HIGH TEMPERATURE ALLOYS FOR THE HTGR GAS TURBINE: REQUIRED PROPERTIES AND DEVELOPMENT NEEDS

Transcription

1 HIGH TEMPERATURE ALLOYS OR THE HTGR GAS TURBINE: REQUIRED PROPERTIES AND DEVELOPMENT NEEDS R. COUTURIER CEREM, CEAGrenole, Grenole "xao'i C. ESCARAVAGE RAMATOMENOVATOME, Lyon rane 1. INTRODUCTION Reent advanes in the design of turomahinery, reuperators and magneti earings provide the potential for the use of the High Temperature Gas Reator (HTGR) with a losed yle gas turine. The reator size has een redued in developing the passively safe module design and the size of industrial gas turine has inreased to aommodate the energy released from a HTGR module. Highly effetive ompat reuperators have een developed, they are a key requirement for ahieving high effiieny. The availaility of large magneti earings has also eliminated the potential prolem of oolant ontamination y the oil of luriated earings. National and international R&D programs are under way to explore areas where tehnial development is needed [1]. Among these programs, the losedyle gas turine onept is investigated in several industrial projets [2]: The Pele Bed Modular reator (PBMR) in South Afria, with a gross eletrial generation of 117 MWe. The projet shedule has een estalished, with a deployment of a first unit in The Gas Turine Modular Helium Reator (GTMHR) developed y an international onsortium, with a targeted 286 MWe generation per module, a prototype single unit is sheduled in Russia in Test Reators are eing ommissioned in Japan (High Temperature Test Reator HTTR) and China (HTR10) to evaluate the safety and performane of HTGR. These reators are designed with an indiret onversion yle, ut they will support R&D ativities like eletriity generation via the gas turine and high temperature proess heat appliations. A ommon European approah to the renewal of HTR tehnology through the diretion of a European HTR Tehnology Network (HTRTN) has also een estalished to enale and enourage workshared strutures within this nulear R&D field. Among these reent R&D programs, ramatome and CEA are involved in the materials development for the key omponents of the HTGR. The development of advaned HTGR onepts requires materials data and understanding of materials ehaviour under reator operating onditions and environment. The omponents for the primary iruit operate at temperatures aove 600 C and up to 850 C in order to reah high effiienies. or these materials and omponents, onsiderale data and knowhew exists, ut industrial and tehnial feasiility are not well estalished for the most reent designs. or example, a signifiant effort is needed for the turine omponents, for whih the expeted working onditions are eyond the today's industrial apailities. The fundamental tehnologies required for the design of the turomahine have een proven for aerospae and industrial gas turines. However, the HTGR gas turine requires a design that inludes high temperature apaility and long term endurane. The required design properties, assoiated with the large sizes of omponents, an e seen as a major issue. 163

2 In this work, a review with a seletion of most relevant materials and proesses is presented, for oth turine lades and disks. The fous of this work is to disuss the hoie of high temperature materials in aordane with the reent HTGR design speifiations. The GT MHR turine design is used as a referene for high temperature materials seletion. Also an evaluation of reent advanes in materials for industrial gas turine is presented, with a rief overview of assoiated fariation proesses. 2. HTGR TURBINE DESIGN SPECIICATIONS The GTMHR module onsists of a nulear soure of heat (reator system) and the Power Conversion System. Details of the general design an e found in [2] and [3]. The Power Conversion System (PCS) reeives aout 600 MW of thermal energy from the reator system and onverts 286 MW of net usale eletrial energy, with an overall effiieny of aout 47%. The PCS inludes the turomahine, the preooler and interooler, and onneting pipelines. The turomahine onsists of the turoompressor, the eletrial generator, earings and seals. The turoompressor inludes the turine and two ompressor setions (low pressure and high pressure ompressor). The helium is reeived y the PCS from the hot gas dut. The helium then expands trough the gas turine whih is oupled to the eletrial generator. rom the turine exhaust, the helium flows trough the hot side of the reuperator, transferring heat to helium returning to the reator. The helium leaving the hot side of the reuperator is ooled (preooler) efore passing trough the lowpressure ompressor, interooler and highpressure ompressor. The helium then passes in the old side of the reuperator where it is heated for return in the reator system. The entire assemly is installed in a vertial orientation and is rotating at 3000 rpm (50Hz). The turine design is ased on the tehnology availale for large industrial engines. Sustitution of helium for air in this nulear gas turine modifies aerodynami requirements y removing Mah numer limitations. As the rotational speed is fixed (synhronous generator), the size of the turine is ditated y the hoie of lade speed. The highest lade speed is desirale to limit the numer of stages, ut it is limited y the high temperature stress limits for the lades. In the GTMHR onept, a 12 stages turine with very high effiieny was estalished. With turine inlet temperature of 850 C, lade and disks ooling are not onsidered as neessary in the design. Salient features of the GTMHR turine are given in tale CRITERIA OR MATERIAL SELECTION or the material seletion, the key points are the first stages turine disks and lades where the stresses and temperatures are the highest. Tale 2 summarizes the thermal and mehanial loads for the turine disks and lades. The materials for these omponents should ensure a safe operation for at least hours. Therefore, a ground rule for the material seletion of the most ritial parts was proposed as following [5]: for the lade alloy for the disk alloy 164

