Journal of Central South University

Khallaf, A. Hegazy; Bhlol, M.; Dawood, O. M.; Elkady, Omayma A.

doi: 10.1007/s11771-022-5181-8pmid: N/A

(CrFeCoNi) high-entropy alloy (HEA) was reinforced with various contents of WC particles from 5 wt% to 20 wt%, and prepared by powder metallurgy. The mixed powders were compacted under 700 MPa and then sintered at 1200 ° C in a vacuum furnace for 90 min. Density, phase composition, and microstructure of sintered samples were investigated. Hardness, compressive strength, wear resistance and coefficient of thermal expansion (CTE) were estimated. The results revealed the improvement of the density with the addition of WC. XRD results revealed the formation of new FCC chromium carbide phases. Scanning electron microscopy (SEM) results show a good distribution of the carbide phases over the alloy matrix. The CTE was decreased gradually by increasing the WC content. Compressive strength was improved by WC addition. A mathematical model was established to predict the behavior of the strength of the HEA samples. The hardness of the investigated HEAs was increased gradually with the increasing of WC content about 20.35%. Also, the wear rate of HEA without WC is 1.70×10−4 mm3/(N·m), which is approximately 4.5 times the wear rate of 20 wt% WC HEA (3.81×10−5 mm3/(N·m)), which means that wear resistance was significantly improved with the increase of WC content.

Zhang, Quan-da; Sun, Fu-zhen; Liu, Meng; Liu, Wen-cai

doi: 10.1007/s11771-022-4968-ypmid: N/A

In this paper, the indirect thermal tensile experiments of 7075 aluminum alloy including the pre-deformation process at room temperature and the final heat tensile process were carried out, the plastic deformation behavior and forming limit of the material in the compound forming process were investigated considering three pre-deformation amounts 4%, 9%, 14%, two strain rates 0.001 s−1, 0.01 s−1 and four forming temperatures 300 °C, 350 °C, 400 °C, 450 °C. In the indirect hot forming process, the material is sensitive to the pre-deformation, strain rate, and forming temperature, when the strain rate is 0.01 s−1, the pre-deformation amount is 4%, and the forming temperature is 400 °C, respectively, the maximum tensile deformation is 50 mm. Finally, taking the process in which the forming temperature is 450 °C as an example, according to the observation of the microstructure appearance of fracture, the fracture type in the hot forming process was judged as the ductile fracture. By analyzing the microstructure of the specimen treated with the quenching and artificial aging process, the eutectic T (AlZnMgCu) phase and α(Al) matrix formed a network of non-equilibrium alpha binary eutectic.

Salehi, M.; Eskandari, M.; Yeganeh, M.

doi: 10.1007/s11771-022-5175-6pmid: N/A

In the present study, the effects of microstructure, grain size, and texture after thermomechanical processing on the corrosion behavior of AISI 321 austenitic stainless steel (ASS) were studied. The as-received, coarse-grained steel ((35±3) µm) was subjected to 20%, 50% and 90% thickness reduction through cold rolling at liquid nitrogen temperature, followed by annealing at 750, 950 and 1050 °C for 15 min. Recrystallization occurred after annealing at 750 °C, and with the increasing of annealing temperature to 950 °C and 1050 °C, secondary recrystallization (abnormal grain growth) and grain growth were observed. The results showed that, after 20% thickness reduction, corrosion resistance increased significantly (21.1 kΩ·cm2) compared with the as-received condition (3.9 kΩ·cm2) due to the enhancement of γ-fiber and the creation of ∑3 boundaries. In contrast, the corrosion resistance decreased with the increasing of thickness reduction to 90% during rolling, but still depicted higher corrosion resistance compared with the as-received specimen. After annealing the 90% cold rolled (CR) specimens at 750 and 950 °C, the corrosion resistance increased in comparison with the as-received sample as a result of the more uniform microstructure, appearance of Goss and brass texture components, and grain refinement. However, significant grain growth ((112±76) µm) followed by a non-uniform structure was observed after annealing at 1050 °C and resulted in the lowest corrosion resistance (1.3 kΩ·cm2).

