OFES Fusion Materials PI Workshop Advanced Copper Alloys

OFES Fusion Materials PI Workshop Advanced Copper Alloys for Fusion Structural Application Lance Snead Ying Yang Steve Zinkle Knoxville, July 26 th 2016

OFES Fusion Materials PI Workshop

OFES Fusion Materials PI Workshop

OFES Fusion Materials PI Workshop Advanced Copper Alloys for Fusion Structural Application ? • U. S. Program is in early stages…. let’s discuss…. . • The E. U. is now focusing on extending the ITER technology to DEMO, essentially squeezing more performance out of existing materials or developing new materials to fit into a similar diverter design philosophy- water cooled tungsten diverter.

OFES Fusion Materials PI Workshop ITER SDC-IC Annex A

OFES Fusion Materials PI Workshop Predicted Temperature Profiles in the Cooling Tube (coolant temp: 150°C) Li, You: Fusion Eng. Des (2015)

OFES Fusion Materials PI Workshop Plastic Strain in Tube Li, You: Fusion Eng. Des (2015)

OFES Fusion Materials PI Workshop Cyclic High Heat Flux Damage : Non-irradiated Pintsuk (ICFRM 2015)

OFES Fusion Materials PI Workshop Material from J-H You Meeting with Prof. Zinkle, 10 -2015

OFES Fusion Materials PI Workshop U. S. Development of High Strength, Creep Resistant Copper Alloys Current commercial Cu alloys not specifically designed for high T operation Room temperature strength and thermal conductivity

OFES Fusion Materials PI Workshop High strength in Cu alloys is traditionally achieved from finely dispersed particles (precipitation or dispersion hardening) Cu. Cr. Zr Cu. Ni. Be Requires special heat treatment or fabrication (e. g. , powder metallurgy for ODS) Potential difficulties in achieving good strength in large components or after joining Cu. Al 2 O 3 Cu. Cr. Nb

OFES Fusion Materials PI Workshop Creep begins to dominate deformation above 300 -400°C for existing Cu alloys 300°C Grain boundary sliding (“Coble creep”) is a dominant contributor to high temperature creep in conventional Cu alloys Add g. b. particles to suppress g. b. sliding Include moderate density of matrix precipitates to minimize dislocation creep

Microstructure of existing alloys Cu-(0. 6 -1. 0)Cr-(0. 1 -0. 2)Zr, Cu. Cr. Zr wt%, 970 -990 C/0. 2 -1 h, WQ, 450 -480 C/2 h aging o o Existing Cu. Cr. Zr alloys provide good resistance to dislocation creep due to the uniformly dispersed Cr matrix precipitates, but do not contain suitable precipitates to suppress grain boundary sliding

OFES Fusion Materials PI Workshop Historic NASA Alloy: Microstructure of existing Cu. Cr. Nb alloys Cu-(6. 5 -6. 7)Cr-(5. 5 -5. 9)Nb, wt%, extrusion of canned powder at 860 o. C Cu. Cr. Nb alloy developed by NASA (GRCOP-84) has good resistance to grain boundary sliding, but lacks distributed small (~10 nm) matrix precipitates to inhibit dislocation creep.

OFES Fusion Materials PI Workshop Understanding of deformation mechanisms can be used to guide the development of new creep-resistant Cu alloys Design principles: • Specifically tailored microstructural features with bimodal particle distribution: uniformly distributed small Matrix particles (~10 nm, N>1022/m 3 ) to suppress dislocation (matrix) creep, and intermediate sized particles preferentially associated with grain boundaries (d>20 nm, N~1020/m 3) to inhibit diffusional (g. b. ) creep simultaneously. • Thermally stable microstructure up to high temperatures; • Sufficient sink strength to enable suitable radiation resistance.

