Investigation on Sustainable Refractory Systems for Investment Casting Manufacturing of Titanium Alloys

Lead Research Organisation: University of Birmingham
Department Name: Chemical Engineering

Abstract

The light-weight titanium alloys are promising for high temperature application owing to their low density, high strength and excellent corrosion resistance. However, the difficulty of casting titanium alloys arise from their reactivity with nitrogen and oxygen even when in low concentrations in standard vacuum furnaces. Melting and casting needs to be done in furnaces with very high vacuum or inert gas to avoid dissolving oxygen and nitrogen in the molten titanium. In addition to gaseous elements and species, the major challenge for the investment casting foundry is the high reactivity between molten titanium and silica based ceramic moulds. It has been found that molten titanium alloys will react with silica, freeing oxygen which dissolves into solution and forms an embrittled surface layer upon cooling, commonly referred as alpha case. Increasingly inert refractory systems are being devised to accommodate these requirements and this study would bring understanding to a proposed cost effective route to minimizing alpha case formation. Traditionally the material selection is based on free energy of formation of the oxides from Ellingham diagrams. Although yttria appeared to be the best candidate for replacing silica as a face-coat material, limiting factors on the use of this oxide are that yttria sols are exceptionally unstable and very expensive. Pure oxides such as alumina and zirconia still have significant interaction with the alloy which need to be removed by chemical milling. The proposed investigation will lead to a sustainable non-silica based multi-mineralic ceramic system with reduction in metal/ceramic interaction for casting reactive alloy. In order to support this study, tools capable of handling multicomponent, multi-phase (i.e. multi mineral) systems will also be developed. These models allow the calculation of realistic activities of alloy components and multiple oxides. All the necessary information can be obtained from Gibbs energies, as used in the Calphad approach. While the Ellingham diagram covers formation of pure oxides, from pure elements and oxygen, the Calphad method will go beyond this and treat non-ideal systems. This information is invaluable when rationalising the reactivity of new slurry and shell systems and crucial in tailoring shell systems for specific alloys. Studying the colloidal properties of selected systems will give fundamental understanding on the stability of current and future slurry systems, which is crucial for the investment casting community.

Planned Impact

There is potential within this project to benefit all companies in the supply chain involved in the production or use of investment cast advanced alloy components. This is a significant number of companies from large multi-nationals to SMEs and thus there is a potential to influence the employment of many. Of these companies, alloy manufacturers, foundries, ceramic powder suppliers and end users are notable beneficiaries.

This research opens up the possibility of using multi-component ceramic oxide systems as engineered solutions based on the level of interaction with real multi-element alloys. This is an important step in allowing the exploitation of previously difficult alloys such as titanium alloy due to the amount of interaction between molten metal and ceramic containment. Suppliers will benefit from the increase demand for raw materials based on the new development. The ceramic mould manufacturing community will benefit from the ability to produce inert moulds which perform successfully in casting titanium alloys with significant reduction in material cost. Foundries will benefit from ability to cast existing and possibly new alloys at higher temperatures. Users of castings will potentially benefit from better performance and efficiency of the future alloy components which could give enormous benefit. Also the techniques developed here will be applicable to the casting of more highly alloyed metals for the automotive, chemical and medical industries. Greater longevity of components with light weight in service is economically sound for the aviation industry and therefore the people it serves. It could also be used in the engine so giving fuel economy which further contributes to the future of aviation as an effective transportation system. For the foreseeable future there is little real alternative to the turbine engine for air transport we must make them as efficient as possible to prolong the fuel supply. In the broader context the process also reduces the overall consumption of rare earth materials which are categorised as critical materials and are in short supply.

Excellent links are already in place with the British Investment Casting Trade Association (BICTA) now part of the Cast Metals Federation (CMF), European Investment Casting Federation (EICF) and American Investment Casting Institute (ICI). This will allow effective reporting of the project results.

Publications

10 25 50
 
Description Properties of single oxide materials such as alumina, yttria and zirconia were investigated as facecoat material to build the investment casting shell for the casting of titanium alloys as baseline material. The facecoat layer has potential to undergo extensive reaction with the molten metal, degrading casting structure and properties. Novel mixed oxide systems are developed in comparison with those baseline materials. These systems show great promise as in some cases they are almost as resistant to dissolution by titanium as the single oxide systems and have the advantage of being significantly lower cost. Initial thermodynamic calculations have shown that the relative stability of the studied single oxide systems can be predicted from readily available thermodynamic data. A model adapting the Numerical-Kampmann-Wagner approach is being developed to simulate multiple chemical reactions occurring simultaneously. To obtain supporting experimental kinetic data on rates of reaction, we have developed a new experimental system based on the encapsulation of titanium foils in the ceramic mould formulations prior to heat treatment and subsequent chemical analysis across the interface between the metal and mould. A new high-temperature furnace with the required control of temperature and atmosphere has been purchased and commissioned. Experimental design calculations that showed the heating cycle needs to be controlled and the sample quenched from temperature rapidly to allow the observations required to be made were addressed by integrating a sample handling device. Preliminary experiments were completed to determine the correct experimental operating parameters - reaction temperatures, times and cooling rate) and samples characterised. Further experiments will be progressed through ongoing use by a project aligned research student.
Exploitation Route The work conducted to date indicates that there will be a significant opportunity here for the development of a cost-effective and stable process for the investment casting titanium alloys. The programme continues with this in view and exploitation routes will be developed over the next seven months.
Sectors Aerospace