Peng, Hao-ping; Ma, Ming; Xi, Shi-heng; Liu, Ya; Lei, Yun; Su, Wei; Su, Xu-ping

doi: 10.1007/s11771-022-5025-6pmid: N/A

Based on the diffusion channel, the influence of Si content on the microstructure evolution of iron-based hot-dip Al-χSi coating was analyzed (χ=0, 1.5 wt%, 3.0 wt% and 7.0 wt%). The results show that the introduction of Si makes the reaction interface change from the lingual-tooth interface of hot-dip Al to the flat interface of hot-dip Al-Si. It also reduces the thickness of the alloy layer in the coating, especially the Fe2Al5 layer. When the Si content is 1.5 wt% or 3.0 wt%, the diffusion channel crosses the conjugate line of the two-phase region (FeAl3+liquid phase) into the FeAl3 single-phase region, and then moves to the region with higher Si content. Next, the diffusion channel cuts off the conjugate line of FeAl3 phase, τ1/τ9 phase, and Fe2Al5 phase, which promotes the form of τ1/τ9 phase. The formed τ1/τ9 phase inhibits the diffusion between Fe and Al atoms. When the Si content is 7.0 wt%, the diffusion channel passes through the two-phase region (liquid phase+τ5) and enters the τ5 single-phase region. The form of τ5 single-phase region has a strong inhibitory effect on the interatomic diffusion of Fe and Al, thereby reducing the thickness of the coating, especially the Fe2Al5 layer.

Zouheir, Morad; Tanji, Karim; Navio, Jose Antonio; Hidalgo, María Carmen; Jaramillo-Páez, Cesar Augusto; Kherbeche, Abdelhak

doi: 10.1007/s11771-022-5172-9pmid: N/A

In this paper, the combined addition of copper or iron and sulphate ions onto TiO2 prepared by a simple sol-gel method is studied for formic acid photocatalytic conversion. A wide structural and morphological characterization of the different photocatalysts was performed by X-ray diffraction (XRD), N2-physisorption for BET surface area measurements, scanning and transmission electronic microscopies (SEM and TEM), UV-Vis diffuse spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS), in order to correlate the physico-chemical properties of the materials to their photocatalytic efficiencies for formic acid oxidation. Results have shown important differences among the catalysts depending on the metal added. Sulphated TiO2/Cu (1%Cu) was the best photocatalyst obtaining about 100% formic acid conversion in only 5 min. The appropriate physico-chemical features of this photocatalyst, given by the addition of combined copper and sulphate ions, explain its excellence in photocatalytic reaction.

Wang, Hui-ling; Jiang, Feng; Tong, Meng-meng; Wu, Ming-jin; Jiang, Jing-yu

doi: 10.1007/s11771-022-5168-5pmid: N/A

Two kinds of bronze-graphite-MoS2 self-lubricating materials with copper-coated MoS2 and uncoated MoS2 were prepared by powder metallurgy. Friction and wear experiments were carried out under 4 N and 10 N loads respectively, and the effects of copper-coated MoS2 on the friction performances of the materials were studied. Results showed that the way of copper-coated on the surface of MoS2 could reinforce the bonding between MoS2 and matrix, and inhibited the formation of MoO2. Moreover, both materials formed a MoS2 lubricating film on the surface during the friction process. While the lubricating film formed after copper coating on MoS2 was thicker and had uneven morphology, it was more conducive to improving the friction performance of the material. Compared with conventional materials, the wear rate of copper-coated materials was reduced by one order of magnitude, and the friction coefficient was also reduced by 22.44% and 22.53%, respectively, when sliding under 4 N and 10 N loads. It shows that copper-coated MoS2 can improve friction properties of bronze-graphite-MoS2 self-lubricating materials furtherly.

