EP0143889A2 - Coated hard metal body - Google Patents

Abstract

A coated hard metal body consisting of a hard metal base containing cobalt and tungsten carbide and a binder metal-free, oxygen-containing hard material layer is described, the hard metal base of which has a 0.2 to 20 µm thick zone on its surface, which contains the phase CoWB in addition to the hard metal components. It is particularly advantageous if the binding metal-free, oxygen-containing hard material layer consists of aluminum oxide, zirconium oxide or aluminum oxynitride. It is further provided that at least one further binder-metal-free hard material layer made of carbides, nitrides, borides and / or oxides is applied to the binder-metal-free hard material layer. The coated hard metal body can advantageously be used as a cutting insert for machining metallic materials. The coated hard metal body is produced by gas phase boronization and a subsequent hard material coating using the CVD process.

Description

The invention relates to a coated hard metal body composed of a hard metal base body containing cobalt and tungsten carbide and a hard metal layer free of binding metal, the hard material layer being composed of hard oxides or of a mixture of hard oxides and hard nitrides or of a mixed crystal of hard oxides and hard nitrides. The invention further relates to a method for producing the coated hard metal body.

From DE-OS 2,233,699 carbide parts are known that are provided with an up to 50 _/ um thick coating of at least one hard refractory compound. Hard oxides, in particular magnesium oxide, hafnium oxide, chromium (III) oxide and / or aluminum oxide, hard nitrides, in particular silicon nitride, vanadium nitride, niobium nitride, aluminum nitride, boron nitride, titanium nitride, zirconium nitride, tantalum nitride and / or hafnium nitride, in particular and hard boron, can be used as heat-resistant compounds Titanium diboride, tantalum diboride or hafnium diboride can be used. According to DE-OS 2 233 699, the coating of the hard metal part can also consist of mixtures or mixed crystals of the aforementioned hard materials. The hard metal base body of the coated hard metal part proposed in DE-OS 2 233 699 consists of hard metal, which consists of a binding metal and of tungsten carbide, titanium carbide, tantalum carbide and / or niobium carbide is composed.

It has been shown that the oxygen-containing hard material layers, in particular the hard material layers consisting of oxides, have only insufficient adhesive strength on the hard metal and flake off even with comparatively little stress. There has therefore been no lack of attempts to improve the adhesive strength of the oxygen-containing hard material layers.

DE-PS 2 253 745 proposes a cutting insert made of a hard metal base body, an intermediate layer and a binder-free surface layer made of one or more extremely wear-resistant deposits made of aluminum oxide and / or zirconium oxide, in which the intermediate layer consists of one or more carbides and / or nitrides of the elements titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, silicon and / or boron and is free of binding metal. A good bond between the oxidic surface layer and the hard metal base body is to be achieved with the hard metal intermediate layer consisting of carbides and / or nitrides. DE-OS 2 525 185 proposes a wear-resistant molded part which consists of a hard metal base body, an intermediate layer made of one or more borides and an outer layer made of aluminum oxide and / or zirconium oxide. The intermediate boride layer, which is composed in particular of the diborides of the elements titanium, zircon, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, is also intended to improve the adhesive strength of the extremely wear-resistant outer oxidic hard material layer. Finally, it is known from US Pat. No. 3,261,673, first of all a nickel layer on a tungsten carbide hard metal body to apply and to spray on an aluminum oxide layer, the nickel intermediate layer to achieve better adhesion of the aluminum oxide layer and an improvement in the heat and corrosion resistance of the composite body.

The invention has for its object to improve the adhesive strength of binder-free, oxygen-containing hard material layers on hard metal bodies, the application of a separate and some _/ um thick intermediate layer should be avoided, since the production of the intermediate layer complicates and increases the cost of producing the coated hard metal body.

