The thermal dissipation of a bimetallic material, based on Cu periodic foams filled with a classical sintered braking pad material, is studied in the present work. First, foam design (size, porosity, angle and cross-section) and finite element method (FEM) simulation were carried out to investigate the global and local thermal diffusivity of the bimetallic materials. The samples were prepared by a mixed process of investment casting and hot pressing. The global and local thermal dissipation of the bimetallic materials were measured by laser flash analysis (LFA) and a scale-reduced tribological test bench, respectively. Finally, a thermal enhancement mechanism of foam to the bimetallic materials is discussed. The heat dissipation behavior of the bimetallic materials can be predicted due to the architecture of the foams. It is shown by both simulation and experiments that the local thermal dissipation of the bimetallic materials can be improved with decrease in representative elementary volume (REV) size of foams. The maximum diffusion distance of heat from the filler material to the foam decreases with the decrease in REV size. As a result, the heat transfer efficiency at interface increases and then the Cu foam acts as a rapid pathway, transferring the heat from the interface to the bulk.

A comprehensive study of ZrCr 2 Laves phases is important for both fundamental research and technological applications. The ZrCr 2 compound is a typical precipitate observed in Zr-based alloys including the newly developed Cr-coated Zr cladding known as Accident Tolerant Fuel cladding. The brittle behavior of the Laves phases and the low melting point at the interface zone between the precipitates and the Zr matrix are considered as governing the thermomechanical behaviors of these newly developed nuclear fuel claddings for normal operating conditions but more dramatically in case of Loss Of Coolant Accident (LOCA) conditions. The aim of the present study is to investigate the various ZrCr 2 Laves polymorphs and their thermodynamic features particularly where conflicts exist in the literature. Based on diffraction experiments of annealed samples, it has been established that the transformation from the C14 high -temperature form to the C15 low -temperature form is of displacive nature without the C36 polymorph forming as an intermediate phase. The stable and metastable domains of C14 and C15 and their thermodynamic properties have been determined. The specific heat of both C14 and C15 types was measured over a wide range of temperatures from 2 to 1063 K by coupling relaxation calorimetry and DSC. The experimental data were fitted using a modified Einstein model. The room temperature entropies of the C14 and C15 phases were evaluated. The enthalpy of formation was measured for the first time using drop solution calorimetry in liquid Al at 1173 K in a Tian - Calvet calorimeter. The experimental value is in good agreement with Density Functional Theory (DFT) calculations. Finally, all these new results are discussed regarding the abundant literature on the ZrCr 2 Laves phases.

High entropy alloys present many promising properties, such as high hardness or thermal stability, and can be candidates for many applications. Powder metallurgy techniques enable the production of bulk alloys with fine microstructures. This study aimed to investigate powder metallurgy preparation, i.e., mechanical alloying and sintering, non-equiatomic high entropy alloy from the Al-Cr-Fe-Mn-Mo system. The structural and microstructural investigations were performed on powders and the bulk sample. The indentation was carried out on the bulk sample. The mechanically alloyed powder consists of two bcc phases, one of which is significantly predominant. The annealed powder and the sample sintered at 950 °C for 1 h consist of a predominantly bcc phase (71 ± 2 vol.%), an intermetallic χ phase (26 ± 2 vol.%), and a small volume fraction of multielement carbides—M6C and M23C6. The presence of carbides results from carbon contamination from the balls and vial during mechanical alloying and the graphite die during sintering. The density of the sintered sample is 6.71 g/cm3 (98.4% relative density). The alloy presents a very high hardness of 948 ± 34 HV1N and Young’s modulus of 245 ± 8 GPa. This study showed the possibility of preparing ultra-hard multicomponent material reinforced by the intermetallic χ phase. The research on this system presented new knowledge on phase formation in multicomponent systems. Moreover, strengthening the solid solution matrix via hard intermetallic phases could be interesting for many industrial applications.

High Entropy Alloys of FeCrMnAlMo thin coatings obtained by magnetron sputtering were studied. The influence of the powder mixing method to obtain the targets used in the physical vapor deposition reactors was evaluated concerning the mechanical and tribological properties of the coatings. The microstructural characterization was also performed. The high purity element powders of 34Fe-22Cr-19Mn-19Al-6Mo were mixed in two ways: mechanically alloyed for 35 h (MS coating) and the other by conventional mixing for 30 min (CM coating). The coatings showed a poorly crystallized structure, almost amorphous. X-ray photoelectron spectrometry results evidenced that the MS coating contains approximately 8 at.% C, while no carbon was detected in the CM coating. The coatings presented hardness values determined by nanoindentation of similar to 8.7 GPa and 7.4 GPa for MS and CM coatings, respectively. A better reciprocating dry sliding wear resistance with specific wear rate (k) of similar to 3.33 x 10(-5) mm(3) N-1 m(-1) for MS coating/substrate system was found, while for the CM coating/substrate system was of similar to 8.23 x 10(-5) mm(3) N-1 m(-1). The abrasive wear mechanism was observed with the formation of ploughing, scratching and debris wear adhered to the alumina counterpart ball.

