ホローカソード方式イオンプレーティング法で作製したＴｉ／ＴｉＮ多層皮膜の耐食・耐摩耗性

Abstract

Attempts have been made to reveal a desirable design for a Ti/TiN multilayer as a protector for corrosion and wear at-tacks. Multilayers of Ti/TiN were deposited on two types of chromium molybdenum steels and on a high speed tool steel by switching on and off a reactive gas feed valve. Layer thicknesses were determined by scanning electron microscopy and also estimated from Ti depth profiles obtained by grow discharge atomic emission spectrometry (GD-AES). Corrosion resisitance was evaluated by two types of tests : one is the method where the coated steels were exposed to the gas generated through hydrolyzing a resin mixture of ABS and PVC at 443 K under a pressure of 2.87 MPa, and the other is the critical passivation current density method where a deaerated solution of 0.5 kmol/m3H2SO4-0.05 kmol/m3KSCN was used as an electrolyte. Ttribology tests were carried out under unlubricated conditions with a reciprocating type testing apparatus. Substrate current is a fairly useful indicator for precise control of layer thickness. GD-AES offers an exact estmation of layer thickness in the matter of minutes, for example, only within 0.4 ks for a multilayer of 56 μm in total thickness. Corrosion tests show that TiN coatings with a thicker Ti underlayer are more protective and that the multilayer coatings possess a better protective function when the ratio of cumulative thickness of Ti layers to that of TiN layers, ∑XTi to ∑XTiN, is within 1 to 2. It is possible that an increase in thickness of the outer TiN layer brings about reduction of protection performance. With an increase in intrinsic compressive stress in the TiN layer, abrasive damage progresses more rapidly toward a substrate. The Ti layer contacting to the outer TiN layer suppressed the progression; for multilayers, therefore decreasing the thickness of the outer TiN layer resulted in a decrease in wear loss.