Hasil untuk "Mining engineering. Metallurgy"

Beti Andonovic

Wenlu Yu, Kaifang Li, Lihe Qian et al.

In bainitic steels, enhancing strength often comes at the expense of ductility. In this paper, a medium-carbon multiphase bainitic steel was produced through intercritical annealing (IA) at various temperatures, followed by isothermal bainite transformation (IBT) at 300 °C, and its microstructural evolution and mechanical properties were systematically investigated. The final microstructure primarily consists of intercritical ferrite, bainite, retained austenite (RA) and fresh martensite. During IA, acicular and globular morphologies of reverted austenite were observed, with acicular austenite exhibiting a near Kurdjumov–Sachs orientation relationship with intercritical ferrite. Higher IA temperatures shorten the incubation and completion times of bainite transformation through two synergistic mechanisms. First, the increased volume fraction of acicular austenite promotes bainite nucleation by lowering the energy barrier. Second, elevated IA temperatures enhance C and Mn diffusion, accelerating the growth of reverted austenite, increasing its size, and reducing the C and Mn concentrations at austenite/ferrite interfaces. These effects alleviate the C/Mn-induced retardation of bainite transformation and accelerate the bainite formation. Moreover, higher IA temperatures lead to a higher bainite fraction and a reduced intercritical ferrite content, both of which contribute to improvements in yield and tensile strength. Higher IA temperatures also increase the RA volume fraction after IBT, enhancing the transformation-induced plasticity (TRIP) effect by promoting austenite-to-martensite transformation. The increased bainite content improves the stress shielding effect on adjacent RA, promoting the mechanical stability of RA. These combined effects are believed to be mainly responsible for the enhanced tensile strength and ductility of the steel.

Fengman Li, Xiangyu Chen, Lipeng Ding et al.

Al–Cu–Li alloys have shown great potential for aerospace application due to their good combination of high strength and low density, but their high planar anisotropy have always hindered their application. In the present work, the influence of different deformation processes, including hot rolling (HR), cold rolling (CR), hot rolling + cold rolling (HR + CR), hot rolling + intermediate annealing + cold rolling (HR + IA + CR) on the microstructure and property anisotropy is systematically investigated for a 2195 Al–Cu–Li alloy. Among the four rolling processes, the HR sample exhibits the lowest yield strength, the highest elongation and the highest anisotropy level. The CR and HR + CR samples have a higher yield strength, decreased elongation and anisotropy level. While the HR + IA + CR sample achieves the combination high yield strength, good elongation and the lowest anisotropy level. The different rolling processes can affect the number density and size of the coarse Al7Cu2Fe phase (>1 μm), which can promote the recrystallization by PSN mechanism. As the number density of Al7Cu2Fe phase in the four samples follow: HR + IA + CR > CR > HR + CR > HR. The HR + IA + CR sample with the highest PSN particles density exhibits highest level of recrystallization and random texture distribution, giving rise to the low anisotropy of the alloy. The low number density of PSN particle and the occurrence of dynamic recrystallization suppress the recrystallization of the HR sample during solution treatment, resulting in strong anisotropy of the alloy. These results can provide key information for optimizing the mechanical properties of Al–Cu–Li alloys for aerospace applications.

Jiaming Xu, Ping Zhang, Puyou Ying et al.

