Specific Coatings

Nitrides

The most common hard coatings being deposited with the cathodic arc process are the nitrides. The evaporation of Ti. 2r, Hf. or Cr in a nitrogen atmosphere produces nitrides with excellent wear and corrosion properties. TiN has been the most common material available through arc, evaporation, sputtering, and ion plating, and has been characterized for many applications. The arc deposited TiN demonstrates a high adhesion, and high micro-hardness and has the adaptability to be deposited effectively to thicknesses of 15 to 20 Hm.

ZrN films demonstrate a higher hardness, smoother finish, and lower coefficient of friction than the TiN coatings. Tests with ZrN coated tooling demonstrated a longer life machining titanium than uncoated or TiN coated tools. Applications of ZrN are not as extensive as TiN, but the characteristics of the film would indicate there is good potential for hard surface treatment where wear and corrosion are concerned (Attachment B). Hf and Cr, while obtainable through the cathodic arc process have not been characterized for specific applications.

Carbides

Titanium, tungsten, vanadium, and tantalum, are the noted materials

■for carbide development. These are primarily films for high hardness applications. Due to the tendency of the carbides to fracture under heavy repeated loads, the need for toughness may preclude their use for this type of duty.

The cathodic arc provides an effective means of depositing carbides. It appears that high ionization efficiencies, like that of the cathodic arc, are needed to complete properly the compound formation. Previous efforts to accomplish the formation involved heat treating at high temperatures which limited the types of materials that could be coated. The cathodic arc carbides have been deposited as low as ^00° C. This coating adhered well and had a hardness as high as 3000 Kg/Hme.

Oxides

Oxides provide an excellent hard coating both for corrosion and wear resistance and for optical properties. Aluminum, titanium, and zirconium oxides are being developed for specific applications.

Metals

The cathodic arc has demonstrated its production capabilites in depositing copper and chrome at rates of several micrometers per minute. These coatings.are well adhered, dense, and very uniform. Aluminum films exhibit good adhesion and ma.y require no additional processing, after coating to form a good corrosion barrier.

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