بررسي و مشخصه يابي پوشش هاي پاشش حرارتي اسپينل Al2O3-MgO همراه با ذرات تقويت كننده ZrO2

چكيده انگليسي :

Charactrisation of Thermally Sprayed Coating of Al2O3 MgO Spinel Doped with ZrO2 Mehdi Zarei mehdi zarei@ma iut ac ir Date of Submission 2011 04 18 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor M Salehi A MonshiAbstractThick thermal plasma coatings of hard refractory oxides have numerous applications for example in the field ofcommon wear materials Spinel are double oxides that crystallize in the cubic crystallographic system The spinelMgAl2O4 has many interesting properties including a high melting point a low thermal expansion coefficient lowdielectric losses and excellent resistance to acid and alkali but its poor mechanical properties at room temperaturelimit its field of applications A well known method for the enhancement of the mechanical properties of ceramics isthe dispersion of micrometric ZrO2 particles as a discrete second phase In the present study Spinel Zirconiacomposite coating on steel substrates has been studied by utilizing advanced plasma spray process In the plasmaspraying process the thermal energy of an electric arc together with a plasma forming gas either nitrogen or argon is utilized in the melting and projecting of the deposit material at high velocities onto a substrate Plasma spraying isa rapid heating cooling and solidification process that often results in the formation of deposits characterised by acoarse grain structure significant porosity and a lamellar morphology Three kind powders namely Spinel Spinel MgO and Spinel ZrO2 are produced In this regard critical plasma parameters were studied by various samples inorder to obtain the best parameters for the coating To assess the coatings conducted phase analysis was carried outby X ray diffraction XRD and microstructure study was conducted by scanning electron microscopy SEM Themicroscopic observations and measurement were carried out by SEM and image analyser software respectively tostudy the porosities The results are indicative of low porosity in the coating structure and relatively suitabledistribution of doping material in Spinel matrix Moreover they show that during coating no phase variationdevelops in the structure which indicates the stability of coatings In order to evaluate the coating quality a hardnessprofile from the surface to the depth of each coating was obtained by micro hardness measurement The obtainedresults showed that by adding Ziconia to Spinel matrix causes a huge increase in the coating hardness Theroughness and adhesion strength of the coatings were also measured Adhesion is a very important factordetermining the life of coated parts The coatings must be properly bonded to the substrates Adhesion depends onsubstrate preparation The results showed that Spinel Zircona coating have the best roughness and adhesion strength Wear is closely related to the adhesion of the coating to the substrate because if the adhesion is poor the coatingswill wear off quite rapidly and the extent of deterioration of the substrates by environmental factors will be greatlyaccelerated A study of wear of the obtained coatings was carried out on Pin on Disk Meanwhile curves for frictioncoefficient and a change in the volume of wear for the coatings were drawn for the evaluation of tribologicalbehavior The studies of mechanisms affecting the wear of these coatings were also carried out The results showSpinel ZrO2 has the highest wear resistance and Spinel MgO has the lowest friction coefficient Key words Spinel Thermal spray Composite Zirconia Atmospheric plasma spray

زارعي، مهدي

بررسي و مشخصه يابي پوشش هاي پاشش حرارتي اسپينل Al2O3-MgO همراه با ذرات تقويت كننده ZrO2

پاشش پلاسمايي , كامپوزيت , زير كونيا , سايش