CuZr-Mo bimetals for CLIC accelerating structures for CLIC accelerating structures Introduction Introduction HIP diffusion bonding Explosion bonding p g Brazing-thermal treating Others Forum on Materal and Surface Technologies - 1 CERN 21/11/2008 G. Arnau Izquierdo
Bimetals for CLIC. Introduction. CLIC (Compact Linear Collider) two beam scheme: � Acceleration of main e+/e- beam to 1.5+1.5 TeV: use high accelerating � field to limit the machine length Demonstration of technical feasibility. Structure technology development � (amongst other issues) 2 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
Bimetals for CLIC. Introduction. � Hybrid Dumped accelerating Structures (HDS) concept. ▲ Copper prototype of ¼ of HDS structure containing 10 cell cavities. g ▲ Detail of HDS cells ▲ Detail of HDS cells geometry. 3 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
The material problem. High H field regions. � Periphery: regions with pulses of magnetic field ◄ Surface magnetic g inducing surface currents field distribution in � ∆ T= 56 K, 2.3x10 10 cycles HDS cell. � pulsating compressive l ti i ▼ Surface of Cu and stress 0 to 155 MPa CuZr specimens after � fatigue surface damage equivalent tests of thermal induced fatigue (laser simulation) � use of CuZr, or improved mechanical strength high h i l t th hi h conductivity alloy. CuZr Cu 4 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
The material problem. High E field regions. � Iris: regions with surface electric field >300 MV/m ◄ Surface electric (originally) field distribution in HDS cell. � high field and breakdown events events � geometry modification ▼ Accelerating structures in Mo and Cu after RF and Cu after RF � use of Mo, or alternative tests at SLAC. refractory metal. � But found that for low breakdown probability Mo is less favourable : the baseline is now all the structure made of copper- b based material ! d t i l ! 5 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
Aims Bimetallic CLIC accelerating structures may be needed for enhanced Bi t lli CLIC l ti t t b d d f h d � performance Regions of high electric field: � � pure Mo (or alternative refractory & low P � pure Mo (or alternative refractory & low P vap alloy) Regions of high pulsed currents: � � CuZr alloy UNS C15000 in the best ll UNS C15000 i th b t C Z achievable temper state (or alternative copper alloy with best match of conductivity and fatigue resistance: ODS Cu, CuCrZr, …) � Find a way of producing bimetallic raw material with: suitable geometry � sufficient bond strength and soundness � limited effect on bulk material properties � � Explore and develop bonding methods � Quantify their performance set up acceptance criteria set up acceptance criteria 6 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
Bonding techniques Promising bonding techniques explored so far: � HIP diffusion bonding (METSO Oy /FI) � Explosion bonding (Research Institute of Impulse Processes / BY) � Brazing (Politecnico di Torino /IT, running) � Also attempts of coextrusion and vacuum casting Also attempts of coextrusion and vacuum casting � � Reminds on the materials: � Pure Molybdenum � Unsuitable DBTT if recrystallised (recrystallisation may occur at � temperatures above 900 °C depending on time exposure and previous cold work) k) CuZr, UNS C15000 � Solution annealing at 900 °C to 980 °C (5 min to 30 min), followed by rapid � cooling Artificial ageing 450 °C to 550 °C (1 h to 4 h) � The best (mechanical strength) temper states are obtained by addition of � cold work before or/and after ageing. 7 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
