1997 TMS Annual Meeting: Thursday Abstracts

INTERNATIONAL SYMPOSIUM ON RHENIUM AND RHENIUM ALLOYS: Session XI: Single Crystal Technology--Rhenium and Rhenium Containing Alloys

Session Chairpersons: Dr. Amber M. Dalley, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904; R.H. Titran, NASA Lewis Research Center, 21000 Brookpark Road, Mail Stop 49-1, Cleveland, OH 44135

8:30 am

DEVELOPMENT AND TURBINE ENGINE PERFORMANCE OF THREE ADVANCED RHENIUM CONTAINING SUPERALLOYS FOR SINGLE CRYSTAL AND DIRECTIONALLY SOLIDIFIED BLADES AND VANES: Robert W. Broomfield, David A. Ford, Harry K. Bhangu, Rolls-Royce Plc., Derby and Bristol, U.K.; Malcolm C. Thomas, Donald J. Frasier, Phil S. Burkholder, Allison Engine Company (Rolls-Royce plc), Indianapolis, IN; Ken Harris, Gary L. Erickson, Jacqui B. Wahl, Cannon-Muskegon Corporation (SPS Technologies Inc.), Muskegon, MI 49443

Turbine inlet temperatures over the next few years will approach 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and power levels approaching 442 kN (100,000 lbs). High reliability and durability must be intrinsically designed into these turbine engines to meet extended over-water, large twin engine aircraft (ETOPS) certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, design technology for stresses and airflow, single crystal and directionally solidified casting process improvements, the development and use of rhenium (Re) containing high y' nickel-base superalloys with advanced coatings, including full-airfoil ceramic thermal barrier coatings. Re additions to cast airfoil superalloys not only improve creep and thermo-mechanical fatigue strength but also environmental properties, including coating performance. Re dramatically slows down diffusion in these alloys at high temperature turbine operation conditions. A team approach has been used to develop a family of two single crystal alloys (CMSX-4. containing 3% Re and CMSX.-10 containing 6% Re) and a directionally solidified, columnar grain alloy (CM 1 86LC. containing 3% Re) for a variety of turbine engine applications. A range of critical properties of these alloys are reviewed in relation to component turbine engineering performance through engine certification testing and service experience. Industrial turbines are now commencing to use this aero developed turbine technology in both small and large frame units in addition to aero-derivative industrial engines. These applications are demanding with high reliability required for turbine airfoils out to 25,000 hours. with perhaps greater than 50% of the time spent at maximum power. Combined cycle efficiencies of large frame industrial engines is scheduled to reach 60% in the U.S. ATS program. Application experience out to a total 2 million engine hours and 28,000 hours individual blade set service for CMSX-4. first stage turbine blades is reviewed for a small frame industrial engine.

8:50 am

THE SIGNIFICANCE OF RHENIUM FROM PRODUCTION TO USE IN HIGH TEMPERATURE MATERIALS: Paul Forde, H. C. Starck Inc., 45 Industrial Place, Newton, MA 02161-1961

The major use of Rhenium is in catalysts primarily in the petrochemical industry. However, due to increased demands in high temperature turbine applications, Re is becoming a critical alloying element primarily in nickel base, single crystal superalloys. As a member of the refractory metal family of elements, Re is a higher cost member, in pat due to the expense associated with production. This paper briefly address the new significance of Re in superalloy applications, where its use was practically non-existent in polycrystalline alloys. Also included is an overview of the raw materials from which Re is processed as well as the production techniques currently in use.

9:10 am

MECHANICAL PROPERTIES OF Mo-Re SINGLE CRYSTALS AND BICRYSTAL ALLOYS: A. Yastrebkov, Yu. Aleynikov, O. Petrova, and Yu. Ivakin, RI SIA "LUTCH", 142100 Podolsk, Moscow Region, Zheleznodorozhnaya 24, Russia

Rhenium influence (at content up to 30 at.%) on the character of the change of the crystal and intercrystalline boundary mechanical properties was studied using single crystal and bicrystal alloy specimens produced by electron beam zone melting. Tensile tests of single crystals were carried out at 20°C, their impact strength was studied at temperatures from -200°C up to +300°C, the depth of microcracks appearing at electrodischarge treatment and hardness was measured. Bicrystal specimens of the alloys having 5,10 and 2Q at.% of Re were tested for impact strength at 20°C, microcrack depth in the crystals and on the intercrystalline boundaries after electrodischarge treatment was studied. Disorientation angle ranges of the twist intercrystalline boundaries were 7-9° and 18-21°. It is shown that alloying strengthens crystals and improve their ductility. Single crystal strengthening has not monotonous nature. Minimum of hardness, ultimate strength and yield strength was observed at 3-4 at.% of Re. The alloying decreases microcrack depth after electrodischarge treatment both in crystals and on the intercrvstalline boundaries however the depth of the last ones is always more.