The underlying the invention, object is achieved in that the hard metal base body, a 0.2 to 20 _/ has on its surface by thick zone containing in addition to the hard metal components, the phase CoWB. It is surprising that an extraordinarily good adhesive strength of the oxygen-containing hard material layers is achieved by the incorporation of the CoWB phase into the surface of the hard metal base body, because this phase deteriorates, according to experts, the properties of the hard material-coated hard metal body. Thus, in the publication by Zeman, Mayerhofer and Kulmburg, lectures of the Plansee seminar 1981, pages 443 to 457, it is said that brittle phases are formed by the diffusion of boron into the substrate material, since the boron prefers with the cobalt binding phase of the hard metal Formation of the CoWB phase responds. In order to avoid the formation of CoWB, the authors therefore propose that a titanium carbide intermediate be deposited before the deposition of a titanium diboride hard material layer on a hard metal body deposit layer. In contrast, when the coated hard metal body according to the invention was created, it was recognized that the CoWB phase greatly improved the adhesive strength of hard material layers composed of hard oxides or of a mixture of hard oxides and hard nitrides or of a mixed crystal of hard oxides and hard nitrides , so that there is no need to apply separate intermediate layers which promote the adhesive strength. The hard metal body coated according to the invention has very good wear properties.

According to the invention it is further provided that the hard material layer has a thickness of 0.2 to 20 _/ um and consists of aluminum oxide, zirconium oxide or aluminum oxynitride, the nitrogen content of the aluminum oxynitride being 0.1 to 10 atom%. It has surprisingly been found that of the oxide-containing hard material layers, in particular the hard material layers consisting of aluminum oxide, zirconium oxide or aluminum oxynitride have an extraordinarily good adhesive strength on the hard metal base body which has the zone containing CoWB.

According to the invention it is also provided that at least one further binder-metal-free hard material layer made of hard carbides, nitrides, borides and / or oxides of the elements aluminum, silicon, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum is provided on the binder-metal-free hard material layer. tungsten and / or yttrium is applied, wherein the thickness of all the hard coatings _/ um is 0.5 to 30th It has been shown that the properties of the hard metal body according to the invention can be improved further if the hard metal layer is free of binding metal at least one further binder-free hard material layer is applied. Sandwich coatings made up of several differently composed hard material layers have proven particularly useful.

The object on which the invention is based is further achieved by a method for producing the coated hard metal body, in which the hard metal base body forms the CoWB-containing zone for 3 to 60 minutes at a temperature of 800 to 1200 ° C., preferably 950 to 1050 ° C. and a pressure of 5000 to 100000 Pascals is treated with a gas mixture of boron trichloride and hydrogen, the partial pressure of the boron trichloride being 1 to 10% of the pressure, then the binder-metal-free hard material layer and then, if appropriate, the further binder-metal-free hard material layers from the gas phase in a known manner be deposited using the CVD process. By boronizing the surface of the hard metal base body before the actual hard material coating, it is advantageously achieved that CoWB phase is formed in one zone by reaction of the boron with the cobalt and tungsten carbide contained in the hard metal, which phase is present in the surface zone along with the other constituents of the hard metal . A residual binder metal content could still be detected in the CoWB-containing zone, while no boron carbide was identified there. In the zone containing CoWB, up to 66% of the cobalt content of the hard metal base body has passed into the CoWB phase as a result of the reaction with boron, a decrease in the concentration of the CoWB phase naturally occurring within the zone from the outside. The CoWB-containing zone has a boron content of 0.3 to 3% by weight, preferably 0.5 to 2% by weight. Since the boration of the hard metal base body only takes a few minutes, while applying a plurality of _/ um thick requires Hartstöff interlayer few hours, resulting sichdurch process of the invention considerable advantages by saving energy and the furnace chamber.

