Method of producing thin, hard coating

DETAILED DESCRIPTION An object of this invention is the provision of a hard, tenacious, anti-galling and corrosion-resistant coating on at least the seal gland and bearing surfaces of a rolling cone rock bit.
Another advantage of this invention is the provision of a very hard, slippery and wear-resisting coating, which is applied at low temperature, on the surfaces of the seal gland and bearings of a rolling cone rock bit.
Still another advantage of this invention is the provision of a very thin and very uniform surface coating on the surfaces of a seal gland and bearings of a rolling cone rock bit which is a finished surface, requiring no further treatment of any kind.
In a modified physical vapor deposition process, a selected coating will be thinly and uniformly deposited upon at least selected areas of otherwise finished manufactured parts.
The coating is comprised of carbide, oxide, or nitride, of an element selected from a list consisting of Ti, Hf, Zr, Nb, Ta, W, B, Al, Co, and Cr.
The parts to be coated, having at least the surfaces to be coated fully machined, are thoroughly cleaned using methods of vapor degreasing and typical preplating type acid and basic baths.
The parts are placed in a vacuum chamber and pumped down to a pressure of 1.
times.
10.
sup.
-5 torr.
Spaced apart from the fixtured parts are a multiplicity of electric arc cathodes.
These cathodes are fabricated of the chosen metallic component of the coating specie.
Each cathode has an adjacent copper striker electrode used to initiate the arc.
Once initiated, the chamber walls are used as anodes.
The fixtured parts, being negatively biased by a high potential of from about 500 volts to about 5000 volts relative to the cathodes are heated and cleaned by cation bombardment, when the arcs are powered, to a required process temperature between about 200.
degree.
Fahrenheit and 400.
degree.
Fahrenheit.
A reactant gas is supplied to the vacuum chamber to a partial pressure of about 1.
times.
10.
sup.
-3 torr.
The bias potential is reduced to a range of about 50 volts to about 500 volts and controlled to adjust the velocity of the metallic cations