In this context, Taguchi experimental design definitely offers an excellent tool for optimizing the total cost without compromising the performance output. In this work, this method has been adopted to investigate the influencing parameters like torch input power, molten particle velocity, stand-off distance, and powder feed rate on the adhesion strength of splat-substrate interface.2. Experimental Details2.1. Synthesis of Nanostructured Powders by Sol-Gel RouteThe nanostructured YSZ powders employed in this study were synthesized through sol-gel technique [22]. A water based solution of zirconium oxychloride and yttrium oxide was prepared in order to get 8mol% yttria stabilised zirconia (YSZ). Precursor materials were taken according to the proper stoichiometric, and an excess amount of nitric acid was added to the solution.
Final solution was homogenized by constant stirring at 100�C120��C temperature. After 5-6h of constant stirring and heating, the translucent solution (with little amount of citric acid) was heated on a hot plate (at about 200 �� 250��C) until it turned into a black viscous gel, which on continued heating burned due to a vigorous exothermic reaction. Black ashes obtained after combustion were treated at 350��C in air for 1h to eliminate the carbonaceous residues and calcined at 600��C for 2h resulting in YSZ powder.XRD pattern of synthesized powder, as shown in Figure 2, reveals that the powder is composed of tetragonal zirconia phase (t-ZrO2). TEM image shows that the grain sizes of nanoparticles are between 20 and 30nm.
Figure 2TEM micrograph and XRD pattern of as-synthesized YSZ particles.2.2. Coating MaterialThe synthesized powders were then reconstituted to form micrometer-size agglomerates (40�C70��m) that are large enough to be used as commercial powder feeders. The reconstitution process is done through spray drying [23]. The agglomeration of nano-YSZ was carried out in a Buchi B-290 research model spray dryer. A suspension of the nanoparticles was prepared using 300mL of deionized H2O, 7g of polyethylene glycol (PEG), and 70g of nano-YSZ. The polymeric binder, PEG, in solution uses Vander Waals forces to bind the nanoparticles together and forms spherical droplets during atomization. The nano-YSZ slurry was attained via vigorous magnetic stirring for 30min and heating to 300K.
The preheating of the solution assists in the slurry formation and in lowering the enthalpy Dacomitinib needed during the drying process for moisture removal. The final product is a feedstock of size ~50��m spherical agglomerates containing nanograins of size 20�C30nm as shown in Figure 3.Figure 3FESEM micrograph of spray dried YSZ particles.3. Materials and MethodsThe most important step in plasma spray coating technique is the preparation of the substrate surface in order to increase the mechanical anchoring between the substrate and the coating. The surface of the substrate was subjected to grit blasting to make the surface rough.