AT505908B1 - METHOD FOR PRODUCING A TI (C, N, O) COATING LAYER - Google Patents

Description

2 AT 505 908 B1

The invention relates to a method for producing a coating, wherein a coating layer contains titanium, carbon, nitrogen and oxygen or consists of these elements. Furthermore, the invention relates to a tool or a tool insert, in particular a cutting tool insert such as an indexable insert, with a substrate of a hard metal, which is provided with a coating of one or more coating layers, wherein a coating layer of the elements titanium, carbon, nitrogen and Oxygen and optionally further metallic elements is formed. 10

Machining tools or tool inserts, such as indexable inserts, on the one hand be wear-resistant and highly stressable and on the other hand be designed so that a friction occurring in the application, which is gege-15 ben in a relative movement of the workpieces to be machined and the employed tools or tool inserts, for example, in a turning of a steel, is minimized.

For these purposes, cutting tools or tool inserts are usually provided with multi-layer coatings, starting from the substrate first a plurality of wear resistance of a tool or tool insert increasing Beschich-20 processing layers and then or workpiece side lubricating having outermost coating layer are provided.

In connection with this, it is known to use coatings with outermost coating layers or sliding layers of titanium oxide. However, in particular in the case of titanium oxide layers which are deposited by means of chemical vapor deposition (CVD), an unsatisfactory adhesion of these coating layers to the substrate or to an underlying coating layer can frequently be ascertained. In addition, such layers are often porous, which is also disadvantageous in terms of durability of these coating layers in use. 30

From EP 1 118 688 A1 it has become known coating layers of Ti (C, N, 0) by means of medium temperature chemical vapor deposition (MTCVD) by deposition from a reaction gas containing H2, N2, CH3CN, TiCl4 and CO2 and / or CO at a Temperature of 700 ° C to 900 ° C produce. By adding C02 and / or CO to the reaction gas, uniform coating of lubricating Ti (C, N, O) coating layers of small, approximately round grains is achieved, whereas without addition of CO 2 and / or CO to the reaction gas, coating layers with elongated crystallites are formed from titanium carbonitride. 40 The invention has for its object to provide a method of the type mentioned above, wherein the coating layer with titanium, carbon, nitrogen and oxygen adheres well to the substrate or an underlying coating layer, is substantially dense and can serve as a sliding layer and these Coating layer has a structure that this gives a high stability at the same time. 45

This object is achieved by a method of the aforementioned type, which comprises the following steps: a) providing a substrate; so b) optionally depositing one or more coating layers on the substrate; c) then commencing the deposition of a coating layer of titanium carbonitride which has substantially homogeneously distributed regions of higher carbon content and lower nitrogen content or vice versa; d) simultaneous oxidation of the coating layer 55 developing further in step c) or subsequent oxidation of the coating obtained after the completion of step c); e) then optionally depositing a coating layer of a titanium oxide.

The advantages achieved by the invention can be seen in particular in that a favorable microstructure formation for the subsequent oxidation is created by the titanium carbonitride coating layer, which in some cases contains more carbon than nitrogen and some nitrogen than carbon in some cases in step c) in the oxidation, primarily the higher carbon content regions are oxidized while the higher nitrogen content regions show less tendency to oxidize. Thus, in oxidizing, a favorable structure can be provided in which the more oxidized regions of higher carbon content prior to oxidation are important to the lubricating effect, whereas the less oxidized regions of higher pre-oxidation nitrogen content impart stability to the coating layer. Since the oxidation is only started and carried out when at least part of the coating layer has been deposited, good bonding to the substrate or an underlying coating layer is achieved. In addition, the coating layer is also dense. Moreover, the coating layer produced in this way is also excellently suited for depositing titanium oxide coating layers which can be readily adhered and densely sealed by means of a CVD process, so that the sliding properties can additionally be optimized.

Although the coating layer prepared in step c) can be subsequently oxidized, it is more favorable for a homogeneous microstructure in the coating layer if the oxidation is started even after formation of a thin bonding region and continued during a further growth of the coating layer growing in step c). It has proven to be particularly favorable when in step c) with respect to nitrogen and carbon, a gradient layer is formed, in such a way that towards the end of the construction of the coating layer, a nitrogen concentration is zero. As a result, a particularly dense outer surface of the coating layer can be achieved, which consists predominantly of a titanium oxide and can serve both as a working layer and as a bonding layer for further coating layers.

The individual coating layers, in particular the coating layer produced in step c) or step d), are preferably deposited by a CVD method. It is advisable for the longest possible service life of the coating layer in use that the in step c) or step d) building or in step c) obtained coating layer with a thickness of more than 10 pm, in particular more than 15 pm created becomes. This is particularly recommended if this coating layer is used as a working coating layer in the tool.