Although AlTiN is the preferred hard-coating material for cutting tools, its limited thermal stability causes problems at high cutting temperatures. Multielement nitride coatings such as AlCrN coatings doped with Si, W, and Y lead to the enhanced hardness and thermal stability of cutting tools. In this study, (Al,Cr,Ti,Si,Y)N multielement nitride coatings were fabricated via multiarc ion plating from an AlCrTiSiY alloy target and vacuum annealed at various temperatures. The surface morphologies, crystal structures, mechanical properties, and wear performances of the samples were analyzed. The number of surface defects on the (Al,Cr,Ti,Si,Y)N coatings reduced as the treatment temperature increased to 1000 °C, but the number of these defects increased at higher temperatures. X-ray diffraction revealed a phase transition from the face-centered cubic structure to wurtzite-AlN of the (Al,Cr,Ti,Si,Y)N coatings after annealing at 1100 °C; the same phase transition was observed at 900 °C in (Al,Ti)N coatings, which were prepared for comparison. Nanoindentation tests revealed that the hardness of the (Al,Cr,Ti,Si,Y)N coatings peaked at 40.81 GPa after annealing at 900 °C and remained high (33.73 GPa) even after annealing at 1100 °C. Meanwhile, the hardness of the (Al,Ti)N coatings markedly decreased after annealing at 800 °C. Friction tests revealed stable wear resistance of the (Al,Cr,Ti,Si,Y)N coatings with a wear rate of ∼2 × 10−6 mm3/N·m after annealing at 1000 °C. The wear rate nearly doubled to ∼3.75 × 10−6 mm3/N·m at 1100 °C. Overall, the (Al,Cr,Ti,Si,Y)N coatings demonstrated improved thermal stability than the (Al,Ti)N coatings, showing promising potential for demanding high-temperature applications.

Qihong XU, Zhian LIANG, Zhongmei SUN et al.

There are 0.27% WO3 in a scheelite Ore. The grade of scheelite concentrate produced on site is 53.11%. Because the grade of the concentrate is low, the pricing coefficient of the concentrate is low. In order to improve the grade of scheelite concentrate, according to the properties of the ore, combined collector was used for flotation at room temperature, sodium sulfide was used as an auxiliary inhibitor at heating flotation. After the flotation reagent is optimized, the grade of scheelite concentrate can be significantly increased to 66.18%, the recovery rate of the concentrate remains basically unchanged，and the dosage of inhibitor sodium silicate is significantly reduced. The technical and economic effects of the optimized process are significantly improved.

Prosper Chimunhu, Erkan Topal, Mohammad Waqar Ali Asad et al.

Machine learning (ML) applications are increasing their footprint in underground mine planning, enabled by the gradual enrichment of research methods. Indeed, improvements in prediction results have been accelerated in areas such as mining dilution, stope stability, ore grade, and equipment availability, among others. In addition, the increasing deployment of equipment with digital technologies and rapid information retrieval sensor networks is resulting in the production of immense quantities of operational data. However, despite these favourable developments, optimisation studies on key input activities are still siloed, with minimal or no synergies towards the primary objective of optimising the production schedule. As such, the full potential of ML benefits is not realised. To explore the potential benefits, this study outlines primary input areas in production scheduling for reference and limits the scope to six key areas, covering dilution prediction, ore grade variability, geotechnical stability, ventilation, mineral commodity prices and data management. The study then delves into the literature of each before examining the limitations of existing common applications, including ML. Finally, conclusions with recommendations/solutions to enhance resilience, global optimality, and reliability of the production schedule through synergistic nexus with function-specific optimised input models are presented.

Wenwen Song

Jiaao Wu, Zhihao Liu, Haohua Zhang et al.

Magnesium hydride (MgH2) is an exceptional material for hydrogen storage, but its high desorption temperature and slow kinetics limit its applicability. In this study, the hydrogen storage performance of MgH2 was enhanced using highly dispersed Ni-nanoparticle–doped hollow spherical vanadium nitride (Ni/VN), which was synthesized via a solvothermal process. The MgH2 system doped with the synthesized Ni/VN exhibited an outstanding hydrogen-storage capability. Specifically, 5.6 wt.% of H2 was released within 1 h at a relatively low temperature of 513 K, whereas 6.4 wt.% of H2 was released within 180 s at 598 K, followed by an almost complete dehydrogenation after 10 min at 598 K. At 423 K, the developed material absorbed ∼6.0 wt.% of H2 within 5 min. The activation energy for dehydrogenation was determined to be 78.07 ± 2.91 kJ·mol−1, which was considerably lower than that of MgH2 produced by ball milling (120.89 ± 5.74 kJ·mol−1), corresponding to a reduction of 35.4%. It was deduced that the formation of Mg2Ni/Mg2NiH4 (hydrogen pump) through the reaction of Ni nanoparticles during dehydrogenation/hydrogenation facilitated hydrogen transport and synergistically catalyzed hydrogen absorption and desorption by MgH2, improving its hydrogen storage capability. These findings offer novel perspectives for the utilization of MgH2 in large-scale applications.

