The objective of Greater Operating Temperature Alloy [GOTA] was to select a titanium alloy capable of being fabricated into intermediate compressor casings, and enduring operating temperatures of at least 500 deg C in this service. Industrial manufacture of the selected alloy was demonstrated, by the production of rolled rings; gravity cast and centrifugally cast samples; sheets, welding wire, and welded samples.
- TIMET UK Ltd., [TIMET] was the Principal Participant, and led the Management of the project.
- Swansea University led the review of literature and prior industrial work. A candidate alloy (Ti+) was selected based on this review, and on commercial and industrial factors.
- TIMET supplied Ti+ billets to Forgital Italy S.p.A. which will manufacture, heat treat, and sample rolled rings.
- TIMET supplied Ti+ casting stock to Deritend International, which manufactured stepped section cast samples by both gravity and centrifugal casting, aiming to overcome the prior low ductility reported in castings of highly creep resistant titanium alloys.
- TIMET manufactured sheet; welding wire, and welded samples of the Ti+ alloy. Significant process development work is required in this task.
- Swansea University tested the samples of the candidate to generate a database of mechanical properties for this titanium alloy in cast, wrought and welded forms and analyse the samples to rationalise the test results.
- The tests consisted of tensile; creep; LCF; and fatigue crack propagation tests at both room temperature and 500 deg C. Also, tensile tests were repeated after exposure to air at 500 deg C for extended time periods, to check for deterioration in ductility.
- TIMET UK Ltd., led the reporting of the project, and the Participants disseminated the results through industrial meetings with potential end users (principally Volvo Aero and Rolls Royce) and through publications in academic journals and conferences.
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 summarise 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.