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The effect of initial alloy state on hot deformation and dynamic recrystallization (DRX) of GH984G alloy, used to manufacture large scale forgings for 700 °C advanced ultra-supercritical (A-USC) coal-fired power plants, was studied by isothermal compression test. The experimental results show that the apparent activation energy of hot deformation for the as-cast alloy is larger than that of the hot-rolled alloy. The reasonable ranges of processing parameters for the as-cast and hot-rolled alloys are 1100–1200 °C/0.01–0.5 s−1 and 1100–1200 °C/1.0–10 s−1, respectively, based on the processing maps. The flow instability domain of the as-cast alloy is larger than that of the hot-rolled alloy. The different hot deformation behaviors of the as-cast and hot-rolled alloys result from the various initial grain sizes and DRX mechanisms. The main DRX nucleation mode of the as-cast alloy with large grains is continuous dynamic recrystallization (CDRX). However, for the hot-rolled alloy with fine grains, the discontinuous dynamic recrystallization (DDRX) is dominant. • Investigate the effect of initial state on hot deformation of a Ni-Fe based alloy. • The main DRX mechanism of as-cast and hot-rolled alloys is CDRX and DDRX. • Establish the relationship between the optimal deformation parameter and DRX mechanism. • Confine the initial alloy state in the isothermal compression test. [ABSTRACT FROM AUTHOR]

Magnetic properties and microstructure of Sm(Co 0.647 Fe 0.28 Cu 0.053 Zr 0.02) 7.84 magnets prepared by HD powder with different residual hydrogen content (25, 715, 1512 ppm) have been investigated. The squareness and coercivity increase from 0.56 to 0.63 and 24.03 to 26.37 kOe as the hydrogen content increased from 25 to 1512 ppm. TEM results show that similar cellular structure and lamellar structures are formed in these magnets. Due to superabundant vacancies induced by hydrogen, the average grain size of final magnets increases from 50.22 to 62.29 μm with the increase of hydrogen in HD powder. Larger grain size results in fewer grain boundary areas where no clear cellular structure formed. The kerr observation indicate that the reversal domain formed at the grain boundary areas is easier to grow up, while the reversal of in-grain domain shows much harder. • The sintered 2:17 type Sm-Co magnets are prepared by powders with hydrogen. • The H cj and squareness can be improved with higher H content in HD powder. • Larger grain size in 2:17-type SmCo magnets with higher H content in HD powder. • Larger grain size, less grain boundaries, less weaker pining sites. [ABSTRACT FROM AUTHOR]

Abstract Grain boundary modification induced giant coercivity enhancement from 945 kA/m to 1904 kA/m was achieved in Sm 25 Co 48 Fe 20 Cu 5 Zr 2 magnets by doping 0.4 wt% CuO. Different magnetization reversal behaviors were clearly observed between un-doped and doped magnets. Compared with un-doped magnets, Cu enrichment along grain boundary promoting regular cellular structure was obviously found in doped magnet. The in-situ Kerr observation indicated that complete cellular structure could strengthen the pinning field of grain boundary regions and the propagations of magnetization reversals into interiors of grains were restrained by the modified grain boundaries, which resulted in the remarkable coercivity increment. Highlights • Enhanced coercivity from 945 kA/m to 1904 kA/m is achieved. • Complete cellular structure is formed in modified grain boundary areas. • Magnetization reversal differences occur between un-doped and doped SmCo magnets. [ABSTRACT FROM AUTHOR]

In this work, the effect of Zr content on magnetic properties and electrical resistivity of Sm(Co bal Fe 0.09 Cu 0.09 Zr x ) 7.68 ( x  = 0.020, 0.025, 0.030, 0.035) high temperature magnets has been investigated. More Zr content results in the decrease of average cell size and the increase of the density of lamellar structure. In addition, a large number of phase boundaries between lamellar phase and cellular structure have also been formed. The intrinsic coercivity of 550 °C enhances from 3.21 kOe to 6.05 kOe with the increase of Zr content. Furthermore, electrical resistivity shows obviously different variation in different directions with increasing Zr content. At room temperature and 127 °C, the electrical resistivity improves from 68.2 μΩ cm to 91.7 μΩ cm and from 87.1 μΩ cm to 103.3 μΩ cm with increasing x from 0.020 to 0.035 in the direction parallel to c -axis, respectively. However, there is only a slight increase in the electrical resistivity in the direction perpendicular to c -axis. The rise of electrical resistivity in different directions has been discussed. Research results indicate that increasing the density of the lamellar phase is an effective way to increase electrical resistivity in the 2:17-type Sm-Co magnets. [ABSTRACT FROM AUTHOR]

