Neutron Irradiation Effects on Grain-refined W and W-alloys

Transcription

1 25th IAEA Fusion Energy Conference October 2014 Saint Petersburg, Russian Federation MPT/1-4 Neutron Irradiation Effects on Grain-refined W and W-alloys A. Hasegawa a, M. Fukuda a, T. Tanno a,b, S. Nogami a, K. Yabuuchi a, T.Tanaka c and T.Muroga c a Graduate School of Engineering, Tohoku University, Sendai, Japan b Japan Atomic Energy Agency, Oarai, Ibaraki, Japan c National Institute for Fusion Science, Toki, Japan

2 1. Introduction Outline 2 2. Summary of neutron irradiation effects of Tungsten based on previous data. 3. Prediction of microstructural development of tungsten under fusion reactor irradiation conditions. 4. Tungsten alloys development by grain refining and alloying for fusion application. 5. Current status of material evaluation of unirradiated state.

3 Tungsten in Fusion Reactor 3 Tungsten is candidate material for first wall and divertor components in fusion reactor. Resistance to High-Hear-Load and High- Density-Particle Irradiation High melting temperature High resistance to sputtering Low hydrogen retention Divertor : Impurity exhaust apparatus Blanket Cooling Block Coating on plasma facing surface (Thickeness:1mm for TBR) Cooling component

4 3450 Temperature Dependence on Microstructure and Physical Properties of Tungsten 4 Residual stress Elongation Physical properties of W DBTT UTS Thermal conductivity High temperature strength RT Temperature / Grain structure of W Strategy of material development of Tungsten Recovery Recrystallization Grain growth Melting Recrystallization Temp. Decrease DBTT (Ductile-Brittle-Transition- Temperature) Improve low temperature embrittlement. Increase recrystallization temperature. Increase high temperature strength.

5 Improvement of Mechanical Properties by Microstructure Control Alloying decrease DBTT increase recryst. temp. Cold work decrease DBTT decrease recryst. temp. Cold work Alloying Arc melting Particle (or hole) dispersion Obstacles of GB sliding and motion Improve high temp. strength & recrystallization behavior Stability of the obstacles Decrease DBTT Increase recryst. temp. Increase high temp. strength Fine grain Powder Metallurgy Mechanical Alloying Fine grain by working and stabilized by dispersed obstacles 5 Fine Grain Improve low temp. embrittlement Introduce defect sink Particle dispersion

6 Examples of Microstructure Control of W PM W Full Recrystallize ( R ) PM W Recrystallize (R) PM W Stress Relief (SR) 6 Coarse Grain Grain size 100x100μm Arc Melt W(as-cast) Coarse Grain Grain size 100x50μm MA W-TiC UFG Layered Structure Layer thickness<10μm K-doped W Coarse Grain Grain size ~1mm CVD W Ultra fine grain Grain size nm バブル Dope hole dispersion La-doped W Columnar 100nm x 1μm Ultra Fine Grain (<100nm) with Carbide precipitates on GB 粒子 La 2 O 3 particle dispersion

7 1. Introduction Outline 7 2. Summary of neutron irradiation effects of Tungsten based on previous data. 3. Prediction of microstructural development of tungsten under fusion reactor irradiation conditions. 4. Tungsten alloys development by grain refining and alloying for fusion application. 5. Current status of material evaluation of unirradiated state.

8 Irradiation temperature, o C Summary of Damage Structure Map of W Void Hasegawa, FED 89 (2014) 1568 EBR-II [1] EBR-II [2] EBR-II [3] EBR-II [4] Void Lattice JOYO HFIR JMTR Displacement damage, dpa 20 nm g=330 Void Loop dpa In JOYO #Void was observed above 0.1dpa irradiation, above 400 up to #Loop was also observed above 400. Upper limit of loop formation could not be confirmed. #Void lattice formed after higher level irradiation (>1dpa). [1] Williams(1983), [2] Sikka(1972), [3] Sikka(1973),[4] Rau (1969)

9 538 / 0.96 dpa Damage Structure of W and W-Re Alloys Irradiated in JOYO (first neutron spectrum reactor) Arc W Arc W (Void lattice) Arc W - 5Re Arc W - 10Re W - 3Os / 1.54 dpa g= nm Void Void Void Lattice [ - 110] [110] 100 nm Prec. ( c ) g= nm Void Void & Precipitate Prec. ( s ) Void & Precipitate Prec. ( c ) g=110 Prec. ( s ) Void Precipitate g=110 Precipitate Arc W Arc W (Void lattice) Arc W - 5Re Arc W - 10Re Arc W - 26Re Void & Loop Loop Void Lattice Void & Precipitate Loop Precipitates ( c ) Precipitate Precipitate Prec. ( c ) g= nm [ - 110] [110] 100 nm g= nm Prec. ( c ) [ - 110] [110] g=110 # Void lattice were observed in pure W. ( pure W W-1.5Re-0.05Os after 1.5dpa) # Void formation was drastically suppressed in W-Re and acicular precipitates were observed above 5%Re. T. Tanno, Mater. Trans 52 (2011) 1447

