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Greater Operating Temperature Alloy

Final Report Summary - GOTA (Greater Operating Temperature Alloy)

Executive Summary:
• Identify a titanium alloy (Ti+) capable of operating in intermediate compressor cases (ICC) at 50°C hotter than the incumbent alloy, Ti 6242S, which is limited to 450°C;
• Manufacture representative samples of rolled rings; gravity and centrifugal castings; sheet; weld wire; casting repair welds, and laser welds;
• Generate a mechanical test database relevant to the application, and make metallurgical examinations required to understand the behaviour quantified.
WP2: Existing Technologies. Swansea University wrote a literature review, and led a feasibility study of candidate titanium alloys. This concluded that Timetal 834 (Ti834) should be selected as the ‘Ti+’ alloy.
WP3: Wrought Products. TIMET supplied Ti 834 billets to Forgital, which conducted process trials, and then produced Ti 834 rings for testing and a report to document the processing.
WP4: Cast Products. TIMET supplied Ti 834 casting stock to Deritend, which produced gravity castings via subcontractor University of Birmingham; HIP’d and heat treated them; and wrote a report to document the processing. Deritend also produced centrifugal castings in Ti834 and benchmark alloy Ti6242S through its affiliate Doncasters SETTAS; HIP’d and heat treated them; and wrote a report to document the processing.
WP5: Welded Products. TIMET produced Ti 834 wire via subcontractor G&S Titanium. TIMET supplied sheets of Ti6242S ex-current production. TIMET conducted development scale manufacturing trials on the production of Ti 834 sheet and, after some difficulty, produced sample Ti 834 sheets and wrote a report to document the processing. TIMET used subcontractor University West, Trollhattan, to develop parameters for autogenous laser welding of Ti 834 sheet, and to produce welded samples for testing, and wrote a report.
TIMET produced a report to summarize the wrought , cast and welding processing.
WP6: Material Testing. Swansea University executed mechanical testing and metallurgical examination of the materials supplied by the consortium, using test conditions supplied by the Topic Manager. Test results on wrought Ti 834 samples were generally satisfactory, but tests on cast and welded Ti 834 revealed instability during thermal exposure, the cause of which was investigated. Results were reported.
The results of the work performed so far are mixed. It remains possible that an intercase of viable durability (at 50ºC hotter than existing materials currently used in ICC applications) may be fabricated using wrought and machined sections, possibly using solid state welding , or mechanical joints. However, the prospect of using cast and fusion welded Ti-834 alloy in this application currently appears to be challenging.

Results from the project are being disseminated through scientific and industrial channels.

Project Context and Objectives:

State of the art – Background

Intermediate compressor casings for turbofan engines are typically manufactured in titanium alloy Ti 6242. The maximum operating temperature of this alloy limits the operating temperature of the compressor, and hence limits one factor in the efficiency of the engine. It is desirable to identify a titanium alloy capable of operating in this application at a temperature 50°C higher than the limiting operating temperature of Ti 6242. Fabricated intermediate compressor casings require raw materials in various forms, so it is necessary to manufacture and test representative material samples in each condition, and to evaluate welds made by the proposed joining method.
The objectives of this project are to:
• Select a titanium alloy for long term service at temperatures 50°C higher than those currently applied to Ti-6242S
• Demonstrate that this titanium alloy is available in cast and wrought form, and, critically, can be welded
• Generate a database of mechanical properties for this titanium alloy in cast, wrought and welded forms
• Demonstrate that, after exposure to the proposed operating temperature, the mechanical properties for this titanium alloy in the various forms remain satisfactory for employment in Intermediate Compressor Casings (ICC).

