Modelling reactions between Ti-alloys and ceramic shells in turbine component castings

Future jet engines will have to be lighter and more fuel efficient. A major contribution to this will come from creating lighter rotating parts, which are still being able to endure extremely high temperatures. Light weight Titanium alloys are therefore widely regarded as extremely interesting materials in this context. Turbine blades are the jet engine component that would benefit most from using Titanium alloys, and indeed Titanium is already use here to a some extent. These components are commonly cast, as an efficient way to produce complex geometries is needed. This involved pouring liquid Titanium alloy into a ceramic shell, followed by cooling until the metal solidifies. One of the main challenges of this process is the high reactivity of Titanium alloys. This damages the shell and creates unwanted by-products, such as non-metallic particles, which ending up in the finished casting. Although reactivity differs between different alloys, all Titanium alloys show a strong tendency to be reactive. The strategy to overcome this limitation is developing new ceramic shell systems, which either inert or at least less reactive. Traditionally shell systems are developed using the Ellingham diagram and a lot of experience, which discards specific properties of the alloy that is cast.
This project aims to improve this approach, and will allow for shell systems to be tailored for specific alloys. To achieve this goal, a science based tool to engineer new, inert shell materials will be developed, based on thermodynamic properties of both, metallic alloy and ceramic shell. Calculations will involve modelling reactions between alloying elements and ceramic components, plus diffusion in the liquid alloy. The model will predict how the alloy reacts with the shell, and how long it will take until critical damage is done. Work is thus done at the exciting interface between metallic and ceramic systems.
The project will work in close collaboration with a team working on the experimental aspects of the problem and has strong links to a leading jet engine manufacturer.