10 1. Introduction Outline Summary of neutron irradiation effects of Tungsten based on previous data. 3. Prediction of microstructural development of tungsten under fusion reactor irradiation conditions. 4. Tungsten alloys development by grain refining and alloying for fusion application. 5. Current status of material evaluation of unirradiated state.

11 Re Concentration [mass%] Summary and Prediction of Microstructural Development of W JMTR JOYO HFIR Temperature JMTR Fission Reactor JOYO DEMO DEMO 3-6%Re 15-30dpa Void+Precipitate 1 JMTR JOYO ITER Fusion Reactor Precipitates Void Loop dpa ITER Below 1%Re Around 1dpa Void (Lattice?) Hasegawa, FED 89 (2014) 1568

12 Irradiation hardening, DHV Background of Grain Refined W Development 12 Irradiation hardening of advanced W alloys JMTR 873K, 0.15dpa JMTR 1073K, 0.22dpa Joyo 804K, 0.44dpa Joyo 856K, 0.47dpa Joyo 1029K, 0.42dpa Fukuda, JNM 442 (2013) S273-S276

13 Defect Clusters in Matrix after JOYO Irradiation 13 Irradiation conditions Calculate void swelling (%) Pure W La-doped W K-doped W 531 o C, 0.44dpa o C, 0.47dpa o C, 0.42dpa Fukuda, JNM 442 (2013) S273-S276 Irradiation response of the advanced W alloys were almost the same as pure W. Matrix condition for defect clustering were considered to be similar between these specimens.

14 1. Introduction Outline Summary of neutron irradiation effects of Tungsten based on previous data. 3. Prediction of microstructural development of tungsten under fusion reactor irradiation conditions. 4. Tungsten alloys development by grain refining and alloying for fusion application. 5. Current status of material evaluation of unirradiated state.

15 15 Fabricated W and W-alloys in LHD Project Name of fabricated alloys Pure W W 1%Re K doped W W 3%Re K doped W 3%Re La doped W 3%Re Pure-W K doped W K doped W 3%Re Pure W 13mmt 1 2 By A.L.M.T. Corp. 1PM and hot rolled plates 5mmt or 7mmt 2PM and swaged rod 20mmφ,10mmφ Example of impurities C O N Re K Al Si [ppm] [ppm] [ppm] [%] [ppm] [ppm] [ppm] Pure W 10 < 10 < 10 < 5 < 2 < 5 W-1%Re 10 < 10 < < 5 < 2 < 5 K doped W 10 < 10 < Relative density Pure W : 99.0% W 1%Re: 99.1% K doped W: 99.1% ρ 0 :19.1 g/cm 3

16 Grain Structure (As received) 16 As received : Heat treated at 900 for 20min Hot rolled structure Layered structure

17 Average grain size, mm Recrystallized Behavior of Rolled Plate P: number of grain boundary intersections per unit length of test line Pure W K-doped W W-3%Re K-doped W-3%Re P C R.D. P ave =(P A P B P C ) 1/ Heat treatment temperature, o C P B P A

18 Ultimate tensile strength, MPa Temperature Dependence of Strength 18 Strength increase by K-dope (at RT: 64% up, 1500 : 36% up) Strength increase above 900 by Re addition to K-dope W. K-doping Fine grain size Obstacles for dislocation and GB sliding, and recrystallization Pure W K-doped W K-doped W-3%Re X-direction R.D. Re addition Solute Re Solution softening(<900 ) Solution hardening(>900 ) SS-J (R.D.//T.D) Temperature, o C

19 Ultimate tensile strength, MPa Ultimate tensile strength, MPa Ultimate tensile strength, MPa Fukuda, to be presented in TOFE (2014) Anisotropic Tensile Strength 19 Anisotropy was observed in the temperature range of R.T o C. Y Z X X Y Z Ductile X Y Z R.T X Y Z X-direction Y-direction Z-direction X-direction Y-direction Z-direction X-direction Y-direction Z-direction 1000 Pure W 1000 K-doped W 1000 K-doped W-3%Re Temperature, o C Temperature, o C Temperature, o C