Miaomiao Wang, Xing Ming, Qiao Wang et al.

Magnesium potassium phosphate cement-based (MKPC) coating is regarded as an attractive green coating that improves the corrosion resistance of metals. Unfortunately, practical use remains challenging owing to the rapid solidification and hardening of MKPC coating. To overcome this issue, this work proposes a novel strategy to substitute a portion of potassium dihydrogen phosphate (KDP) with dipotassium hydrogen phosphate trihydrate (DKP) as phosphate source. Samples with or without KDP replacement were named KDP-DKP cement/coating and KDP cement/coating, respectively. The initial condensation time of KDP-DKP coating is more than 3 h, which is longer than that of KDP coating and can demand the actual construction needs. The anti-corrosion performance results display that protection efficiency (Pe%) of KDP-DKP coating is 95.33%, which is higher than 87.56% of KDP coating, indicating that the anti-corrosion performance of KDP-DKP coating is superior than that of KDP coating. Furthermore, durability and anti-corrosion mechanism of KDP-DKP coating were also investigated and explored through immersion and potentiodynamic polarization tests. The consequences demonstrate that KDP-DKP coating has excellent durability, and both magnesium and phosphate ions in the coating suppress the corrosion rate of Fe. In summary, this work developed a durable and eco-friendly MKPC coating, which provides feasible guidance for the practical application of MKPC anti-corrosion coating.

Yihan Xu, Yihan Li, Tianyan Chen et al.

Due to its exceptional quality as a biomedical metal, stainless steel is often utilized to produce a broad range of medical tools. The resistance of stainless steel to corrosion is a key indicator of how long and how effective it will serve its intended purpose, and it is an important factor in determining the biocompatibility of the material. However, due to the complex physiological environment within the human body, the corrosion management of medical-grade stainless steel is facing several challenges. In this article, an overview of the factors that influence the corrosion performance of medical-grade stainless steel is provided, and new technologies and methods that have been developed in recent years to improve the corrosion resistance are discussed. These cutting-edge methods are expected to improve the corrosion resistance and longevity of medical-grade stainless steel, providing strong support for the increased applicability of the material in the medical industry.

José Ignacio Verdeja González, Daniel Fernández-González, Luis Felipe Verdeja González

Yuksel Asli Sari, Mustafa Kumral

Sergey Mokrin, Vladimir Gubernov, Sergey Minaev

In this work, the behavior of a lean premixed stretched flame stabilized in a flat channel near a heated wall was studied. Dependences of the flame front position on the stretch rate parameter at temperatures of the heated wall of 1000 and 1200 K and the combustible mixture composition (ϕ = 0.7 and 0.6) were obtained experimentally. The reduced thermal diffusive model was used in numerical simulation for an explanation of obtained experimental results. Theoretical estimates are in qualitative agreement with the experiment. The performed qualitative analysis may be useful in estimation of the combustion product temperature and the residence time of the nanoparticles forming in combustion products before their impact with the hot wall.

Qi YIN, Liping JIANG, Fengjia GUO et al.

In the present study, an investigation is conducted into the effect of different aging treatments on the hardening properties of the 6151 aluminum alloy sheet. According to the research results, the artificial aging hardening response of the pre-aging sheet is significantly stronger compared to natural aging after the solution treatment. In the stage of artificial aging, 120 oC pre-aging treatment produces a more significant strengthening effect than 80 oC and 100 oC pre-aging treatment. The longer the artificial time, the higher the hardness value. When the artificial aging temperature reaches 200 oC, the time taken to achieve peak aging is the shortest, and the occurrence of softening is evident in the over-aged state. When the artificial aging temperature is 200 oC, the softening effect becomes more significant. Natural aging can inhibit the strengthening effect of artificial aging. With the extension of natural aging, the hardening effect of artificial aging diminishes gradually.

Jairo Alberto Muñoz, Egor Dolgach, Vanina Tartalini et al.

