Intergranular precipitation-enhanced wetting and phase transformation in an Al0.4CoCrFeNi high-entropy alloy exposed to lead-bismuth eutectic
Publisher : Elsevier
After exposure to oxygen-poor (10^-13–10^-14 wt%) liquid lead-bismuth eutectic (LBE) at 500°C for 500 h, LBE penetrates more than one order of magnitude deeper in an FCC Al0.4CoCrFeNi high-entropy alloy (HEA) deco-rated with a network of BCC (Ni, Al)-rich intergranular (IG) precipitates than in a single-phase, FCC Al0.3CoCrFeNi HEA without the IG precipitate network. This deterioration of corrosion resistance is attributed to the energetic nature of the BCC/FCC interphase boundaries (IBs) and resultant IB wetting. The LBE ingress ﬁlm selectively leaches nickel located at those low-indexed crystalline planes, resulting in phase transformation from FCC to BCC structure.
Environmental degradation of structural materials in liquid lead- and lead-bismuth eutectic-cooled reactors
SHORT, Michael P.
Publisher : Elsevier BV
Liquid lead (Pb)- and lead–bismuth eutectic (LBE)-cooled fast neutron reactors (Gen-IV LFRs) are one of the most technologically mature fission reactor technologies, due to their inherent safety, high power density, and ability to burn nuclear waste. Accelerator-driven systems (ADS), in particular, promise to address the issues of long-lived radiotoxic nuclear waste, emerging uranium ore shortages, and the ever-increasing demand for energy. However, the conditional compatibility of conventional structural materials, such as steels, with liquid Pb and liquid LBE is still an important concern for the deployment of these advanced nuclear reactor systems, making the environmental degradation of candidate structural and fuel cladding steels the main impediment to the construction of Gen-IV LFRs, including ADS. This article presents a comprehensive review of the current understanding of environmental degradation of materials in contact with liquid Pb and liquid LBE, with a focus on the underlying mechanisms and the factors affecting liquid metal corrosion (LMC) and liquid metal embrittlement (LME), which are the two most important materials degradation effects. Moreover, this article addresses the most promising LMC and LME mitigation approaches, which aim to suppress their adverse influence on materials performance. An outlook of the needed future work in this field is also provided.
Modelling and Optimization of Machining of Ti-6Al-4V Titanium Alloy Using Machine Learning and Design of Experiments Methods
Publisher : MDPI AG
Ti-6Al-4V titanium is considered a difficult-to-cut material used in critical applications in the aerospace industry requiring high reliability levels. An appropriate selection of cutting conditions can improve the machinability of this alloy and the surface integrity of the machined surface, including the generation of compressive residual stresses. In this paper, orthogonal cutting tests of Ti-6Al-4V titanium were performed using coated and uncoated tungsten carbide tools. Suitable design of experiments (DOE) was used to investigate the influence of the cutting conditions (cutting speed Vc, uncut chip thickness h, tool rake angle γn, and the cutting edge radius rn) on the forces, chip compression ratio, and residual stresses. Due to the time consumed and the high cost of the residual stress measurements, they were only measured for selected cutting conditions of the DOE. Then, the machine learning method based on mathematical regression analysis was applied to predict the residual stresses for other cutting conditions of the DOE. Finally, the optimal cutting conditions that minimize the machining outcomes were determined. The results showed that when increasing the compressive residual stresses at the machined surface by 40%, the rake angle should be increased from negative (−6°) to positive (5°), the cutting edge radius should be doubled (from 16 µm to 30 µm), and the cutting speed should be reduced by 67% (from 60 to 20 m/min).