The basic metal body, which is provided with a zone containing CoWB, consists of a binder metal phase and a hard material phase. The binder metal phase must contain cobalt and the hard material phase must contain tungsten carbide. In addition to cobalt, the binder metal phase can also contain the binder metals iron and / or nickel, and the hard material phase can also contain the ureas titanium carbide, tantalum carbide and / or niobium carbide in addition to the tungsten carbide. The dimensions of the hard metal base body do not change its dimensions; no boride-containing intermediate layer grows during the boronization. Because of the good wear properties of the coated hard metal body, according to the invention, it should be used as a cutting insert for machining metallic materials, in particular cast steel, since it is particularly suitable for this purpose. has been proven by appropriate investigations.

The subject matter of the invention is explained in more detail below on the basis of exemplary embodiments.

example 1

Into a CVD reactor, inserts made of a hard metal from the ISO machining application group K10 were introduced, which consisted of 5.5% by weight of cobalt and 94.5% by weight of tungsten carbide. After heating the indexable inserts to a tempera At 1010 ° C, a gas mixture consisting of 1.3% boron trichloride and 98.7% hydrogen was passed through the reactor at a pressure of 40,000 Pascals for 10 minutes. Was then carried out at the same temperature, the deposition of a 2 to 3 _/ um thick layer of aluminum oxide by passing a gas mixture of 2.7% aluminum, 4.3% carbon dioxide, 2.6% hydrogen chloride and 90.4% hydrogen, where the total pressure 6000 Pascal was. The percentages of the individual substances in the two gas mixtures relate to vol.% And at the same time indicate the proportion of the partial pressure of the individual substance to the total pressure.

After cooling in flowing hydrogen, the indexable inserts were removed and subjected to various tests. After the preparation of a metallographic bevel cut, the borated zone and the applied aluminum oxide layer were examined microscopically. There was no chipping of the hard material layer. The hard metal consisting of tungsten carbide grains and the binding metal cobalt showed no changes in the microstructure up to the adjacent aluminum oxide layer. The observation of the structure with the aid of a scanning electron microscope led to the same result. A fine area analysis using an electron beam microsensor found that the surface zone of the hard metal contained about 0.8% by weight of boron in addition to the elements cobalt, tungsten and carbon, the concentration of boron decreasing from the outside in. The CoWB-containing zone had a thickness of approximately 3 to 5 μm. Some of the coated plates were examined using the X-ray diffraction method. In doing so observed eugungslinien numerous other _B in addition to the diffraction lines of contained in the substrate and the hard coating materials cobalt, tungsten carbide and alumina, all of the known phase CoWB could be assigned (see Acta Crystallographica, Volume B 24, 1968, pages 930-934). Finally, an examination with a transmission microscope at a magnification of 50,000 times showed that the tungsten carbide grains lying near the surface had partially converted into the CoW _B phase. In summary, it can be said as a result of these investigations that a composite body was obtained by the process according to the invention, which consisted of a hard metal base body made of tungsten carbide and cobalt with particles of the phase CoWB embedded on its surface and an aluminum oxide layer adhering firmly to it.

The indexable inserts of the form SNUN 120408 (according to ISO standard) coated in accordance with the invention were subjected to a cutting durability test, the particularly abrasive cast steels GGG 260 HB and hard cast GH 500 being machined on a lathe. For comparison, commercially available indexable inserts of the same geometry were also tested, which were coated in a known manner with a double layer of titanium carbide and aluminum oxide. The test conditions and results are shown in the table below:

The size of the wear was determined in a known manner by measuring the crater depth and the wear mark width. It was found that the composite bodies according to the invention showed only very little wear despite the lower overall thickness of the hard material coating.

Example 2

• Hartmetall mit borierter Zone -Aluminiumoxinitrid-Titannitrid-Aluminiumoxinitrid-Titannitrid-Aluminiumoxinitrid-Titannitrid-Aluminiumoxinitrid-Titannitrid. Die Gesamtdicke der Hartstoffbeschichtung betrug ca. 4 bis 5_/um, und die CoWB-haltige Zone war 3 bis 5_/um tief.

