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To enhance the friction and wear properties of alloys, AlCrTiVNbx high-entropy alloys (HEAs) with various Nb contents were prepared using the arc melting technique and then annealed at 1000 °C for 2 h. The microstructure and hardness changes in the AlCrTiVNbx (x = 0.3, 0.4, and 0.5) HEAs after casting and annealing were studied via scanning electron microscopy, X-ray diffractometry, optical microscopy and the Vickers hardness test. The MFT-EC400 ball disc reciprocating friction and wear tester was used to investigate the wear resistance of the HEAs before and after annealing. The results show that the annealed AlCrTiVNbx HEAs changed from a single-phase structure to a multi-phase structure, and the content of the face-center cubic (FCC) phase and hexagonal close-packed (HCP) phase further increases with the increase in Nb content. The hardness value of the annealed HEAs is greatly enhanced compared with the casting state, and the hardness of the Nb0.5 HEA is increased from 543 HV to 725 HV after annealing. The wear resistance of the alloys after the annealing treatment is also greatly improved, among which Nb0.5 has the best wear resistance. The average friction coefficient of Nb0.5 is 0.154 and the wear rate is 2.117 × 10−5 mm3/(N·m). We believe that the precipitation strengthening after the annealing treatment and the lubrication effect of the FCC phase are the reasons for the significant improvement in wear resistance. The morphology of the samples indicates that the wear mechanism of the alloy includes adhesive wear, abrasive wear and a certain degree of oxidation wear. [ABSTRACT FROM AUTHOR]

Due to its high hydrogen storage efficiency and safety, Mg/MgH2 stands out from many solid hydrogen storage materials and is considered as one of the most promising solid hydrogen storage materials. However, thermodynamic/kinetic deficiencies of the performance of Mg/MgH2 limit its practical applications for which a series of improvements have been carried out by scholars. This paper summarizes, analyzes and organizes the current research status of the hydrogen storage performance of Mg/MgH2 and its improvement measures, discusses in detail the hot studies on improving the hydrogen storage performance of Mg/MgH2 (improvement measures, such as alloying treatment, nano-treatment and catalyst doping), and focuses on the discussion and in-depth analysis of the catalytic effects and mechanisms of various metal-based catalysts on the kinetic and cyclic performance of Mg/MgH2. Finally, the challenges and opportunities faced by Mg/MgH2 are discussed, and strategies to improve its hydrogen storage performance are proposed to provide ideas and help for the next research in Mg/MgH2 and the whole field of hydrogen storage. [ABSTRACT FROM AUTHOR]

In this work, the anisotropic microstructure and mechanical properties of selective laser melted (SLMed) Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy before and after aging treatment are investigated. Owing to the unique thermal gradient, the prior columnar β grains with {001} texture component grow in the building direction, and the mechanical properties of the as-fabricated Ti-55511 alloy exhibit slight anisotropy. Aging treatment creates uniform precipitation of the α phase at the boundaries as well as the interior of β grains. Due to the microstructure of the aged samples with a weak texture, the mechanical properties exhibit almost isotropic characteristics with an ultimate tensile strength of 1133 to 1166 MPa, yield strength of 1093 to 1123 MPa, and elongation from 13 to 16%, which meet the aerospace allowable specification very well. By XRD and EBSD analyses, the total dislocation density of the aged samples (~134.8 × 1013 m−2) is significantly lower than that of the as-fabricated samples (~259.4 × 1013 m−2); however, the aged samples exhibit a higher geometrically necessary dislocation (GND) density (~28.5 × 1013 m−2) compared with the as-fabricated samples GND density (~2.9 × 1013 m−2). Thus, a new approach to strengthening theory for estimating the anisotropic mechanical properties of AM alloys is proposed. [ABSTRACT FROM AUTHOR]

As it is known, beryllium bronze, an important copper alloy, is widely used in the field of aerospace. Since the performance of domestic and imported beryllium bronze alloys have obvious differences, domestic beryllium bronze QBe2.0 and imported C17200 alloy were adopted, and the hardness and tensile properties of imported and domestic beryllium bronze alloys in the peak aging state were compared and analyzed. In addition, the microstructure morphologies of the C17200 alloy and QBe2.0 alloy were analyzed by SEM, EBSD, and TEM. This study adopted a data-driven exploration approach to elaborate the differences between C17200 and QBe2.0 alloy. After aging at 300 °C for 2 h (peak aging), the tensile strengths of the C17200 alloy and QBe2.0 alloy were 1357 MPa and 1309 MPa, the yield strengths were 1195 MPa and 1188 MPa, and the elongations were 5.5% and 4.0%, respectively. In the peak-aged state, the grain size, uniformity, small angle grain boundary, and twin density of the C17200 alloy were much better than those of the QBe2.0 alloy, which led to more significant grain refinement and twin strengthening effects. A large amount of γ' phase, γ phase, and β phase were precipitated in both alloys, but the precipitation density of the γ' strengthening phase in the C17200 alloy was much greater than that of the QBe2.0 alloy. The C17200 alloy exhibited better mechanical properties under the combined effects of the various strengthening mechanisms, which provided a guideline for the subsequent improvement of domestic alloys and laid a solid foundation for the development of new copper alloys. [ABSTRACT FROM AUTHOR]

Cobalt-chromium ferrite, CoCrxFe2−xO4 (x = 0–1.2), has been synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD) indicates that samples calcined at 800 °C for 3 h were a single-cubic phase. The lattice parameter decreased with increasing Cr concentration. Scanning electron microscopy (SEM) confirmed that the sample powders were nanoparticles. It was confirmed from the room temperature Mössbauer spectra that transition from the ferrimagnetic state to the superparamagnetic state occurred with the doping of chromium. Both the saturation magnetization and the coercivity decreased with the chromium doping. With a higher annealing temperature, the saturation magnetization increased and the coercivity increased initially and then decreased for CoCr0.2Fe1.8O4. [ABSTRACT FROM AUTHOR]