Precipitation hardening (applied to CuZr) � The aim is to have � The aim is to have 400 400 358 • fine precipitates for optimum mechanical strength 350 Cu-Zr equilibrium diagram 316 • and minimum Zr dissolved in the matrix for 300 maximum conductivity Cu-OFE OS050 250 220 C15000 200 205 200 TB00 Solution annealed, no cold worked 200 � The way is with a series of thermal treatments: TF00 Aged, no cold worked Cu-Zr liquid 150 1. Solution heat treatment: go and stay in the TH02 Cold worked 45% and aged 100 92 90 91 solubility region (900 to 980 ºC) to dissolve Cu5Zr 100 Solid (Cu) 69 64 54 50 45 + 41 2. 2. Quench: end by fast cooling to metastably keep Quench: end by fast cooling to metastably keep 50 50 Cu-Zr liquid C Z li id 15 15 that dissolved microstructure at RT 972 ºC 0 Solid (Cu) 3. Age or precipitate: stay a limited time at Rp0.5 (MPa) Rm (MPa) A (%) (%IACS) intermediate temperature (450 to 550 ºC) to favour Yield Strength Ultimate Strength Ductility Elec. Cond. fine precipitation fine precipitation or � Do not over-age: by doing to hot or two long such ure ºC that precipitates become coarse Solid (Cu) matrix � Avoid a too slow cooling Avoid a too slow cooling + or or Temperatu Cu 5 Zr � To boost hardening cold-work can be added before and/or after ageing or Temperature 20 ºC Weight %Zr g 0 15 %Zr 0.15 %Zr T C15000 Time 8 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion bonding 9 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion. Bonding advantages and concerns � HIP-diffusion bonding (Metso OY /FI) � Cylindrical configuration Mo insert CuZr matrix � Cylindrical configuration, Mo insert, CuZr matrix � Attempt to have the CuZr in a solution treated state right after the HIP cycle • HIP temperature set up to match solution treatment temperature of CuZr (900 ºC) • Cooling after HIP as fast as possible (HIP quenching) Cooling after HIP as fast as possible (HIP quenching) � Test pieces produced for characterization � One piece produced for machining a first bimetallic HDS prototype � Concerns: � Soundness of the bond � Avoid recrystallization of the Mo insert � Achievable strength on the CuZr matrix 10 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion. Test pieces produced � 1 st piece: • Ø50 mm x 100 mm, insert Ø 5 mm , • from extruded CuZr bar commercially available � 2 nd piece: • more careful preparation of surfaces faster cooling capable size for HDS structures • Ø 87 mm x 300 mm, insert Ø 8.6 mm • from forged CuZr bar for functional diameter � 3 nd piece: � 3 piece: • Ø 87 mm x 300 mm, insert Ø 8.6 mm • insert coated with pure opper 11 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion. Tests performed. Bond characterization Bond characterization � Bond strength � • Shear tests • Pull tests • Pull tests • Fractography Microstructure � Al (111) [Holder] Mo 50000 0.5 µ m • Metallography OM-SEM • Metallography OM-SEM • EDS diffusion profile, phases Mo CuZr 40000 • XRD Mo base material (recrystallisation?) Mo base material (recrystallisation?) � � ) Lin (Counts) 30000 • Metallography / hardness 30 02) [Holder] ion [w%] CuZr base material characterization � 25 Cu 20000 Mo As received As received Zr Zr Al (20 � malised concentrat 20 Mo2Zr (311) Cu (111) CuZr matrix Mo (110) • Grain size Mo insert 15 10000 • Hardness 10 • Tensile tests • Tensile tests Norm 0 5 36 40 • Electrical conductivity 2-Theta - Scale 0 S f f M d f AS Ni filt Fil AS ll d After further treatment 2 0 2 4 6 8 � Distance from the interface [µm] • Idem • Idem Machining test � 12 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion. As produced. Bond strength 1 st piece showed several detachments � 2 nd piece 2 piece � Shear: � • 30 % shear in CuZr, 70 % interface Pull: � ☺ Plastic deformation of CuZr before breakdown ☺ Final breakdown partially through Mo � 1 over 4 presented poor adhesion 2 nd 1 st 1 average average Shear strength 1 6 5 ± 9 2 0 6 1 6 2 1 7 4 1 6 3 1 7 4 1 5 3 ( MPa) Pull strength 1 7 5 ± 1 8 detached 1 8 3 1 8 7 1 5 4 detach. ( MPa) ( ) 13 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
HIP diffusion. As produced. Bond microstructure 1 st piece Showed local lack of adhesion � Regions with porosity at the interface Regions with porosity at the interface � � Composition profile: � diffusion of Cu in Mo along 14 µm, in � agreement with calculations agreement with calculations CuZr Mo CuZr Mo Intermetallic layer Zr-rich, confirmed by � XRD 100 Al (111) [Holder] Al (111) [H ld ] 50000 ration [w%] 90 Cu 80 Mo 40000 70 Zr ised concent 60 CuZr matrix Mo insert Lin (Counts) 30000 50 [Holder] 40 20000 30 30 Al (202) Normal 20 Mo2Zr (311) Cu (111) Mo (110) 10 10000 0 5 0 5 10 15 20 0 Distance from the interface [µm] 36 40 2-Theta - Scale S f f M d f AS Ni filt Fil AS ll d 14 Forum on Materal and Surface Technologies - CERN 21/11/2008 G. Arnau Izquierdo
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