الفهرس 
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Abstract
Metal surfaces are continuously exposing to many applications. That makes them suffering from the mechanical stress during service. It was necessary to improve the mechanical properties of these surfaces to bear these applications. These metals can be used in various industries such as engines and engine combustion chambers. The use of thermal barrier coatings TBCs as a coating for the surfaces of the combustion chambers reduces the heat loss that leads to increase the heat inside the combustion chambers which make complete combustion of fuel reduces pollution rates and increases the efficiency of the engine. Atmospheric Plasma spraying (APS) and laser coating (cladding) (LC) techniques had been used for obtaining coating of Nickel – 5%Aluminum as a bond coat followed by separated series of thermal barrier coatings TBCs: (i) Magnesia-Stabilized Zirconium Oxide (ZrO2 - 24% MgO), (ii) Calcia-Stabilized Zirconium Oxide (ZrO2-5%CaO) and mixture from both materials as a top coat on the surfaces of Stainless Steel 304 (S.S. 304) specimens. The APS coating was done by using a PLASMA-TECHNIK AG Switzerland and F4-MB (machine-plasma torch). On the other hand, CW 1.06 μm Nd-YAG diode pumped laser with maximum output power 2200W has been used for LC. The microstructure and mechanical properties of both coatings were investigated by (i) scanning electron microscopy, (ii) X-ray diffraction, (iii) wear resistance (only for APS technique) and (iv) microhardness tests. The results showed the preference of the LC technique over the APS technique for coating. In other words, the internal microstructure showed more dense and homogeneity of LC than APS coatings, where the LC process involved complete melting of the coating powder in the laser generated melt pool followed by rapid solidification. Furthermore, the maximum hardness values of the coating layer were 1637 Hv compared with only 340 Hv for the APS coating.