20 Fukuda, to be presented in TOFE (2014) Strain Rate and Temperature Dependence of Strength Time dependent mechanical properties 20 R.D. SS-J (R.D.//T.D)

21 Strain Rate Dependence of Tensile Behavior Time dependent mechanical properties 21 DBTT of tensile deformation is decreased about 100 by K-dope process. R.D. SS-J (R.D.//T.D) Fukuda, to be presented in TOFE (2014)

22 Thermal Diffusivity [mm 2 /s] Thermal Diffusivity [mm 2 /s] Thermal Diffusivity Effects of grain boundary and microstructure anisotropy. 22 Evaluated by Laser flash method. 70 Pure W (10mmφx2mmt, C) 70 Pure W (5x5mm x 1mmt) 単結晶 W Single Crystal Poly Crystal 多結晶 W A B C Temperature [ ] Temperature [ ] TD of poly crystal is lower than TD of single crystal, but difference is small. Anisotropy of TD of pure W(poly-X) is not observed.

23 Thermal Diffusivity [mm 2 /s] Thermal Diffusivity of W and W alloys mmφ x 2mmt, C-plane Pure W Pure W K-doped W W-1%Re W-3%Re K-doped W-3%Re La-doped W-3%Re Temperature [ ] TD of W alloys are lower than pure W. Temperature dependence of TD was not significant by 3%Re addition.

24 Thermal conductivity, W/m/K Thermal Conductivity of W and W alloys mmf, 2mmt Cp : Thermal Conductivity : Thermal Diffusivity : Density C p : Specific Heat Pure W K-doped W K-doped W-3%Re Temperature, o C Cp : Thermal Conductivity : Thermal Diffusivity : Density C p : Specific Heat Trend is the same as thermal diffusivity

25 1. Introduction Outline Summary of neutron irradiation effects of Tungsten based on previous data. 3. Prediction of microstructural development of tungsten under fusion reactor irradiation conditions. 4. Tungsten alloys development by grain refining and alloying for fusion application. 5. Current status of material evaluation of unirradiated state.

26 Temperature, o C Thermo-mechanical Analysis 26 W OFHC-Cu CuCrZr Thermo-mechanical analysis of the W and its alloys mono-block tile under heat load using FEA is now in progress Pure W K-doped W K-doped W-3%Re Heat load A Point A Heat load, MW/m 2 Pure W K-doped W K-doped W- 3%Re Time, s 20 MW/m 2 10 s Fukuda, to be presented in TOFE (2014)

27 Recrystallization 27 In the case of pure W, the depth of the recrystallized area was ~8 mm from the top surface. The depth of the recrystallized area were 6 and 3 mm from the top surface for K-doped W and K-doped W-3%Re, respectively. Increase in recrystallization temperature by K and Re dope decreased recrystallized depth. Pure W K-doped W K-doped W-3%Re >1100 o C >1300 o C >1800 o C 20 MW/m 2 10 s

28 Temperature, o C Recrystallized depth from top surface, mm Recrystallization The threshold temperature of the recrystallization was estimated as ~11, ~12, and 15 MW/m 2 for pure W, K-doped W, and K-doped W-3%Re, respectively. The recrystallization depth was linearly increased with increasing heat load. Thermal conductivity decrement Recrystallization temperature increment Point A A < 10 8 Mechanical property Embrittlement resistance Trade off Pure W K-doped W K-doped W-3%Re Thermal property Pure W K-doped W 2 K-doped W-3%Re Heat load, MW/m Heat load, MW/m 2

29 Summary # Microstructural data of neutron irradiated Tungsten (W) obtained by neutron irradiated W up to 1.5dpa irradiation in the temperature range of C were compiled quantitatively. Nucleation and growth process of these defects were clarified and a qualitative prediction of the damage structure development and hardening of W in fusion reactor environments were made taking into account the solid transmutation effects for the first time. # Powder metallurgically processed pure W and W-alloys were fabricated to improve mechanical properties, recrystallization behavior and radiation resistance of W by grain refining and alloying processes. # Mechanical property and thermal property of the alloys were obtained. Improvement of strength, low temperature embrittlement and recrystallization behavior of the W-alloys compared to pure W were demonstrated. Neutron irradiation experiment of these materials using a fission reactor (HFIR) will start during # Trade-off between the thermal conductivity and mechanical property, embrittlement resistance by the structural control must be considered quantitatively to design diverter cooling component. The thermo-mechanical analysis of the diverter block made of the alloys considering thermal diffusivity and recrystallized temperature were performed by finite element analysis. 29

30 30 Thank you for your attention.

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