SAMULET Project 1 - High Efficiency Turbomachinery
Lead Research Organisation:
University of Birmingham
Department Name: Metallurgy and Materials
Abstract
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Organisations
Publications
Yuan C
(2015)
Investment casting of Ti-46Al-8Nb-1B alloy using moulds with CaO-stabilized zirconia face coat at various mould pre-heat temperatures
in Ceramics International
| Description | The aero engine runs more efficiently at higher temperatures but of course increasing the operating temperatures cause problems with component life due to interaction with the operating environment. The hot, high pressure air entering the turbine causes large oxidative stress on the blades and measures must be taken to prevent damage and increase the lifetime of the blades. The addition of reactive rare earth metals such as yttrium and lanthanum to the blade alloy have a marked effect on the lifetime of the alloy in use by increasing its resistance to oxidation and on improving adhesion of the thermal barrier coating. High rates of loss with varying solifification times in a single component preclude attaining a relatively narrow range of acceptable dopant levels. Therefore less reactive mould and core materials are required. As Y and La are expensive overdosing is economically and environmentally unsound. Thus the aim of this project was to develop refractory systems which inhibit the element loss during casting and evaluate the process for reaction products and cast product uniformity. Initial experiments were conducted with conventional refractory materials to establish baseline data for rates of loss and reaction pathways. This work also enabled the analytical methods to be developed for characterising the interactions. It was found that the dynamic wetting behaviour of the metal in contact with the refractory could be correlated with the loss off Y and La from the alloy allowing rapid evaluation of new refractory compositions. Methods for estimating the doping element distribution in the metal and ceramic were developed using electron microscopy. Initial results confirm those of previous workers where less than 10% of added yttrium was retained in the single crystal alloy when cast in a standard shell. Losses could be compensated by over doping the alloy but non-uniform loss renders some sections over doped with detrimental effect on alloy properties. It was shown that the rate of loss depends on the cast environment as well as the selected refractory. Standard free energies of formation of various oxide materials were examined, allowing formulations of new shell/core materials to be developed. The data indicated limited options in pure oxides and new formulations were evaluated in the programme containing mixed oxide materials. Through application of background IP the range of candidate materials was expanded considerably. The results were very encouraging showing significant improvements in retention and uniformity. It has been demonstrated that the system made of silica and alumina, formulated to form mullite (3Al2O3 - 2SiO5) during sintering, showed similar behaviour to the current standard refractory system. A system combining silica mixed with low free energy oxides generated intermediate phases during sintering that proved to be more stable than a single oxide system of nominally lower free energy. Thus the ranking of the investigated formulations did not always follow the expected trend relative to free energy of formation of the oxides and hence there is a need for further investigation to develop detailed understanding of the kinetics and phase relationships from the data gathered in the mixed oxides and single oxide systems. This research developed understanding of ceramic systems which allow cost effective introduction of oxidation resistant alloys helping to maintain and advance UK competitiveness. A more uniform product through greater control of composition will lead to greater reliability. |
| Exploitation Route | The principal research partner (Rolls-Royce) required development of more inert moulds for casting of rare earth element doped nickel based superalloys. The scientific understandings established as a result of the project are being applied by them in an industrially sponsored follow on project to develop novel refractory material systems for casting of highly reactive alloys. Since completion the research has been translated to innovation in ceramic mould materials for net shape casting of gamma titanium aluminide alloy low pressure turbine blades for civil aeroengines. This has led to a number of publications in high quality journals, in which the techniques developed and reported findings are of use to others working in the field. |
| Sectors | Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology |
| Description | The project has resulted in a new design shell facecoat which is being adopted for the Rolls-Royce Trent 1000 aero-engine. If the technology proves successful then it will be adopted on all future Rolls-Royce engines. |
| First Year Of Impact | 2014 |
| Sector | Aerospace, Defence and Marine |
| Impact Types | Economic |
| Description | Rolls-Royce Plc |
| Amount | £60,000 (GBP) |
| Organisation | Rolls Royce Group Plc |
| Sector | Private |
| Country | United Kingdom |
| Start | 03/2012 |
| End | 09/2012 |