In a variant of the method according to the invention, the coating layer which is built up in step c) or step d) or obtained in step c) is oxidized only in the region of a surface zone facing away from the substrate. The coating layer then comprises on the substrate side a hard and wear-resistant zone of titanium carbonitride and a workpiece-side zone made of Ti (C, N, O), which in use brings about the desired sliding properties. It has proven to be expedient if the surface zone in a range of less than 5 pm, measured from the freely accessible surface, is oxidized.

The oxidation may in itself be carried out with any gases which allow the desired oxidation of at least the higher carbon content regions. For example, the coating layer that builds up in step c) or step d) or obtained in step c) can be oxidized with oxygen.

It is particularly preferred that the coating layer which is formed in step c) or step d) or obtained in step c) is oxidized by the introduction of CO 2, since with CO 2 a milder oxidation than with oxygen can be achieved. Moreover, in addition to C02, 4 AT 505 908 B1 CO can also be used: At average reaction temperatures of about 1000 ° C, CO2 is in equilibrium with CO and C (Boudouard equilibrium). The amounts of CO 2 and CO introduced can be used to precisely control the equilibrium and therefore the oxidation.

It is likewise particularly preferred if the coating layer in step c) is prepared first without supply of oxidizing gases directly on the substrate or a coating layer deposited in step b) and then, with further construction of the coating layer, an oxidizing gas with the already partially deposited coating layer Contact is brought. In this case, the partial construction of a titanium carbonitride coating layer first results in a good bond to the substrate or an already deposited coating layer. The portion of the coating layer beyond this connection region is then oxidized in order to ensure the desired lubricating effect. In this case, it is possible, for example, to proceed by first starting the construction of a coating layer of titanium carbonitride in the CVD method and to produce a coating layer of up to 10 μm thick. Subsequently, CO 2 is added to the reaction gas, wherein the CO 2 content continuously increased or the proportions of the remaining reaction gas are reduced until finally pure CO 2 is used together with a titanium-releasing component such as TiCl 4. This results in an oxidized region having an average composition of Ti (C, N, O) and then, deposited thereon, substantially pure titanium oxide.

With regard to a setting homogeneously distributed areas with different carbon or. Nitrogen contents, it is advantageous if the layer in step c) or step d) or in step c) layer obtained by depositing a reaction gas containing TiCl 4, CH 4, N 2i radical H2 at a reaction temperature of 900 ° C to 1100 ° C, preferably 930 ° C to 1070 ° C, is created. The reaction temperature is initially maintained at about 950 ° C for example for about 30 minutes, after which the reaction temperature is raised to about 1020 ° C. In such a reaction regime, the coating layer is formed with titanium carbonitride crystal lites having a core-shell structure wherein the core contains more nitrogen than carbon and the shell contains more carbon than nitrogen. If the oxidation is carried out, the cladding is primarily oxidized, which on the one hand is more easily accessible and on the other hand has more carbon and therefore oxidizes more easily.

Although the method according to the invention is fundamentally applicable to all types of substrates, it is preferably used in situations in which the substrate is a hard metal. In particular, the method according to the invention is suitable for coating cutting tool inserts, in particular indexable inserts for machining steel.

According to the teaching presented above, a further object of the invention is to provide a tool or a tool insert, which is provided with a favorable for a machining of steel coating.

This object is achieved by a tool or a tool insert, in particular a cutting tool insert such as an indexable insert, with a substrate of a hard metal, which is provided with a coating of one or more coating layers, wherein a coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements homogeneously distributed regions having higher carbon content and lower nitrogen content or vice versa, wherein at least the regions of higher carbon content are at least partially oxidized and wherein said coating layer as viewed from the substrate is an outermost coating layer or a coating layer of titanium oxide, which supports the outermost coating layer is reached.

Advantages of a tool or tool insert according to the invention can be seen, in particular, in that the tool or the tool insert comprises a highly adherent, stable and outermost coating layer which has good sliding properties simultaneously with the machining of a steel. Depending on the requirement or requirement profile, further coating layers may be provided between the substrate and the outermost coating layer (s), which increase the wear resistance of the coating. It is advantageous if the coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements has areas with a core-shell structure, wherein, based on a composition in atomic percent, the core more nitrogen than in total carbon and Oxygen and the mantle in total more carbon and oxygen than nitrogen.

An average crystallite size in the coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements is preferably less than 0.3 μm, preferably less than 0.2 μm, in particular less than 0.1 μm.

The next optional titanium metallic elements, such as chromium, should have a maximum of 30 atomic percent, based on the content of all metallic elements in the coating layer, in order to achieve in the production of the advantageous structural formation.

