基于同步辐射成像技术的原位观察装置及金属凝固过程原位表征研究进展

金属材料的凝固过程对其最终显微组织和性能起着决定性的作用。因此,采用先进的原位表征技术探究金属的凝固过程具有重要意义。同步辐射X射线成像技术是直接观察金属凝固过程的有效手段。本文作者总结了与同步辐射光源相配套的凝固装置的发展,包括定向凝固装置、电阻炉、多场耦合装置、半固态成形装置、气动悬浮装置和激光增材制造装置。重点介绍了应用同步辐射X射线成像技术揭示不同原位环境下金属凝固行为的最新研究进展,并对该技术在凝固领域的前沿研究方向进行了展望。可以预见,同步辐射X射线成像技术的发展将在不同尺度上深入理解金属和其他材料的凝固过程发挥重要作用。

Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical（USC） rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s^（-1）. The softening mechanism was dynamic recovery（DRV） at 950°C and the strain rate of 1 s^（-1）, whereas it was dynamic recrystallization（DRX） under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ ×mol^（-1）. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate（θ）–flow stress（σ） and-θ/σ–σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s^（-1）, with a power dissipation efficiency η greater than 31%.

Constitutive analysis and optimization on hot working parameters of as-cast high Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests on the as-cast high-Cr ultra-super-critical rotor steel with columnar grains were carried out in the temperature range from 1223 to 1523Kand at strain rates from 0.001 to 1s^（-1）.The compression direction was parallel to the longitudinal direction of columnar grains.The constitutive equation based on Arrhenius model was presented,and the processing maps based on the dynamic material model were developed,correlating with microstructure observation.The main softening mechanism was dynamic recovery at 1223 Kunder strain rates from 0.1to 1s^（-1）,whereas it was dynamic recrystallization under other deformation conditions.The constitutive equation modified by strain compensation reasonably predicted the flow stresses.The processing maps and microstructure evolution mechanism schematic indicated that the optimum hot working parameters lay in the zone defined by the temperature range from 1423 to 1473Kand the strain rate range from 0.001 to 1s^（-1）.

In situ Study on the Growth Behavior of Primary Al_3Ni Phase in Solidifying Al–Ni Alloy by Synchrotron Radiography

The growth behavior of Al_3Ni intermetallic compounds（IMCs）during the directional solidification of Al-10 wt%Ni alloy was investigated by synchrotron radiography.Two main growth patterns of primary Al_3Ni phase,I-like and V-like,appeared during solidification,and I-like Al_3Ni phase grew faster than V-like phase,which can be explained by the minimum energy criterion.The growth of I-like phase can be divided into two stages and was mainly affected by undercooling and Ni concentration.We also found that V-like Al_3Ni phase can evolve into M-like phase during solidification.