HCD方式反応性イオンプレーティング法により形成したチタン窒化物皮膜の化学組成と硬さに及ぼす成膜条件の影響

抄録

The influence of process parameters on nitrogen-to-titanium ratio, [N]/[Ti], has been investigated. Titanium nitride films were deposited onto substrates of high speed steel, SKH51. Chemical composition of the films was determined through the quantitative analysis method proposed before for electron probe microanalysis. Hardness was measured by Vickers hardness indentation at 0.098-0.49N loads. Process parameters which elevate the substrate temperature bring about a higher ratio [N]/[Ti]. Depth profile by glow discharge spectrometry revealed that the ratio decreased in the direction toward a film-substrate interface. Higher deposition rates of titanium on the substrate reduced the ratio. The ratio increased remarkably by applying a little bias voltage to a substrate, whereas an excess increase in the voltage decreased the ratio slightly. The ratio reduced as total gas pressure lowered; the result is probably due to a decrease in nitrogen partial pressure and to an increase in deposition rate of titanium on a substrate. Although a decrease in gas mixture ratio, [N₂]/[Ar+N₂], reduced nitrogen partial pressure, the change of the ratio [N]/[Ti] was slight; this must be attributed to a decrease in deposition rate of titanium on the substrate. Attempts have been made to clarify the relationship between the ratio [N]/[Ti] and film hardness. Hardness increased with decreasing the ratio from stoichiometry within the region of single-phase TiN. Also, the in-plane lattice parameter increased simultaneously. These results imply that internal compressive stress in the films affected the hardness. Results show that a variation in the hardness with composition cannot be due to the ratio [N]/[Ti] of TiN but rather to other factors e.g., grain size and strain. Precipitation of α-Ti in the films containing Ti₂N causes the hardness to decrease. For single-phase α-Ti, an increase in the nitrogen content gave rise to a remarked increase in the hardness.