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Rapid Synthesis of W–Cr Solid–Solution by Dielectric-Barrier Discharge-Plasma-Assisted Ball Milling
S. F. Hong,Z. C. Lu,Y. H. Liu,Q. M. He,W. Jiang,M. Q. Zeng 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12
Supersaturated solid–solutions in a W–Cr alloy system were fabricated by conventional milling and plasma milling. The differentextension mechanisms of the solid solubility that were created by ball milling with and without discharge plasma werestudied. The solid–solubility of Cr in W for the P-milling W–Cr alloy system was higher, which indicates that plasma millingpromotes the formation of W(Cr) solid–solution more easily than conventional milling. According to Miedema’s model, inthe W–Cr alloy system, the free-energy change to form a W(Cr) solid solution by plasma milling is reduced compared withconventional milling because of the heating effect of the discharge plasma. Therefore, a higher stored energy in the grainboundaries and dislocations of the W–Cr nanograins during plasma milling makes it easier to overcome the thermodynamicbarrier in the formation of a solid–solution, when compared with conventional milling.
Loss-Separation Study on Silica-insulated Gas-atomized Fe-Si-Al Soft Magnetic Composites
T. T. Xu,B. W. Zhang,Z. Shi,W. W. Guan,K. Wan,X. Y. Shi,W. Liu,H. L. Su,Z. Q. Zou,Y. W. Du 한국자기학회 2020 Journal of Magnetics Vol.25 No.2
Fe-Si-Al soft magnetic composites were composed of gas-atomized Fe-9.6wt.%Si-5.4wt.%Al alloy powders insulated with silica nanoparticles. The influence of silica insulation content on the core’s magnetic properties was studied. It was found that increasing the silica mass ratio deteriorated the effective permeability and core loss in the frequency range of 40-120 kHz, while improved the quality factor at 100 kHz and DC-bias performance. The effective demagnetizing field reflected by density and the core’s volume resistivity may cause the variations of these magnetic parameters. Loss separation fitting was performed using the Bertotti formula, indicating that silica insulation increased the hysteresis loss and reduced the eddy-current loss. The hysteresis loss took over at the frequency lower than 120 kHz in this work. With increasing the frequency, the eddy-current loss grew more quickly than the hysteresis loss. Therefore, different methods should be adopted to reduce the core loss according to the core’s application frequency.
P. Z. Si,X. L. Wang,X. F. Xiao,H. J. Chen,X. Y. Liu,L. Jiang,J. J. Liu,Z. W. Jiao,H. L. Ge 한국자기학회 2015 Journal of Magnetics Vol.20 No.3
Cr₂O₃ nanoparticles were prepared via one-step reactive laser ablation of Cr in oxygen. The metastable CrO₂ phase was obtained through the subsequent oxidation of Cr₂O₃ nanoparticles under O₂ with gas pressures of up to 40 MPa. The as-prepared Cr₂O₃ nanoparticles are spherical or rectangular in shape with sizes ranging from 20 nm to 50 nm. High oxygen pressure annealing is effective in producing meta-stable CrO₂ from as-dried Cr₂O₃ nanoparticles, and the Cr₂O₃ nanoparticles exhibit a weak ferromagnetic behavior with an exchange bias of up to 11 mT that can be ascribed to the interfacial exchange coupling between uncompensated surface spins and the antiferromagnetic core. The Cr₂O₃/CrO₂ nanoparticles exhibit an enhanced saturation magnetization and a reduced exchange bias with an increasing faction of CrO₂ due to the elimination of uncompensated surface spins over the Cr₂O₃ nanoparticles when exposed to a high pressure of O₂ and/or possible phase segregation that results in a smaller grain size for both Cr₂O₃ and CrO₂.
M. Q. Zeng,J. L. Tu,M. Zhu,W. Wang,J. W. Liu,Z. C. Lu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
The effects of plasma discharge intensity on the microstructure evolution of ball-milled tungsten (W)–carbon (C)–cobalt (Co)mixtures and the formation mechanism of ultrathin plate-like tungsten carbide (WC) grains prepared by ball milling with andwithout plasma discharge were investigated. It was found that increasing the plasma discharge intensity during ball millingobviously promoted the formation of a thin flake-like W phase because of the electroplasticity effect and simultaneouslylowered the carburization temperature between W and C. A combination of high hardness and transverse rupture strength of92.9 HRA and 3659 MPa, respectively, was obtained for the WC–8Co alloy fabricated by plasma milling at a gas pressure of5 × 103 Pa with a dielectric barrier discharge layer thickness of 3 mm. These properties were mainly attributed to the markedlylowered activation energy of the WC phase and generation of highly oriented ultrathin plate-like WC grains by plasma milling. The combination of the flake-like structure of the plasma-milled W aggregate and high specific interfacial area and shortdiffusion distance of W/C were readily inherited by the ultrathin plate-like WC grains in the sintered WC–Co hardmetals.