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Hot Isostatic Pressing (HIP) Assisted Diffusion Bonding Between Cucr1zr

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Hot Isostatic Pressing (HIP) Assisted Diffusion Bonding Between Cucr1zr Hot Isostatic Pressing (HIP) assisted diffusion bonding between CuCr1Zr and AISI 316L for application to the Super Proton Synchrotron (SPS) internal beam dump at CERN S. Pianese,1, ∗ A. Perillo Marcone,1, y F.-X. Nuiry,1 M. Calviani,1, z K. Adam Szczurek,1 G. Arnau Izquierdo,1 P. Avigni,1 S. Bonnin,1 J. Busom Descarrega,1 T. Feniet,1 K. Kershaw,1 J. Lendaro,1 A. Perez Fontenla,1 T. Schubert,2 S. Sgobba,1 and T. Weißg¨arber2 1CERN, 1211 Geneva 23, Switzerland 2IFAM, Winterbergstrasse 28, 01277 Dresden, Germany (Dated: November 17, 2020) The new generation internal beam dump of the Super Proton Synchrotron (SPS) at CERN will have to dissipate approximately 270 kW of thermal power, deposited by the primary proton beam. For this purpose, it is essential that the cooling system features a very efficient heat evacuation. Diffusion bonding assisted by Hot Isostatic Pressing (HIP) was identified as a promising method of joining the cooling circuits and the materials of the dump's core in order to maximise the heat transfer efficiency. This paper presents the investigation of HIP assisted diffusion bonding between two CuCr1Zr blanks enclosing SS 316L tubes and the realisation of a real size prototype of one of the dump's cooling plate, as well as the assessments of its cooling performance under the dump's most critical operational scenarios. Energy-dispersive X-ray (EDX) spectroscopy, microstructural analyses, measurements of thermal conductivity and mechanical strength were performed to charac- terize the HIP diffusion bonded interfaces (CuCr1Zr-CuCr1Zr and CuCr1Zr-SS 316L). A test bench allowed to assess the cooling performance of the real size prototype. At the bonded interface, the presence of typical diffusional phenomena was observed. Moreover, measured tensile strength and thermal conductivity were at least equivalent to the lowest ones of the materials assembled and comparable to its bulk properties, meaning that a good bonding quality was achieved. Finally, the real size prototype was successfully tested with an ad-hoc thermal test bench and with the highest operational thermal power expected in the new generation SPS internal beam dump. These results demonstrated the possibility to use HIP as manufacturing technique for the cooling plates of the new generation SPS internal beam dump, but they also open up the way for further investigations on its exploitability to improve the cooling performance of any future high intensity beam intercepting device or in general devices requiring very efficient heat evacuation systems. I. INTRODUCTION m of TZM and ∼0.4 m of pure tungsten, enclosed within 2.5 m long CuCr1Zr cooling plates and under ultra-high The new generation internal beam dump (Target In- vacuum conditions (UHV). Whenever high energy pro- ternal Dump Vertical Graphite, TIDVG#5 [1] of the Su- ton beams need to be dumped (i.e. in case of emergency, per Proton Synchrotron (SPS) at CERN, built in the during LHC beam setup or LHC filling, machine devel- framework of the Large Hadron Collider (LHC) Injectors opments and to dispose of the part of the beam for fixed Upgrade (LIU) Project [2] has been installed in the long targets remaining after the slow-extraction process), they straight section 5 (LSS5) of the SPS during the CERN's are deflected onto the absorbing blocks by an upstream Long Shutdown 2 (LS2), 2019-2020. Higher beam in- set of three vertical and three horizontal kickers. The tensities and energies, resulting from the LIU upgrades, CuCr1Zr cooling plates must dissipate most of the ther- are making the cooling of this device, and in general mal power carried by the proton beam and diffused by of most beam intercepting devices at CERN, increas- conduction from the absorbing blocks to the CuCr1Zr ingly demanding. A key problem is obtaining high lev- heat sinks. As a consequence, their heat evacuation ef- els of heat transfer efficiency between the core beam ab- ficiency is crucial for the survivability of the absorber sorbing materials and the cooling circuits. Specifically, system. the SPS internal beam dump is required to evacuate a arXiv:2011.07942v1 [physics.ins-det] 16 Nov 2020 In the previous generation device [4], the CuCr1Zr maximum average beam thermal power of approximately plates were mechanically clamping stainless steel tubes. 