GB2186000A - A method of processing a metal surface - Google Patents

Abstract

A method for processing a metal surface is disclosed, in which two layered coatings consisting of a prime thin hard coating selected from chromium nitride,titanium nitride or titanium carbide and of a secondary thin coating selected from elemental metals and their corresponding alloys capable of dry-plating are provided on a metal material by an ion-plating process. An essential feature of the invention is to provide the secondary thin coating by means of the ion-plating process in the absence of an inert gas, such as an argon or helium gas, which is different from the conventional method for ion-plating the elemental metal in the presence of such inert gas. <IMAGE>

Description

SPECIFICATION A method of processing a metal surface This invention relates two a method of processing a metal surface, particularly in which a metal material is coated with a primarythin film of hard metal compound and furtherthereon with a secondarythin film of an elemental metal or an alloy by use of an ion-plating techniqueto form a beautiful and glossy metal surface of high durability on a whole surface of the metal material or in a desired pattern.

There have been known a numberof articles, such as a wristwatch, cuffs, an eye-glassframe, a tie-pin,a brooch, a stationery and other accessories or outer decorations, as well as a cap crown for a tooth or dental prosthetics in which a metal material is plated with a noble metal, such as gold. There have also been wellknown in the art several methods forthe purpose. These conventional articles, however, have a disadvantage in that the noble metal coating tends to come off and form specks in areas offrequent use, which adversely affect durability and appearance of the articles. Further, metal articles having on their surfaces lustrous patterns are also commercially available, which are, however, poor in durability and tend to come off by rubbing.

In orderto overcome those disadvantages, there has been proposed an ion-plating method forforming a primary thin coating of hard metal compound on a surface of a metal material followed by a further ionplating procedureforforming a secondarythin film of an elemental noble metal oran alloy having asimilar colour tone to that ofthe primary coating (GB 2000812A). The applicant has also developed a method of forming a primary and a secondaryfilm over a whole area of a metal material or in a desired pattern, utilizing similarlythe ion-plating technique (GB 2162205A).

In general, a film-forming method utilizing the ion-plating technique comprises ionization of a portion of vaporized metal particles followed by deposition thereof on a solid surface to form a film, in which the ionization in the presence of an inert gas (such as argon or helium) provides a film of pure metal (elemental metal), whereas the ionization in the presence of an active gas (such as oxygen or nitrogen) provides a hard film of metal oxides or nitrides. Such procedure has been generally known as a conventional method for ion-plating in the art (Scientific Dictionary, Maruzen & Co., Ltd., Page 53 (1985).

GB 200081 2A has also utilized the conventional method, as described in Examples, in which a primaryflim is formed in the presence of nitrogen as the active gas while a secondaryfilm is formed in the presence of argon as the inert gas.

It has now been found outas a result of continued study offorming the two layered coatings of primary and secondaryfilms by means of the ion-plating technique that the ion-plating procedure in the absence of the inert gas (such as argon or helium) during formation of the secondary film of elemental metal or its alloy differently from the conventional method may avoid an operation, such as involving a high frequency output of argon gas pressure, and improve its operability. Further, a spattering phenomenon with an argon ion may be eliminated to increase a rate of forming a thickness of the film and to lower a treatmenttemperature,so that the material may be prevented from damage.In the absence of the inert gas (such as argon or helium), it has also been found outthatthe ionization may occur only with an evaporated metal to enable vacuum in an apparatus to be reduced to 106 - 1 O5Torrwhich is lower by 102- 1 O3Torrthan the order of 108Torr in the conventional method, to increase purity of the resulting film due to the absence of inclusion of, for example, the argon ion and to prevent pin holes, resulting in improvement of corrosion-resistance. Further, the enhan ced ionization of the evaporated metal permits working in a place of lower voltage applied to a cathode, thereby to reduce troubles due to abnormal discharge.

An object of the invention is to provide a method of processing a metal surface by means of an ion-plating technique, which is superior in operability, economy and properties of products to conventional ion-plating methods when a hard primary metal film is formed on a surface of a metal material followed by a secondary film of elemental metaloritsalloythereon.

