BODY WITH SUPERHARD COATING

Abstract: The present invention relates to a compound body con­ sisting of a substrate with a surface coating of one or more dense, finegrained diamond layers, where the diamond grains are directly bonded to each other. Extreme hardness makes the compound body suitable for wear parts- and tools applications. Very good heat conductivity and an extremely high electrical isolation resistance makes the compound body extremely useful to lead away heat in electronic com­ ponents.

Description: The present invention relates to a compound body comprising a substrate with a surface coating of one or more dense, fine-grained diamond layers, where the diamond grains are directly bonded to each other. The coating is characterised by an extremely high hardness, which makes the compound body suitable for wear parts and tools applications. The coating is also characterised by a very good heat conductivity combined with an extremely high electrical isolation resistance, which makes the compound body most useful in the electronic industry to conduct heat in electronic components. Diamond coatings have earlier been produced by sintering diamond powder on a substrate at high pressure and high temperature. A drawback with this method is that the choice of substrate materials is very limited. In practice only various hard metals can be a possible choice. Furthermore, it is not possible to obtain pure diamond coatings since a certain amount of the substrate material penetrates the diamond layer. A further drawback is that only small parts can be coated. The dimensions can in no direction exceed about three centimetres. A further method of obtaining diamond layers is known. By CVD (Chemical Vapour Deposition) layers with some micrometers thickness can be obtained. The method is described in several Russian and Japanese papers e.g.: 1. Vapour Growth of Diamond on Diamond and Other Surfaces. B. V. Spitsyn et al., J. of Crystal Growth 52 (1981), 219-26 2. Growth of Diamond Particles from Methane-Hydrogen Gas. S. Matsumoto et al., J. of Materials Science 17 (1982), 3106-12 3. Japanese Patent. Kokai 58-91100. Matsumoto. May 30, 1983 4. Japanese Patent. Kokai 58-110494. Matsumoto. July 1, 1983 5. Japanese Patent. Kokai 58-135117. Matsumoto. Aug. 11, 1983 Drawbacks with the method are that you can not obtain such thick layers as often desired, and further that the layers often have bad adherence to the substrate material. The use of a non-diamond bonding layer between the substrate and the diamond coating is also well known in the art. In e.g. JP-A-58-126972 (Patent Abstract of Japan, Oct. 19, 1983, C-191, page 1380) it is described that the surface of a hard metal containing one or more carbides and/ or nitrides is coated with an intermediate layer of carbide, nitride, oxide and/or boride on which a diamond layer is applied. It has now turned out that improved adhesion of diamond layers is obtained on a certain metal such as titanium with high affinity to carbon but also to most noble metals. By coating the substrate with a thin layer of some of the above mentioned materials prior to the diamond deposition, improved adhesion is obtained. By interrupting the diamond deposition process with equal intervals and depositing layers of the above mentioned materials a thick coating can be built up, consisting mainly of diamond, and having good adhesion to the substrate. It should be observed, that the non-diamond layers may be extremely thin, e.g. about 10 Å, but they may also be thicker e.g. up to about 10 µm. According to the invention there now exists a compound body with improved adhesion and a thick diamond coating. In one embodiment the substrate can comprise carbides, nitrides, carbonitrides, oxycarbides and borides of metals from group 4b to 6b of the periodic system bonded by metals of the iron group. The carbides in this embodiment comprise carbides such as WC, TaC, TiC, Mo₂C, Cr₃C₂, VC, MoC and the like. Carbonitrides such as (Ti, Mo) (C, N) and oxycarbides such as Ti(C, O) are also possible. The nitrides comprise all metal nitrides with the exception of salt-like nitrides such as the alkali and earth alkali metals. The useful nitrides are generally those of the transition metals. They are generally described just as the carbides, borides and silicides as refractory hard materials. Compounds of the metal nitrides and compounds of nitrides with carbides in solid solution are also useful in this invention. Special examples of nitrides and compounds that can be mentioned are: silicon nitride, titanium nitride, zirconium nitride, vanadium nitride, chromium nitride, niobium nitride, molybdenum nitride, tantalum nitride, tungsten nitride and hafnium nitride. Boride include: titanium borides, zirconium borides, chromium borides, cobalt borides, molybdenum borides, niobium borides, iron borides and others. Among the materials included in this embodiment is cemented carbide. In