Monte Carlo simulation and characterisation of phase formation in Pt-based alloy thin films

[摘要] English: From Icarus' mythical flight to escape Crete to manned space flight to the moon,mankind's dream to fly has impacted this world immensely. Technologicaladvancements made in metallurgy and alloy development has played a huge role inrealizing this dream. Developing materials and superalloys with higher meltingtemperatures and greater strength has allowed for the design of the modern turbine jetengines. Economical and (today more than ever) environmental concerns continue toprovide ample motivation for operating the engines at ever increasing temperatures,thereby improving the thermodynamic efficiency and reducing pollutant emissions.One of the most aggressive man made environments is that of the high pressureturbine section of a modern gas turbine engine. During operation, after combustion,highly oxidizing gas enters the turbine. This happens at temperatures exceeding 200°C above the melting point of the superalloy turbine blade. Newer generations ofcivil aircraft will have turbine entry temperatures (TET) that will exceed 1800 K attake-off. Increased power and improved fuel consumption remains a continuingdemand in modern aero-gas turbine engines as this result in an increase in TET. Onestrategy to achieve this goal is by coating the turbine blades with a thin filmcomposed of alloy material. These films can be engineered to have specific heatresistant,oxidation-resistant properties. Two coating techniques that show promise inachieving these goals are pulsed laser ablation (PLD) and electron beam physicalvapour deposition (EB-PVD). These techniques are investigated in this study inparticular of platinum-aluminium alloys. The appearances of droplets on the thin filmsurface that arise due to the pulsed laser ablation technique itself are investigated. Asuitable technique to minimize the appearance of these droplets by using ambient gasand ambient gas pressure is discussed. The stoichiometric transfer of material fromthe target to a substrate was also investigated. A lot of insight into engineering thesetypes of coatings can be gained from computer simulations of the processes governingthe diffusion of the individual elements making up the superalloy. Therefore, in thisstudy, a chemical potential Monte Carlo (CPMC) model was developed to simulatediffusion of platinum-aluminium binary alloys. The change in microstructure duringdiffusion as the pure elements diffuse into each other to form an alloy with a specificcomposition is investigated. In the model, data structures, search algorithms and arandom number generator were developed and employed in an object-orientated code 6to simulate the diffusion of binary metals during annealing. Several simulations wereperformed at different compositions. The results are compared to experimentallymeasuredelemental maps of EB-PVD prepared thin film samples.

[发布机构] University of the Free State