According to the invention there is provided a method of processing a metal surface characterized in that a metal material is subjected to bombard treatment in the presence of an inert gas followed by a firstionplating process in the presence of an active gas to form on a surface of said metal material a primarythin coating of hard metal compound selected from chromium nitride, titanium nitride and titanium carbide, and that the resulting metal material with the primary thin coating is then subjected to a second ion-plating process in the absence of an inert gas to form on said primarythin coating a secondarythin coating of an elemental metal or an alloy capable of dry-plating.

As the inert gas used forforming the primary film, there may be preferably mentioned argon and helium, especially argon, while nitrogen is preferred for the active gas. During formation of the secondary film, both of these inert and active gases are not used, of course.

As the elemental metal for the secondary film, there may be mentioned metal capable of dry-plating, such as gold, silver, platinum, copper, zinc, palladium, chromium, rhodium, indium, nickel, germanium, cobalt, zirconium,tungsten,tantalum, niobium, manganese, molybdenum,tin, iron or aluminium.

Asthe alloyforthe secondaryfilm,there may be mentioned an alioy capable of dry-plating selectedfrom alloys of gold, silver, platinum, copper, palladium, chromium, rhodium, indium, nickel, germanium, cobalt, zirconium, tungsten, tantalum, niobium, manganese, molybdenum, tin, iron, zinc and aluminium.

The primary and/orthe secondaryfilms may be formed over a whole surface of the metal material or in a desired pattern. The latter case is suitable for providing a brand name oran initial on an outer accessory.

In accordance with the invention, the secondary metal film is formed on the primary hard metal film in the absence of the inert gas (such as argon), so that operation such as involving thigh frequency output ofargon gas pressure may be avoided two improve its operability,that a spattering phenomenon with an argon ion may be eliminated to increase a rate offorming a thickness of the film and to lower a treatmenttemperature,and thatthe ionization may occur onlywith an evaporated metal to enable vacuum in an apparatus to be reduced upto 105 105 - 1 Torrwhich is lower by 1 o2 103 Torrthan the order of 108 Torr in the conventional method,to increase purity of the resulting film due to the absence of inclusion of the argon ion and to prevent pin holes, resulting in improvementof corrosion-resistance. Further, the enhanced ionization oftheevaporated metal permits working in a place of lower voltage applied to a cathode,therebyto reduce troubles due to abnormal discharge.

The invention will now be described, byway of example, with reference to the accompanying drawings7 in which: Figure lisa sectional view of a finished product prepared by the method according to the invention; Figure2 is a sectional view of the product after use for some period oftime; Figure3 is a perspective view of another product with a patterned coating; and Figure 4 is a schematic view of an apparatus used for ion-plating the secondary metal film.

In Figure 1, reference numeral 1 represents a cap crown formed of a zinc alloy, for example, as a metal material and applied to a cured tooth. A surface of the crown 1 is coated with a prime coating oftitanium nitride as a hard metal compound in a thickness of 3 ii by means of an ion-plating process.

Thus, the surface of the crown 1 is coated with the prime coating of golden colour, which has a surface hardness of 1720 HD and a high corrosion-resistance. The golden colour, however, is somewhat inferiorto thatofa true gold.

Then, a surface of the prime thin coating 2 is coated with a secondary thin coating 3 of metal gold in a thickness of 5- 10 . In order to form the secondary coating 3, the ion-plating process is essentially carried out in the absence of an inert gas, such as an argon or helium gas.

The crown 1 thus processed has a secondary thin coating 3 of gold, which shows the true gold colour.

However, the gold as the secondary coating 3 is very soft and weak, sothatfrequentuse of the crowned tooth may cause the coating 3 to wear away, as shown in Figure 2. Underthe secondary coating 3, however,there exists the prime coating 2 oftitanium nitride, which shows a golden colour similarto the true gold, therebyto prevent specks from appearing after the secondary coating 3 has worn away. Usually, the cap crown 1 of such type is used for a back tooth, so that the apparent golden colour may be kept for a long period of use.