In this study, a novel high entropy alloy from the Al-Cr-Fe-Mn-Mo family was successfully prepared by mechanical alloying followed by hot press sintering. The samples were investigated by x-ray diffraction, electron backscatter diffraction, and scanning and transmission electron microscopy. The sintered samples consist of a unique new multielement body-centered cubic solid solution (more than 98 vol.%). Moreover, it is shown that, by controlling the processing conditions, it is possible to limit the formation of carbides and oxides, which are common when using powder metallurgy processing routes. The mechanical properties were investigated by micro-indentation and compression tests from room temperature up to 800°C. The results showed high micro-hardness up to 950 HV1N. The hot compression results revealed promising mechanical properties, especially at high temperatures, e.g., at 600°C, the yield strength was 1022 MPa, the maximum compressive stress was 1327 MPa, and the strain at failure was 21.8%.

The UMo/Al dispersion fuel in plate form is considered for the conversion of high-performance research reactors in Europe. In the framework of the UMo fuel qualification program, the adequate margin of safety performance by considering several technological solutions associated with the fabrication parameters, such as heat-treatment of the UMo particles, coating with a diffusion barrier material and powder size distribution as some examples. All these parameters, along with the effect of the hot-rolling process were evaluated by means of image processing and detailed microstructural characterizations for fresh samples i.e. prior to irradiation tests. Principle macroscopic features of powder batches include the size and shape distributions and coating surface examinations. Microscale investigations explored both the coating and kernel microstructures as well as the interface layer between them. Finally, nanoscale analyses examined the UMo–coating interface. The extensive stresses associated with the hot-rolling process have a significant impact on the deformation of the UMo kernels and the degradation of the coated film. The UMo kernels mostly lost their spherical shape for faceted and elongated shapes whereas three types of film degradations were identified including cracks, chippings and delamination.

This study aimed to prepare a composite of the high-entropy alloy from the Al-Cr-Fe-Mn-Mo system reinforced by in-situ formed carbides using powder metallurgy techniques. The alloyed powder was prepared by mechanical alloying in ball-mill devices from pure elemental powders with the addition of a process control agent, namely stearic acid. Then, the alloyed powder was consolidated by hot-press sintering. The structure and microstructure of powder and bulk samples were investigated. The mechanical properties of the bulk sample were evaluated. The investigations revealed two bcc phases in the mechanically alloyed powder. The powder annealing at 950 degrees C triggered the phase transformations, which led to the formation of the multielement matrix bcc phase (a = 2.91 angstrom) reinforced by two carbides molybdenum-rich M6C (a = 11.15 angstrom) and chromium-rich M23C6 (a = 10.66 angstrom). A similar composite structure was present in the bulk sample. The investigations suggested that the primary carbon source for carbide formation was the process control agent - stearic acid. The produced bulk composite revealed promising mechanical properties, such as very high hardness up to 1223 +/- 99 HV2 and Young's modulus of 246 +/- 10 GPa.

For the understanding of severe accidents in sodium cooled fast reactors (SFR), it is necessary to understand two prototypic accident scenarios such as ULOF (Unprotected Loss of Flow Accident) and UTOP (Unprotected Transient OverPower). As the base knowledge, it is also important to understand high temperature chemical interaction among major core materials such as MOx fuel (MOx: mixed oxide of uranium and plutonium), steel cladding and B4C neutron absorber have to be investigated. This study aims at providing experimental data on phase formation and phase-stability at various temperature and pressure conditions. A first series of samples containing a mixture of B4C and steel were prepared to obtain a homogenous metallic solid. In a second step, these metallic samples were mixed and melted with small UO2 pieces by arc melting. Then these samples underwent a heat treatment at 1900 degrees C for 1 hour. EDS, EBSD and EPMA analyses were performed to identify the phases formed during the solidification. In addition, thermodynamic calculations were performed for the interpretation of the results, revealing that a carbo-reduction reaction occurs: UO2 + 2 C = 2 CO + U. A significant amount of uranium from the fuel is dissolved in the metallic liquid phase, leading to the formation of mixed borides (UM3B2, UMB4, UM4B, M=Fe,Cr,Ni). In comparison with the UO2/steel interaction, the present results show that the presence of B and C in the melt improves the wetting behaviour of the metallic liquid towards UO2. (C) 2021 Elsevier B.V. All rights reserved.