270 kW, more than 4 times the limit of its predeces- However, interfaces play a major role in the heat evacu- sor TIDVG#4 [3]. As shown in Figure 1, the core of ation mechanism as they represent a resistance to the the SPS internal dump is made of an array of absorb- heat transfer. For this reason, a possible way to ob- ing blocks consisting in 4.4 m of isostatic graphite, 0.2 tain the highest possible thermal contact conductance was identified by means of diffusion bonding. Hot Iso- static Pressing assisted diffusion bonding was previously ∗ [email protected] identified as promising joining technique between copper y [email protected] alloys and stainless steel [5]; by combining elevated tem- z [email protected] peratures (up to 2000°C) and isostatic gas pressure (up 2 acterize the diffusion bonded interfaces by means of mi- crostructural analyses, Energy-dispersive X-ray (EDX) spectroscopy and measurements of thermal conductiv- ity and mechanical strength. Measurements of electri- cal conductivity and Brinell hardness were performed on the bulk of CuCr1Zr to quantify the evolution of these properties after the HIP cycle and the following thermal treatments. The rest of the prototype was used within a built-in-house test bench to assess its cooling perfor- mance under the dump's most critical operational sce- nario. A. Materials FIG. 1. Cross section of the new generation SPS internal dump core, TIDVG#5 The prototype to be assembled by HIP diffusion bond- ing (Figure 2) consisted of two precipitation hardened to 200 MPa), HIP is mainly used to heal casting or ad- CuCr1Zr blanks from ZOLLERN GMBH (Germany), 2.7 ditive manufacturing defects and for powder metallurgy m long, embedding in a sandwich two U-bent SS 316L parts consolidations [6{8]. Although HIP has been ex- (EN 1.4435) tubes. Table I and Table II show the chem- tensively studied as joining technique for several materi- ical composition of this copper alloy and the SS 316L, als [9{11], it has not been used so far to manufacture by respectively. The SS 316L cooling tubes are cold bent diffusion bonding large cooling plates for ultra-high vac- and annealed. The annealing cycle for SS 316L consists uum (UHV) applications. The core of the new generation in a heating-up phase at 200-300 °C/h up to 950 °C, fol- SPS beam dump is 5 m long, but, given the maximum di- lowed by a plateau at this temperature of at least 2h mensions of HIP ovens available, the HIPed cooling plates and natural cooling-down to ambient temperature. The were divided in four parts of 2.5 m each: two bottom up- furnace employed was of the type \Grand-Four" UGINE stream/downstream and two top upstream/downstream for thermal treatments under vacuum, manufactured by (Figure 1). The objective of this work was to character- Alstom in 1974. It has an exploitable inner diameter ize the HIP diffusion-bonded interfaces between CuCr1Zr of 990 mm for 6000 mm height and a maximum capac- and SS 316L, as well as between CuCr1Zr and CuCr1Zr, ity of 1000 kg. The maximum reachable temperature and to assess the cooling performance of a real size pro- is 1100 °C with heating rates ranging from 50 °C/h to totype of cooling plate under the dump's most critical 300 °C/h. The cooling is for natural convection. The operational scenario. CuCr1Zr blanks are multi-directionally forged according The use of HIPing to diffusion bond CuCr1Zr with to the standard EN 12420 and heat treated as described SS316L has also been used with success for the CERN below. Refs. [17, 18] indicate that the following ther- Proton Synchrotron (PS) Internal dump [12] as well as for mal treatments sequence, applied on CuCr1Zr, allows to the Beam Dump Facility target prototype beam test [13] obtain the highest values of electrical and thermal con- to diffusion bond dissimilar refractory metals. Because of ductivity, hardness, tensile properties, good ductility and increasingly demanding particle beams, this manufactur- machinability: ing technique could be of interest to improve the cooling • Solution annealing between 950-1000 °C for 30 min performances of many other beam intercepting devices followed by water quenching; (BIDs) such as the new ISOLDE beam dumps, planned to be refurbished by 2025 within the scope of the EPIC • Precipitation hardening through ageing at 480- Project [14], the new 30 kW beam dump of the J-PARC 500 °C for 2 h and slow cooling in air. Main Ring (MR) [15], as well as absorbing devices within Hereinafter in the paper, the material shall be considered the Proton Improvement Plan-II (PIP-II) Project [16] at to have followed this treatment and it will be referred as FNAL, the International Linear Collider (ILC) photon \precipitation hardened CuCr1Zr" or simply \CuCr1Zr". dumps or in general any other device requiring very effi- After the HIP cycle, despite the high temperatures, cient heat evacuation systems. the grains' structure does not change, most likely due to the hydrostatic pressure at which the material is exposed during treatment, but the thermal and mechanical prop- II. METHODOLOGY erties need to be recovered using the same treatment. Table III shows how electrical conductivity and Brinell The needed components for a real size cooling plate hardness, measured on the rear side of the prototype, prototype were manufactured, assembled at CERN and change after HIP and following the different steps of the diffusion bonded by a HIP cycle.
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