9:30 am

THE RHENIUM IMPACT ON THE MASS TRANSFER IN Mo-Re SINGLE CRYSTALS UNDER SHOCK LOADING: S.V. Divinski, L.N. Larikov, M.N. Belyakova, V.V. Zholud, V.F. Mazanko, Institute of Metal Physics, National Academy of Sciences, 36 Vernadsky Str., Kiev-142, 252142, Ukraine

An abnormally high depths of marked atom penetration at shock loading have been discovered for Fe and then were observed for a number of metals. In this work, this phenomenon is thoroughly investigated for the Mo-Re single crystals. It was found that Re moderates substantially the mass transfer. The derth of penetration of the Ni-63 isotopes decreases to 17 and 3 percents of that value for pure Mo if the Re content is 10 and 17 at.%, respectively. These results are discussed in a framework of Re impact on generation and migration of interstitials under movement of jugged screw dislocations. Moreover, the Re alloying increases the contribution of twinning to the plastic deformation. A computer model of enhanced mass transfer at shock loading has been proposed and the Re impact was numerically studied.

9:50 am BREAK

10:10 am

STRUCTURE EVOLUTION IN RHENIUM SINGLE CRYSTALS AT ROLLING AND ANNEALING: S.V. Divinski, L.N. Larikov, M.N. Belyakova, V. Rafalovski, Institute of Metal Physics, National Academy of Sciences, 36 Vernadsky Str., Kiev-142, 252142, Ukraine

Structure of Re single crystal with the {0001}<1120> orientation subjected to rolling has been investigated. Initial orientation is unstable and single crystal is transformed to polycrystalline state. This texture evolution has been analyzed by a computer model. A good agreement with experiment has been achieved. Strain dependence of density of the Re crystal reveals abrupt increase at about 22% of strain, although visible cracks at external surface appear only at ~30% of strain. The last value corresponds to pronounced intensifying of the subsequent recrystallization under annealing. Influence of rotational deformation modes have been numerically studied and their substantial impact on axial textures of Re was predicted.

10:30 am

EFFECTS OF THE RHENIUM ADDITIONS ON THE STRUCTURE AND MECHANICAL PROPERTIES OF THE TUNGSTEN SINGLE CRYSTALS: O.A. Bilous, V.N. Minakov, D. Ye. Ovsienko, E.I. Sosnina, V.I. Trefilov, I.N. Frantsevich Institute for Problems of Material Science, Institute for Physic of Metals, 3 Krzhizhanovsky Str., Kiev 252180, Ukraine

The structure and mechanical properties of single crystals W and binary alloys W-Re that were grown by electron beam zone technology with low carbon concentration (10-6÷10-7Torr) in the direction axis <100>±(1÷1.5). The yield stress and the ductile-brittle transition temperature of the W and W-Re single crystals of the specimens that were cut normally to the direction of crystals growing have been determined to be lower than in parallel cut ones. That is determined by dislocation structure anisotropy of single crystals. Alloying tungsten single crystal with rhenium results in considerable decrease of cold brittleness temperature Tb was shown. The most effective are the lowest rhenium concentration. Thus, adding of o.1 at.% Re decreases Tb from -40°C and 4.3 at.% Re only to -60°C in parallely cut specimens, for example. It should be marked, yield stress grows proportionally the rhenium content in alloys.