Meng, Xiang-juan; Zeng, Xiao-min; Jiang, Wei; Li, Si-yuan; Du, Qiao-kun; Ji, Ze-kai; Zhu, Wei-wei; Liu, Chuang; Liang, Cheng-du; Ling, Min; Yan, Li-jing

doi: 10.1007/s11771-022-4919-7pmid: N/A

Since the volume variation of silicon particles during cycling, the binding spots between Cu current collector and silicon anode raised to be one of the critical binding problems. In this work, an amino-modified Cu current collector (Cu*) is fabricated to tackle this issue. The amino groups on Cu* surface increase its hydrophilicity, which is conducive to the curing process of aqueous slurry on its surface. Meanwhile, these amino groups can form abundant amide bonds with carboxyl groups from the adopted polyacrylic acid (PAA) binder. The combined action composed of the covalent bond and mechanical interlocking could reduce the contact loss inside the electrode. However, high concentration silane coupling agent treatment will weaken the surface roughness of Cu* and weaken mechanical interlocking. What is more, the insulation of silane coupling agent reduces the conductivity of Cu and increases the impedance of battery. Considering the effect of silane coupling agent comprehensively, electrochemical performance of Cu*−0.05% is best.

Wu, Xue-ling; Liao, Wan-qing; Peng, Tang-jian; Shen, Li; Qiu, Guan-zhou; Erdenechimeg, Dolgor; Zeng, Wei-min

doi: 10.1007/s11771-022-5166-7pmid: N/A

Acid mine drainage (AMD) has become a widespread environmental issue and its toxicity can cause permanent damage to the ecosystem. However, there are few studies focusing on the formation of AMD under moderately thermophilic conditions, hence we employed X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and 16S rRNA sequencing to study the dissolution of pyrite and bornite by a moderate thermophilic consortium, and explored the role of free and attached microorganisms in the formation of AMD. The consortium mainly comprised Acidithiobacillus caldus, Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans. The results indicated that total iron in pyrite solution system reached 33.45 g/L on the 12th day, and the copper dissolution rate of bornite dissolution reached 91.8% on the 24th day. SEM results indicated that the surfaces of pyrite and bornite were significantly corroded by microorganisms. XRD and XPS results showed that ore residues contained jarosite, and the dissolving residue of bornite contained elemental sulfur. The dominant bacterial genus in pyrite dissolution was A. caldus, and L. ferriphilum in bornite dissolution. To sum up, microbes significantly accelerated the mineral dissolution process and promoted the formation of AMD.

Zhao, Gang; Zhou, Xiao-tong; Li, Fang-xu; Fu, Guang-qin; Shang, Xing-ke

doi: 10.1007/s11771-022-5182-7pmid: N/A

In order to improve the recovery of tungsten ores containing tin minerals, anisic hydroxamic acid (p-methoxy benzohydroxanic acid, PMOB) was synthesized and introduced as novel collector in the flotation of scheelite, wolframite and cassiterite. The flotation performance and adsorption mechanism were investigated by micro/batch flotation, zeta potential measurements and density functional theory (DFT). The micro flotation results showed that the recoveries of scheelite, wolframite and cassiterite using PMOB as collector are 97.45%, 95.77% and 90.08%, respectively, and the corresponding recoveries are 91.00%, 84.30% and 84.67% for benzohydroxamic acid (BHA). The batch flotation results revealed that the collector dosage could be reduced by about 45% for PMOB compared with BHA, in the case of similar flotation indicators. Zeta potential measurements indicated that PMOB could be adsorbed on the mineral surfaces by chemisorption. Moreover, density functional theory (DFT) calculation results showed that the substituent group −OCH3 endues PMOB stronger electron donation ability and hydrophobicity compared with benzohydroxamic acid (BHA), p-methyl benzohydroxamic acid (PMB) and p-hydroxyl benzohydroxamic acid (PHB).