DE19521007A1 - Deposition of diamond coatings on hard substrates - Google Patents

Abstract

The coating of hard substrates with a diamond film, comprises: (a) depositing a first intermediate diffusion barrier film; (b) depositing a second intermediate layer contg. a mixt. of the diffusion barrier material and a material with good diamond film adhesion; (c) depositing a third intermediate layer of good diamond film adhesion; and (d) depositing an outer diamond film. The prod. from the above process is also claimed.

Description

Background of the Invention 1. Field of the invention

This invention relates to a method for users Chemical vapor deposition of an adhesive diamond coating on a hard substrate. The invention relates to fer ner on composite objects that have a hard substrate with a adhesive surface coating made of diamond. in the the invention particularly sees diamond-coated cutting tools, drill bits and the like made from cemented Carbides, cermet, ceramic materials, steel and the like are manufactured and improved hardness and wear resistance exhibit.

2. Description of the Prior Art

Diamond has always been of great interest to industrialists Applications because of its great hardness, great thermal conductivity, Resistance to chemical attack and wear resistant been. However, such industrial applications have been limited due to extremely high costs for natural and synthetic diamonds. Over the past few decades Process for chemical vapor deposition under low pressure (in hereinafter referred to as "CVD") from diamond to different Developed substrates that use such diamond coated objects for cutting, grinding, polishing etc. enabled at a significantly lower cost. Different techniques were developed for low pressure CVD by the most important of which were supported by hot filament CVD (using a tungsten or tantalum filament) and the plasma activated CVD (using microwave and High-frequency plasma). The latter "plasma acti fourth "method is used in conjunction with the present inven tion described, and it should be understood that the invention is not is limited to this.

It has been recognized that adhering diamond coatings are caused by CVD on carbide-forming metals, metal carbides, metal nitrides  and metal carbonitrides can be applied. Are against Substrates made of metals that are not carbides form (e.g. cobalt and nickel), metal oxides such as aluminum and Zircon, and various types of steels are not suitable for Diamond coating using CVD, as the full adhesion of the Coating on the substrate is prevented. Especially the diamond coating on cemented carbides suffers because of the poor adhesion of the diamond layer on the substrate the use of cobalt as a binder in cemented Carbides. In order to solve this problem, it has been suggested that Cobalt content of the cemented carbide tops to be coated to reduce the area or the cobalt content completely from the Eliminate surface, e.g. B. by chemical acid etching, such as in U.S. Patent No. 5,100,703, issued March 31, 1992 to Mika et al. granted, described, or by physical pretreatment of the cemented carbide surface, e.g. B. by scratching or vigorous mechanical processes, such as by ultrasonic grinding with hard abrasives, or by conventional grinding technology niken. However, these methods suffer from the disadvantage that the Surface area of the cemented carbide from which the cobalt has been removed, porous and of poor mechanical Strength is, and although the diamond coating on the Carbide surface, it is not fixed with the Body connected to the wearer himself, and can be comparative easily along with the surface layer of the cobalt-free Carbides are removed.

Another solution for coating cemented carbides with diamond is the application of a diamond coating a film made of a refractory material, e.g. B. tungsten, which then with the cemented carbide support by brazing is connected. An alternative solution is to apply one single layer of pure Group Vb or VIb metal the substrate, and then attaching the CVD diamond film this pure metal, as published in on November 19, 1992 open European patent application 0 514 032 A1 from Porat was laid. This single layer of pure metal allows not always the optimal connection between metal and Substrate, as well as between metal and diamond film. It is also possible to choose an effective interlayer material that  bonds firmly with diamond and further improves adhesion sert. U.S. Patent No. 4,707,384 discloses the use of an inv common titanium carbide intermediate layer open. U.S. Patent No. 4,998,421 and 4,992,082 disclose the use of a variety of Layers of separate diamond or diamond-like part open between the layers of a leveled connection materials are laid.