Losses and lifetimes of metals in the economy
CHARPENTIER PONCELET, Alexandre
Publisher : Springer Nature
The consumption of most metals continues to rise following ever-increasing population growth, affluence and technological development. Sustainability considerations urge greater resource efficiency and retention of metals in the economy. We model the fate of a yearly cohort of 61 extracted metals over time and identify where losses are expected to occur through a life-cycle lens. We find that ferrous metals have the longest lifetimes, with 150 years on average, followed by precious, non-ferrous and specialty metals with 61, 50 and 12 years on average, respectively. Production losses are the largest for 15 of the studied metals whereas use losses are the largest for barium, mercury and strontium. Losses to waste management and recycling are the largest for 43 metals, suggesting the need to improve design for better sorting and recycling and to ensure longer-lasting products, in combination with improving waste-management practices. Compared with the United Nations Environmental Programme’s recycling statistics, our results show the importance of taking a life-cycle perspective to estimate losses of metals to develop effective circular economy strategies. We provide the dataset and model used in a machine-readable format to allow further research on metal cycles
Environmental consequences of policies in construction sector: combining economic simulation with consequential LCA
ALMEIDA, Denise T.L.
Publisher : EDP Sciences
Consequential Life Cycle Assessment (CLCA) can be particularly relevant for studying the changes proposed by new policies since they may result in important displacements of environmental, social and economic impacts. For example, the financial aids for encouraging the use of new technologies may increase the demand for some materials of which production is constrained and the marginal suppliers may be more impacting than the average ones. The goal of this project was to propose a method for calculating the potential environmental burdens and benefits from new policies in the construction sector. Consequential Life Cycle Inventory must include all processes that are actually affected by the studied changes, considering the market effects. The economic models can be helpful on this matter. The proposed method couples a Stock-Flow Consistent (SFC) to the CLCA methodology to obtain the flows and stocks that are affected by the new policy. The model goes further in order to obtain the second-order effects, i.e., the monetary redistribution effects resulting from an economic perturbation. The main result is a novel method that couples an SFC model to CLCA. It is tested in a case study where the evolution of carbon tax in France (economic shock) leads to an increase in thermal retrofitting works in the French existing built stock. These results may help the construction sector to anticipate important rebound effects that are not usually included in the current studies used for decision and policy-making.
Application of the re-cycling method to support design for and from end-of-life
MARTÍNEZ LEAL, Jorge
Publisher : Cambridge University Press (CUP)
AbstractNowadays, the world is shifting towards a more sustainable way of life, and product designers have an important part in this change. They have to eco(re)design their products to make them environmentally conscious throughout their lifecycle, and especially at their end-of-life (EoL). However, one can observe that synergy between product designers and recycling-chains stakeholders is lacking, mainly due to their weak communication. While many design-for-EoL approaches coexist in the literature, design from EoL must also be taken into account to fully develop a circular economy.RE-CYCLING is an innovative design approach that supports both design for and from EoL. This paper focuses on the recycling EoL-option and the validation of the associated indicators. To validate the design-for-recycling indicators, the recyclability of three smartphones is assessed. It is expected that indicators provide a similar score as none of them was designed to be recycled; results comply with expectations. In parallel, the convenience of using recycled materials in smartphones is analysed to validate our design-from-recycling indicators. It is found that the proposed indicators can indeed support designers integrating recycled materials in products.
A novel approach for nondestructive depth-resolved analysis of residual stress and grain interaction in the near-surface zone applied to an austenitic stainless steel sample subjected to mechanical polishing
The choice of the grain interaction model is a critical element of residual stress analysis using diffraction methods. For the near-surface region of a mechanically polished austenitic steel, it is shown that the application of the widely used Eshelby-Kr¨oner model does not lead to a satisfactory agreement with experimental observations. Therefore, a new grain interaction model called ’tunable free-surface’ is proposed, allowing for the determination of the in-depth evolution of the elastic interaction between grains. It has a strong physical justification and is adjusted to experimental data using three complementary verification methods. It is shown that a significant relaxation of the intergranular stresses perpendicular to the sample surface occurs in the subsurface layer having a thickness comparable with the average size of the grain. Using the new type of X-ray Stress Factors, the in-depth evolution (up to the depth of 45 μm) of residual stresses and of the strain-free lattice parameter is determined.