Description of work
A consortium of TIMET UK Ltd.; Deritend International Ltd.; Forgital S.p.A; and Swansea University has collaborated to review the state of the art of high temperature titanium alloys, and selected Timetal 834 (Ti834) as the preferred candidate alloy. The consortium has converted Ti 834 provided by TIMET into various forms: gravity and centrifugal castings; rolled rings; sheet; and welding wire; and has developed procedures for autogenous laser welding the alloy. Samples of Ti 6242 were also provided for benchmark comparisons. The various materials were provided to Swansea University for mechanical testing appropriate to the target application. Materials were tested as-manufactured and after thermal exposure to mimic service at the intended temperature.
The results of the work performed so far are mixed. It remains possible that an intercase of viable durability (at 50ºC hotter than existing materials currently used in ICC applications) may be fabricated using wrought and machined sections, possibly using solid state welding , or mechanical joints. However, the prospect of using cast and fusion welded Ti-834 alloy in this application currently appears to be challenging.

a) Timeline & main milestones

Project start: 1st October 2012
The consortium has reviewed the prior art and selected Ti 834 as the preferred candidate alloy. Ti 834 billets have been converted into castings; rings; sheet and wire; and laser welds and TIG welds have been produced. Tensile; creep; Low cycle fatigue and fatigue crack growth tests have been carried out on the various materials forms before and after thermal exposure; and metallographic examination and analytical techniques used to understand the results.
Project end: 30th April 2016.

b) Environmental benefits
By increasing the engine operating temperature significant reductions in gashouse gas emisions can be achieved, while at the same time, due to improvements in combustion performance, specific fuel consumption can also be improved. At the technical maturity level of the current work it is impossible to quantify the benefits.

c) Dissemination / exploitation of results

The results generated in the GOTA project have been disseminated to the SAGE 3 collaborators via monthly reviews and with the Topic Manager, and detailed written reports. Also Swansea University has presented and published results:
• Proceedings of 14th World Conference on Titanium (San Diego 2015),
• HEXMAT Workshop, Oxford University, 2016,
• Acta Materialia, Vol 117, 15th September 2016, Pages 51-67,
• Further papers under discussion.

d) Communication

The GOTA consortium has held regular progress calls, initially weekly, then fortnightly later in the program. Face to face meetings have been held when necessary for detailed technical discussions. Monthly reviews have been held by webex / teleconference with the Topic Manager. The Principle Coordinator Contact visited the Topic Manager for a wrap up meeting.

Project Summary

Acronym: GOTA
Name of proposal: Greater Operating Temperature Alloy

Involved ITD: SAGE 3
Grant Agreement: 323378
Instrument: Clean Sky
Total Cost: Budget Euro 796,726
Clean Sky contribution: Maximum: Euro 488,252
Starting date: 1st October 2012
Ending date: 30th April 2016
Duration: 43 months (after formal extension granted)
Coordinator contact details:
PO Box 704,
B6 7UR
Project Officer: Jean-Francois Brouckaert

Participating members:
Deritend International Ltd.,
Forgital S.p.A.
Swansea University

Project Results:
The description of the S&T results is given in the attached PDF report 'GOTA Milestone 7'.

Potential Impact:
Impacts of the Work Programme
Completion of the GOTA Work Program has advanced the state of the art of creep resistant titanium alloys, by demonstrating that the appropriate product forms can be manufactured and by improving the understanding the durability of Timetal 834 in tests relevant to the ICC application at temperatures 50°C greater than the prior art titanium alloy, Ti-6242S. It has also demonstrated the capability of a European supply chain to produce these state of the art materials, and position the participants to win market share in their relevant businesses. Furthermore, the improved technology may improve the competitiveness of the Clean Sky Partners active in the design and construction of aircraft engines.
TIMET UK Ltd. has benefited by the introduction of a set of high performance products in a premium alloy, displacing a generically available alloy, which is anticipated to enable increased market share in the supply of materials for ICC construction. Also, these products may have applications elsewhere in aircraft – in the nacelle; engine pylon; or exhaust system, for example.
Forgital S.p.A. has benefited by extending the range of titanium alloys that it can offer to the market as rolled rings, and by introduction to the supply chain for ICCs. Currently, the majority of rolled rings for ICCs are produced in the USA
Doncasters SETTAS has benefited by extending the range of titanium alloys that it can offer to the market as castings, and by introduction to the supply chain for ICCs. Currently, the majority of castings for ICCs are manufactured in the USA
University of Swansea, has benefited by continuing to build its knowledge of materials; test methods; and applications in the field of structural titanium alloy applications. It has also added to its list of industrial collaborators, and increased its geographical reach.

