Nanoporous structure of vacuum condensates of nickel

Abstract

The nanoporous structure of nickel vacuum condensates produced by the EB PVD method was investigated. The nanoscale pores were analyzed using small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) techniques. It was observed that the set of these nanopores can be considered a bimodal system with characteristic sizes of approximately 1–3 nm and 20–30 nm. It is assumed that the smaller pores form as a result of the coalescence of individual vacancies into clusters during the nickel vapour phase deposition in a vacuum. These pores have a close to a spherical shape and are located inside the grains. After annealing, the characteristics of the nanopore ensemble change: the presence of 1–3 nm pores is almost negligible, while the 20–30 nm pores are partially preserved. Based on this, it is suggested that at elevated temperatures, the 1–3 nm nanopores decompose into individual vacancies, which then migrate towards sinks such as grain boundaries and micropores. This vacancy generation and migration process towards sinks can explain the experimentally observed enhanced diffusion mobility of atoms in vacuum condensates at relatively low annealing temperatures.