Inserts from the ISO machining application group M15 were used for the coating, which, in addition to the cobalt binding material and the tungsten carbide hard material, also contained a cubic mixed carbide of the composition (W, Ti, Ta, Nb) C with the lattice constant a = 0.436 nm. Following the like performed in the first example, treatment in a boron trichloride-hydrogen gas mixture was about _/ deposited by thick layer of hard material in known manner, a 1, containing in addition to the main constituents aluminum and oxygen even about 1 wt .-% nitrogen. On the Aluminiumoxinitridschicht was then about _/ deposited in a known manner, a 0.25 micron thick titanium nitride layer. Were prepared following immediately afterwards in the exchange still further three approximately 1 _/ um thick and about Aluminiumoxinitridschichten _/ titanium nitride layers deposited by thick 0.25, so that a composite body resulted with the following layer structure:

• Tungsten carbide with borated zone -aluminium oxynitride-titanium nitride-aluminum oxinitride-titanium nitride-aluminum oxynitride-titanium nitride-aluminum oxynitride-titanium nitride. The total thickness of the hard material coating was approx. 4 to 5 _/ µm and the CoWB-containing zone was 3 to 5 _/ µm deep.

The indexable inserts were examined using the same methods as described in the first example. The CoWB phase was again found in the edge zone of the hard metal. The X-ray diffraction diagram showed diffraction lines of the phases cobalt, tungsten carbide, mixed carbide, CoWB, aluminum oxynitride and titanium nitride. Electron diffraction also revealed very small amounts of the W ₂ Co2 ₁ B ₆ phase, which presumably arises as an intermediate stage in the formation of the CoWB phase. Other phases, such as B. Boron carbide, titanium diboride and titanium carbide could not be found. The analyzes thus showed that the composite body consisted of a mixed carbide-containing hard metal with CoWB fractions embedded near the surface and of four successive aluminum oxynitride layers separated by a thin titanium nitride layer or sealed off from the outside. The layer adjacent to the borated hard metal was an aluminum oxynitride layer.

Turning tests were then carried out with the indexable inserts of the form SNUN 120408, which yielded the following results:

Although the commercially available indexable insert corresponding to the prior art had a much greater total layer thickness than the inventive insert, the latter showed considerably less crater wear.

Claims (5)

1. Coated hard metal body from a cobalt and tungsten carbide-containing hard metal base body and a binder-free hard material layer, the hard material layer being composed of hard oxides or of a mixture of hard oxides and hard nitrides or of a mixed crystal of hard oxides and hard nitrides, characterized in that the hard metal base body its surface has a 0.2 to 20 _/ um thick zone, which contains the phase CoWB in addition to the hard metal components. 2. Coated hard metal body according to claim 1, characterized in that the hard material layer has a thickness of 0.2 to 20 _/ um and consists of aluminum oxide, zirconium oxide or aluminum oxynitride, the nitrogen content of the aluminum oxynitride being 0.1 to 10 atom%. 3. Coated hard metal body according to claims 1 and 2, characterized in that on the binder-metal-free hard material layer at least one further binder-metal-free hard material layer made of hard carbides, nitrides, borides and / or oxides of the elements aluminum, silicon, titanium, zirconium, hafnium, vanadium, niobium , tantalum, chromium, molybdenum, tungsten and / or yttrium is applied, wherein the thickness of all the hard coatings _/ um is 0.5 to 30th 4. A process for producing the coated hard metal body according to claims 1 to 3, characterized in that the hard metal base body for forming the CoWB-containing zone for 3 to 60 minutes at a temperature of 800 to 1200 ° C, preferably 950 to 1050 ° C, and a pressure of 5000 to 100000 pascals is treated with a gas mixture of boron trichloride and hydrogen, the partial pressure of the boron trichloride being 1 to 10% of the pressure, then the binder-metal-free hard material layer and then optionally the further binder-metal-free hard material layers in a known manner from the gas phase be deposited using the CVD process. 5. Use of the coated hard metal body according to claims 1 to 3 as a cutting insert for machining metallic materials.