3 TABLE 1. GTMHR TURBINE CHARACTERISTICS AT ULL POWER [4] Power, MW Rotational speed, rpm numer of stages Expansion oeffiient Adiaati effiieny, % hu diameter, mm Inlet parameters temperature, C pressure, MPa He mass flow, kg/s pressure losses, MPa lade height, mm Outlet parameters temperature, C pressure, MPa pressure losses, MPa lade height, mm TABLE 2. PRELIMINARY STRESS ANALYSIS OR THE GTMHR TURBINE [5] Blade root setion area, mm 2 lade height, mm entrifugal fore reated y a lade, N Blade root setion stresses, MPa Radial stress Bend stress Total stress Stesses in the disk (rotor), MPa Annular Radial Stage 1 (850 C) Stage 12 (510 C) The use of high temperature materials for nulear systems will require an extension of material design rules and odes urrently used. rom the designer side, inreasing the temperatures means a hange from timeindependent to timedependent harateristis (reep, reepfatigue). igure 1 illustrates the maximum temperature of metalli omponents in urrent and future reator systems, hi addition, figure 1 indiates the maximum temperature onsidered in the design odes. Although some existing odes use timedependent properties in design (ASME Code Case N47 now inorporated as susetion NH of setion HI and RCCMR), the temperature limits of materials inluded in the design odes availale to day are signifiantly lower ompared to HTGR needs and therefore a signifiant step forwards is required. 165

4 The first riteria eing high temperature tensile strength and stress to rupture, other properties as resistane to thermal fatigue must e onsidered in design. Noth sensitivity is also proaly detrimental to the high yle fatigue of rotating parts of ompliated shapes. Possile orrosion effets of environment should also e onsidered for the materials' hoie as helium impurities an influene the metalli material properties in servie via arurisation and oxidation mehanisms. Part 6 will disuss the orrosion performane of several alloys in term of weight gain that an e related to the redution of effetive load earing thikness. However, for the omplete assessment of strutural integrity, the omined effet of different failure modes must e onsidered and partiularly the following: reepfatigue: it is generally onsidered that the amount of fatigue endurane redution y reep or relaxation is inreased when the material has low reep strength. Creep dutility an also e onsidered as a limiting parameter in reepfatigue. fatigue and environment effet: initiation of raks partiularly in ase of thermal fatigue takes plae at the surfae of the material and an e influened y the effets of the environment on the material surfae as pointed out at the end of setion 6. reepfatigue and environment effet: the effet of environment an e important in reepfatigue and in thermal fatigue, and experiments have shown that the redution of fatigue life y hold times in relaxation an e quite different in vauum from what is oserved in air. The orresponding mehanisms are diffiult to larify for a quantitative predition, the helium effets eing suspeted to e intermediate etween vauum and air effets. As long term servie is needed, long term staility of material properties must e assessed: this point is disussed in part 7. When the optimum strength is otained y a heat treatment at temperature lower or nearly equal to the servie temperatures, there are some douts aout the staility of the orresponding mirostruture. err.ti sieei u5ter.(i; steei and Hi os? alloys i os? i>oys lime independent propsrtie dependent properties Projet (He/He ne;t e<.huriq;»i, heat ip i reformer furnae *u3«, o \ itshot dut, turine M'Jdesi & y, ^ ii.x.^^v^^^^^^y ps^npsv 4VR {steam generator) <\ NX^ X istgor^ generof^r i IG.l. Material temperature and design odes for metalli appliations (partly from [6]). omponents in nulear 166

