Transactions of Nonferrous Metals Society of China最新文献

In order to ameliorate microstructure and optimize properties of Inconel 718 alloy, a novel heat treatment method combining high-temperature ultra-short annealing at 980 °C for 1 min with subsequent double aging was proposed. The results showed that ultra-short annealing generated partially recrystallized microstructure and recrystallized nuclei were formed even in deformed grains, which was confirmed by KAM maps. Therefore, high-temperature ultra-short annealing overcame recrystallization barrier, and the subsequent recrystallization process could be completed during aging treatment with relatively low temperature, resulting in the uniformly refined microstructure (∼3.59 µm). The 980-1min-aged sample exhibited outstanding tensile properties. The room temperature ultimate strength and total elongation were 1600 MPa and 19%, respectively. The corresponding values of high- temperature (650 °C) tensile tests were ∼1350 MPa and ∼26%. Consequently, ultra-short annealing can be a promising route to enhance the properties of Inconel 718 alloy.

The electrochemical behavior of MgCl₂ and the co-deposition mechanisms of Mg and Sr in the SrCl₂−KCl eutectic system were evaluated using various electrochemical techniques, including cyclic voltammetry (CV), square wave voltammetry (SWV), and open-circuit potential (OCP) analysis. It was observed the Mg(II) reduction on the tungsten electrode in SrCl₂−KCl melt occurred in a single-step process involving the transfer of two electrons, exhibiting a quasi-reversible mode. The electrochemical co-deposition of Mg and Sr in the SrCl₂−KCl−MgCl₂ melt involved the formation of two types of Mg−Sr intermetallic compounds. The evolution in the co-deposition mechanism of the nucleation type with changing overpotential was explored through chronoamperometry (CA). It is shown that the nucleation pattern on the electrode surface was depended on the substrate materials and the electrode reaction products. Early-stage nucleation was attributed to Mg(II) reduction under all overpotential conditions. With the co-deposition of Mg and Sr, Mg(II) was reduced to form the Mg nucleus on the electrode surface, followed by underpotential deposition of Sr(II) on the Mg surface accompanied by Mg deposition simultaneously. Additionally, increasing MgCl₂ concentration in the SrCl₂−KCl melt resulted in a higher current density during the Mg−Sr co-deposition process.

Bioleaching treatment was used to decontaminate pyrite-bearing waste rocks, mitigating the risk of acid mine drainage (AMD) generation at source. The bioleaching results showed that nearly 82% of Fe and S could be removed from pyrite-bearing waste within 40 d in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans). Kinetics study showed that the removal of pyrite from waste ore was mainly in the control of the chemical reaction and internal diffusion. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicated that the formed biogenic jarosite could passivate the residual pyrite under the mediation of A. ferrooxidans. Secondary bioleaching experiments on the residual samples revealed no noticeable decrease in solution pH and only 8 and 160 mg/L of iron dissolved from the two residual mine waste samples, respectively, indicating that the acid and iron release capacity of the mine waste samples was weakened.

Refractory Mo_0.5NbTiVCr_0.25 high-entropy alloy coatings were fabricated on TC4 substrates using laser cladding technology. The coatings were aged at 600, 800 and 1000 °C for 24 h and then water-cooled. The phase composition, microstructure, and mechanical properties of the high-entropy alloy coatings were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), Vickers hardness testing and universal friction wear testing. The results showed that high-entropy alloy coatings retained a body-centered cubic structure after different aging heat treatments. After the aging heat treatment at 800 °C, the coatings exhibited Ti-rich precipitation phases, which were verified as Ti(O,N) face-centered cubic structures by TEM technique. The optimum aging temperature was 600 °C and the hardness of the coating was HV_0.2 410. The wear mechanisms of the coatings were adhesive and abrasive wear.

The electrochemical deposition of zinc/gold dendrite-free alloys was achieved from deep eutectic solvents based on a mixture of choline chloride and ethylene glycol, without using any additives. Potentiostatic electrodeposition was carried out at relatively low Zn electrodeposition overpotential at different Zn(II) concentrations. Insight into the electrochemical mechanism of the Zn electrodeposition was revealed by cyclic voltammetry (CV) and chrono- amperometry (CA). The morphology and structure of the obtained electrodeposits were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), while the elemental analysis was determined by energy dispersive spectroscopy (EDS) technique. The CV results showed that Zn electrodeposition commences with zinc underpotential deposition (UPD) and proceeds through the zinc overpotential deposition (OPD) region. The deposition potential of the Zn/Zn(II) couple shifts towards more positive value with increased Zn(II) concentration. CA analysis demonstrated that in the zinc OPD region, 3D progressive nucleation starts, followed by 3D growth of depositing zinc. Morphological analysis revealed that electrodeposition commences with the formation of compact Zn islands and proceeds through dendrite-free zinc/gold alloys formed. A formation of several intermetallics, namely cubic AuZn₃ and AuZn along with metallic zinc were identified by XRD analysis.

