Search Results
Rare-earth-free MnAl-C-Ni permanent magnets produced by extrusion of powder milled from bulk
Rare-earth-free MnAl-C-Ni permanent magnets have been produced for the first time by extruding powders milled from bulk. The resulting materials, fabricated using different conditions, contained a large volume fraction (> 0.92) of the desired τ-phase. In terms of the maximum energy product, the best performance obtained for a whole, transverse section of the extruded material was (BH)max = 46 kJm−3, and was (BH)max = 49 kJm−3 for a sample taken from near the edge of this section. Analysis showed that this material was comparable to the long-established benchmark, comprising MnAl-C-based magnets extruded in industry from bulk or from gas-atomised powder. Such materials are no longer available. The microstructure of the materials produced here consisted of fine, recrystallised grains, which exhibited an <001> fibre texture with intermediate texture quality and of larger, non-recrystallised regions, which contained hierarchical twinning and a high density of defects. The volume fraction and size of the non-recrystallised regions was greatly reduced by decreasing the size of the initial powder particles. This led to a large increase in the squareness factor of the demagnetisation curve and consequently to the high (BH)max values observed.
Determination of fluoride component in the multifunctional refining flux used for recycling aluminum scrap
In this paper, the optimum fluoride component in the multifunctional refining flux used for recycling aluminum scrap was determined. Theoretical analysis of solid fluxing shows that strong stripping ability of oxide layer on aluminum surface for the flux and appropriate interfacial tensions between Al melt / inclusion (σM-I), flux / inclusion (σF-I), and flux / Al melt (σF-M) are indispensable for making the flux achieve the properties of covering, drossing, and cleaning simultaneously. In term of four preliminarily selected fluoride salts, i.e., KF, AlF3, K3AlF6 and KAlF4, the results of interfacial tension measurements indicates that, combined addition of A-type fluoride (KF) and B-type fluoride (AlF3, K3AlF6 and KAlF4) to equimolar NaCl-KCl can just offset the shortage of single addition of KF which means worsening the separating effect of flux from melt surface and weakening the wettability of flux on the inclusions due to the lower σF-M and the higher σF-I respectively. Additionally, coalescence behaviors of aluminum droplets in molten fluxes reveals that, KF, K3AlF6 or KAlF4 possesses stronger stripping ability of oxide layer, while the stripping ability of oxide layer for AlF3 is weaker. Ultimately, the combination of KF with K3AlF6 or/and KAlF4 is ascertained to be an optimum selection for fluoride component in the multifunctional refining flux.
Dynamic cooling strategy based on individual animal response mitigated heat stress in dairy cows
Technological progress enables individual cow's temperatures to be measured in real time, using a bolus sensor inserted into the rumen (reticulorumen). However, current cooling systems often work at a constant schedule based on the ambient temperature and not on monitoring the animal itself. This study hypothesized that tailoring the cooling management to the cow's thermal reaction can mitigate heat stress. We propose a dynamic cooling system based on in vivo temperature sensors (boluses). Thus, cooling can be activated as needed and is thus most efficacious. A total of 30 lactating cows were randomly assigned to one of two groups; the groups received two different evaporative cooling regimes. A control group received cooling sessions on a preset time-based schedule, the method commonly used in farms; and an experimental group, which received the sensor-based (SB) cooling regime. Sensor-based was changed weekly according to the cow's reaction, as reflected in the changes in body temperatures from the previous week, as measured by reticulorumen boluses. The two treatment groups of cows had similar milk yields (44.7 kg/d), but those in the experimental group had higher milk fat (3.65 vs 3.43%), higher milk protein (3.23 vs 3.13%), higher energy corrected milk (ECM, 42.84 vs 41.48 kg/d), higher fat corrected milk 4%; (42.76 vs 41.34 kg/d), and shorter heat stress duration (5.03 vs 9.46 h/day) comparing to the control. Dry matter intake was higher in the experimental group. Daily visits to the feed trough were less frequent, with each visit lasting longer. The sensor-based cooling regime may be an effective tool to detect and ease heat stress in high-producing dairy cows during transitional seasons when heat load can become severe in arid and semi-arid zones.
A multi-method psychometric assessment of the affinity for technology interaction (ATI) scale
In order to develop valid and reliable instruments, psychometric validation should be conducted as an iterative process that “requires a multi-method assessment” (Schimmack, 2019, p. 4). In this study, a multi-method psychometric approach was applied to a recently developed and validated scale, the Affinity for Technology Interaction (ATI) scale (Franke, Attig, & Wessel, 2018). The dataset (N = 240) shared by the authors of the scale (Franke et al., 2018) was used. Construct validity of the ATI was explored by means of hierarchical clustering on variables, and its psychometric properties were analysed in accordance with an extended psychometric protocol (Dima, 2018) by methods of Classical Test Theory (CTT) and Item Response Theory (IRT). The results showed that the ATI is a unidimensional scale (homogeneity H = 0.55) with excellent reliability (ω = 0.90 [0.88-0.92]) and construct validity. Suggestions for further improvement of the ATI scale and the psychometric protocol were made.