5 Based on these requirements, the seletion of metalli materials for lades and disks is disussed in the next setions. The hemial ompositions of alloys that are evaluated is given in appendix MATERIALS OR THE TURBINE DISKS At this stage, it remains unlear if alloys ontaining sustantial additions of oalt or tantalum would e seleted for use in the turine of a HTGR. In some past studies, alloys ontaining more than residual levels of these elements have often een exluded from the list of referene alloys for the primary iruit, eause of potential radioative ontamination. However, many of the high temperature alloys with Coalt have the highest mehanial properties and they are examined in the ase of further aeptaility [7,8]. Inonel alloy 718 was seleted for the HTGR turine disks in reent studies [8]. Alloys IN718 is a nikelased preipitation hardened material. It has the neessary strength, short term reep and orrosion resistane only in the ase of ative ooling of the disk. With a turine inlet temperature of 850 C, IN718 will require ooling to lower the temperature of the disks to around 650 C. Alternatively, alloys ontaining oalt may e etter in terms of high temperature strength (like Udimet 720 with af^=245mpa). rom the GTMHR design reports issued from OKBM, lassial nikelase superalloys used for industrial gas turines (IN 718, Waspaloy) do not ahieve the long term stress level requirements [5]. or OKBM, the only existing alloy that ould e envisaged for a nonooled first stage disk is the alloy MA MA 6000 is an Oxide Dispersion Strengthened (ODS) superalloy that offers very high strength and mirostrutural staility. The reep strength of this grade ould reah values higher than 185 MPa for hours at 850 C. This grade is produed y mehanial alloying of powders and susequent Hot Isostati Pressing or hot extrusion [9]. The main diffiulties with using ODS grades are that the proess route is not mature and that muh work is needed to produe large ingots with homogeneous mehanial properties. Among the ast alloys that ould serve as a asis for further grades optimisation, OKBM proposes ZhS6 and VZhL12U grades, VZhL12U hemial omposition eing very lose to that of IN 100 alloy. In the frame of the Dragon projet, Graham has proposed A286 and IN 706 as referene grades for the disk prodution. These are enicr preipitation hardened grades with suffiient forgeaility for large disks prodution ut medium high temperature properties. Again, these grades an only e envisaged in the ase of ooled turine disks [7]. In the ase of large omponents as the GTMHR turine disks, the manufaturing apaility is losely related to the strength of the alloy. In the ase of nikelase superalloys, the two major issues are the following: to otain large ingots (~510 tons) without solidifiation porosities and marosegregations. or reent superalloys, manufaturing route inludes a vauum indution melting, a vauum ar remelting and/or eletroslag remelting. The powder metallurgy would allow to produe high quality ingots with highly alloyed grades. In this ase, mirostrutural inhomogeneities would e limited to the size of the powder partile. 167