another embodiment the substrate contains ceramic and refractory material such as BN, Si₃N₄, oxides of metals from groups 4b to 6b in the periodic system and Al and Si, SiAlON, AlON and mixtures of Al₂O₃ with TiC and TiN. Among the ceramic oxides the following can be mentioned: SiO₂, Al₂O₃, ZrO₂, TiO₂ and the like. The ceramic materials useful in the invention comprise a great number of products from crystalline to completely vitreous substances. The ceramic comprises also non oxide materials such as the metal carbides, -nitrides, -borides and -silicides already mentioned as well as mixtures with the above mentioned oxides. Ceramics according to the invention also include what is called cermets and composites of ceramics and metal. The compound body according to the invention can be produced through deposition on a certain substrate of a combination of layers of non-diamond and CVD-diamond said non-diamond or bonding layer being defined in claim 1. When the coating comprises more than one layer of diamond the orders in which they are deposited can be any. E.g. a layer of diamond can be deposited first after which a second layer of non-diamond can be deposited after which further layers can be deposited comprising either only diamond or combination of diamond and non-diamond layers. The diamond layers can be deposited with CVD according to known technique with the use of a mixture of gaseous activated hydrocarbon and hydrogen which are brought in contact with the heated substrate. Each individual layer can be 0.1-10 µm thick, preferably 0.2-2 µm. When the coating comprises several layers the total thickness can reach 500 µm or more depending on the thickness of every individual layer and number. The number of layers can be two or more and comprise several layers of diamond separated by non-diamond layers. The non-diamond layers can be deposited according to well-known CVD- or PVD-methods. Coated bodies according to the invention have many applications within the industry. One use is for parts subject to intensive wear e.g. extrusion dies, seal rings and thread-guides, milling and turning tools and the like for machining of metals as well as other material such as wood, plastic laminates and fibre composites. Tools equipped with inserts according to the invention have increased hardness and machining efficiency as well as pronounced increased wear life. This applies especially when coating comprises several diamond layers as the increased total diamond thickness effectively contributes to increased wear resistance. Furthermore, bodies according to the invention are useful as surgical tools. Finally, diamond layers are of use as radiation detectors in the medicine or nuclear technique for control of radiation dose. The following examples illustrate the invention except the comparative Example 1. Example 1 (not forming part of the invention) A cemented carbide insert is coated first with a 2 µm thick TiC-layer according to known CVD-technique. Thereafter the insert is coated with an about 2 µm thick diamond layer. Finally the insert is coated with a 2 µm thick TiN-layer with PVD (Physical Vapour Deposition). The insert has excellent properties when machining Si-containing Al-alloys. Example 2 Example 1 is repeated with the following exception: Between the TiC- and the diamond layer an about 0.1 µm thick titanium layer is deposited with PVD in order to improve the adhesion. This multilayer coating gives excellent results by reducing the tool failures during milling. Example 3 A thread guide of Al₂O₃ is first coated with a 0.1 µm thick layer of titanium and thereafter with an about 2 µm thick diamond layer. Double wear life is obtained. Example 4 A cemented carbide insert is coated alternating with a 0.1 µm titanium layer and a 2 µm diamond layer to a total thickness of about 100 µm. The insert is used with good result for machining of sandstone.

Claims: Compound body comprising a core of a material taken from the group consisting of a metal-bonded hard metal compound, ceramic or mixtures thereof, said core being at least partially covered with a coating comprising one or more CVD-deposited layers of polycrystalline diamond, characterized in that the coating is bonded to the substrate by a layer of a material being different from the substrate material and consisting of the metal titanium. Compound body according to claim 1, characterized in that the coating comprises at least one intermediate layer of a metal able to form stable carbides, preferably titanium between the diamond layers. Compound body according to any of the preceding claims, characterized in that the total thickness of the coating is between 0.1 and 500 µm.

Inventors: LUX, BENNO, SCHACHNER, HERBERT, STJERNBERG, KLAS GOERAN, THELIN, ANDERS GOESTA, TIPPMANN, HEINZ, Stjernberg, Klas Göran, Thelin, Anders Gösta
Applicants: SANTRADE LTD.
Application year: 1985
Main classification: C23C16
IPC codes: C23C30, C23C16, B23B27