Perspectives from CO+RE: How COVID-19 changed our food systems and food security paradigms
[no abstract available]
Microstructure, mechanical properties and machinability of particulate reinforced Al matrix composites: a comparative study between SiC particles and high-entropy alloy particles
In this study, 2024Al matrix composites reinforced by SiC particles (SiC-2024Al) and nanocrystalline high-entropy alloy particles (HEA-2024Al) fabricated by powder metallurgy were systematically compared for the first time. There is a significant difference in microstructure and mechanical properties as well as machinability between two kinds of composites. In term of microstructure, when the volume fraction of reinforcements was 10%, both SiC-2024Al and HEA-2024Al composites showed a homogeneous particle distribution in the matrix. With the increase of reinforcement content, HEA-2024Al composites presented denser microstructure than that of SiC-2024Al composites. The composites with 10, 20 and 30 vol.% HEA reinforcements all showed better plasticity than that of the SiC-2024Al composites with same volume fraction of reinforcements, which was related with better particle distribution and interface bonding. However, the strength showed the opposite tendency in the two kinds of composites. Selecting 10SiC-2024Al and 10HEA-2024Al composites as examples to explore the difference in the yield strength of two kinds of composites, it is ascribed to the dislocation punched zones around interface between the Al matrix and reinforcements, which was analyzed in detail by a combination of calculation, nanoindentation tests and finite element analysis. Additionally, HEA-2024Al composites showed better machinability than those of SiC-2024Al composites. This work provides insight into the application of particulate reinforced Al matrix composites.
Ion dynamics in Al-Stabilized Li7La3Zr2O12 single crystals – Macroscopic transport and the elementary steps of ion hopping
Li7La3Zr2O12 (LLZO) garnet-type ceramics are considered as very promising candidates for solid electrolytes and have been extensively studied in the past few years. Several studies report on an increase in ionic conductivity by doping with ions, such as Al3+ and Ga3+, to stabilize the cubic modification of LLZO. Unfortunately, so far ion dynamics have mainly been studied using powdered samples. Such studies may suffer from chemical heterogeneities concerning Al distribution. Here, we took advantage of Al-stabilized LLZO single crystals to throw light on the elementary steps of ion hopping. We used 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements and conductivity spectroscopy to probe dynamic parameters from both a microscopic and macroscopic point of view. At 293 K the total conductivity turned out to be 0.082 mS cm−1, which is remarkably good for LLZO exhibiting an Al-content of only 0.37 wt%. Most importantly, 7Li NMR spin-lock transients revealed two overlapping diffusion-induced processes. Overall, activation energies from spin-lock NMR excellently agree with that from conductivity measurements; both techniques yield values around 0.36 eV. The corresponding diffusion coefficients deduced from NMR and conductivity measurements almost coincide. The magnetic spin fluctuations sensed by NMR provide an in-depth look at the elementary jump processes, which can barely be revealed by macroscopic impedance spectroscopy providing average values. In particular, we were able to precisely measure the local hopping barrier (0.20 eV) characterizing forward-backward jumps between the sites 24d and 96h. © 2019 The Author(s)
The influence of mean strain on the high-cycle fatigue of Nitinol with application to medical devices
One of the contentious issues associated with the high-cycle fatigue of Nitinol, a nominally equiatomic alloy of nickel and titanium, is the claim that increasing the applied mean strain can increase, or at least have no negative impact, on the fatigue lifetime, in conflict with reported behavior for the vast majority of other metallic materials. To investigate this in further detail, cyclic fatigue tests in bending were carried out on electropolished medical grade Nitinol at 37 °C for lives of up to 400 million cycles of strain involving various levels of the mean strain. A constant life model was developed through statistical analysis of the fatigue data, with 90% reliability at a confidence level of 95% on the effective fatigue strain. Our results show that the constant life diagram, a plot of strain amplitude versus mean strain, is monotonic yet nonlinear for lives of 400 million cycles of fatigue loading. Specifically, we find that in contradiction to the aforementioned claim, the strain amplitude limit at zero mean strain is 0.55% to achieve a 400 million cycle lifetime, at 90% reliability with 95% confidence; however, to achieve the same lifetime, reliability and confidence level in the presence of a 3% or more mean strain, the required strain amplitude limit is decreased by over a factor of three to 0.16%. Moreover, for mean strains from 3% to 7%, the strain amplitude limit that allows a 400 million cycle lifetime, at 90% reliability with 95% confidence, is ~ 0.16%, and essentially independent of mean strain. We conclude that the debatable claim that an increase in the applied mean strain can increase the fatigue life of Nitinol components is not supported by the current data.
Tailoring biocompatible Ti-Zr-Nb-Hf-Si metallic glasses based on high-entropy alloys design approach
Present work unveils novel magnetic resonance imaging (MRI) compatible glassy Ti-Zr-Nb-Hf-Si alloys designed based on a high entropy alloys approach, by exploring the central region of multi-component alloy phase space. Phase analysis has revealed the amorphous structure of developed alloys, with a higher thermal stability than the conventional metallic glasses. The alloys exhibit excellent corrosion properties in simulated body fluid. Most importantly, the weak paramagnetic nature (ultralow magnetic susceptibility) and superior radiopacity (high X-ray attenuation coefficients) offer compatibility with medical diagnostic imaging systems thereby opening unexplored realms for biomedical applications.