6 to forge these ingots whih usually offer a very low hotworkaility. Isothermal forging is used, ut with the most reent superalloys (like Udimet 720), the maximum forgeale size is muh lower than the GTMHR disk diameters. Again, elaoration of nearnet shapes omponents y Hot Isostati Pressing of powders appears promising for these large disks, as hipping furnaes with large diameters are availale (~1.4 m). 5. MATERIALS OR TURBINE BLADES Materials seletion and testing for HTGR turine lades has een extensively studied. Essentially 2 types of metalli materials were investigated: Nikelase ast superalloys. Molydenumase grades Niase ast superalloys hi several past R&D programs, seleted alloys were ranked y their high temperature strength, astaility and oalt ontent. Most promising alloys for the lades are therefore: 713LC [6,7,8,10,11,12,13] M21 [7,10,12] MARM 004 [7,13,12] Alloy 713 LC is a ast nikel ase preipitation hardened alloy that omines superior astaility and reep resistane. Alloy 713LC has the advantage of wide industrial experiene in onventional gas turine (turine housings, ase, stator) [8]. Alloy 713 LC neither ontains Co or Ta and should therefore not present any ontamination prolems, hi HTGR environment, alloy 713LC an e suseptile to arurisation and sulfidation prolems, and oatings have to e envisaged. Alloy 713LC is well suited for the turine lades required speifiations, exept for the first row of lades where ooling would e neessary to ahieve the required lifetime [8]. Diretionally Solidified (DS) or Single Crystal (SC) lades would solve this prolem, ut alloys ommonly used for DS or SC lades ontain aout 10% oalt (DS Mar M 247, SC Rene N4). Alloy 713LC was used for the fariation of the turine lades in the HHV projet [11]. During this projet held in Germany, a fullsale test turine driven y HTGRtype helium was uilt. During the short high temperature lifetime experiened ( 325 hours at 850 C), no material prolems appeared with the working lades. Alloy M21 is a low hromium nikel ase alloy that omines preipitation hardening and solid solution hardening ( 10% tungsten addition). It was seleted for its superior orrosion resistane in impure helium. Alloy MM004 has een developed from alloy 713LC and is laimed to have a etter toughness eause of Hafnium addition [13]. Among alloys that were also studied for a potential use as HTRG turine lades, there are: IN 100 grade with good orrosion resistane [10]. IN 100 is the referene alloy for PBMR powerturine ooled lades [1]. 168

7 Nimoni 80A with medium reep rupture strength whih is envisaged for the last row of lades (lower temperature) [6,13]. Alloys Nimoni 90, 105 and 115, Udimet 520 et 700, IN 591, IN738, IN 792, Rene 80, M22, MARM 247, Nx 188 were also proposed in various studies [7,13,14]. IS 145 alloy was developed in Germany for HTGR appliations. It omines preipitation and solid solution hardening ( 13.5% tungsten) with a high astaility [13]. In figure 2, a omparison of several lade alloys properties is shown, for reep rupture performed in oth air and helium. Jakoeit pointed out the sharp derease in reep strength for long times at 850 C, exept for the Moase alloy. This derease is less pronouned at lower temperatures, supporting the idea of a design with ooled lades to inrease the lade lifetime [13]. LTZM is the strongest alloy in figure 2, this Moase grade is presented in the next setion. Alloys proposed y OKBM in the GTMHR projet inlude preision investment ast Niase alloys (ZhS6K, CNK8M) and single rystal alloys (ChS120M that is lose to CSMX2 grade) [5] LTZM IS 145 Alloy 713LC MM004 Nimoni Nimoni80A 10 5 IG. 2. Creep rupture strength of different turine lade materials at 850 C [13] Molydenumase alloys The molydenumase alloy TZM (Mo0.5Ti0.08Zr) has not een used in industrial gas turines eause of its poor oxidation resistane in air. However, R&D efforts performed in German HTGR programs have demonstrated a promising appliation for this alloy for helium turine lades. As shown in figure 2, MoTZM exhiits a ompletely different reepresistane ehaviour as ompared to the nikelase alloys, mainly eause of its high melting point (2607 C) [15]. Almost flat reep urves make a 100 OOOh life time appear possile with an unooled lade, as shown in figure 3 [12]. 169