Similar problems are encountered when trying to get a diamond coating on a ceramic material based on Apply oxides and additives. There is no affinity between the ceramic object and the diamond coating, and no unified connection is established between the two posed. This problem is particularly troublesome when semiconductors be coated with a layer of diamond that acts as heat arrester acts to the large generated in such semiconductors To dissipate heat. If the diamond coating is not The effect is perfectly connected to the semiconductor substrate significantly reduced heat dissipation.

Steels are also not suitable for coating with diamond suitable because of the high affinity between diamond and steel Dissolution of the diamond in the metal leads.

Objects and summary of the invention

An object of the present invention is to provide a method for Producing improved adhesion between a cemented Carbide substrate and a CVD diamond coating.

Another object of the present invention is to provide a Process for adhering a CVD diamond film to to provide a variety of different substrates that do not normally allow the CVD diamond film to adhere well.

Yet another object of the present invention is a process for CVD diamond coated cutting tools, To provide drill tips and the like.

Accordingly, one form relates to the present Invention on a process for coating a hard sub strats with a diamond film containing the steps: Application of a first intermediate layer made of a material that is a diffusion barrier film; Applying a second intermediate  layer that is a composite of the diffusion barrier film material and contains a material with good diamond film adhesion; Aufbrin a third intermediate layer, which is a material with good Contains diamond adhesion; and applying an outer film layer of diamond.

Another form of the invention relates to a process for coating a cemented tungsten carbide substrate with a diamond film, comprising the steps of: applying a first intermediate layer containing TiN; Applying a second intermediate layer, which is a mixture of TiN and a Si Contains material which consists of SiC and Si₃N₄ Group is selected; Applying a third intermediate layer, which contains a Si material, which consists of the SiC and Si₃N₄ existing group is selected, and the same Si material is like the one used in the second step; and Application of an outer layer of diamond.

Yet another form of the invention relates to the Products manufactured according to the disclosed processes.

Preferred embodiments of the invention, as well as others Embodiments, objects, features and advantages of this invention will be apparent from the following detailed description, which should be read in conjunction with the accompanying examples.

Description of the preferred embodiments of the invention

The present invention can be better understood from the specification can be understood in conjunction with the accompanying examples.

It is known in the microelectronics industry that a film of TiN is an effective diffusion barrier against many metals, including cobalt. This property of TiN is advantageously used in the hard metal industry to prevent the diffusion of cobalt to the surface through coatings such as TiC and Al₂O₃. For example, a straightforward process for "sealing" the cobalt in the cemented carbide substrate by means of a diffusion barrier film made of TiN is available. Since TiN is a well accepted coating for cutting tools with excellent high temperature and wear resistance properties, the process of applying a CVD-TiN coating is well known to those familiar with cutting tool technology. However, since TiN has a very high coefficient of thermal expansion (9 × 10 ^-6 / ° C) compared to diamond (1.1 × 10 ^-6 / ° C), the adhesion of diamond to TiN is not very good. Because of the lack of chemical affinity between diamond and TiN, crystal bonding of diamond to TiN is also difficult. On the other hand, it is well known that diamond easily forms a crystal bond to silicon, SiC and Si₃N₄. With a better match of the lattice parameters and the coefficient of thermal expansion, crystal bonding and the growth of diamond on these latter materials allow the formation of an adhesive film.

Surprisingly, now in accordance with the The present invention recognized that thin, adhesive coating diamond through CVD on various hard metals and Ceramic substrates can be applied, provided that those substrates first with thin intermediate layers by OvD are coated, which consist of a first intermediate layer a TiN, a second intermediate layer made of a composite of TiN and SiC or Si₃N₄ and a third intermediate layer made of SiC or Si₃N₄ exist.

