Two grades of austenitic stainless steel, type 304 and 316L, were cold rolled to different reductions by unidirectional and by cross rolling. Subsequent solutionizing of the cold rolled samples ...produced noticeable textural differences in type 304, but insignificant differences in type 316L. Both the solutionized materials had however the same trend in grain boundary character distribution (GBCD): an increasing fraction of random boundaries with an increasing pre-solutionizing reduction percentage. The degree of sensitization (DOS) was measured by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test in both the alloys. The susceptibility to intergranular corrosion was assessed by the standard weight loss technique (practice B, A262 ASTM) in type 304 alloy. These increased with increase in random boundary concentration, but then dropped significantly beyond a ‘critical’ concentration—a pattern observed in both the grades. Such a pattern may be explained from a balance between nucleation rate of Cr-carbides and grain boundary Cr-flux, though postulating an exact model is premature at this stage. The present study, however, demonstrates a clear possibility of remarkable improvement in DOS and IGC through extreme grain boundary randomization.
Abstract
The main source of systematic uncertainty on neutrino cross section measurements at the GeV scale originates from the poor knowledge of the initial flux. The reduction of this uncertainty to ...1% can be achieved through the monitoring of charged leptons produced in association with neutrinos. The goal of the ENUBET ERC project is to prove the feasibility of such a monitored neutrino beam. In this contribution, the final results of the ERC project, together with the complete assessment of the feasibility of its concept, are presented. An overview of the detector technology for a next generation of high precision neutrino-nucleus cross section measurements, to be performed with the ENUBET neutrino beam, is also given.
Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to ...differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr
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films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.
Austenitic stainless steels like SS 304L are prone to intergranular corrosion (IGC) in boiling nitric acid media. A major cause is sensitisation induced in the heat affected zone of the weldments. ...Developments in sensitisation resistant materials have lead to the minimisation of degradation due to IGC. Corrosion in nitric acid medium is essentially controlled by oxidising potentials in the transpassive potential regime. The corrosion potential of stainless steel in nitric acid is a function of the concentration of acid, temperature and concentration of specific oxidising ions. In this work, a 'master curve' for the dependence of corrosion rates on the applied potentials was generated for type 304L stainless steel (nitric acid grade) in 6M nitric acid at near boiling (95°C) condition. The master curve was validated by measuring the corrosion rates at 48 h exposure in 6M near boiling nitric acid, in which various oxidising ions had been added. It was illustrated that there is a threshold potential (at transition to transpassivity) above which the non-sensitised stainless steel also undergoes IGC. A methodology for the prediction of corrosion rate has thus been proposed that can be applied to austenitic stainless steels at any given operating condition/component in operating plants where nitric acid media are used as process fluid. The effect of the temperature/area ratio of stainless steel on corrosion has been illustrated.
Friction and wear properties of the pack aluminized IN-RAFMS were studied at different loads and frequencies under reciprocative sliding, using a counterbody of cemented tungsten carbide (WC-Co) and ...hardened steel ball. The value of COF and specific wear rate were measured as 0.6 and 4.5 × 10−5 mm3/N-m, respectively at 20 N load and 10 Hz frequency, for the as-coated aluminized IN-RAFMs using WC-Co counterbody. Optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) were used to analyze the wear mechanism and chemistry of debris. Abrasive wear was the main mechanism identified for uncoated steel, while tribo-oxidation was found to be the main wear mechanism for aluminized steel. A finite element (FE) model was developed to predict thermal stress and coating integrity in coating interface during thermal cycling. The aluminized RAFMS having Fe2Al5 phase as the coating layer was found to be corrosion resistant in static lead-lithium eutectic and showed promising compatibility when tested at 500 °C for 500 h.
Complementary to the physics research at the LHC, several fixed-target facilities receive beams from the LHC injector complex. To serve the fixed-target physics programme at the super proton ...synchrotron, high-intensity proton beams from the proton synchrotron are extracted using the multiturn extraction technique based on trapping parts of the beam in stable resonance islands. Considering the number of protons requested by future experimental fixed-target facilities, such as the proposed search for hidden particles experiment, the currently delivered beam intensities are insufficient. Experimental studies were conducted to optimize the multiturn extraction technique, pushing its capabilities in the domain of high-intensity proton beams, and their results are presented in this paper. The success of these studies led to the decision to discontinue the former continuous transfer and remove the related hardware from the accelerator. Therefore, the multiturn extraction becomes standard operational practice for delivering proton beams for the fixed-target physics programme at the CERN super proton synchrotron.