8 4001 x: jdesign range ' ^. ^ for tursne lade ' [ower onfidene IG.3. Stress for rupture in 10 h versus design temperature for HTGR turine lade [12]. Preision forged lades were fariated, starting from vauumarmelted or powder metallurgy ingots. These lades showed a very high orrosion resistane in impure helium, ut several fariation diffiulties and inherent drawaks were enountered, and efforts for further development are almost aandoned today: MoTZM is rittle at temperatures up to C and the noth sensitivity remains high at HTGR servie temperature. in ase of air ingress in the iruit, this alloy will suffer a massive oxidation, mirostruture is heterogeneous in the lade, as a result of loally non uniform deformation state during hot forging. Low strength areas were found in fatigue and reep, espeially in the airfoil/root transition zone [15]. 6. EECT O HELIUM ENVIRONMENT The main orrosion effets of metalli materials in HTGR helium environment have een extensively studied, espeially for high temperature materials. Corrosion derives from the presene of low partial pressures of H2O, CO, and CH4 in helium. Hydrogen also plays a role in ontrolling the oxygen potential trough the H2/H2O ratio. A reent review has given the following general trends [16]: elow 850K (577 C), orrosion is limited. Only mild steels an suffer dearurisation. Steels with additions of hromium are slightly oxidized. from 850 to 1173K ( C), reep resistant alloys form a hromium rih oxide sale. Internal mirostrutural hanges are oserved (preipitate free zones, arurised zones), espeially when the surfae sale is porous. under 1173K, rapid arurisation or dearurisation an our, the dominant mehanism eing ontrolled y the environment hemistry. Conerning the high temperature alloys for lades and disks, the mains onlusions are: MoTZM alloy is almost insensitive to He environment up to 1000 C [7]. Jakoeit has oserved a 30 um thik MO2C surfae sale formed after hours at 850 C. This surfae modifiation does not influene the reep resistane [13]. 713 LC alloy and more generally nikelase superalloys develop an oxide surfae sale (Cr2O3) with an internal oxidation (AI2O3) and arurisation (Q^Ce). The 170

9 arurised zone is depleted in y' preipitates. Creep tests with 713LC speimens performed from 500 to 850 C in HTGR helium and air show virtually no environment effet on rupture time for test durations; up to hours [13]. The first way of optimisation to deal with orrosion prolems is the optimisation of alloy omposition, as shown in figure 4. Several hemial ratios were proposed as ontrolling parameters for the formation of stale protetive surfae sales: Alloys with high Al/Cr ratios (M21, IN591) are muh more sensitive to orrosion than alloys with the same Al ontent and a redued Cr ontent (MarM004, 713LC). Alloys with low Cr and high Ti develop a stale oxide sale. or this reason, alloys IN 100 and IN738 appear promising; for HTGR appliations if the onstraints on oalt ontents are lowered [7]. Alloys with a ratio Al/Ti around unity develop more stale surfae oxides than alloys with Al/Ti<l (as 713LC, M21) [10]. The seond way to prevent orrosion prolems is to apply a oating on the surfae. An industrial experiene exists for aluminide oatings for alloy 713LC, whih then offers a stale ontinuous AI2O3 film [8]. W6ISHT SAM (mgjstr?) 8 3 TSME(fxTOOO) IG.4. Weight gain of ast Niase alloys in HTGR environment at 900 C [Graham! 6]. The main onern with design of high temperature alloys in impure helium is whether the surfae orrosion influenes the strength (and lifetime) of the omponents. rom the literature availale on reep rupture properties, it appears that degradation of mehanial properties after elevated exposure in helium is similar to degradation experiened in air [8,13]. Therefore the degradation is mainly due and thermally ativated strutural hanges rather than orrosion. However, when dealing with rak propagation properties, a study on ast Niase alloys has shown that environment effets are not similar in fatigue and reep rak propagation [14]. Complex mehanisms an our at the rak tip (oxidation/plastiity interations) whih are diffiult to model and predit. 7. LONG TERM MATERIALS PROPERTIES Most of Niase superalloys investigated for turine lades and disks are heat treated efore use for maximum strength, usually with a solution treatment followed y aging treatments. They are strengthened y a very fine dispersion of oherent preipitates (y' or y") with some 171

