Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
2001-05-08
2004-11-23
Turner, Archene (Department: 1775)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S439000, C423S44500R, C428S408000
Reexamination Certificate
active
06821497
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a protective coating applied to a sliding member and the like for the purpose of enhancing the wear resistance and decreasing the friction coefficient. More particularly, the present invention relates to hard carbon film as the protective coating and a method for producing the hard carbon film. Furthermore, the present invention relates to mechanical parts coated with an amorphous hard carbon film, used for automobiles and household electric appliances. In the present invention, the term “hard” is used in accordance with the general terminology of tribology (c.f. for example “Tribologist” (in Japanese) Vol. 44, No. 9, 1999, small special edition “hard materials”). Specifically, a sliding member harder than the opposite member, can be said to fulfill the hard property. Particularly, the hardness of hard film is Hv (Micro-Vickers Hardness Number) 1000 or more, more particularly Hv 1500 or more. Several examples of the amorphous hard carbon film applications are reviewed in Tribologist Vol. 41, No. 9, 1996, pages 760-771.
2. Description of Related Art
The conventional surface-treatment methods of metallic material for enhancing the wear resistance and scuffing resistance include nitriding, PVD (physical vapor deposition) and CVD (chemical vapor deposition). Metal carbide, e.g., TiC, or metal nitride, e.g., TiN, has been applied by the latter two methods as a hard film on the surface of the metallic material of a tool, metal die, and the like. Since these coating layers are as hard as Hv 2000-3000, but the friction coefficient lies in the range of from approximately 0.2 to 0.8 and is relatively high, sliding resistance with the opposite material increases according to circumstance. As a result, there arises problems of wear of the coating layer and damage of the opposite material.
The sliding members of the internal combustion engine of an automobile are exposed to severe sliding conditions, particularly an outer peripheral surface of a piston ring. A vane of a compressor and a plunger (piston) of a fuel injection pump are exposed to severe sliding conditions, too. The wear resistance required for these parts is, therefore, at a high level.
Heretofore, in order to ensure satisfactory sliding properties, particularly the wear resistance of these parts, high-grade wear-resistant materials are used and subjected to surface hardening treatment, such as nitriding and carburizing. However, the conventional method involves a problem in that it uses expensive material. In addition, since the surface hardening treatment must be carried out at high temperature of from several hundred degree C. to 1000° C., dimensional accuracy is lowered due to thermal deformation and the hardness of the substrate (work piece) material is also lowered.
The plunger of a fuel injection pump is operated under a poor lubricating gasoline environment. A composite plating with dispersed hard particles is, therefore, applied on a surface of the plunger. The heat treatment must be carried out at approximately 400° C. to enhance the hardness of the composite to the required level. High-grade material equivalent to SKD 11 (Cold Work Tool Steel) should, therefore, be used so as to avoid softening during the heat treatment. Under such circumstances, it has been desired to develop a method for forming wear resistant hard film at low temperature.
The amorphous hard carbon film formed by the CVD method with the aid of plasma or ion beam has high hardness in the range of from approximately 2000 to 3000 Hv. This film has attracted attention as the material of highly wear resistant coating. The amorphous hard carbon film may be referred to as a diamond-like carbon film, i-carbon film, hydrogenated amorphous carbon film (a-C:H) and the like. Each of these films mainly comprises amorphous carbon.
Although applications of such amorphous hard carbon film to sliding members have been considered, the inherently large compressive stress in the film reduces adhesion of the film to the substrate material and makes a thick coating of the film impossible.
It has been proposed to enhance the adhesion of the amorphous hard carbon film to the substrate by means of sandwiching between the substrate and the film an intermediate layer consisting of metal, metal nitride and metal carbide. For example, Japanese Examined Patent Publication No. 5-82472 discloses the use of carbide, carbo-nitride, oxy-carbide, carbo-oxy-nitride and carbo-boride of 4a, 5a and 6a family metal of Periodic Table, as well as carbide or carbo-nitride of Si as the intermediate layer. Japanese Unexamined Publication No. 10-130865 discloses an intermediate layer, which mainly comprises at least one metal element or its oxide, nitride or carbide selected from the group consisting of Al, Cr, Sn, Co. However, these proposals to improve the adhesion are connected with the intermediate layers rather than the surface layers which are directly involved in the sliding.
Surface Coating Technology, 47, 710-721 (1991) and Japanese Unexamined Patent Publication No. 3-240957 (Japanese Patent No. 2971928) discloses that low friction coefficient is obtained due to the adsorption of environmental gas to the silicon oxide (SiO
2
) formed on the sliding surface of an amorphous hard carbon-hydrogen-silicon film. Note that this silicon oxide is formed on the surface of the hydrogenated amorphous carbon film, which preliminarily contains Si in the film, during its sliding with the opposite member. In other words, silicon oxide is not present in the film from the beginning. The friction coefficient is, therefore, high at the beginning of sliding, and a prolonged time is necessary to attain a low level of friction coefficient.
SUMMARY OF INVENTION
It is, therefore, an object of the present invention to overcome the problems involved in the prior art and to provide an amorphous hard carbon film having high hardness low friction coefficient and good adhesion.
It is an another object of the present invention to provide mechanical parts, which are coated with an amorphous hard carbon film containing metal oxide on the sliding surfaces.
It is a further object of the present invention to provide an amorphous hard carbon film which contains metal oxide and which attains stably low friction coefficient from the beginning of sliding. Incidentally, the conventional amorphous carbon film cannot exhibit such friction coefficient from the beginning.
It is yet an object of the present invention to provide a method for producing the amorphous hard carbon film having the properties described above. A method for forming the amorphous hard carbon film on sliding surface of the mechanical parts according to the present invention should be such that high temperature is unnecessary.
The amorphous hard carbon film according to the present invention mainly comprises carbon and hydrogen and is characterized by containing metal oxide in the film. The metal oxide may be an oxide of at least one element selected from the group consisting of Si, Ti, B and W. The content of oxygen in the film is preferably from approximately 0.1 to 10 atomic %.
The amorphous carbon film, which comprises mainly carbon hydrogen and metal oxide, can be formed by means of introducing carbon material, metal-containing material and oxygen into a vacuum chamber, in which a substrate is placed.
The amorphous carbon film according to the present invention exhibits high hardness, improved wear resistance, and low friction coefficient. The amorphous carbon film according to the present invention can, therefore, be applied to the mechanical parts which have a sliding portion and are operated under conditions where lubrication is difficult.
The minor components of the amorphous hard carbon film according to the present invention are mainly oxide and contain fluorine, bromine, chlorine and the like contained in the starting materials in addition to a small amount of oxygen not combined as the oxide, and metallic elements.
In the present invention, the main components, i.e.,
Kabushiki Kaisha Riken
Kubovcik & Kubovcik
Turner Archene
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