Effects of grain size and orientation on mechanical and tribological characterizations of nanocrystalline nickel films

The mechanical and tribological properties of nanocrystalline nickel films affected by the grain size and preferred orientation are studied. Nickel films were produced by the supercritical electroplating process. The preferred orientations and the grain sizes of nickel films were determined by substrates (brass or phosphonic copper), reaction time and chamber pressure. The (111), (111)+(200) and (200) preferred orientation of nickel films were made. The XRD, SEM, AFM, and TEM tests were applied to confirm the preferred orientation and the grain size of a nickel film. The nanoindentation, nano-scratch and nano-wear test were used to obtain the informations regarding the hardness, friction coefficient and wear depth, respectively. The mechanical and tribological properties of nickel films are improved by reducing the grain size. Nevertheless, under smaller grain size conditions (i.e. <30 nm), due to the reverse Hall-Petch relation induced by internal stress, the improvements might be terminated or even decay. In the meantime, one can found that (111) nickel film possesses better mechanical and tribological properties. It is because that, in (111) crystal plane, the nickel atoms accumulate in the most compact form, and a stronger binding energy exists between the atoms. Therefore, if the grain size is in the nanoscale regime, the mechanical and tribological properties are under the influence of the anisotropy of a nickel film.