10 arides and orides. They are therefore inherently sujeted to strutural instailities in high temperature servie. Mirostrutural hanges are of fundamental importane for HTGR material seletion as most of the foreseen grades were developed for aeronautial turines with muh shorter lifetimes. or example, preipitation of hard rittle phases must e ontrolled for omponent lifetimes greater than hours. igure 5 shows an example of large mirostrutural hanges of 713LC alloy after a reep test at high temperature. or the HTGR turine, lade and disks alloys will endure thermal aging and there will e a strong need to understand the indued hanges in strength, reep dutility and remaining life [17]. reep ruptured IG 5. Optial (upper) and sanning eletron (lower) mirographs of alloy 713LC efore (left) and after (right) a reep test at 1000 Cfor hours [17]. 8. POTENTIAL BENEIT O RECENT ADVANCES IN GAS TURBINE MATERIALS 8.1 Evolutions in turine tehnology There has een a onsiderale development in natural gas fired advaned landased turines with omined yles (reahing 60% thermal effiieny). These units are intended for aseload operations, with power ontinuously inreasing: from 6070 MW in the 70's to 280 MW today and around 500 MW in the next years (GE MS 7001H turine in 2001). Reviews of reent ahievements in turine tehnology and assoiated materials developments an e found in [18,19]. The need to inrease engine omustion temperature to inrease the effiieny of gas turines has resulted in a large inrease in Turine Inlet Temperature (TIT), for oth landased and aero turines, hi the last 50 years, the TIT has risen from around 800 C to nearly 1600 C [18,20]. This inrease has een aompanied y several hanges in the materials for the hottest parts. Reent advanes in material proessing and strength apaility are now presented, as they ertainly offer new possiilities to ahieve the HTGR requirements. 172

11 8.2. Advanes in disk materials This inrease in TIT has a signifiant impat on turine disks tehnology. Turine disks rim temperatures have risen to 680 C and will exeed 700 C in future aeroengines. In the past, Waspaloy has een used extensively, and Alloy 718 and Udimet 720 are now replaing it. However, even U720 approahes its limits. Therefore, major efforts are made to produe disks with temperature apailities aove 700 C [20]. Alloy 718 has a large propensity for segregation during asting. or aeroengines, melting tehnology advanes have allowed to produe the required disk diameters of largest engines. However, for power generation, turine disks an e typially 1.5 meters or more in diameter. Suh large omponents require the prodution of around 10 tons ingots with susequent forging. This has not een possile with 718 alloy eause of low astaility, and a new grade with less Mo and N was developed (IN 706). This grade allows the prodution of large disks with modest diminution in mehanial properties. However, melting tehnology of large 706 ingots remains omplex, and the alloy reahes today the limits of its performane. Again, large efforts are put to produe large disks in more resistant 718 grade, and also Udimet 720 for the future [21]. Large segregation during solidifiation of highly alloyed grades has fored to move to powder metallurgy proessing for whih segregation is not an issue. Alloys suh as Merl 76 (Pratt &Whittney), Rene 88DT (General Eletri) and N18 (Snema) represent the urrent state of the art for aeroengines [22]. In the past, hipped powder ompats yielded exellent stati; properties, however lowlife fatigue failure ourred in servie. These failures were initiated at defets on powder partile oundaries due to powder ontamination. To overome these prolems, atomisation and handling of the powders were improved, and posthtp isothermal forging used to mitigate the influene of ontamination. Today, powder metallurgy offers two interesting perspetives [21]: Prodution of Niase superalloy grades that are almost not astale (due to exessive segregation) and alloys with a low forgeaility. Prodution of net shape parts with minimum final mahining. Reently, there has also een interest in the development of EITGR erami turine disks in Japan [2]. Ahieving a rotor of lightweight and high strength ould indeed failitate the turine design. With the HTGR helium environment, C/C omposite was hosen, and the fariation of a representative disk was ahieved in Tests showed poor rotating properties, ut further fariation and tests are under way. Many tehnial prolems still need to e resolved for this longterm solution of disk fariation Advanes in lade materials The rise in TIT has een met y replaing the forged lades y ast lades (T 1 1 $ j)^1«805 o C and a^q^0h «175MPa for IN 738 [18,22]), and the susequent introdution of diretionally solidified (DS) and single rystal (SC) lades (T ^» 1 «870 o C[18]). Today peak metal temperatures of over 1100 C are experiened in some turine piarts, with servie lives around hours ahievale [20]. The DS proess allows lades to operate at temperatures aout 25K higher than onventional lades. An additional temperature inrease of aout 25K is ahieved y using lades made of single rystal materials (no grain oundaries). Thermal 173

