A series of CoCrFeNb_xNi（x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2） high entropy alloys（HEAs） was prepared to investigate the alloying effect of Nb on the microstructures and mechanical pr...A series of CoCrFeNb_xNi（x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2） high entropy alloys（HEAs） was prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. The results indicate that the prepared CoCrFeNb_xNi（x 〉 0） HEAs consist of a simple FCC solid solution phase and a Laves phase. The microstructures of the alloys change from an initial single-phase FCC solid solution structure（x = 0） to a hypoeutectic microstructure（x = 0.25）, then to a full eutectic microstructure（x = 0.45） and finally to a hypereutectic microstructure（0.5 〈 x 〈 1.2）. The compressive test results show that the Nb0.45（x = 0.45） alloy with a full eutectic microstructure possesses the highest compressive fracture strength of 2558 MPa and a fracture strain of 27.9%. The CoCrFeNi alloy exhibits an excellent compressive ductility, which can reach 50% height reduction without fracture. The Nb0.25 alloy with a hypoeutectic structure exhibits a larger plastic strain of 34.8%. With the increase of Nb content, increased hard/brittle Laves phase leads to a decrease of the plasticity and increases of the Vickers hardness and the wear resistance. The wear mass loss, width and depth of wear scar of the Nb1.2（x = 1.2） alloy with a hypereutectic structure are the lowest among all alloy systems, indicating that the wear resistance of the Nb1.2 alloy is the best one.展开更多
对比分析一次电子束冷床炉熔炼(EBCHM)加一次真空自耗电弧炉熔炼(VAR)和三次真空自耗电弧炉熔炼生产的φ820 mm TC17钛合金铸锭的化学成分均匀性,以及由这两种铸锭经相同工艺锻造得到的棒材的组织均匀性。结果表明,通过原材料控制和工...对比分析一次电子束冷床炉熔炼(EBCHM)加一次真空自耗电弧炉熔炼(VAR)和三次真空自耗电弧炉熔炼生产的φ820 mm TC17钛合金铸锭的化学成分均匀性,以及由这两种铸锭经相同工艺锻造得到的棒材的组织均匀性。结果表明,通过原材料控制和工艺参数设计,两种熔炼方式均可生产出化学成分均匀、杂质含量可控的大规格TC17钛合金铸锭,且EBCHM+VAR工艺在残钛回收方面具有优势;两种工艺得到的铸锭,经相同的锻造工艺可获得组织均匀的棒材,为航空转动件提供材料支撑。展开更多
针对混合关键性系统的多重认证需求,研究多核处理器平台中全局调度算法fixed-priority and Earliest Deadline First by Virtual Deadline(fp EDF-VD)的可调度性分析问题。fp EDF-VD结合处理器利用率和虚拟截止期两个方面来计算任务优先...针对混合关键性系统的多重认证需求,研究多核处理器平台中全局调度算法fixed-priority and Earliest Deadline First by Virtual Deadline(fp EDF-VD)的可调度性分析问题。fp EDF-VD结合处理器利用率和虚拟截止期两个方面来计算任务优先级,系统可调度性取决于是否存在可行的虚拟截止期调整参数。考虑到现有可调度分析方法仅测试有限数量的调整参数候选值,不能有效地判定系统可调度性,故提出了一种改进的判定方法。该方法基于传统(非混合关键)任务调度算法fp EDF的可调度利用率约束条件,利用函数图像分析研究不同关键性级别的系统可调度性需求,并在此基础上给出有效虚拟截止期调整参数的确切范围。通过实例分析及与现有判定方法的比较,验证了该方法的正确性和高效性。与理论分析一致,基于随机生成任务集的仿真实验结果表明改进后的方法具有更优越的可调度性能,能显著地提高任务集的可调度接受率。展开更多
基金supported by the National Natural Science Foundation of China (Nos. 51134013, and 51471044)funds for the central universities, key laboratory of basic research projects of Liaoning Province Department of Education (No. LZ2014007)the Natural Science Foundation of Liaoning Province (No. 2014028013)
文摘A series of CoCrFeNb_xNi（x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2） high entropy alloys（HEAs） was prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. The results indicate that the prepared CoCrFeNb_xNi（x 〉 0） HEAs consist of a simple FCC solid solution phase and a Laves phase. The microstructures of the alloys change from an initial single-phase FCC solid solution structure（x = 0） to a hypoeutectic microstructure（x = 0.25）, then to a full eutectic microstructure（x = 0.45） and finally to a hypereutectic microstructure（0.5 〈 x 〈 1.2）. The compressive test results show that the Nb0.45（x = 0.45） alloy with a full eutectic microstructure possesses the highest compressive fracture strength of 2558 MPa and a fracture strain of 27.9%. The CoCrFeNi alloy exhibits an excellent compressive ductility, which can reach 50% height reduction without fracture. The Nb0.25 alloy with a hypoeutectic structure exhibits a larger plastic strain of 34.8%. With the increase of Nb content, increased hard/brittle Laves phase leads to a decrease of the plasticity and increases of the Vickers hardness and the wear resistance. The wear mass loss, width and depth of wear scar of the Nb1.2（x = 1.2） alloy with a hypereutectic structure are the lowest among all alloy systems, indicating that the wear resistance of the Nb1.2 alloy is the best one.
文摘对比分析一次电子束冷床炉熔炼(EBCHM)加一次真空自耗电弧炉熔炼(VAR)和三次真空自耗电弧炉熔炼生产的φ820 mm TC17钛合金铸锭的化学成分均匀性,以及由这两种铸锭经相同工艺锻造得到的棒材的组织均匀性。结果表明,通过原材料控制和工艺参数设计,两种熔炼方式均可生产出化学成分均匀、杂质含量可控的大规格TC17钛合金铸锭,且EBCHM+VAR工艺在残钛回收方面具有优势;两种工艺得到的铸锭,经相同的锻造工艺可获得组织均匀的棒材,为航空转动件提供材料支撑。
文摘针对混合关键性系统的多重认证需求,研究多核处理器平台中全局调度算法fixed-priority and Earliest Deadline First by Virtual Deadline(fp EDF-VD)的可调度性分析问题。fp EDF-VD结合处理器利用率和虚拟截止期两个方面来计算任务优先级,系统可调度性取决于是否存在可行的虚拟截止期调整参数。考虑到现有可调度分析方法仅测试有限数量的调整参数候选值,不能有效地判定系统可调度性,故提出了一种改进的判定方法。该方法基于传统(非混合关键)任务调度算法fp EDF的可调度利用率约束条件,利用函数图像分析研究不同关键性级别的系统可调度性需求,并在此基础上给出有效虚拟截止期调整参数的确切范围。通过实例分析及与现有判定方法的比较,验证了该方法的正确性和高效性。与理论分析一致,基于随机生成任务集的仿真实验结果表明改进后的方法具有更优越的可调度性能,能显著地提高任务集的可调度接受率。
