GRAIN-SIZE DEPENDENCE OF HARDNESS OF TIN FILMS DEPOSITED BY REACTIVE HCD ION PLATING

Experiment has been made to gain an overall picture for an variation in hardness of TiN films deposited by reactive hollow cathode discharge ion plating with process parameters: deposition temperature, deposition time, electron beam current, substrate bias voltage, gas pressure, mixture ratio of nitrogen to argon, distance from an evaporation source to a substrate, and tilt angle of a substrate axis. Furthermore, an attempt has been made to find out factors controlling the hardness and reveal the relationship between a factor and hardness. The films of single phase TiN were deposited onto a substrate of high speed tool steel, SKH51. Line broadening of X-ray diffraction was utilized to determine the grain size of the films. Substrate temperature plays an important role in a variation in hardness. An increase in deposition temperature, deposition time and electron beam current brings about a higher substrate temperature and thereby gives the films of larger grains and lower hardness. On the contrary, an increase in distance from an evaporation source to a substrate and in tilt angle of a substrate axis leads to a lower substrate temperature, which results in finer grains and higher hardness. Increasing the substrate bias voltage gives rise to higher hardness mainly because of the grain size reduction which is presumably due to renucleation; however, an excess increase in the bias raises the substrate temperature and thus slightly lowers the hardness. The hardness values varies Linearly with the inverse square root of the grain diameter, according to the Hall-Fetch relationship.