Appeal No. 2003-0208 Page 10
Application No. 08/578,996
Takiguchi teaches (page 5, line 16, to page 6, line 17) that
According the method of the present invention, deposition of chromium is
started without introducing nitrogen into the chamber so that a layer of metal
chromium is at first formed on the surface of the base material. The layer of
chromium which may be referred as the base layer has a thermal expansion
coefficient which is close to that of the base material. Therefore, there will be
least possibility that the coating is peeled off the base material under a thermal
effect. Thus, an improved adhesive power can be obtained. Further, the
chromium rich layer adjacent to the base material has an excellent resiliency.
This will further improve the anti-peel-off property of the coating.
The nitrogen concentration is gradually and continuously increased while
the chromium is being deposited to form the coating on the sliding surface of the
base material. A part of the vaporized chromium is then nitrided and deposited
on the base material forming a part of the coating. The layer of the coating thus
formed which may be referred as the second layer contains a mixture of
chromium and chromium nitride[7] and is of a greater hardness as compared with
the base layer of chromium adjacent to the base material so that it possesses a
higher wear resistant property than the base layer. Further, the second layer has
.a sufficient resiliency so that the adhesive property of the base layer will not be
adversely affected by the second layer.
The coating in accordance with the present invention can be used in any
type of sliding member such as a piston ring and an oil ring of an internal
combustion engine and a rail on which a rolling or sliding member is moved.
Komuro discloses a sliding member, such as a piston ring, in which the surface
of a substrate is coated with a compound containing at least chromium nitride, wherein
a columnar crystal structure is present in a tension fracture surface of the coating, the
7 We understand chromium nitride as used by Takiguchi as meaning either CrN, Cr2N or a mixture
of Cr2N and CrN.
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