In the present work, a Si/Zr based sol–gel (SG) coating was deposited on 316L stainless steel plates, previously treated by passivation (SSO) or electropolishing (SSEP) producing two different surface states. The SG coatings were compared for SSO and SSEP substrates in terms of morphology, topography and tribocorrosion response. The coating topography revealed a smoother surface for the Si/Zr-SSEP system. The coating deposited on the smoothest surface (Si/Zr-SSEP) presented half of the thickness of the one deposited on the roughest surface (Si/Zr-SSO). Tribocorrosion behavior was studied under potentiostatic control at anodic potential with a continuous recording of current (I) during sliding (pin-on-disc and alumina ball counterbody). Both SG systems showed an increase of current upon 100 sliding contact cycles indicating corrosion activity. After tribocorrosion tests, both systems revealed scratches, typical of abrasion, and coating removal in the wear tracks; the alumina counterparts presented accumulation of wear particles adhered to their surfaces. In conclusion, the initial surface state of the substrate modified the coating thickness, topography but did not significantly alter the tribocorrosion response of the studied SG systems.

The calendering process aims at enhancing the electrode energy density, and improving the electronic conductivity, and determines the final porous electrode micro/mesostructure. In this sense, one of the main parameters of interest is its impact in the electrode porosity (ε) and the electrochemical performance. Here, we present a systematic study of the calendering conditions (applied calender pressure and roll temperature) effect on the final NMC-based electrodes ε in terms of the active material/carbon additive/binder composition and the amount of solvent used during the preparation of the slurries. The calendering processability was assessed through the cathodes compressibility resistance and minimal attainable ε, the electrode mechanical properties (hardness and elastic deformability), the pore size distribution, the electrode film mesostructure and the C-rate cathode electrochemical performance. Based on our results, it was found that the distribution and organization of the inactive carbon black (CB)/PVdF phase and the electrode mesostructure are the key parameters that control the cathode processability through calendering. Electrodes with high CB/PVdF content and prepared with higher amounts of solvent in the slurry ensure a good electronic conductivity and a film-like structure of the electronic conducting phase around the NMC particles which upon calendering outputs a better electrochemical performance.

Plasma electrolytic oxidation (PEO) is a versatile and cost-effective technique to obtain protective oxide coatings in light metals, although its intrinsic porosity is a drawback for long-term corrosion resistance. Sol-gel layers are pointed as a useful tool to seal PEO porosity and increase its corrosion resistance, although little is known about its influence on the wear performance of PEO coatings. In this study, a PEO coating obtained on AA2024 was sealed with a hybrid sol-gel via dip-coating. Two withdrawal speeds were set in order to investigate the influence of the sol-gel filling in its sealing ability. Both sol-gel application conditions were able to fill the PEO pores and microcracks and change its wettability. EIS results showed samples sealed with sol-gel maintained the protective behavior upon 28 days and increased the resistance of the system by several orders of magnitude in comparison to unsealed PEO coatings. Pin-on-disk tests indicate the sol-gel decrease the shear stresses of the coating, decreasing its wear rate in 40% compared to the unsealed PEO.

The optimization of the calendering process represents one of the key tasks for tuning the lithium‐ion battery performance. In this study, we present a systematic statistical‐based study of the three main calendering parameters (namely, the applied pressure, roll temperature, and line speed) effect on the porosity, electrode mechanical properties and electronic conductivity. Our work main goal is to understand how by changing the calendering parameters, the electrode properties can be tuned and up to which degree they determine the electrode capacity of Li(Ni 0.33 Mn 0.33 Co 0.33 )O 2 ‐based cathodes. The statistical tools used for the analysis were the analysis of the covariance (ANCOVA), the principal components analysis (PCA), and the unsupervised machine learning k‐means clustering algorithm. Our results showed that while porosity and the mechanical properties depend mainly on the applied pressure, the electrode's conductivity correlates mainly with the temperature. All of them were found to influence the cathode's capacity (at a rate equal to C), being the best condition applied pressures between 60 and 120 MPa and roll temperatures between 60 and 75 °C.