Considerations on refractory metals, including results from a discussion with Plansee

1. HI-LUMI meeting, 4/09/2012, brainstorming shielding, beam screen and beam tube Considerations on refractory metals, including results from a discussion with Plansee Stefano Sgobba EN-MME-MM CERN

2. 1. Shieldingmaterial, W Message from Ezio in date 16/05 “Si tratterebbe di 20 magneti di 8 m di lunghezza. Ciascuno con 4 inserti di tungsteno a calotta, raggio di curvatura 64.3 mm, spessore massimo di 2.3 mm, e quindi sottendenti un angolo di 30 gradi. Tolleranze dell'ordine del 0.1 mm.” 2 /10

3. RemarksfromPlansee: Suggest to applyheavy W machinablealloys, namelyWNiCu (non-magnetic) grades 3 /10

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6. Resultsfrom discussion: • 8 m could not beachieved, length to befilledfrom short pieces • Not extrudable, at least not direct experience in Plansee (Lutch ?) • 3. The thinnest, the mostrealistic to beobtained net shaped or withlimitedmachining • Thickpieceswillrequire more extensive machining • Production could go throughdeepforming of sheets + machining • In case, alternative machinable W alloyscouldbeenvisaged • Cost: 180 – 250 EUR/kg 6/10

7. 2. Beamscreenmaterial, Ta • Readily weldable by EB • Weldable in TIG and laser, but very sensitive to embrittlement from interstitial impurities such as O, H, C, N • Requires perfect gas shielding (e.g. glove box enclosure) • Low CTE, approx. half of AISI 300 austenitic SS, to be compensated due to the presence of components in 316LN or similar • Young modulussimilar to austenitic SS, 183 (191) GPaat RT (4 K) 7/10

8. Yield strength up to 120 ksi (830 MPa) at • – 200 °C (Bechtold, 1944, reported by Barrett, 1957) or above 100 ksi (690 MPa) at 77 K (Wessel, 1956, ibidem). • Valid for veryhighpuritymaterial • bcc refractory metals but belonging to V-A transition element group • Maintains sone cryogenic ductility, contrary to other refractory bcc of VI-A group (W, Mo e Cr) with marked DBTT, even above RT • Welds could be less favourable ("pick-up" of interstitials) • UTS reported at 20 K: 130 ksi - 900 MPa (Ogden et al., 1961) • Reduction in area keeps high, no ductile-to-brittle transition temperature (DBTT). Elogation at breakdown of 9 % reported at 77 K (ibidem) • At 4.2 K "ductility is retained in tensile tests down to 4.2 K" (Basinski reported by Barrett) 8/10

9. Resultsfrom discussion withPlansee: • Ta readily rolled • Good formability • Rolled and welded tube nominally possible • Weld restrictions (EB, or total absence of contamination during welding...) • Fully different approach than actual beam screen: rolling in strips not possible • Limited ingot sizes, sheets with max. 2 m length for a thickness of 1.5 – 2 mm and the usual 600-700 mm width • Usual lengths 0.5 m – 1 m • Colamination with Cu (requiring strips) not possible • Seamless pipes can be processed up to 50 mm diameter • Sheet to sheet production • Cost: 800 - 1000 EUR/kg for sheets + additionaloperations, comparedwith P506 SS for beamscreen (40 – 70 sFR/kg) 9/10

10. Conclusions • Shielding W based components feasible, with more or less machining required • Outgassing of material (vacuum firing) recommended • A feasibility study could be proposed to Plansee based on production of few components, to test in particular near net shaping and forming • For beam screen and cold bore, we suggest to stick to conventional metallic material solutions, taking into account costs, industrial feasibility and post installation processing • More exotic solutions like Ir: • - high Young’s modulus 556 GPa a RT, 557 at 4 K • - hot formable, including by extrusion (Ohriner et al.) • - limited RT formability, including by rolling (warm or through several annealings) • - weldable by EB • - cost up to above 10000 CHF/kg (CES Granta), spot price up to 23000 USD/kg o 42000 USD/kg depending on puritiy • - fcc but DBTT unless very high purity 10/10