The ENUBET ERC project (2016–2021) is studying a narrow band neutrino beam where lepton production can be monitored at single particle level. For this purpose, the decay tunnel is instrumented with ...longitudinally segmented calorimeters. Three different specialized calorimeters have been designed and tested, two of which based on the shashlik calorimetric concept with a compact readout while the third is a less compact version with a lateral readout. All of the prototypes are composed of thick steel absorbers coupled to plastic scintillators. Regarding the shashlik modules, a matrix of 3 × 3 fibers runs transversely with a density of one fiber/cm2. The fibers are coupled individually to silicon photomultipliers mounted on a custom PCB allowing to reduce the dead zones between adjacent modules to an extremely small level compared to the “fiber bundling” configurations. This setup allows a very effective longitudinal segmentation and hence e/π separation. The second shashlik module is based on polysiloxane scintillators which come in liquid form, are poured around the fiber arrays and finally made solid with a thermal treatment. Finally, the lateral readout module, light is collected from both sides of each scintillator tile and the 10 fibers from the same UCM are bundled to a single SiPM. Here are discussed the results of test beams performed in 2016–2018 at the CERN-PS East Area and the characterization of SiPMs of different cell size (12μm and 15μm) before and after being exposed to neutron fluxes up to 1012/cm2 at the INFN-LNL CN accelerator facility.
The effects of cold work and low-temperature sensitization heat treatment of non-sensitized austenitic stainless steels have been investigated and related to the cracking in nuclear power reactors. ...Types 304, 304L and 304LN developed martensite after 15% cold working. Heat treatment of these cold worked steels at 500 °C led to sensitization of grain boundaries and the matrix and a desensitization effect was seen in 11 days due to fast diffusion rate of chromium in martensite. Types 316L and 316LN did not develop martensite upon cold rolling due to its chemical composition suppressing the martensite transformation (due to deformation) temperature, hence these were not sensitized at 500 °C. The sensitization of the martensite phase was always accompanied by a hump in the reactivation current peak in the double loop electrochemical potentiokinetic reactivation test, thus providing a test to detect such sensitization. It was shown that bending does not produce martensite and therefore, is a better method to simulate weld heat affected zone. Bending and heating at 500 °C for 11 days led to fresh precipitation due to increased retained strain and desensitization of 304LN due to faster diffusion rate of chromium along dislocations. The as received or solution annealed 304 and 304LN with 0.15% nitrogen showed increased sensitization after heat treatment at 500 °C, indicating the presence of carbides/nitrides.
Crab cavities (CCs) constitute a key component of the High Luminosity LHC (HL-LHC) project. In case of a failure, they can induce significant transverse beam offsets within tens of microseconds, ...necessitating a fast removal of the circulating beam to avoid damage to accelerator components due to losses from the displaced beam halo. In preparation for the final design to be employed in the LHC, a series of tests were conducted on prototype crab cavities installed in the Super Proton Synchrotron (SPS) at CERN. This paper summarizes the machine protection requirements and observations during the first tests of crab cavities with proton beams in the SPS. In addition, the machine protection implications for future SPS tests and for the use of such equipment in the HL-LHC are discussed.
Abstract
The ENUBET ERC project, also included in the CERN Neutrino Platform as NP06/ENUBET, is developing a new neutrino beam based on conventional techniques in which the flux and the flavor ...composition are known with unprecedented precision (
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(1%)). Such a goal is accomplished monitoring the associated charged leptons produced in the decay region of the ENUBET facility. Positrons and muons from kaon decays are measured by a segmented calorimeter instrumenting the walls of the decay tunnel, while muon stations after the hadron dump can be used to monitor the neutrino component from pion decays. Furthermore, the narrow momentum width (<10%) of the beam provides a precise measurement (
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(10%)) of the neutrino energy on an event by event basis, thanks to its correlation with the radial position of the interaction at the neutrino detector. ENUBET is therefore an ideal facility for a high precision neutrino cross-section measurement at the GeV scale, that could enhance the discovery potential of the next-generation of long baseline experiments. It is also a powerful tool for testing the sterile neutrino hypothesis and to investigate possible non-standard interactions.
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