SmFe 12 -based permanent magnet materials with ThMn 12 structure have received extensive attention in the exploration and development of new rare-earth-lean permanent magnets. However, the coercivity influence mechanism has not been clearly defined, hindering the development of high coercivity. In this work, the synergistic effect of Sm content and annealing process on phase formation and microstructure evolution has been investigated. The results demonstrate that the SmFe 12 hard magnetic phase can be obtained massively in ingots with x from 0.95 to 1.2, however, α-Fe can be completely eliminated only when x exceeds 1.0. Simultaneously, continuous grain boundary has been proposed by annealing at 1180 °C for 1 h in the Sm 1.1 (Fe 0.8 Co 0.2) 10.5 Ga 0.5 Ti alloy, accompanied by the purification of ThMn 12 -type phase. Elemental distribution analysis demonstrated that Sm and Ga prefer to enter grain boundary during the annealing process, providing the possibility of obtaining continuous non-ferromagnetic grain boundary. However, the distribution of Sm and Ga in the grain boundary is not uniform, and there are some other regions with more Fe and Co, which is difficult to achieve effective demagnetization coupling between grains, resulting in the easy de-magnetization of the grains. TEM results show that nano-sized weak magnetic 1:9 phases are observed and exist around the 1:12 phase, which may be a region prone to demagnetization in an opposing magnetic field. Overall, this work reveals some new and important factors restricting the development of high performance in ThMn 12 -type magnets. • Sm and Ga tend to enter grain boundary during annealing but their distribution in the grain boundary is heterogeneous. • Nanoscale weak magnetic 1:9 phase in the grain epitaxial region may hinder the development of 1:12 sintered magnets. • 1:12 phase formation is sensitive to annealing temperature and time, with the optimum annealing process is 1180 ℃, 1 h. [ABSTRACT FROM AUTHOR]

The segregation of Cu is crucial for the magnetic properties of 2:17 type SmCo magnets, which is firstly affected by the ordering process during aging treatment. In this research, the ordering process is successfully regulated by doping nano ZrO 2 , which achieves a prolonged ordering process and an increased duration of twin boundaries in 2:17 type SmCo magnets. The continuous migration of twin boundaries in a longer period drives extra Cu to converge towards the cell boundary center, resulting in about 10.52 kOe coercivity only by isothermal aging treatment. The precipitation sequence of the lamellar phase and the cell boundary phase is exchanged. A new understanding of Cu segregation contributes to the development of high performance 2:17 type SmCo magnets. [Display omitted] • The ordering porcess was significantly prolonged with ~17 h in 2:17 type SmCo magnets. • The coercivity with over 1 T was achieved without slow cooling treatment. • The higher efficient of Cu segregation was achieved. [ABSTRACT FROM AUTHOR]

Transition metal nanocluster graphene composite exhibits better performance in energy storage materials than heteroatom graphene composite. In catalytic function separator materials for lithium-sulfur batteries, the introduction of functionalized graphene into asymmetric separators effectively seals and anchors soluble polysulfides, largely mitigating the notorious "shuttle effect". Here, we report the development of a novel asymmetric domain-limited electrochemical (ALE) exfoliation of graphite foils (natural-scaled graphite) to prepare Co-nanocluster graphene composite nanosheets (labeled as Co-G). Co-G has a large lateral size, many surface folds, and few intrinsic defects (I D /I G = 0.38). Co-nanocluster graphene composite promotes redox kinetic conversion, and its high electronic conductivity allows it to act as a second collector, accelerating charge transfer, improving the utilization of active material, and increasing cyclic stability. A lithium-sulfur battery incorporating a Co-G modified separator achieved an initial discharge capacity of 1315.5 mAh/g at 0.5 C with excellent multiplicity performance (932.3 mAh/g specific capacity at 2 C multiplicity) and cycling stability (848.4 mAh/g after 400 cycles). The asymmetric domain-limited electrochemical (ALE) method is a viable approach to the preparation of catalytic function separator materials for lithium-sulfur batteries that will have high magnification and high cyclic stability. • Preparation of transition metal graphene composites by ALE method. • Enhanced anchoring to polysulfides. • Homogeneous active sites for accelerated conversion of polysulfide species. [ABSTRACT FROM AUTHOR]