Defence and Marine

Manufacturing

including Industrial Biotechology

Transport

 
Description Advanced Research into Crystallographic Anisotropy & Nucleation Effects in single crystals (ARCANE)
Amount £4,496,423 (GBP)
Funding ID EP/X025454/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 05/2023 
End 05/2028
 
Description School Funding
Amount £75,000 (GBP)
Organisation University of Birmingham 
Sector Academic/University
Country United Kingdom
Start 03/2019 
End 02/2022
 
Title Quench interrupted high temperature controlled atmosphere furnace 
Description The contact time between molten titanium alloys and the mould materials in to which they are cast are typically very short, although reaction may continue as a casting coold after it has solidified. In order to research the inertness of ceramic materials in contact with molten metal whilst avoiding post-solidification effects a horizontal high temperature furnace apparatus capable of operating at temperature up to 1750 C under a controlled inert atmosphere has been developed. Using this it is possible to rapidly heat small samples of metal contained within a container of the ceramic material, hold it in the molten state for a defined period of time and then rapidly solidify and cool it to a temperature where further reactions are suppressed. In this manner high quality data can be obtained for use in estimation of thermodynamic quantities. 
Type Of Material Improvements to research infrastructure 
Year Produced 2021 
Provided To Others? Yes  
Impact Data generated from the apparatus is under assessment and will be published in due course. The apparatus is now also being used to support the following project: MR/T019174/1 UKRI Future Leaders Fellowship "Bcc-superalloys: Engineering Resilience to Extreme Environments" PI A Knowles https://gtr.ukri.org/projects?ref=MR%2FT019174%2F1 
 
Title Reaction model for mixed oxide systems 
Description A numerical method to model multiple oxides interacting with multi component liquids using realistic thermodynamic data was developed. It was applied to demonstrate that the right combinations of three oxides stabilises a single oxide that would otherwise be unstable on contact with molten titanium. The monotonically declining reaction path of a single oxide system is altered to a non-monotonic reaction path controlled by the mutual interactions of the three oxides. This approach will enable merit indices to be developed for multiple oxide systems and their formulation for specific alloys and may be applied to other alloy and ceramic systems. 
Type Of Material Computer model/algorithm 
Year Produced 2023 
Provided To Others? No  
Impact The model will be applied as a foundational tool within the EPSRC Prosperity Partnership grant reference EP/X025454/1. 
 
Description Rolls-Royce plc 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution Working on materials of interest to the company which they have supplied to be cast.
Collaborator Contribution Provision of raw materials
Impact Wilson P. J.; Blackburn S.; Greenwood R. W.; et al. "The role of zircon particle size distribution, surface area and contamination on the properties of silica-zircon ceramic materials "31 (9), 1849-1855, DOI: 10.1016/j.jeurceramsoc.2011.03.005, 2011 Wilson P. J.; Blackburn S.; Greenwood R. W.; et al."The effect of alumina contamination from the ball-milling of fused silica on the high temperature properties of injection moulded silica ceramic components" Journal of the European Ceramic Society, 31(6) , 977-C. Yuan, X. Cheng, S. Blackburn and P. Withey " Influence of polymer content and sintering temperature on yittria facecoat moulds for TiAl casting" Journal European Ceramic Society, in Press 2012. C. Yuan, S. Blackburn and P. Withey "Effect of the incorporation of zirconia layer upon the physical and mechanical properties of investment casting shell, J. Mat. Sci. Tech., 29, 1, 30-35, DOI: 10.1179/1743284712Y.0000000076, 2013 X. Cheng, C. Yuan , S. Blackburn, P. A.Withey., "Influence of Al2O3 concentration in yttria based face coats for investment casting Ti-45Al-2Mn-2Nb-0.2TiB alloy", Journal of Materials technology, DOI: 10.1179/1743284713Y.0000000467, 2014. X. Cheng, C. Yuan, S. Blackburn and P. A. Withey, "A comparisons of the chemical inertness of two Y2O3-Al2O3-ZrO2 and Y2O3-Al2O3 face coat materials through sessile drop and investment casting methods" Metall. Mater. Trans. A 45 (2014), pp3116-3124 DOI: 10.1007/s11661-014-2261-x X. Cheng, C. Yuan, S. Blackburn and P. A. Withey, "'The study of the influence of binder systems in an Y2O3-ZrO2 facecoat material on the investment casting slurries and shells properties" J. Eur.Ceram. Soc. 34 (2014) pp3061-3068 DOI: 10.1016/j.jeurceramsoc.2014.03.005 X. Cheng, C. Yuan, S. Blackburn and P. A. Withey, "The influence of ZrO2 concentration in an yttria based face coat for investment casting a Ti-45Al-2Mn-2Nb-0.2TiB alloy using sessile drop method" Metall. Mater. Trans. A, 46 (2015) pp1328-1336; DOI: 10.1007/s11661-014-2724-0 C. Yuan, M Riley and Blackburn, Development of Alumina Core System towards Investment Casting Reactive Alloy, being modified for Ceramics International (CERI-D-15-01295) Lee K., Blackburn S. and Welch, S.T., Adhesion tension force between mould and pattern wax in investment castings, Journal of Materials Processing Technology 225 (2015) pp 369-374. Standring T., Blackburn S. and Wilson P., Investigation into paraffin wax and ethylene vinyl acetate blends for use as a carrier vehicle in ceramic injection moulding, Polymer-Plastics Technology and Engineering, 55, (2016), pp802-817 Blackburn, S., Lee, K. & Welch, S.T. , A more representative mechanical testing of green state investment casting shell, Ceramics International, 2016.