Radiation Embrittlement Database for High Temperature Refractory Alloys

Transcription

1 Radiation Embrittlement Database for High Temperature Refractory Alloys S.J. Zinkle Metals & Ceramics Division, Oak Ridge National Lab presented at the APEX Study Meeting PPPL, May 12-14, 1999

2 Possible Structural Materials for High Wall Loading Concepts Low-activation materials Vanadium alloys Ferritic/martensitic (8-9%Cr) steels, ODS steels SiC/SiC composites Refractory alloys Nb-1Zr Nb-18W-8Hf T-111 (Ta-8W-2Hf) TZM (Mo-0.5Ti-0.1Zr-0.02C) Mo-Re W-25Re Ni-based superalloys Porous-matrix metals and ceramics Intermetallics TiAl Fe 3 Al Composites C/C metal matrix composites Cu-graphite Ti 3 SiC 2 composites Conventional structural alloys Austenitic stainless steel

3 Factors Affecting Selection of Structural Materials Unirradiatiated mechanical and thermophysical properties Chemical compatibility/corrosion effects Materials availability / fabricability / joining technology Radiation effects < focus of this presentation Safety aspects (decay heat, induced radioactivity, etc.)

4 Resources for Structural Materials Database Fusion Materials Properties Handbook / ITER Materials Properties Handbook, ed. J.W. Davis (Boeing/St Louis) - V alloy chapter has not been updated in latest version of IMPH (pub. 5) - limited or no information for F/M steels, SiC/SiC Aerospace Structural Metals Handbook ( ), ed. W.F. Brown, Jr. - mechanical and thermophysical properties of refractory alloys vs. temperature Proc. Conf. on Refractory Alloys for Space Nuclear Power Applications, eds. R.H. Cooper, Jr. and E.E. Hoffman, CONF (1984) ITER Materials Assessment Report G A1 DDD W01.1 (Chapter 2.2, W alloys) Original research publications

5 Ultimate Tensile Strength (MPa) Ultimate Strength of Group VI Refractory Alloys W Data from Tietz & Wilson 1965, Conway 1984, Buckman 1994, Gubbi 1996, ITER MPH, Aerospace Struct. Metals Hndbk 1969, Bryskin 1998 W Mo (TZM) Filled symbols: Stress relieved Open symbols: Recrystallized W-25 Re Temperature ( C)

6 Summary of V-4Cr-4Ti Properties Ultimate Tensile Strength (unirradiated) σ UTS (MPa)= *T *T e-06*T e-10*T 4 (T in C) Yield Strength (Unirradiated) σ Y (MPa)= *T *T e-07*T e-10*T 4 (T in C) Elongation e tot, RA are high in unirradiated and irradiated conditions e u is high in unirradiated conditions, moderate (>2%) after irradiation at T>430 C and low (<1%) for irradiation at T<400 C Elastic constants E Y (GPa) = *T (T in Kelvin) G (GPa) = *T (T in Kelvin) ν=(e Y /2G) - 1 Thermophysical properties α th = *T x10-7 * T 2 C P = / T J/g-K (T in Kelvin) k th = T W/m-K (T in Kelvin) ppm/ C (T in C) Recommended operating temperature limits (structural applications) Tmin = 400 C (due to rad.-induced increase in DBTT at low T irr ) Tmax = 700 C (corrosion/chemical compatibility and thermal creep)

7 Summary of 8-9Cr Ferritic/Martensitic Steel Properties Ultimate Tensile Strength (unirradiated) σ UTS (MPa)= *T *T e-05*T e-09*T 4 (T in C) Yield Strength (Unirradiated) σ Y (MPa)= *T *T e-06*T e-10*T 4 (T in C) Elongation e tot, RA are moderate to high in unirradiated and irradiated conditions (e tot ~8-10% for T irr <400 C) e u is low in unirradiated (0.2-7%) and irradiated (<3%) conditions Elastic constants E Y (GPa) = *T C (T in Kelvin) G (GPa) = *T C (T in Kelvin) ν=(e Y /2G) - 1 Thermophysical properties α th = 10.4 ppm/ C (20 C) to 12.4 ppm/ C (700 C) C P = 0.47 J/g-K (20 C) to 0.81 J/g-K (700 C) k th = 33 W/m-K ( C) Recommended operating temperature limits (structural applications) Tmin = 250 C (due to rad.-induced increase in DBTT at low T irr ) Tmax = 550 C (thermal creep); Tmax~700 C for ODS steels?