10:50 am

STRUCTURE AND PROPERTIES STABILITY OF Re-SINGLE CRYSTALS UPON VACUUM ANNEALING AND THERMOCYCLING: G.S. Burkhanov, V.M. Kirillova, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117911 Moscow, Russia; B.D. Bryskin, Rhenium Alloys, Inc., 1329 Taylor Street, P.O. Box 245, Elyria, OH 44036-0245

Electro-beam zone melting was used to grow high purity Re single crystals with different crystallography orientations. Thermo-electrical moving force (t-c.m.f.) of Re-single crystal was found to insignificantly increase upon 4 h vacuum annealing at 2000°C. In this case anisotrophy of Re-single crystal t-e. m.f. substantially increased. Comparison between Re-single and polycrystals showed that electrical properties of single crystal were stable in contrary of that of the polycrystal. Structure, hardness and specific electrical resistivity of Re-single crystal were established to insubstantially increase upon thermocycling (1600-400°C, 300 cycles). Specimens as 5x5 mm2, 100 mm rectangle (with two sides parallel to basic plane) were cut from Re-single crystal ingot. The shape of this specimens was unchanged upon above mentioned thermocycling. Explanation of stability of Re-single crystal and its application were discussed.

11:10 am

USAGE OF EB FLOATING ZONE MELTING FOR PRODUCTION OF RHENIUM ALLOYS WIRE: A.V. Elutin, I.A. Yudin, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B Tolmachevsky Per., Moscow 109017, Russia

In the eighties in the former USSR some efforts were made to create modern equipment for producing single crystals of refractory metals by electron beam (EB) floating zone melting. Using this EB furnaces, single crystals of tungsten, molybdenum, tantalum, niobium and rhenium were produced. Dimen sions of crystals were up to 35-40 mm in diameter for tungsten and up to 110 mm for niobium. This report contains experimental data in studying process of growing single crystals of rhenium containing alloys based on molybdenum and tungsten, such as Mo48%Re alloys and W-27%Re and polycrystalline as cast rods and bars. It was found that this method is very efficient for producing calibrated bars from these alloys which can be used in wire production without mechanical treatment. This technology provides very high yield of metals.

11:30 am

GROWTH FEATURES OF W-Re SINGLE CRYSTALS UPON PLASMA ARC MELTING: G.S. Burkhanov, V.M. Kirillova, Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninsky Pr. 49, 117911 Moscow, Russia; B.D. Bryskin, Rhenium Alloys, Inc., 1329 Taylor Street, P.O. Box 245, Elyria, OH 44036-0245

Plasma-arc welding was used to grow high purity W-Re single crystals in a wide concentration range (1-20 wt.% Re). Relationship between solidification (growth rate "R", temperature gradient in liquid phase - ''GL', Re concentration - "Co") and growth structure (cellular, dendritic, single- and polycrystalline) of W-Re alloys was determined and shown as "Co - GL/R _"' diagram. Effect of crystallographic instability was discovered for (W-Re) single crystals with [110] and [111] orientation which were changed to preferable [100] growth orientation upon growing. The reason of this orientation and its dynamics were examined. W-Re single crystals of 1st melt were characterized by considerable misorientation of 1st order subgrains from seed to the top of ingot and "striped" microstructure. Such structure and instability of crystallographic growth were examined by concentration undercoolings. The ways for improving of W-Re single crystals structure perfection are suggested.

11:50 am

METHOD FOR PRODUCING HIGH-PURITY RHENIUM FOIL: A.V. Elutin, K.S. Kovalev, T.B. Danilina, State Research Centre-State Institute of Rare Metals-GIREDMET, 5 B. Tolmachevsky Per., Moscow 109017, Russia

For some applications, such as manufacturing of the thermionic cathodes of mass spectrometers and other purposes a rhenium foil of 20-40 mcm thickness with a base metal content of 99.99-99.999% is used. For producing of high-purity rhenium foil we use rhenium bars made by EB floating zone melting which have 20-30 mm in diameter, 200-500 mm in length, single-crystal line structure and 99.999% purity. During the foil production significant advantages may be obtained by using single crystalline billets having a crystallographic orientation that is favorable for deformation. With this approach, it becomes possible to achieve by rolling total reduction value of up to 50-65% as compared to some 5-7% in case of using polycrystalline billets of identical purity, and to obtain after a first annealing a relatively homogeneous fine-grain recrystallized structure that is favorable for subsequent rolling steps. It was shown by practice that the above described method makes possible to produce rhenium foil with 99.99% purity and upwards.