Influences Of Thermal Spraying Parameters On Splat Morphology

Thermal barrier coatings(TBCs),which are primarily used in key parts of gas turbines and other high-working-temperature engines,can improve the working efficency of engines by increasing the stable working temperature of engine key parts to about 200 K higher by providing protecting layer on the surface of the hotzone parts.The thermal performance of TBCs is influenced by several factors,like the thickness,the surface morphology,the coating microstructure and composition of TBCs.These characteristic parameters of the thermal barrier coating are primarily determined during manufacture process.So,it is important to study the influences of the process parameters to guide the manufacture and to improve the performence of TBCs.In this thesis,firstly several important key process parameters,such as impact velocity and initial temperature of droplet,intital temperature of substrate,and thermal contact resistance between droplet and substrate,are studied to investigate their influences on splat morphology together with solidification rate.Secondly,based on the studies have done by other researchers,analysis is carried for splat morphology and the corresponding influence parameters by both experimental and simulation.Meanwhile,a modification is conducted on the model of solidification analysis,which was proposed by Rajeev Dhiman et al.,by considering the overheat of YSZ droplets into the model.Finally,several transition curves and transition surfaces are achieved by the study of the analytical model results and simulations of different spray parameters.Comparisons between the results of simulation and analytical studies are conducted.The models are used to study the influence of the spray parameters on the splat morphology which would give guidence to practical coating manufacture process.The results show that there are transition curves or transition surfaces,through which the morphology of YSZ splats can change from break-up to disk-shape,finally to splashing.By changing the processing parameters,such as adjusting the impact velocity,overheat of YSZ droplet,initial temperature of substrate and thermal contact resistance between droplet and substrate,the morphology of the splats could be controlled.