluding Cr2O3 Ag nanoparticles with volume percentage of Ag 0 2 5 and 10 suitable for spray drying wasproduced by horizontal mill with zirconia balls The suspension was agglomerated to a nanostructured compositepowder particle size 30 80 m by centrifugal disk atomizer spray dryer Finally Cr2O3 Ag nanostructuredcomposite coatings were produced on a NiAl bond coat on steel substrate by atmospheric plasma sprayingtechnique APS For development of bimodal structure coatings consist of both molten particles microstructure and semi molten particles nanostructure in APS the plasma spray condition of nanostructured coatings was soadjusted that part of nanoparticles were not melted in the plasma jet The characterization of coatings performedusing x ray diffraction scanning electron microscope energy dispersive spectroscopy microhardness indentationand surface profilemeter The results showed that in spite of growth of crystallite size and the decrease of internallattice strain of nanoparticles in nanostructured coatings the crystallite size of these coatings was still lower andtheir internal lattice strain was higher than conventional coatings Furthermore due to existence of semi moltennanostructured particles in the microstructure of coatings microhardness and fracture toughness of nanostructuredcoatings were lower and higher than conventional coatings respectively The tribological assessment of thecoatings was so designed to simulate the working condition of high temperature moveable devices in aerospaceapplication For this reason the tribological tests were done by a pin on disc wear tester under the condition of 10N load linear velocity of 0 3 m s temperature of 25 300 and 500 C and WC ball counterface At all three testtemperatures neither weight loss nor a characteristic wear mechanism was observed on wear tracks The resultsindicated high wear resistance of Cr2O3 matrix plasma sprayed coatings Moreover both two evaluated factors inthis research the nanostructure processing and the presence of Ag lubricant particles lead to decrease in frictioncoefficient by reducing the brittleness of Cr2O3 coating and formation of Ag thin film on contact surface respectively in all three test temperatures Among the evaluated coatings Cr2O3 5 Ag nanostructured coating hadthe best frictional behavior at 25 300 500 C temperatures KeywordsChromium oxide Silver Friction behavior Solid lubricant Coatings Plasma spray Nanostructure

صدري، احسان

پاشش پلاسمايي و ارزيابي تربيولوژيكي پوشش كامپوزيتي نانو ساختار Cr2O3-Ag

اكسيد كروم , نقره , خواص اصطكاكي , روانكار جامد