Charactrisation of Thermally Sprayed Coating of Al 2 O 3 -MgO Spinel Doped with ZrO 2 Thick thermal plasma coatings of hard refractory oxides have numerous applications, for example in the field of common wear materials. Spinel are double oxides that crystallize in the cubic crystallographic system. The spinel MgAl 2 O 4 has many interesting properties, including a high melting point, a low thermal expansion coefficient, low dielectric losses, and excellent resistance to acid and alkali, but its poor mechanical properties at room temperature limit its field of applications. A well-known method for the enhancement of the mechanical properties of ceramics is the dispersion of micrometric ZrO 2 particles as a discrete second phase. In the present study, Spinel-Zirconia composite coating on steel substrates has been studied by utilizing advanced plasma spray process. In the plasma spraying 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 is a rapid heating, cooling and solidification process that often results in the formation of deposits characterised by a coarse grain structure, significant porosity and a lamellar morphology. Three kind powders namely Spinel, Spinel-MgO and Spinel-ZrO 2 , are produced. In this regard, critical plasma parameters were studied by various samples in order to obtain the best parameters for the coating. To assess the coatings conducted, phase analysis was carried out by X-ray diffraction (XRD), and microstructure study was conducted by scanning electron microscopy (SEM). The microscopic observations and measurement were carried out by SEM and image analyser software respectively to study the porosities. The results are indicative of low porosity in the coating structure and relatively suitable distribution of doping material in Spinel matrix. Moreover, they show that during coating, no phase variation develops in the structure which indicates the stability of coatings. In order to evaluate the coating quality, a hardness profile from the surface to the depth of each coating was obtained by micro-hardness measurement. The obtained results showed that by adding Ziconia to Spinel matrix causes a huge increase in the coating hardness. The roughness and adhesion strength of the coatings were also measured. Adhesion is a very important factor determining the life of coated parts. The coatings must be properly bonded to the substrates. Adhesion depends on substrate preparation. The results showed that Spinel-Zircona coating have the best roughness and adhesion strength. Wear is closely related to