The present invention thus provides a wear-resistant, composite-coated article comprising a hard substrate made of cemented carbides, TiN-based, sintered cermet, ceramic materials and steel, a first coating made of TiN, a second coating made of a composite of TiN and SiO or Si₃N _4, and a third coating of SiC or Si₃N _4, and an outer layer of diamond, all layers being applied by chemical vapor deposition. Furthermore, the layer of TiN and the layer of SiC or Si₃N₄ can be applied in under different steps or in a single process. Therefore, the present invention provides for the construction of a multi-layer architecture in which a logical and effective transition from the substrate, particularly a cemented tungsten carbide to diamond substrate, is made in a series of steps involving the application of graded interlayers on the surface of the substrate includes.

The substrates used in the manner described above Diamond can be coated including z. B. zemen  tated carbide-based carbides with cobalt as Binder and optional addition of cubic carbides Titanium carbonitride based Germet materials with cobalt, Nickel, molybdenum or combinations thereof as binders and with the addition of cubic carbides, on oxides such as Alumi ceramic materials based on oxide, possibly with selected addition of carbides, nitrides, oxides and carbo nitrides of tungsten, molybdenum, titanium, vanadium, zirconium, Hafnium, tantalum, niobium, chrome and steels, especially high speed and alloy steels.

The materials used in the present invention Application of the intermediate layers between the substrate and the Diamond are suitable, include nitrides of transition metals, such as TiN, ZiN, HfN and the like for the first intermediate layer; SiC, Si₃N, Si, Si-Al-O-N composites and the like for the third intermediate layer. The first intermediate layer sees a diffusion barrier film to the cobalt or other, for the diamond coating to isolate harmful metals. The third intermediate layer sees a strong bond for the diamond film and the second intermediate layer sees one strong bond between the first and the third intermediate layer before. The currently preferred material for the first Interlayer is TiN and the currently preferred material for the third intermediate layer is SiC or Si₃N₄, the second intermediate layer made of a transition composite of TiN and SiC or Si₃N₄ is.

The intermediate layers are covered by CVD according to the tech nik well-known procedures applied. Appropriate procedures are z. B. in the on January 5, 1971 to Darnell et al. issue ten U.S. Patent No. 3,552,939, which issued on February 8, 1972 Glaski et al. issued to U.S. Patent No. 3,640,689 and in which am U.S. March 1, 1988 to Konig U.S. Patent No. 4,728,579 as well as according to K.A. Gesheva and G.S.Beshkoe in Journal de Physique, Vol. 50 (many, 1989). As shown below The intermediate layers of the present invention can be found under Use of these known CVD techniques can be applied.

On top of the intermediate layers, according to the present Invention applied a thin diamond coating by CVD, either by CVD assisted with hot filament or by  Plasma supported CVD. These techniques are already well known, and a reference can be made to R. Haubner and B. Lux in Journal de Physique, Vol. 50 (May, 1989) and there references made to literature; X.X. Pan, R. Haubner and B. Lux in First euro. Conf. Diamond and Diamond-like Carbon Coating, September 17-19, 1990; "Low-pressure synthesis of super hard coatings ", B. Lux and R. Haubner, Refractory Metals and Hard Materials, Vol. 8, No. September 3, 1989; Kunio Shibuki et al., Surface and Coatings Technology, 36 (1988), pp. 295-302; and U.S. Patent 4,816,286, issued March 28, 1989 to Hirose.

The steps of applying the initial layer of TiN, the Transition layer made of Si₃N₄ + TiN or SiC + TiN composites and the final layer of Si₃N₄ or SiC can be in a single Reactor capable of operating at higher temperatures out, or can be optionally in two different Reactors are running. The examples below illustrate typical process parameters for coating can be used at an atmospheric pressure. Coating at lower pressures can also be used of suitable process parameters that are executed by the given in the following examples may differ or not, and easily determined without undue trying can be. It is further understood that each of the known ones CVD method within the scope of the present invention can be used, including those used in microelectronics industry well-known. The actual rivers and others Application conditions can vary from reactor to reactor, depending on design, process skills and preferences. Since the actual hydrodynamic conditions in a CVD reactor these conditions are highly dependent on the reactor design and parameters well understood by those practiced in technology, like the reactors that every veteran uses, and therefore no further discussion is needed here.

