Thermal stability of nanocrystalline Cu studied by positron annihilation lifetime spectroscopy and X-ray diffraction

Abstract

Thermal stability of nanocrystalline Cu prepared by compacting nanoparticles (mean grain size about 50 nm) under high pressure has been studied by means of positron annihilation lifetime spectroscopy and X-ray diffraction. A gradual increase of mean grain size in the sample is observed with an increase in ageing time at 180°C, indicating an increase of volume fraction of the ordered regions. Furthermore, during the ageing, the increase in average size of the vacancy clusters in grain boundaries is confirmed by the positron lifetime results. The recrystallization is observed at the temperature of about 180°C, and becomes significant above 650°C. Three annealing stages, which are at the intervals 180–400°C, 400–650°C and 650–900°C have been characterized by positron average lifetime. The average volume of the defects almost remains constant in the interval 400–650°C but becomes considerably smaller in the interval 650–900°C.

Keywords:

• positron annihilation
• thermal stability
• nanocrystalline Cu
• microstructure

Acknowledgements

We gratefully acknowledge Professor Z.Q. Chen and the China Academy of Engineering Physics for providing the samples. This work was financially supported by the Natural Science Foundation of China (Project No. 10775107).