OFES Fusion Materials PI Workshop The Calphad approach aided alloy design Thermodynamic database Cu-Cr-Nb-Zr has been developed based on constituent binary and ternary thermodynamic models. Cu-Cr-Nb-Zr Cu-Cr-Nb Cu-Cr Cu-Nb Cu-Cr-Zr Cu-Nb-Zr Cr-Nb Cr-Zr Cr-Nb-Zr Reliability of low-order systems: models simultaneously constrained by different properties of phases. Predictive ability of high-order system: predict phase equilibria in multicomponent systems.

OFES Fusion Materials PI Workshop Alloy design of Cu. Cr. Nb. Zr- low Zr alloys Cu-Cr-Nb-0. 15 wt% Zr at 600 o. C Full scale Fcc(Cu) +Laves_Cr 2(Nb, Zr) +Bcc(Cr)+ Cu 5 Zr Enlarged scale • GB precipitate: Laves_Cr 2(Nb, Zr) • Matrix precipitate: Bcc(Cr), Cu 5 Zr

OFES Fusion Materials PI Workshop Alloy design of Cu. Cr. Nb. Zr- High Zr alloys Cu-Cr-Nb-0. 5 wt% Zr at 500 o. C Enlarged scale • GB precipitate: Cu 5 Zr • Matrix precipitate: Bcc(Cr), Laves_Cr 2(Nb, Zr)

OFES Fusion Materials PI Workshop Sample ID Low-Zr Cu. Cr. Nb. Zr Processing (arc-melting and drop cast followed by) Hardness (HV) CCNZ 5 A Cold roll 70%, solutionized at 970 C for 20 m, water quench, aging at 475 C for 3 h, water quench 123. 2± 1. 9 CCNZ 5 B Cold roll 50%, solutionized at 970 C for 20 m, water quench, aging at 475 C for 3 h, water quench 126. 2± 7. 7 CCNZ 6 A Cold roll 70%, solutionized at 970 C for 20 m, water quench 60. 5± 3. 7 CCNZ 6 B Cold roll 50%, solutionized at 970 C for 20 m, water quench 60. 6± 0. 7 970 C for 20 m, water quench, 475 C for 3 h, 123. 2 HV 970 C for 20 m, water quench, 60. 5 HV

OFES Fusion Materials PI Workshop Microstructure of newly designed Cu. Cr. Nb. Zr alloys Cu-Cr-Nb-Zr, wt%, 970 o. C/20 min, WQ, 475 o. C/3 h aging Optical image Cr 2(Nb, Zr)_Laves Cr • Newly designed Cu. Cr. Nb. Zr alloys showing bimodal distribution of precipitates. Cr 2 Nb-Laves precipitates (~50 nm) are distributed at GBs and dislocations, small Cr (~10 nm) precipitate are distributed in the matrix. SEM BSE image • Conventional, inexpensive alloying process.

OFES Fusion Materials PI Workshop • • Collaboration and Concluding Remarks First alloys possess desired large (50~100 nm) Cr 2(Nb, Zr) GB precipitates and dislocations, and (~10 nm) Cr precipitate in the matrix, showing promising mechanical properties. A US, JA and EU (KIT) collaboration to begin for the development of creep resistant alloys. E. U. JA Divertor Design Composite Dev. Alloys Fatigue Thermophysical Proposed US-KIT 2017 - 2. 5 -20 dpa tensile HFIR rabbit - Cu. Cr. Zr-X - FG-Cu. Cr. Zr - Steels, He effects, tungsten, exploratory materials Irrad Micro. X HHF Components Thermophysical Micro. X HHF Testing Process Scaling Fundamental Reff Alloy Development U. S. Replace Nb with Ta

OFES Fusion Materials PI Workshop Concluding Remarks • New low-Zr Cu. Cr. Nb. Zr alloys have been successfully made by extending the current database and using computational thermodynamics with traditional ingot making method. The first alloys possess desired large (50~100 nm) Cr 2(Nb, Zr) precipitates at GBs and dislocations, and (~10 nm) Cr precipitate in the matrix, showing promising mechanical properties. • Next we will explore replacing Nb with Ta and carrying out additional small heats with accompanying creep and othermomechanical properties.