12 arriers oatings are extensively used in airraft turines, allowing another temperature inrease of aout 100K [23]. 9. CONCLUSION UTURE DEVELOPMENTS uture developments in materials will e assoiated with new turine designs. Multistruture disks, optimised for low yle fatigue in the ore and reep resistane in the rim, are today under development [24]. This proess route is likely to e more expensive, ut it offers the designer to optimise independently the properties of the ore and the rim. This will result in etter performane and disk endurane [20]. Oxide Dispersion Strengthened alloys (ODS) like MA6000 are promising for their high temperature strength and staility. These grades are indeed more suited for stati omponents (vane, omustion hamers) than for rotating parts. This is eause the strength advantage of ODS ours at stresses whih are lower than the stresses in the lades. ODS alloys only eome superior where a large mirostrutural staility is required, at medium stresses and temperatures higher than the y' oarsening temperature: o^$q^0h «250MPa for MA 6000, ompared to af^0h «175MPa for IN 738[25]. The modelling of prodution proesses will need further development, essentially for ost savings, hi fat, typially 70% of the prie of semifinished parts of lades and disks is the input material ost. Then, the final mahining doules the omponent ost. Therefore, ost savings an only e done y produing netshape omponents to redue the material input weight. This will e done y preise modelling of the prodution steps: solidifiation, hot working or Hot Isostati Pressing [20]. The development of large landased turines like in HTGRs also requires progress in material mehanial testing and life modelling [25]. The total lifetime required for the hot omponents will e greater than in the past: around hours instead of hours. Low yle and thermal fatigue will still e life determining failure modes, ut high temperature oxidation and reep rupture may eome more important, hi servie degradation of the alloy mirostruture will lead to a redution in the reep rupture strength, and it will e needed to predit aurately the life of "degraded" omponents. This will e possile y developing experimental tests to quantify and to evaluate the interation etween reep damage mehanisms and mirostrutural evolutions. REERENCES [1] INTERNATIONAL ATOMIC ENRGY AGENCY, Design and development of gas ooled reators with losed yle gas turines, IAEATECDOC 899, Vienna, (1996). [2] INTERNATIONAL ATOMIC ENRGY AGENCY, Current status and future development of modular high temperature gas reator tehnology, IAEATECDOC (new), Vienna, (2000). [3] OKBM, Coneptual Design report, Task PL9, Prod. PL94, Rev.0, (1998). [4] OKBM, Turoompressor Design performane (draft report), Task PCS 4, Prod. PCS 4 4, Rev.0, (1996). [5] OKBM, Report on turoompressor materials (inal report), Task PCS 48, Prod. PCS 483, Rev.0, (1997). [6] NICKEL H., SCHUBERT., SCHUSTER H., Evaluation of alloys for advaned High Temperature Reators systems, Nulear engineering and design 78 (1984)

