MONTE CARLO SIMULATION AND CHARACTERISATION OF PHASE FORMATION IN PT-BASED ALLOY THIN FILMS

• Main Author: Harris, Richard Anthony
• Other Authors: Prof HC Swart
• Format: Others
• Language: en-uk
• Published: University of the Free State 2011
• Subjects: Physics
• Online Access: http://etd.uovs.ac.za//theses/available/etd-03232011-085048/restricted/

From Icarusâ mythical flight to escape Crete to manned space flight to the moon, mankindâs dream to fly has impacted this world immensely. Technological advancements made in metallurgy and alloy development has played a huge role in realizing this dream. Developing materials and superalloys with higher melting temperatures and greater strength has allowed for the design of the modern turbine jet engines. Economical and (today more than ever) environmental concerns continue to provide 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 pressure turbine 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 of civil aircraft will have turbine entry temperatures (TET) that will exceed 1800 K at take-off. Increased power and improved fuel consumption remains a continuing demand in modern aero-gas turbine engines as this result in an increase in TET. One strategy to achieve this goal is by coating the turbine blades with a thin film composed of alloy material. These films can be engineered to have specific heatresistant, oxidation-resistant properties. Two coating techniques that show promise in achieving these goals are pulsed laser ablation (PLD) and electron beam physical vapour deposition (EB-PVD). These techniques are investigated in this study in particular of platinum-aluminium alloys. The appearances of droplets on the thin film surface that arise due to the pulsed laser ablation technique itself are investigated. A suitable technique to minimize the appearance of these droplets by using ambient gas and ambient gas pressure is discussed. The stoichiometric transfer of material from the target to a substrate was also investigated. A lot of insight into engineering these types of coatings can be gained from computer simulations of the processes governing the diffusion of the individual elements making up the superalloy. Therefore, in this study, a chemical potential Monte Carlo (CPMC) model was developed to simulate diffusion of platinum-aluminium binary alloys. The change in microstructure during diffusion as the pure elements diffuse into each other to form an alloy with a specific composition is investigated. In the model, data structures, search algorithms and a random number generator were developed and employed in an object-orientated code to simulate the diffusion of binary metals during annealing. Several simulations were performed at different compositions. The results are compared to experimentallymeasured elemental maps of EB-PVD prepared thin film samples.