Materialia最新文献

Voronoi tessellation was innovatively applied to interpret the high-resolution atomic-scale micrographs of the Cr-W-C ternary M₂₃C₆ with and without irradiation to provide mechanistic insight into the phase stability under irradiation. A W concentration-dependent radiation-induced amorphization behavior was observed and the amorphization was confirmed in the 4 W sample (∼12 at.%W). Analysis of the local crystal structure using Voronoi diagrams shows that the average size of each Voronoi cell and its standard deviation are affected by irradiation and W concentration. In addition, the standard deviation of the Voronoi cell size, which is considered an indicator of the uncertainty of the atomic column positions, is also plotted as a function of the lattice parameter change. This mathematical analysis indicates that a higher W concentration tends to cause a more severe disordering of the atomic distribution upon irradiation, which is directly correlated with the occurrence of amorphization.

With the aim of further exploiting the trade-off between formability and strength in Al alloys, this study addresses the influence of Cu in Al-Mg-Si alloys that achieve simultaneously high strength and high ductility via cluster hardening. The study carefully examines the mechanical properties and strain hardening behavior of various Mg/Si ratios with and without Cu and compares the effects of pre-aging and atypical long-term low-temperature aging treatments at 100°C to conventional heat treatments. Interestingly, in all cases adding Cu improved ductility. In the extremal case cluster hardening plus the addition of Cu quadruples elongation, while keeping yield strength similar to the classical T6 state. The results of the study are discussed with a focus on the dense distribution of clusters and partial hardening phases based on atom probe tomography data. Most importantly, the cluster-hardened alloys exhibit pronounced strain-hardening properties, which we evaluate using a Kocks-Mecking approach in combination with a microstructural analysis in the pre-aging and long-term aging condition. The key finding of the study involves the role of Cu in refining clusters/precipitates, where it causes a substantial increase in number density and volume fraction. This refinement, in combination with strain-induced clustering, contributes significantly to improving the alloys’ overall mechanical performance and underlines the central role of Cu in tailoring microstructural features, especially in alloys primarily strengthened by clusters.

In advancing towards carbon neutrality in the automotive industry, polypropylene (PP) plays a crucial role in improving fuel efficiency and reducing carbon emissions as a pivotal lightweight material. However, PP faces challenges in microcellular foaming, including surface quality concerns, intricate molding parameters, and compromised mechanical strength, limiting its broader application. This research introduces an innovative strategy by integrating Olefin Block Copolymer (OBC) into the Talc/PP composite framework using In-mold Decoration/Microcellular Injection Molding (IMD/MIM) techniques to overcome these limitations. Experimental findings reveal that modulating the OBC proportion substantially enhances the PP composites' functionality. Notably, an inclusion of 10 wt% OBC decreases the material's viscosity, and raising the OBC level to 30 wt% markedly improves surface quality with fewer defects. Analyzing cell configuration confirms OBC's beneficial effect on cell size and distribution, particularly in the homogeneity of cells across the material's layers. For mechanical performance, incorporating OBC increased the impact strength from 13.2 kJ/m² to 17.9 kJ/m², highlighting OBC's potential in enhancing PP's toughness. This study enriches our understanding of optimizing PP-based microcellular foamed materials, supporting the development of next-generation lightweight materials. Future efforts will focus on further refinement of the OBC/Talc/PP system for superior performance and practical industrial viability.

Mo, W and Re are all important strengthening elements in either single phase solid solution (SS) alloys or the SS phases in precipitation-strengthened Ni/Co-based superalloys, of which the compositions are usually complicated. To directly compare the effects of Mo, W and Re on the mechanical properties of concentrated SS alloys, a model CoCrNiFe concentrated SS alloy as the base and three alloys with 3 at.% Mo, W and Re additions are fabricated and their mechanical properties are examined in both quasi-static tensile and creep tests at room and two high temperatures. Experimental and modeling results demonstrate that at room and low temperatures, the order of strengthening effect is W > Mo > Re, in accordance with solid solution strengthening model and thermal activation analysis. On the other hand, Re can significantly decrease the minimum creep rate at 1273 K, primarily due to the reduced diffusivity as confirmed from the diffusion couple analysis.

Recycling computer hard disk drives from Waste Electrical and Electronic Equipment (WEEE) has been achieved according to a two-step approach that combines solvothermal treatment and CaH₂ reduction-diffusion, resulting in the production of a single-phase material. The magnets underwent solvothermal treatment, followed by CaH₂ reduction at varying temperatures (200°C, 250°C and 300°C). We examined the impact of CaH₂ as a reducing agent on the final product, using X-ray diffraction, Mössbauer spectrometry and SQUID magnetometry. After the solvothermal treatment, the powder contains both Nd₂Fe₁₄BH_x and Nd(OH)₃ phases. At 200°C, Nd(OH)₃ was reduced without degradation of the magnetic Nd₂Fe₁₄BH_x phase, as confirmed by Mössbauer spectrometry. Furthermore, an analysis of the magnetic properties indicates an increase in magnetization after CaO removal, confirming its successful elimination.