As shown in Figure 3, at first a whole surface of an accessory item 4, such as a tie-pin, cuffs or a brooch, is coated with a thin coating 5 of black titanium carbide bythe ion-plating process under the same condition as for the crown 1. Then, the thin coating 5 oftitanium carbide is masked with a suitable pattern or a name, on which is coated a secondary thin coating 6 of platinum by the ion-plating process in the absence of inert gas, such as argon. Thereafter, the mask is removed to leave the patterned coating.

The prime coating 5 oftitanium carbide has a very high hardness and so is resistant to damage as isthe coating 6 of platinum, so that a durable and luxurious accessory item may be produced.

Alternatively, the surface ofthe metal material may be coated with a thin coating of chromium nitride by the ion-plating proces, which is then further coated with silver alloy by the ion-plating process in the absence of the inert gas to form a durable and luxurious product which does notsufferfrom the occurrence of specks, as in the coating combination of titanium nitride and gold described above.

Similarly, the prime thin coating 5 of hard metal compound, such as chromium nitride, titanium nitride or titanium carbide, which has been coated on the metal material by the ion-plating process, may be coated also by the ion-plating process in the absence of the inert gas with a secondary thin coating 6 of an elemental metal or an alloy capable of dry-plating selected from gold, silver, platinum, copper, zinc, palladium, chromium, rhodium, indium, nickel, germanium, cobalt zirconium, tungsten, tantalum, niobium, manganese, molybdenum, tin and iron, as well as their corresponding alloys,to form durable and beautiful products having lustrous patterns of metal or noble metal.

In accordance with the invention, the surface of the metal material may be coated bythe ion-plating processwith the prime thin coating of hard metal compound; such as chromium nitride, titanium nitride or titanium carbide, which may be then subjected to a further coating process of an elemental metal or an alloy capable of dry-plating, such as copper or its alloy by the ion-plating process in the absence of the inert gas, which its further plated with a suitable metal by a dry- orwet-plating process. Thus, the difficulty of the dry- or wet-plating for the titanium nitride coating may be eliminated by the provision of secondary metal coating through the ion-plating process in the absence of the inert gas. In this case, a similarly durable and beautiful coating may be obtained as in the previous embodiments.

In accordance with the invention, the surface of the metal material may be readily made durable and lustrous at a low cost by ion-plating a combination of the hard prime coating with the secondary coating of elemental metal or alloy over its whole area or in a desired pattern.

Namely, the surface of the metal material is coated bythe ion-plating process with the prime thin coating of the hard metal compound, such as chromium nitride, titanium nitride ortitanium carbide, which prime coating is further coated by the ion-plating process in the absence of the inert gas (such as argon or helium) with the secondary coating of elemental metal or alloy, as described hereinabove, over its whole area or in a desired pattern, so that the wearing away of the secondary thin coating does not form specks of different colours after a long period of use. If a noble metal is used for the secondary thin coating, the metal material may be a base metal for providing a durable and luxurious coating thereon.If copper or an alloythereof capable of dry-plating is used for the secondary thin coating, any suitable metal may be plated thereon bya dry- orwet-plating processto form a durable and beautiful metal surface.

Further, the secondary thin coating may be provided over the whole surface or in a desired pattern to form a durable and luxurious patterned coating, such as figure or names. As the secondary thin coating 6, any suitable metal or alloy may be selected for providing the durable and beautiful coating.

The coating according to the invention may be provided on a cap crown for a tooth, an outer decoration of stationery, a band of a wrist watch, an accessory, a container for toiletries, an eye-glass frame, cuffs, a tie-pin, a brooch or other articles.

The essential feature of providing the secondary thin coating by an ion-plating process in the absence of the inert gas, such as argon or helium, in accordance with the invention may improve operability, work- ability, economy and quality of the products.

The invention will now be illustrated with a few Examples but not limited thereto.

