The grain refinement and macrosegregation control of GCrl5 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring （V-EMS）, in continuous casting. V-EM...The grain refinement and macrosegregation control of GCrl5 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring （V-EMS）, in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which ena- bles the better mixing of the upper part with the lower part of the liquid steel. The results showed that ap- plying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing （SDAS） and reduce the segregation of both carbon and sulfur. After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2.0 to 3.5 m3/h, the dendrite fragments exhibit an obvious aggregation fol- lowing V-EMS. Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.展开更多
At present,improving the properties of aluminum alloys is generally achieved by increasing the cooling rate of the melt and adding micro-nano particles.Controlling the cooling rate of the melt to improve the refining ...At present,improving the properties of aluminum alloys is generally achieved by increasing the cooling rate of the melt and adding micro-nano particles.Controlling the cooling rate of the melt to improve the refining effect of grain refiner is still a difficult problem in the aluminum alloy casting industry.An innovative and environmentally friendly casting process,known as freeze ablation,was introduced during the preparation of an Al–NbB_(2) intermediate alloy.This process significantly enhanced the cooling rate of the melt.The results indicated that the Al–NbB_(2) intermediate alloy produced under high cooling rates had a noticeable refining effect on Al–Cu alloys,with smaller NbB2 particles demonstrating superior refining performance.The average grain size of the refined Al–Cu alloy decreased from 154 to 69μm,the tensile strength increased by 12%,the fluidity increased by 18.4%,and the hot tearing index decreased from 144 to 12.The matching degree between NbB_(2) andα-Al was calculated using high-resolution transmission electron microscopy and the edge-to-edge model.It was found that the atomic interplanar spacing and the interatomic spacing mismatch between NbB_(2)’s<1120>plane and Al were both less than 10%,which further proved that NbB2 could serve as an effective nucleation site forα-Al grains to achieve grain refinement.展开更多
Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth(RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of M...Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth(RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization(DRX) plays a crucial role in refining grain size of Mg wrought alloys.Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized,including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy,are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.展开更多
Control systems are vulnerable to faults in control loops where faults may cause abruptand damaging responses. These systems with fault accommodation are becoming more and moreimportant while appearing in flight contr...Control systems are vulnerable to faults in control loops where faults may cause abruptand damaging responses. These systems with fault accommodation are becoming more and moreimportant while appearing in flight control, robots control and nuclear reactor control etc, andcalling for more rigorous development approach. A formal approach is explored in this parer, basedon Extended Duration Calculus, for the development of such kind of systems. A typical exampleof control system with fault accommodation, two-level control system, is used for illstrating ourapproach. Its high level consists of an event-driven supervisor which reeds to the change of plant dueto faults occurrence, and its low level consists of normal controller, reconfigured controller and othercomponents with FDI (Fault Detection and Isolation) mechanism. Firstly performance and systemspecifications of the case are formulated in EDC; Then they are refined step wisely into specificationsof the supervisor and the low level components. Finally the whole system performance is verified inEDC framework.展开更多
To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and me...To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870A degrees C for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850A degrees C, where grains with a diameter ae<currency> 500 nm accounted for 30% and those with a diameter > 0.5 mu m accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.展开更多
基金supported by the National Natural Science Foundation of China(No.50834009)the Key Project of the Ministry of Education of China(No.311014)the 111 Project of China(No.B07015)
文摘The grain refinement and macrosegregation control of GCrl5 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring （V-EMS）, in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which ena- bles the better mixing of the upper part with the lower part of the liquid steel. The results showed that ap- plying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing （SDAS） and reduce the segregation of both carbon and sulfur. After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2.0 to 3.5 m3/h, the dendrite fragments exhibit an obvious aggregation fol- lowing V-EMS. Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.
基金financially funded by the Fundamental Research Program of Shanxi Province General programs(No.202103021224179).
文摘At present,improving the properties of aluminum alloys is generally achieved by increasing the cooling rate of the melt and adding micro-nano particles.Controlling the cooling rate of the melt to improve the refining effect of grain refiner is still a difficult problem in the aluminum alloy casting industry.An innovative and environmentally friendly casting process,known as freeze ablation,was introduced during the preparation of an Al–NbB_(2) intermediate alloy.This process significantly enhanced the cooling rate of the melt.The results indicated that the Al–NbB_(2) intermediate alloy produced under high cooling rates had a noticeable refining effect on Al–Cu alloys,with smaller NbB2 particles demonstrating superior refining performance.The average grain size of the refined Al–Cu alloy decreased from 154 to 69μm,the tensile strength increased by 12%,the fluidity increased by 18.4%,and the hot tearing index decreased from 144 to 12.The matching degree between NbB_(2) andα-Al was calculated using high-resolution transmission electron microscopy and the edge-to-edge model.It was found that the atomic interplanar spacing and the interatomic spacing mismatch between NbB_(2)’s<1120>plane and Al were both less than 10%,which further proved that NbB2 could serve as an effective nucleation site forα-Al grains to achieve grain refinement.
基金supported by National Key Research and Development Program of China (No.2023YFB3710900)National Natural Science Foundation of China (Nos.U2241235,U2167213,51971053)+2 种基金funded by the Project of Promoting Talents in Liaoning province (No.XLYC2203202)the financial assistance from Young Elite Scientists Sponsorship Program by CAST (2019-2021QNRC001,2019-2021QNRC002,2019-2021QNRC003)the fund from the Fundamental Research Funds for the Central Universities (N2202020)。
文摘Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth(RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization(DRX) plays a crucial role in refining grain size of Mg wrought alloys.Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized,including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy,are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.
文摘Control systems are vulnerable to faults in control loops where faults may cause abruptand damaging responses. These systems with fault accommodation are becoming more and moreimportant while appearing in flight control, robots control and nuclear reactor control etc, andcalling for more rigorous development approach. A formal approach is explored in this parer, basedon Extended Duration Calculus, for the development of such kind of systems. A typical exampleof control system with fault accommodation, two-level control system, is used for illstrating ourapproach. Its high level consists of an event-driven supervisor which reeds to the change of plant dueto faults occurrence, and its low level consists of normal controller, reconfigured controller and othercomponents with FDI (Fault Detection and Isolation) mechanism. Firstly performance and systemspecifications of the case are formulated in EDC; Then they are refined step wisely into specificationsof the supervisor and the low level components. Finally the whole system performance is verified inEDC framework.
基金supported by the National Natural Science Foundation of China(Grant No.51474031)
文摘To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870A degrees C for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850A degrees C, where grains with a diameter ae<currency> 500 nm accounted for 30% and those with a diameter > 0.5 mu m accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.