The influence of printing variables on microstructural and mechanical behaviors on the 316 L stainless steel (316 L SS), produced via an additive manufacturing process, named as bound metal deposition (BMD), was investigated in this study. The printing parameters varied were infill density, diameter of the nozzle, and thickness of layers, which dictate the mechanical properties, surface roughness, and crack morphology of the samples. Based on the experimental investigation, it was found that the tensile properties were increased when the nozzle diameter and infill density were higher. The highest obtained ultimate tensile strength (UTS) was 402 ± 17 MPa, where the sample was fabricated with the following parameters: 0.40 mm nozzle diameter, 25% infill density, and 0.10 mm layer. The influence of the nozzle diameter also impacted the surface roughness, where a worse surface finish was noticed for the larger nozzle diameter.

Microgravity experiments on phase coarsening in solid-liquid mixtures provided an ideal tool to closely and accurately explore the kinetics of phase coarsening because the sedimentation and convective melt flow are eliminated in the International Space Station. In this study, we employed phase-field simulations to systematically investigate the microstructure evolution during phase coarsening at various volume fractions. Simulated microstructure evolution during phase coarsening are compared quantitatively with the microstructure evolution archived from microgravity experiments. Furthermore, kinetics of phase coarsening in Pb-Sn solid-liquid mixtures at various volume fractions is studied theoretically and numerically, which is compared with microgravity experiments. In particular, particle size distribution, relative coarsening rate constants, and scaled maximum particle radii, are predicted from theories, and deduced from microgravity experiments, then calculated from phase-field simulations. This systematic and quantitative study of phase coarsening confirms the consistency to the results from phase-field simulation, microgravity experiments and theories at lower volume fractions, and stimulates more careful microgravity experiments at higher volume fractions ($\ge 0.7$).

Grain boundary (GB) segregation of solute atoms is a key factor affecting the microstructure and macroscopic properties of materials. In this study, first-principles calculations were carried out to investigate the effect of solute atoms (Mg and Cu) segregation on the structural evolution and mechanical response of Al ground-state Σ5(210) GB (GB-Ⅰ) and metastable Σ5(210) GBs (GB-Ⅱ and GB-Ⅲ). The GB energy, segregation energy, and the theoretical tensile strength of the multiple Σ5(210) GBs were calculated. The results show that both Mg and Cu atoms tend to segregate in the boundary plane, thus reducing GB energy and improving GB stability. The segregation of Cu atoms reduced the GB energy more significantly than that of Mg atoms. The segregation of solute atoms can change the symmetric GB structure into an asymmetric one or induce GB phase transformation. The theoretical strength of GB-I is weaker than that of the metastable GB-II with higher GB energy, suggesting that grain boundaries with higher energy are not necessarily unstable. In addition, the effect of solute atom segregation on the GB strength depends not only on the type of element but also on the specific GB structure. The weakening effect of Mg segregation in GB-I and GB-II is due to the weak MgAl bond which enlarges the low charge density region of GB and increases the free volume of GB. The strengthening of GB-I and GB-II by Cu segregation mainly depends on the stronger AlCu bond than AlAl bond along the GB fracture path. The enhanced strength of GB-III with Mg and Cu segregation is attributed to the GB structural phase transformation caused by the segregation of solute atoms. The calculation results further elucidate the relationship between element segregation and grain boundary characteristics.

Shape memory alloys (SMAs) have attracted much attention due to the great demand for biomedical materials. Among the SMAs, the Ti-based SMAs are promising materials owing to their high biocompatibility, non-toxicity, excellent functionalities, and proper mechanical properties. Concerning the Ti-based SMAs, adding other elements is an often-used strategy, and the combinations of the addition materials are unlimited. Among the various Ti-based alloy systems, the Ti-Mo-Al-Zr alloy is one fundamental alloy system, since Mo and Al are served as the specific metals for the calculations of the Mo equivalent and Al equivalent for the evaluation of the alloy stability. While Zr is a neutral element for fine-tuning the properties of the alloys. This fundamental quaternary alloy was thus chosen in this study. In this research series, it has been found that the Ti-5.5Mo-8Al-6Zr alloy performed proper mechanical properties. Therefore, this specific alloy was further subjected to various thermomechanical treatments to further improve its properties. In addition to the Ti-5.5Mo-8Al-6Zr alloy, pseudo-binary alloys of (Ti-Zr)-Mo were also investigated due to their intrinsic low phase transformation temperature compared to the pure Ti and Zr elements. Strategies for the development of these SMAs by conducting thermomechanical treatments have been proposed in this study.