Example 1 A degreased and washed SUS 304 plate of 3 cm x 3 cm square was placed in an apparatus, and 100 ml/min.

of an argon gas was introduced thereinto and a bombard treatment was carried out undera condition of a gas pressure of 0.07 Torr, a voltage of 590 V and a current of 2.2 Afor 30 minutes. Then, 90 ml/min. of a nitrogen gas was introduced to provide a gas pressure of 9 x 1 0-5 - 1.3 x 1 0-4 Torr a nd a titanium metal was evaporated for 40 minutes under a condition of EB voltage and current of 40 V, 65 - 75 A and a bias of 350 -450 V, 405 - 5.0 A. Thereafter, the gas was adjusted to 1 x 10-5 Torr, and a product was removed after cooling for 40 minutes.

Thus the plate with TiN coating was obtained.

Then, the plate with the TiN prime thin coating was placed on a cathode C in an ion-plating apparatus, as shown in Figure 4, which was evacuated to 10-5Torrfor allowing Au (gold) to evaporate, using an evapora tion source A. The evaporated Au atoms provided a vacuum of approximately lO-s - 10-2 Torr between the evaporation source A and an anode B arranged adjacent thereto, thereby to generate an are discharge. In a plasma produced by the are discharge,the Au atom was ionized according to the following equations: Au=Au++e-;Au=Au+++e-- The ionized Au ion was accelerated and deposited onto a cathode (substrate) placed outside the anode to form a thin film.The secondary thin Au coating thus formed in the absence of the argon gas had a high adhesive property with respect to the prime TiN coating. In this example the secondary thin coating was ion-plated under the following condition: Applied Voltage between A* and B* : 40 V Applied Voltage between A* and C* : 200 V Evaporation Rate 0.5g/min.

Treatment Duration 5 min.

(Of course, the inert gas was not present.) Example2 After a square SUS 304 plate of 3 cm x 3 cm had been ion-plated with a primeTiN thin coating as in Example 1, it was subjected to an ion-plating process in the same apparatus and the same operation as in Example 1 in the absence of the inert gas to provide a secondary Pd (palladium) thin coating. This secondary thin coating was formed underthe following condition: Applied Voltage between A* and B* 40 V Applied Voltage between A* and C* : 150 V Evaporation Rate 1 gamin.

Treatment Duration : 3 min.

Example 3 Asample coated with a TiN coating as in Example 1 was placed on the cathode C in the apparatus of Figure 4 and subjected to the ion-plating process in the absence of the inert gas as in Example 1, using Cr (chromium) as an essential elementto form a secondary Crthin coating on the TiN prime coating. In this case, a tungsten thermionic emission electrode was used for generating thermoelectrons between the evaporation source A and the anode B thereby to produce the arc discharge. The secondary thin coating wasformed under the following condition: Applied Voltage between A* and B* Be 80V Applied Voltage between A* and C* : 300 V Evaporation Rate . 1 gamin.

Treatment Duration lOmin.

Supplied PowertotheThermoelectronic Electrode : 150W Note A : Evaporation Source B : Anode C : Cathode Although the invention has been described hereinabove with the preferred embodiments, it will be app reciatedto those skilled in the art that many variations may be made without departing from the scope and spirit of the invention.

Claims (6)

1. A method of processing a metal surface comprising subjecting the metal surface to bombard treatment in the presence of an inert gas followed by a first ion-plating process in the presence of an active gas to form on a surfaceofsaid metal material a primarythin coating of hard metal compound selectedfromchromium nitride, titanium nitride and titanium carbide, and subjecting the resulting metal material with the primary thin coating to a second ion-plating process in the absence of an inert gas to form on said primary thin coating a secondary thin coating of an elemental metal or an alloy capable of dry-plating.

2. A method according to claim 1, wherein the inert gas is argon and the active gas is nitrogen.

3. A method according to claim 1 wherein the elemental metal or the alloy is selected from gold, silver, platinum, copper, zinc, palladium, chromium, rhodium, indium, nickel, germanium, cobalt, zirconium,tung sten,tantalum, niobium, manganese, molybdenum, tin, iron, aluminium and their corresponding alloys.

4. A method according to claim 1,wherein the primary and/orthe secondary thin coatings are formed over a whole area ofthe metal material or in a desired pattern.

5. A method according to claim 1, substantially as hereinbefore described with reference to any one ofthe Examples.

6. A metal surface processed by a method as claimed in any one of claims two 5.