Objectif
The objective of the propose d work is to assess the feasibility of producing high temperature creep resistant titanium alloys (temperature range 400-700C) by the introduction of dispersion strengthening phases into such alloys. A programme of work is therefore proposed in which the dispersion strengthening response of rare earth oxides Y2O3, Ce2O3 or Er2O3 are studied in a near alpha type alloy to cover the range 600- 700C, while the intermediate temperature (400-500C) high strength requirements are investigated using an alpha + beta alloy. The near alpha alloy composition will be based on that of the highest temperature commercially available alloy IMI 834, which will be modified to give increased metallurgical stability at 700C. The intermediate temperatures studies will use either the alpha + beta alloy IMI 550 or the 6-6-2 + Zr alloy produced by CEZUS, as its base. In order to ensure homogeneity and maximum solubility of the rare earth oxides conventional arc melted ingots will be converted to bar for powder atomisation by the rotating electrode process (REP), where cooling rates are in excess 104K/s, thus maximising supersaturation of the oxides in the alloys. Titanium alloys are used extensively throughout the compressor in both civil and military aerogas turbines. In the drive for greater efficiencies, higher compressor delivery temperatures and reduced weight, a need has been identified for higher strength alloys to operate in the temperature range 400-500C and for an extension of titanium alloy temperature capability to about 700C, which is well above the 600C maximum attainable by today's most advanced alloy. The cooperation of six European industries specialized in aircraft component research promises best results for this research project.
The purpose of this work was to assess the feasibility of producing high temperature creep resistant titanium alloys by dispersion of rare earth oxide particles by rotating electrode process (REP) and powder consolidation. An alpha + beta alloy was chosen for applications in the intermediate temperature range 450 to 550 C and a near alpha matrix was selected to provide a temperature capability beyond 600 C (IM1550 and IM1834 type alloys respectively).
During ingot productions, yttrium oxide was directly incorporated in the alloy instead of yttrium in order to maintain the initial oxygen content of the titanium matrix. Alloy electrodes were transformed to powder by REP. For each alloy, about 10 electrodes were made, yielding roughly 3 kg of useful powder. Powder consolidation was performed both by extrusion and hot isostatic pressing (HIP).
Microstructural analysis of the as consolidated products showed significant segregation of very large yttrium oxide particles. The origin of this segregation was attributed to the nondissolution of preexisting large yttria aggregates during REP. Attempts were made to understand why yttrium oxide was not dissolved during REP and to find out means to remedy this difficulty.
Despite the occurrence of the macrosegregation, transverse electromagnetic (TEM) study revealed a fine and homogeneous yttrium oxide dispersion in the as consolidated products of both of the yttria containing alloys indicating that a part of the yttrium oxide was dissolved in liquid droplets during REP.
Mechanical tests conducted on powder metallurgically processed alloys shoe a substantial strength increment of the yttrium oxide containing IMI550 extruded alloy, compared to the yttrium oxide free alloy, particularly around 500 C. Conversely, the addition of yttrium oxide gave no significant improvement in creep strength between 400 to 500 C. The strength increment provided by yttria dispersion to the IM1834 type alloy was significant at room temperat ure. Conversely, at 650 C the strength of both yttrium oxide containing alloys and yttrium oxide free alloys after extrusion was found to be very low and both alloys showed a superplastic behaviour. Significantly high strengths were only observed after consolidation by HIP.
A PROGRAMME OF WORK IS THEREFORE PROPOSED IN WHICH THE DISPERSION STRENGTHENING RESPONSE OF RARE EARTH OXIDES Y2O3, CE2O3 OR ER2O3 ARE STUDIED IN A NEAR ALPHA TYPE ALLOY TO COVER THE RANGE 600-700 CELSIUS DEGREES, WHILE THE INTERMEDIATE TEMPERATURE (400-500 CELSIUS DEGREES) HIGH STRENGTH REQUIREMENTS ARE INVESTIGATED USING AN ALPHA + BETA ALLOY.
THE NEAR ALPHA TITANIUM ALLOY COMPOSITION WILL BE BASED ON THAT OF THE HIGHEST TEMPERATURE COMMERCIALLY AVAILABLE ALLOY IMI 834, WHICH WILL BE MODIFIED TO GIVE INCREASED METALLURGICAL STABILITY AT 700 CELSIUS DEGREES. THE INTERMEDIATE TEMPERATURES STUDIES WILL USE EITHER THE ALPHA + BETA ALLOY IMI 550 OR THE 6-6-2 + ZR ALLOY PRODUCED BY CEZUS, AT ITS BASE.
IN ORDER TO ENSURE HOMOGENEITY AND MAXIMUM SOLUBILITY OF THE RARE EARTH OXIDES CONVENTIONAL ARC MELTED INGOTS WILL BE CONVERTED TO BAR FOR POWDER ATOMISATION BY THE ROTATING ELECTRODE PROCESS (REP), WHERE COOLING RATES ARE IN EXCESS 10 K/S, THUS MAXIMISING SUPERSATURATION OF THE OXIDES IN THE ALLOYS.
TITANIUM ALLOYS ARE USED EXTENSIVELY THROUGHOUT THE COMPRESSOR IN BOTH CIVIL AND MILITARY AERO GAS TURBINES. IN THE DRIVE FOR GREATER EFFICIENCIES, HIGHER COMPRESSOR DELIVERY TEMPERATURES AND REDUCED WEIGHT, A NEED HAS BEEN IDENTIFIED FOR HIGHER STRENGH ALLOYS TO OPERATE IN THE TEMPERATURE RANGE 400-500 CELSIUS DEGREES AND FOR AN EXTENSION OF TITANIUM ALLOY TEMPERATURE CAPABILITY TO ABOUT 700 CELSIUS DEGREES, WHICH IS WELL ABOVE THE 600 CELSIUS DEGREES MAXIMUM ATTAINABLE BY TODAY'S MOST ADVANCED ALLOY.
THE COOPERATION OF SIX EUROPEAN INDUSTRIES SPECIALIZED IN AIRCRAFT COMPONENT RESEARCH PROMISES BEST RESULTS FOR THIS RESEARCH PROJECT.
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CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
- sciences naturelles sciences chimiques chimie inorganique métal de transition
- ingénierie et technologie génie mécanique génie automobile génie aérospatial avion
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92322 Châtillon
France
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