Free-volume type defects, such as vacancies, vacancy-agglomerates, dislocations, and grain boundaries represent a key parameter in the properties of ultrafine-grained and nanocrystalline materials. Such free-volume type defects are introduced in high excess concentration during the processes of structural refinement by severe plastic deformation. The direct method of time-differential dilatometry is applied in the present work to determine the total amount and the kinetics of free volume by measuring the irreversible length change upon annealing of bulk nanocrystalline metals (Fe, Cu, Ni) prepared by high-pressure torsion (HPT). In the case of HPT-deformed Ni and Cu, distinct substages of the length change upon linear heating occur due to the loss of grain boundaries in the wake of crystallite growth. The data on dilatometric length change can be directly related to the fast annealing of free-volume type defects studied by in situ Doppler broadening measurements performed at the high-intensity positron beam of the FRM II (Garching, Munich, Germany).

中文翻译：

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通过正电子湮没和膨胀计的互补技术研究大块纳米晶金属的自由体积。

自由体积型缺陷，如空位、空位聚集体、位错和晶界，是超细晶和纳米晶材料性能的关键参数。在通过严重塑性变形进行结构细化的过程中，这种自由体积型缺陷以高过量浓度引入。本工作采用时差膨胀法的直接方法，通过测量高压扭转制备的块状纳米晶金属（Fe、Cu、Ni）退火时的不可逆长度变化来确定自由体积的总量和动力学(HPT)。在 HPT 变形的 Ni 和 Cu 的情况下，由于微晶生长后晶界丢失，线性加热时发生长度变化的不同子阶段。