The following examples are illustrations of the present Invention, but should not be understood against it that they limit the invention in any way.

Examples example 1

A cemented tungsten carbide tool substrate, the one Cobalt binders and optional cubic gamma carbides and / or a cobalt-enriched surface layer of a few microns Containing thickness is placed in a conventional reactor, the one with low pressure and atmospheric pressure coating is equipped and capable of Temperatures above 1200 ° C up to 1500 ° C too coat. An adhesive TiN coating about 2 µm thick is applied using the following process parameters; Pressure = 1 atmosphere, temperature = 1000 ° C ± 10 ° C, TiCl₄ flow = 2 slm, N₂ flow = 15 slm, H₂ flow = 50 slm, Ar flow = 33 slm, Total flow = 100 slm, duration 30 minutes.

A gold colored TiN film is made with an orientation of (220) / (111) = 3, and a lenticular crystal morphology receive.

Example 2

The process of Example 1 is repeated, except that at the end the TiN application time increases the temperature to 1225 ° C ± 10 ° C becomes. During the duration of the temperature rise, a flow of SiCl₄ started and gradually increased to the final value of 2 slm. During this time the flow of nitrogen is gradually reduced clears and ammonia gas is introduced and its flow gradually increased up to a value of 500 sccm. The transition to the higher temperature and the introduction of the new gas flow and composition takes about 15 minutes. At this point the flow of TiCl₄ is gradually reduced to zero and the application of an adhesive silicon nitride coating continued until a thickness of about 2 microns of α-Si₃N₄ is reached. The transition period during which a mixed Si₃N₄ + TiN coating is applied, can be adjusted to any desired thickness of this transition layer receive. Typical thicknesses are around 2-3 µm. The process is at Atmospheric pressure carried out, or it can also optionally at  lower pressures can be carried out by suitable on position of the process parameters.

Example 3

The cemented sample thus prepared by Example 2 Tungsten carbide is placed in a microwave plasma CVD reactor introduced for diamond coating. Typical coating parameters are: pressure = 25 Torr, microwave power = 1000 W, CH₄ flow = 6 sccm, H₂ flow = 194 sccm, substrate temperature = 925 ° C ± 25 ° C, coating time = 6 hours. A smooth, uniform and adhesive coating with diamond is on the Surface reached. The coating thickness is about 6-8 µm. The Coating has a unique, square-faceted Morphology, typical of one (100) orientation.

Although the illustrative embodiments of FIGS present invention have been described here is to understand that the invention is not based on this embodiment shape is limited, and that various other changes and modifications thereby brought about by those skilled in the art can be made without departing from the scope or spirit of the invention is deviated.

Claims (7)

1. Process for coating a hard substrate with a diamond film, consisting of the steps:

• a) application of a first intermediate layer of a composite material which is a diffusion barrier film;
• b) application of a second intermediate layer containing a mixture of the material of the diffusion barrier film and a material with good diamond film adhesion;
• c) application of a third intermediate layer containing a material with good diamond film adhesion; and
• d) application of an outer film layer of diamond.

2. The process of claim 1, wherein the diffusion barrier film is made of Is TiN and the material with diamond film adhesion is made of SiC. 3. The process of claim 1, wherein the diffusion barrier film is made of Is TiN and the material with diamond film adhesion is Si₃N₄. 4. The process of claim 1, wherein the hard substrate is made of is selected from that of cemented carbides, cermets, Ceramics and steels formed group. 5. Process for coating a cemented tungsten carbide substrate with a diamond film, consisting of the steps:

• a) application of a first intermediate layer containing TiN;
• b) application of a second intermediate layer containing a mixture of TiN and an Si material, which is selected from the group consisting of SiC and Si₃N₄;
• c) applying a third intermediate layer containing an Si material selected from the group consisting of SiC and Si₃N₄, which is the same Si material used in step b); and
• d) application of an outer layer of diamond.

6. The product according to the process of claim 1 will be produced.   7. The product according to the process of claim 5 will be produced.