티타늄계 질화물의 코팅 및 열처리에 따른 내부식 특성

Abstract

The overall success of TiN coating in recent years, can be attributed to high hardness, enhanced wear resistance, low friction coefficient and excellent lubrication properties. It also improved the tribologic behaviour, oxidation resistance, corrosion resistance and life time of many engineering components (drills, cutting tools, dies, etc.). Although TiN coating improves kinds of mechanical properties, but it is considered to get the best quality of engineering components via nitrides coating, i.e, AlN, CrN and ZrN. Recently, Ti based nitride coatings added Al, Cr or Zr has an attention to enhance mechanical properties, For example, TiAlN coating at high temperature has shown superior oxidation resistance reacting with hot air at 800℃, compared to standard TiN coatings which oxidized at 550℃. Furthermore, cutting tools with TiAlN coating have higher machining capability(about two times) than that of TiN coating. It also has a merit in fields of cutting speed and feed rate, which was improved the productivity and tool life about from two to five times. The improvement in the corrosion resistance and tribological properties of TiAlN can be obtained by the addition of other alloying elements such as Zr or Cr, which it forms TiZrN or TiCrN. The purpose of this study was to prepare titanium based-nitride monolayer coating(TiAlN, TiCrN, CrN) and multilayer coating(TiAlN/CrN, TiAlN/ZrN, TiCrN/ZrN) by R.F magnetron sputtering, and corrosion resistance with heat treatment was investigated on monolayer and multilayer coating. The CrN coated layers heat-treated at 400-700℃ have exhibited the columnar structure, forming a direct path for the corrosive medium to pass through the coating defects. On the other hand, the TiAlN coated layer have shown excellent corrosion resistance as compared to that of CrN coated layer. The TiAlN/CrN multilayer coating showed better corrosion resistance than that of the monolayer coating of TiAlN or CrN with heat treatment. Microstructure of TiAlN/CrN coated layer changed by heat treatment at 400℃ from network or cross-linked structure to island grain structure. TiAlN/CrN multilayer coating showed low corrosion current density, high polarization resistance and high corrosion resistance at 400-450℃ TiAlN/ZrN or TiCrN/ZrN multilayer coating has similar behaviour to TiAlN/CrN multilayer coating, but it was influenced on particle size and interconnection between particles and oxidation. The TiCrN/ZrN multilayer coatings heat-treated at 400-450℃ showed the lowest corrosion current density and the highest polarization resistance.