The economical removal of organics from sodium aluminate solutions has been required for decades. Based on security filtration using tricalcium aluminate hexahydrate (TCA) as a filter aid, a novel short process to eliminate impurity particles and remove organics simultaneously was presented. Ultrafine TCA samples with poor crystallization, high TCA content, high surface free energy, and large lattice distortion were prepared in the concentrated sodium aluminate solution. The zeta potential of the TCA binary mixture in alkaline solutions was linearly depended on the TCA content, suggesting the additivity of the zeta potential in the binary mixture. The variation in the electrical double layer of the TCA binary mixture was demonstrated in the alkaline solution. Furthermore, the ultrafine TCA exhibited a high adsorption capacity for organics with long alkyl chains and high relative-molecular-mass. The adsorption capacity of 69.69 mg/g organic carbon for sodium humate was achieved, whereas the digestion at a high temperature remarkably reduced the adsorption capacity of TCA.

A novel Mg−5Sn−2Al−1Zn (TAZ521) alloy was prepared. Direct extrusion (DE) and extrusion−shearing (ES) processes were performed on the alloy to improve its strength and ductility. The microstructure evolution, texture evolution, and strengthening mechanisms of as-homogenized and as-extruded alloy were investigated by XRD, SEM, TEM, EBSD, and tensile tests. The results showed that the mechanical properties of the DE-processed alloy were improved. However, the alloy exhibited a bimodal microstructure consisting of coarse grains and fine DRXed grains. After the ES process, the microstructure became more uniform and a good combination of strength and ductility was achieved. The TYS, UTS, and EL were 212 MPa, 303 MPa, and 21.7%, respectively. Grain refinement and pinning effect by Mg₂Sn precipitates play an important role in the enhancement of strength. Additionally, the improvement of ductility is attributed to the weak basal fiber texture and the activation of non-basal slip.

Thermal spray processes struggle to create a fully dense coating for corrosion protection in the as-sprayed state due to the poor inter-splat bonding. To tackle this problem, Al−15vol.%WC was utilized as the coating material and applied by atmospheric plasma spraying (APS) to produce a dense coating with self-metallurgical inter-splat bonding. The results show that due to the in-flight particle deoxidizing effect by C element and self-metallurgical bonding of the overheated droplet (>1800 °C), dense coating without oxides inclusions is produced under optimized plasma spraying conditions. The fully dense Al−WC coating exhibits excellent corrosion resistance, with corrosion current density lower by four and two orders than that of Mg alloy substrate and bulk Al, respectively. Due to the inclusion of hard WC particles, the Al−WC coating presents one order improvement in wear resistance compared with the bulk Al.

Cu-based brake pad for high-speed train undergoes cyclic oxidation due to the generation and dissipation of friction heat during braking. The oxidation behavior of the Cu-based brake pad was investigated via isothermal oxidation at 300, 400, 500, 600 and 700 °C for up to 50 h. The results show that the oxidation of the Cu-based brake pad presents multiple stages. The combination of the oxidation of Cu and Fe and the oxygen diffusion controls the oxidation process in the earlier stage, while the oxidation of graphite plays a more important role in the later stages above 500 °C. The Cu₂O nanoclusters are firstly formed by the oxidation of copper, then CuO nanowires, and finally fine and coarse equiaxed grains are generated. The rise in temperature promotes the growth and densification of Fe₂O₃ nanosheets, which grow on the Fe₃O₄ layer. However, Fe oxides are gradually covered by Cu oxides because of the larger volume expansion of Cu oxides. The connected pores formed by the graphite burn-off provide oxygen diffusion channels for internal oxidation. The improved surface microhardness is attributed to the formation of oxides.

The deformation and breakup of metallic droplets during gas atomization were simulated using a volume of fluid (VOF) approach that considered droplet cooling and solidification. The correlation between the typical powder morphology and droplet breakup behavior was established to guide the preparation of spherical powder particles. The results showed that upon increasing the ratio of aerodynamic to viscous force of the droplet, the formation of spherical particles was enhanced, while upon decreasing this ratio, the expected droplet breakup mode changed or only droplet deformation occurred. Several typical scenarios were observed from the numerical simulations of the hollow particle formation and evolution process, e.g., open hollow film formation, film closure, bubble centrifugation, and bubble detachment. By increasing the gas velocity or droplet temperature, a higher non-equilibrium Laplace pressure or lower viscous forces was achieved, which separated the bubbles from the interior of the droplet.