The outermost coating layer may be formed as a gradient layer in which a substrate-side zone of the elements titanium, carbon, nitrogen and oxygen merges into a zone consisting essentially of a titanium oxide. The zone consisting essentially of titanium oxide preferably has a thickness of less than 5 μm, in particular less than 3 μm.

Further features, advantages and effects of the invention will become apparent from the following description of exemplary embodiments and the drawings, to which reference is made. Show it:

Fig. 1 is a micrograph of a portion of a coating;

FIG. 2 shows an enlarged detail of a microsection of a coating; FIG.

3 shows a schematic representation of a part of the microstructure of a coating layer according to the invention;

Fig. 4 is a diagram concerning results of wear tests.

On an indexable insert for machining steel workpieces, a multi-layer coating was deposited by CVD. Here, starting from the substrate, first a titanium nitride coating layer with a layer thickness of about 0.5 pm, then at a temperature of about 800 ° C, a coating layer of titanium carbonitride (MTCVD-TiCN) with a layer thickness of about 3 pm , Then another coating layer of titanium carbonitride, prepared according to WO 2007/056785 A1, deposited with a layer thickness of about 5 pm and finally a coating layer of Al 2 O 3 with a layer thickness of about 3 pm. The deposition of the coating layers produced in this way is state of the art.

Subsequently, in the CVD method, in turn, according to WO 2007/056785 A1, a reaction gas containing about 5% by volume of TiCl 4 and CH 4, N 2 and H 2 in a molar ratio of 1:10:25 first at a substrate temperature of about 950 ° C. for about 30 minutes fed and started the deposition of a coating layer. Subsequently, the substrate or reaction temperature was increased to about 1020 ° C and the reaction continued for about 90 minutes, forming a Ti (C, N) coating layer with crystallites having an average crystallite size of less than 50 nanometers , The crystallites in turn formed areas with nitrogen-rich cores and carbon-rich coats, so uneven distribution of elements. Thereafter, the reaction gas was further added to the reaction 6 AT 505 908 B1 or the deposition of a coating layer CO 2, wherein the concentrations of CO 2 and CH 4 in the course of a reaction time of 90 minutes continuously increased and the concentration of N 2 was lowered until finally in the reaction gas, in addition to H2 as the carrier gas, only TiCl4, CH4 and CO2 templates.

1 shows a micrograph of an outer part of a coating layer produced in this way. The coating layer has dark areas corresponding to areas having higher carbon content than nitrogen content prior to oxidation. The bright areas correspond to areas with higher nitrogen contents. It can also be seen from FIG. 1 that the coating layer has an essentially continuous and dense zone in an outermost, ie workpiece-side zone, which is formed at least predominantly of titanium oxide and is formed as a result of the C02 concentration rising towards the end of the reaction.

As can be seen from FIG. 2 and the schematic representation in FIG. 3, a coating layer produced as described above has a structure with regions of a core-shell structure below the region consisting of pure titanium oxide, wherein the jacket regions are at least partially oxidized and appear dark. It is believed that this structure is responsible for the excellent bonding and dense formation of the titanium oxide zone.

Examination of the thus prepared coating layer with X-ray diffraction revealed that about 28% by weight of Ti 509, about 17% by weight of Ti (C, N) and about 1.5% by weight of tungsten carbide originating from the substrate were used in this about 53% by weight of Ti 6 On , In addition, there were further, unspecified phases. Further experiments yielded similar results, with a total titanium oxide content always ranging from about 70 weight percent to 90 weight percent and a Ti (C, N) content from about 8 weight percent to about 25 weight percent. The average crystallite sizes of the titanium oxides were each below 40 nanometers. Due to the proven titanium oxide phases, namely Ti6On and Ti509, it is assumed that in a process according to the invention Magneli phases form at least predominantly, ie phases with a composition TiOx with 1.75 < x i 1.89 and generally Tin02n-i with 4 < n < 9. In line with the proposed reaction mechanism, it was found that the observed Ti (C, N) phases were formed with only a small amount of carbon and that a ratio of carbon to nitrogen was always less than 1: 6.

An indexable insert coated as described above was evaluated for its life in turning a tempered steel shaft. As a reference, an indexable insert was used, in which the coating provided there was basically the same structure, but instead of the final coating layer of Ti (C, N.O) or titanium oxide was formed with an Al203 coating layer.

The cutting parameters were as follows:

Cutting speed vc: 280 m / min;

Cutting depth ap: 2.00 mm;

Feed f: 0.30 rpm;

Setting angle k: 95 °; Cooling: wet.

The wear was measured as a function of the machining time. The wear measurement was carried out according to ÖNORM A 2750, series 10.