Laser Fiber Displacement Velocity during Tm-Fiber and Ho:YAG Laser Lithotripsy: Introducing the Concept of Optimal Displacement Velocity
Publisher : MDPI
Background: Endocorporeal laser lithotripsy (EL) during flexible ureteroscopy (URS-f) often uses “dusting” settings with “painting” technique. The displacement velocity of the laser fiber (LF) at the stone surface remains unknown and could improve EL’s ablation rates. This in vitro study aimed to define the optimal displacement velocity (ODV) for both holmium:yttrium-aluminium-garnet
(Ho:YAG) and thulium fiber laser (Tm-Fiber). Methods: A 50W-TFL (IRE Polus®, Moscow, Russia) and a 30W-MH1-Ho:YAG laser (Rocamed®, Signes, Provence-Alpes-Côte d’Azur, France), were used with 272 m-Core-Diameter LF (Sureflex, Boston Scientific©, San Jose, CA, USA), comparing three TFL modes, “fine dusting” (FD: 0.05–0.15 J/100–600 Hz); “dusting” (D: 0.5 J/30–60 Hz); “fragmentation” (Fr: 1 J/15–30 Hz) and two Ho:YAG modes (D: 0.5 J/20 Hz, Fr: 1 J/15 Hz). An experimental setup
consisting of immerged cubes of calcium oxalate monohydrate (COM) stone phantoms (Begostone Plus, Bego©, Lincoln, RI, USA) was used with a 2 s’ laser operation time. LF were in contact with the stones, static or with a displacement of 5, 10 or 20 mm. Experiments were repeated four times. Stones were dried and -scanned. Ablation volumes (mm3) were measured by 3D-segmentation.
Results: ODV was higher in dusting compared to fragmentation mode during Ho:YAG lithotripsy (10 mm/s vs. 5 mm/s, respectively). With Tm-Fiber, dusting and fragmentation OVDs were similar (5 mm/s). Tm-Fiber ODV was lower than Ho:YAGs in dusting settings (5 mm/s vs. 10 mm/s, respectively). Without LF displacement, ablation volumes were at least two-fold higher with Tm-Fiber compared to Ho:YAG. Despite the LF-DV, we report a 1.5 to 5-fold higher ablation volume with Tm-Fiber compared to Ho:YAG. Conclusions: In dusting mode, the ODVTm-Fiber is lower compared to ODVHo:YAG, translating to a potential easier Tm-Fiber utilization for “painting” dusting technique. The ODV determinants remain unknown. Dynamic ablation volumes are higher to static ones, regardless of the laser source, settings or LF displacement velocity.
Exploring space separation techniques for 3D elastic waves simulations
Publisher : Springer
This paper explores numerical methods dedicated to 3D elastic waves simulations in spatially separable domains such as
plates. The objective is to reduce the computation time and the memory requirements associated to these large simulations
involving fine space and time discretizations. The 3D problem is decomposed into a sequence of lower dimensional problems
with the Proper Generalized Decomposition. The spatial discretization is performed with the Spectral Element Method to
provide more compact separated representations compared to the ones obtained with a finite element discretization. Following
previous works on space separation in elastodynamics, we explore hybrid explicit/implicit time marching schemes to improve
the solution through one direction as needed, without decreasing the time step due to stability constraints. Large 3D numerical
problems with several millions of degrees of freedom are efficiently solved with memory requirements characteristic of 2D
Crystallization behavior and morphological features of ethylene-vinyl alcohol 44 copolymer
Publisher : Budapest University of Technology and Economics
This work is a first attempt to study the crystallization behavior of ethylene-vinyl alcohol copolymer with 44 mol% of ethylene units (EVOH44) and to observe the supermolecular structures developed during its crystallization. Thermal analysis has evidenced a very fast crystallization and the formation of different crystal populations during isothermal crys-tallization. In-situ wide-angle X-ray scattering experiments using a synchrotron radiation source have shown a unique or-thorhombic morphology, independently of the crystallization conditions. Small spherulites (with an average radius of about 1 µm) were observed using polarized optical microscopy and confirmed by typical four-leaf patterns obtained by small-angle light scattering. In-situ atomic force microscopy has revealed stacked lamellae growing from common centers to form small spherulitic entities. Finally, studies of isothermal crystallization have evidenced the existence of partial crystallization (especially at high crystallization temperatures) and the need for higher undercooling to complete crystallization. © BME-PT.