The grain boundary excess volume, i.e., the grain boundary expansion, e{GB}, was experimentally determined for high-angle grain boundaries in nickel using the direct technique of high-precision difference dilatometry. Values of e{GB}=(0.35±0.04)×10{-10}  m and e{GB}=(0.32±0.04)×10{-10}  m were obtained by measuring the removal of grain boundary volume upon grain growth for two different types of ultrafine-grained samples. The results are discussed in comparison to values obtained so far from indirect techniques and from computer simulations. It demonstrates the strength of the presented novel, direct approach for grain boundary expansion measurements.

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