The test results are shown in FIG. 4. It can be seen that an indexable insert coated according to the invention gave a longer service life (line B) than a conventional indexable insert (line A). The extended service life can, as the indexable insert

Claims (19)

Except with the exception of the outermost coating layers, they were of identical design, are attributed to the advantageously acting cover layer of the inventively coated indexable insert. In addition, outermost coating layers produced according to the invention also adhered particularly well to underlying coating layers and could not be removed by irradiation with a mixture of water and corundum even at a pressure of 3 bar. It is also possible for the time being to completely form the coating layer of titanium carbonitride and then to oxidize it, for example, with pure CO 2. In this case, the coating layer is formed identically over its entire thickness or thickness, ie without transition into a surface zone of titanium oxide, which may be favorable for special applications. If required, however, a coating layer of titanium oxide may additionally be deposited separately on this coating layer, in particular by means of a CVD method. Claims 1. A method for producing a coating, wherein a coating layer contains or consists of titanium, carbon, nitrogen and oxygen, comprising the steps of: a) providing a substrate; b) optionally depositing one or more coating layers on the substrate; c) then commencing the deposition of a coating layer of titanium carbonitride which has substantially homogeneously distributed regions of higher carbon content and lower nitrogen content or vice versa; d) simultaneous oxidation of the coating layer further developing in step c) or subsequent oxidation of the coating layer obtained after completion of step c); e) then optionally depositing a coating layer of a titanium oxide. 2. The method of claim 1, wherein the coating layers are deposited by a CVD method. 3. The method of claim 1 or 2, wherein the in step c) or step d) building or in step c) obtained coating layer with a thickness of more than 10 pm, in particular more than 15 pm, created. 4. The method according to any one of claims 1 to 3, wherein the in step c) or step d) building or in step c) obtained coating layer is oxidized only in the region of a surface facing away from the substrate surface zone. 5. The method of claim 4, wherein the surface zone is oxidized in a range of less than 5 pm as measured from the exposed surface. 6. The method according to any one of claims 1 to 5, wherein the in step c) or step d) building or in step c) obtained coating layer is oxidized with oxygen. 7. The method according to any one of claims 1 to 6, wherein the in step c) or step d) building or in step c) obtained coating layer is oxidized by supplying CO 2. 8. The method according to any one of claims 1 to 7, wherein the coating layer in step c) first without supply of oxidizing gases directly on the substrate or a deposited in the 8 b coat 505 908 B1 coating layer is created and then with a further structure of the coating layer oxidizing gas is brought into contact with the already partially deposited coating layer. 9. The method according to any one of claims 1 to 8, wherein the in step c) or step d) building or in step c) layer obtained by depositing a reaction gas containing TiCl4, CH4 and N2 at a reaction temperature of 900 ° C to 1100 ° C, preferably 930 ° C to 1070 ° C, is created. 10. The method according to any one of claims 1 to 9, wherein the substrate is a hard metal. 11. The method according to any one of claims 1 to 10, wherein the substrate is a cutting tool insert such as an indexable insert. 12. tool or tool insert, in particular cutting tool insert such as an indexable insert, with a substrate of a hard metal, which is provided with a coating of one or more coating layers, wherein a coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally other metallic elements homogeneous distributed regions having higher carbon content and lower nitrogen content, or vice versa, wherein at least the higher carbon content areas are at least partially oxidized and wherein said coating layer is an outermost coating layer or a coating layer of titanium oxide, which is the outermost coating layer viewed from the substrate. 13. Tool or tool insert according to claim 12, wherein the coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements having areas with a core-shell structure, wherein, based on a composition in atomic percent, the core more nitrogen as carbon and oxygen in total and the mantle in total more carbon and oxygen than nitrogen. 14. Tool or tool insert according to claim 12 or 13, wherein an average crystallite size in the coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements less than 0.3 pm, preferably less than 0.2 pm, in particular smaller than 0.1 pm. 15. Tool or tool insert according to one of claims 12 to 14, wherein the coating layer of the elements titanium, carbon, nitrogen and oxygen and optionally further metallic elements contains 70 weight percent to 90 weight percent titanium oxides and 8 weight percent to 25 weight percent titanium carbonitrides. 16. Tool or tool insert according to claim 15, wherein the titanium oxides are formed at least predominantly as Magneli phases. 17. Tool or tool insert according to claim 15 or 16, wherein in the titanium carbonitrides, a ratio of carbon to nitrogen is less than 1: 6. 18. A tool or tool insert according to any one of claims 12 to 17, wherein the outermost coating layer is formed as a gradient layer in which a substrate-side zone of the elements titanium, carbon, nitrogen and oxygen merges into a substantially consisting of a titanium oxide zone. 19. The tool or tool insert according to claim 18, wherein the zone consisting essentially of titanium oxide has a thickness of less than 5 μm, in particular less than 3 μm. 9 AT 505 908 B1 For 2 sheets of drawings