8 Ultimate Tensile Strength (unirradiated) σ UTS ~ MPa ( C) Summary of SiC/SiC Properties Proportional Limit Strength (Unirradiated) σ Y (MPa) ~70 MPa ( C) Elongation e tot, eu, RA are very low in unirradiated and irradiated conditions Elastic constants E Y GPa) ~400 GPa C G (GPa) =~165 GPa C ν= C (Sylramic or Hi-Nicalon type S fibers, 10% matrix porosity) Thermophysical properties α th ~ 2.5 ppm/ C (20 C) to 4.5 ppm/ C (1000 C) C P = T e T k th = W/m-K J/kg-K (1000 C) ( C, after irradiation) Recommended operating temperature limits (structural applications) Tmin ~ 500 C? (due to rad.-induced decrease in thermal conductivity) Tmax = 1000 C? (due to cavity swelling)

9 Effect of Strain Rate on the Tensile DBTT of Tungsten Reduction K 1C (MPa-m in Area 1/2 ) (%) Effect of Thermomechanical Processing and Alloying Additions on the Fracture Toughness of W W, W-(La,Y) oxide, 0.2 sw-2%re -1 80%CW, LT and TL 8x10-4 s -1 LT TL W; Podrezov 1987 W-(La,Y)oxide; Podrezov s -1 W-2%Re; Podrezov 1987 W, Marschall&Holden 1966 W, Marschall&Holden s -1 W, stress relieved, LT W, rexl'd, LT Magnusson & Baldwin Temperature ( C) Temperature ( C)

10 K 1C (MPa-m 1/2 ) Fracture Toughness of Pure Tungsten 80%CW ; Podrezov et al W, as wrought, ITER DDD 1998 W, rexl'd, ITER DDD 1998 W, Marschall 1966 LT wrt+str.relief W, Marschall 1966 LT rexl'd Temperature ( C)

11 Effect of Strain Rate on the Tensile DBTT of Tungsten Reduction in Area (%) s s s -1 8x10-4 s -1 Magnusson & Baldwin Temperature ( C)

12 Overview of Radiation Effects in Refractory Metals Void swelling is not anticipated to be a lifetime-limiting issue due to the BCC structure of the high-temperature refractory alloys - existing fission reactor data base indicate moderate swelling (<2%) for doses up to 10 dpa or higher - effects of fusion-relevant He generation on swelling is uncertain - swelling regimes are ~600 to 1000 C for all 4 classes of refractory alloys The Group Vb alloys (Nb, Ta) exhibit better ductility before and after irradiation - very limited mechanical properties data base on irradiated Nb, Ta alloys - extensive mechanical properties data base on irradiated Mo alloys (but at relatively low irradiation temperatures) Very limited or no fracture toughness/charpy impact data on irradiated high temperature refractory alloys - tensile DBTT of Mo, W alloys increases to very high values even for low dose irradiations at moderate temperatures (e.g., 600 C after ~1 dpa irradiation at 300 C for W, W-10Re) Refractory alloys are generally designed for use in stress-relieved condition (rather than recrystallized) in order to achieve of higher strength - radiation-enhanced recrystallization and/or radiation creep effects need to be investigated (designs should use recrystallized strengths to be conservative)

13 Radiation Effects on Mechanical Properties of High-Temperature Refractory Alloys Ta Alloys: T-111 (Ta-8W-2Hf) Significant radiation hardening at 415, 640 C (σ y, UTS>1000 MPa) after 1.9x10 26 n/m 2, E>0.1 MeV (2.5 dpa Ta, 10 dpa steel) --Wiffen 1984 Very little radiation hardening at 800 C (Wiffen 1984) => estimated minimimum operating temperature ~650 C, based on DBTT considerations Mo Alloys: TZM, etc. (largest irradiated data base among high temperature refractories) Pronounced radiation hardening up to ~600 C, 7-34 dpa; tensile strength after irradiation at 800 C, 11 dpa was ~1000 MPa (Hasegawa et al. 1995, 1996) Tensile elongation ~0 for T irr < 700 C, 5-20 dpa in Mo, TZM, Mo-Re alloys (Steichen 1976, Chakin&Kazakov 1996, Fabritsiev & Pokrovsky 1998) Tensile embrittlement observed in Mo-Zr-B for T irr = C, ~10 dpa; tensile DBTT decreased rapidly for T irr >900 C (Chakin&Kazakov 1996) Irradiation data at doses >0.1 dpa is not yet available for radiation embrittlement-resistant Mo-TiC alloys; impact bending specimens are not notched!! (Kurishita et al. 1996) No known fracture toughness data on irradiated specimens => estimated minimum operating temperature ~750 C??, based on DBTT considerations

14 Radiation Effects on Mechanical Properties of High-Temperature Refractory Alloys, continued W and W Alloys: P/M or CVD W, W-1% La 2 O 3, W-Mo-Y (alloy W-13I) Tensile elongation ~0 for T irr = 400, 500 C, x10 26 n/m 2, <2 dpa (Steichen 1976, Wiffen 1984, Gorynin et al 1992); irradiations at 700 C are in progress Un-notched bend bar DBTT>900 C for W, W-10%Re irradiated at 300 C, 0.5x10 26 n/m 2, (~1 dpa); most rapid embrittlement observed for W-10%Re (Krautwasser et al 1990) => estimated minimimum operating temperature ~800 C, based on DBTT considerations (scaling from Mo alloy data base)

15 Estimated Operating Temperature Limits for Refractory Alloys in Fusion Reactors W Mo (TZM) Ta-8W-2Hf Nb-1Zr V-4Cr-4Ti Temperature ( C) Lower temperature limit based on radiation hardening/ fracture toughness embrittlement (K 1C <30 MPa-m 1/2 ) large uncertainty for W due to lack of data Upper temperature limit based on 100 MPa creep strength (2% in 1000 h); chemical compatibility considerations may cause further decreases in the max operating temp.