This research presents the microstructural and mechanical evolution throughout the welded seam of an austenitic stainless steel (ASS) tube. It was found that the main hardness decrement occurred in the fusion zone (FZ), followed by the heat-affected zone (HAZ) and the base material (BM). Optical microscopy indicated a dendritic structure in FZ and heterogeneous austenitic grain size from the HAZ towards the BM, ranging from 100 µm to 10 µm. The welding process generated an intense texture around the FZ and the HAZ, while the BM still showed an extrusion-like texture. In terms of mechanical behavior, the largest austenite grain size in the FZ led to the lowest strength and ductility of all zones due to the earliest strain localization manifested by heterogeneous strain distribution. However, the strain localization in all zones appeared after 0.4 true strain, indicating an overall good ductility of the seam. These high values were related to two microstructure characteristics: (1) the 10% δ-ferrite after solidification in the FZ favored by the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>C</mi><msub><mi>r</mi><mrow><mi>e</mi><mi>q</mi></mrow></msub><mo>/</mo><mi>N</mi><msub><mi>i</mi><mrow><mi>e</mi><mi>q</mi></mrow></msub><mo>=</mo><mn>1.67</mn></mrow></semantics></math></inline-formula> relationship that delayed the crack propagation along the austenite grains and (2) the heterogeneous microstructure made up of soft austenite and hard martensite in the HAZ and BM producing multiple strain concentrations. Kernel Average Misorientation (KAM) maps obtained by Electron Back-Scattering Diffraction (EBSD) allowed observing higher internal misorientations in the FZ than in the HAZ due to interconnected walls between the δ-ferrite grains. However, the largest KAM values were observed in the BM between γ-austenite and the deformation-induced α’-martensite phases. X-ray diffraction revealed that the residual stresses in the cross-section of the welded seam were compression-type and then switched to tension-type in the outer surface.

Nikhil Dhawan, Shrey Agrawal

A. Kaldellis, N. Makris, P. Tsakiridis et al.

Angelos Kaldellis, Nikolaos Makris, Petros Tsakiridis and George Fourlaris Lab. of Physical Metallurgy and Center for Electron Microscopy, School of Mining and Metallurgical Engineering, National Technical University of Athens, 15780 Athens, Greece., United States, Lab. of Physical Metallurgy and Center for Electron Microscopy, School of Mining and Metallurgical Engineering, National Technical University of Athens, 15780 Athens, Greece, Athens, Acharnes, Greece

Margarita Vodyakhina, I. Chekmasova

The article studies the strategy of international brand management of an industrial enterprise. The state of the Ukrainian industry is analyzed. It was revealed that in a crisis, enterprises should make more efforts to maintain their positions in the market. In this case, it is advisable to develop the company's brand. The segment of consumers is separated by such industries as metallurgy, energy, mining and processing, engineering, petrochemical, papermaking and food. When forming a brand strategy, it should be borne in mind that the activities of enterprises in industrial markets usually take place on the basis of B2B sales. The brand in the B2B market performs the functions of "quality assurance", "reliability", "long-term relationship". Also, an important feature of this approach is that companies do not work for the end consumer, but for other legal entities in various fields and industries. Promotion of industrial products through advertising is ineffective, and it is advisable to use public relations and direct marketing. When performing the work, the following methods were used: structural and functional analysis - to study the relationship between the main factors of the B2B market and the formation of branding, statistical analysis - to study the dynamics of the main indicators of the enterprise, financial analysis - to assess the financial condition of the enterprise, comparative analysis - to compare brands of competitors with this enterprise. A brand management strategy for an international company is proposed, taking into account the peculiarities of the functioning of industrial markets. The implementation of the recommendations presented in the work will create a strong brand and, as a result, create a reputation as a reliable supplier, strengthen relationships with existing customers and increase the number of end consumers. The calculated budget of the promotion program and the assessment of the effectiveness of the proposed strategy indicate that the introduction of the brand at the enterprise will allow receiving additional income in the next year. Therefore, based on the results of the analysis, it can be concluded that the proposed brand strategy for an industrial enterprise is effective and is necessary for the enterprise for further development and financial seurity.