Strategic impacts
The primary impact of completing the Work Program has been to demonstrate the feasibility of using Timetal 834 to make a ICC capable of enduring operation at 500ºC, to the standard required for TRL4. It was anticipated that this would be followed by the fabrication and test of a full scale ICC, and subsequent incorporation of this technology into future aircraft engine designs. This was expected to ease a constraint in engine design, and thereby enable a significant reduction in CO2, and NOx emissions from future aircraft engines, and also enable increased engine fuel efficiency. However, two factors, one internal to the project, and one external are currently making this a lower priority for engine manufacturers:
The internal factor is that the use of Timetal 834 appears to be viable using the wrought form, but that castings and welds in the alloy have a durability issue which has not been resolved. Hence use of this alloy in the application is feasible, but less economically attractive than Ti 6242S.
The external factor is that during the execution of GOTA, the emphasis in design of future engines has shifted away from conventional high-bypass ratio turbofans to geared turbofans, as pioneered by Pratt & Whitney, and also developed in Europe under the Clean Sky and ENOVAL ( programs. In conventional turbofans, the ICC temperature capability is a constraint, but in geared turbofan engines it is a consequence of the architecture that the intermediate compressor operates at higher rotational speeds, but lower pressures and temperatures. In that case, the ICC temperature capability is no longer a constraint. There may be other opportunities for application of the GOTA data in this engine architecture, but it is not yet clear what they may be.
It is not possible for the current consortium to quantify the benefits in engine performance that will be enabled by retrofitting Timetal 834 to the ICCs of conventional turbofan engines, but it is understood from discussion with engine manufacturers that the benefit may be significant. Therefore the Program may enhance the competitive position of European aircraft engine manufacturers by enabling an improvement in the efficiency and competitiveness of future upgrades to current engine designs.
An additional impact of successfully completing the Work Program, has been to further enhance the strong competitive position of the EU supply chain in the manufacture of intermediate combustion casings.

Societal impacts
The GOTA project has allowed the feasibility of this enabling technology to be demonstrated. If the technology is further developed and tested, so that it can be applied to future aero engine designs, it is expected to make future aircraft more efficient, leading to reduced CO2, and NOx emissions per passenger mile
Aerospace is a major contributor to the European economy, with over 60% of its products being exported. The continued competitiveness and success of the high technology manufacturers and supply chain are key to retention and growth of employment. Predicted growth rates of air traffic will require more than 12,000 planes in the next seven years with associated engines. In this context there is significant opportunity for growth in market share on the back of enhanced performance
The opportunity for involvement of young researchers, and exposure of manufacturing focused engineers, to collaboration with leading research and manufacturing organisations represents a significant training opportunity. Where appropriate, student internships will be used to support activities. Outcomes anticipated include the personal and professional development of an extended network of individuals, through exposure to central dimensions of the challenges facing society and the opportunity to contribute to development of knowledge and more powerful technologies

Added-value in carrying out the work at a European level
The added value of carrying out the work at a European level has been to allow the construction of a consortium of expertise and facilities which is superior to that available in any nation or region in Europe.
The Clean Sky JTI gave a framework for the selection of topics and projects which gave confidence amongst the participants that the Work Program was appropriate and a high priority item which fits into a coherent bigger picture.

List of Websites:
No public website has been created for the GOTA project.

Contact Details for Scientific Coordinators of the Beneficiaries are:

TIMET UK Ltd.: Roger Thomas,
PO Box 57,
SA1 1XD,
United Kingdom
e mail:
Tel.: +44 1792 870335

Deritend International Ltd.,: Zhu Zhang
Doncasters Technical Centre,
Innovation House,
George Bayliss Rd.,
United Kingdom

Forgital S.p.A.: Doug Rawson,
Via G. Spezzapria, 1,
36010 Velo d'Astico,
localita Seghe (VI)

Swansea University,
Prof. Martin Bache,
Institute of Structural Materials,
Swansea Bay Campus,
Fabian Way,
United Kingdom.