13 [7] GRAHAM L.W., Materials for advaned high temperature reators, Rev. Int. Htes Temp, et Refrat., T13, (1976), pp [8] KOHLER B., GTMHR turoompressor Design Report, Allied Signal report n , (1995) [9] BENN R.C., MCCOLVIN G.M., The development of ODS superalloys for industrial gas turines, Superalloys 1988, Ed. S. Reihman, D.N. Dhul, G. Maurer, S. Antolovith and C. Lund, The Metallurgial Soiety, (1988), pp [10] JOHNSON W.R., THOMPSON L.D., LECHTENBERG T.A., Design of wrought nikelase alloys for advaned high temperature gas ooled reator appliations, Nulear Tehnology vol. 66, (1984), pp [11] WEISBRODT LA., Summary report on tehnial experienes from high temperature helium turomahinery testing in Germany, IAEATECDOC 899, (1996), pp [12] SCHUSTER H., JAKOBEIT W., High temperature alloys for the power onversion loop of advaned HTRs, Proeedings of the symposium "GasCooled Reators with emphasis on advaned systems", Mih, vol. 1, (1976), pp [13] JAKOBEIT W., PELER J.P., ULLRICH G., Evaluation of high temperature alloys for helium gas turines, Nulear tehnology vol. 66, (1984), pp [14] SHAHJMAN P., SADANANDA K., Creep and fatigue rak growth ehaviour of some ast nikelase alloys, Materials Siene and Engineering A108 (1986) [15] JAKOBEIT W., PM MoTZM turine ladesdemands on mehanial properties, Refratory and Hard Metals, Sept. 1983, (1983), pp [16] GRAHAM L.W., Corrosion of metalli materials in HTRhelium environments, Journal of Nulear materials, vol. 171, (1990), pp [17] MONMA Y., Creep and stressrupture / long term, Superalloys, Superomposites and Supereramis, Ed. Tien and Caulfield, Aademi Press, (1989), pp [18] VISWANATHAN R, SCHEIRER S., STRINGER J., Materials advanements in land ased gasturines, Proeedings of PowerGen International, Orlando, 1998 (1998). [19] MATERIALS SOLUTIONS 98, Gas turine materials tehnology, Conferene proeedings from Materials Solution'98, Pu. ASM International, (1998). [20] WINSTONE M.R., PARTRIDGE A., BROOKS J.W., The ontriution of advaned materials to future aeroengines, Proeedings of the fifth international Charles Parsons Turine Conferene, July 2000, (2000), pp [21] OAKES G., SHAW L.H., COULSON W., The use of aerospae materials and manufaturing tehnology for power generation gas turines, presented at the fifth international Charles Parsons Turine Conferene, July 2000, (2000). [22] THOMAS M., Materials Development in aero gas turines, Proeedings of the fifth international Charles Parsons Turine Conferene, July 2000, (2000), pp [23] BECKER B., Potential Benefits of advaned Materials for performane and life yle ost of large industrial gas turines, Proeedings of the fifth international Charles Parsons Turine Conferene, July 2000, (2000), pp [24] BURLET H., LUTHI T, MCCOLVIN G., GALLET S, OLSCHEWSKI J., PETEVES S, RAISSON G., VOGEL., Development of Bimetalli Gas Turine Components, presented at the fifth international Charles Parsons Turine Conferene, July 2000, (2000). [25] SINGER R.., Advaned materials and proesses for landased gas turines, Materials for advaned power engineering part 2, ed. D. Coutsouradis et al., (1994), pp [26] STRINGER J., VISWANATHAN R, Gas turine hot setion materials and oatings in eletri utility appliations, Proeedinds of ASM 1993 ongress materials, Pittsurgh, (1993), pp

14 Appendix 1 CHEMICAL COMPOSITION O INVESTIGATED ALLOYS Possile alloys Alloy 713LC MARM 004 IN 738 IN 792 Rene 80 M21 M21Z IN 591 IN 100 Udimet 700 MARM 247 Nx188 Nimoni 80A Nimoni 90 Nimoni 105 IS145 Nimoni 115 Udimet 520 ReneN4 MoTZM for lades proess CDS C, SC C,P (weight %) Ni Cr Co Mo Al Ti w N others 0.07C, O.lZr, 0.009B 1.3Hf, 0.065C,0.3Ta 1.75Ta,0.11C,0.04Zr, 0.01B 3.75Ta, 0.52Hf, 0.11C, 0.012B, 0.09Zr 0.16C, 0.017B, 0.04Zr 0.1C, 0.02B, O.lZr 0.1C, 0.02B,0.5Zr 0.1C, 0.03B, 0.37Zr,3Ta 0.18C,0.014B,0.06Zr, IV 0.08C 0.15C, 3.0Ta, 1.3Hf 0.04C 0.04C, 1.86e, 0.045Zr 0.09C 0.14C, 0.051Zr 0.11C, 0.88Hf 0.16C 0.05C, 0.005B 4Ta 0.015C, 0.09Zr : wrought or forged, C : as Cast, P : Powder Metallurgy, DS : Diretionally Solidified, SC : Single Crystal. Possile alloys for disks (weight %). Alloy A 286 IN 706 Waspaloy Udimet 720 (PER 72) Merl 76 Rene 88DT N18 IN 718 MA6000 ZhS6 VZhL12U proess,p P P P P C C Ni Cr Co Mo Al Ti w N others ease, 0.05C, 0.015B ease, 0.03C, 0.08C, 0.006B, 0.06Zr 0.03C, 0.033B, 0.03Zr 0.02C, 0.5Hf 0.05C, 0.05Zr 0.13e,0.03Zr,0.5Hf, 0.015B,0.018C 19e 2.0Ta, 0.05C, 0.01B, 0.15Zr, 1.1Y2O3 0.11C,0.9V,0.9Hf 0.17C, 0.75V : orged, C : as Cast, P : Powder Metallurgy. 176