Hard metal object

Abstract

The invention relates to an object, in particular a cutting tool such as a cutting insert, comprising a main body and a coating applied to same, wherein the main body is formed from a hard metal, wherein the main body is formed with a metal carbide and a binding metal, comprising rhenium and / or ruthenium, and the coating is formed with at least one layer of aluminium titanium nitride and / or aluminium chromium nitride. The invention also relates to a use of an object of this type.

Description

[0001] Hard metal object

[0002] The invention relates to an object, in particular a cutting tool such as a cutting plate, comprising a base body and a coating applied thereto, wherein the base body is formed from a hard metal.

[0003] Furthermore, the invention relates to a use of such an object.

[0004] For the machining of metallic objects, especially metals and alloys, cutting tools and inserts with a hard metal base body are used. Coatings are typically applied to these base bodies to extend the service life of the cutting tool or insert.

[0005] The cemented carbide base body for a cutting tool or insert typically consists of a hard material and a binder metal. Tungsten carbide (WC) and titanium carbide (TiC) are particularly suitable as hard materials. Commonly used binder metals are cobalt, nickel, and iron. The hard materials, which make up the majority of the base body and are generally present in a proportion of more than 80 percent by weight (wt.), impart a high degree of hardness to the base body. The binder metal serves, on the one hand, to bind the particulate hard material. On the other hand, the binder metal imparts a certain toughness to the base body. Through appropriate adjustments, the properties of the base body can be adjusted within certain limits.

[0006] The use of binder metals is not necessarily limited to the aforementioned elements cobalt, nickel, and iron. These binder metals are frequently used, especially cobalt, because they have proven themselves over decades and are also relatively inexpensive compared to other metals. However, efforts have also been made to use other metals as alternatives or in addition to achieve the aforementioned properties. According to the state of the art, this includes, for example, the use of rhenium as an additional binder metal alongside cobalt, as disclosed, for example, in WO 2004 / 065645 A1. Cutting tools, and in particular cutting inserts made of hard metal, are usually provided with a coating intended to increase their service life. Such coatings are usually deposited using chemical vapor deposition (CVD) or physical vapor deposition (PVD).The coatings or coating systems should be designed to increase service life for the respective application. This is subject to continuous development.

[0007] Cutting inserts have also been developed for heavy-duty machining by milling. These inserts are designed according to the type and have a coating. In heavy-duty machining operations, such as the milling of crankshafts, there is a desire to further increase the service life of cutting tools such as cutting inserts, so that fewer cutting inserts are required overall, leading to greater material efficiency. This is a challenging goal, since milling operations involve intermittent cutting. This means that the cutting insert is not continuously in use, but is repeatedly applied to the body to be machined and milled away or removed under corresponding compressive loads, particularly on the cutting edges and adjacent areas such as a rake face.

[0008] Based on this, it is the object of the invention to provide a generic object which can provide an increased service life in use.

[0009] Furthermore, it is an object of the invention to illustrate a use of such an object.

[0010] The object of the invention is achieved if, in an object of the type mentioned at the beginning

[0011] - the base body is formed with a metal carbide and a binder metal comprising rhenium and / or ruthenium, and

[0012] - the coating is formed with at least one layer of aluminium titanium nitride and / or aluminium chromium nitride.

[0013] A particular advantage achieved by the invention is that the combined coordination of the material-chemical composition of the base body and the coating creates an optimized system with which objects can be optimally designed for permanent, but especially also changing, load scenarios when in contact with metallic materials. This particularly applies to cutting tools such as cutting inserts used in machining operations, especially milling. If the cutting inserts are designed accordingly, an increased service life is achieved even with intermittent cutting, for example when machining crankshafts. This can be attributed, without being scientifically bound to it, to the fact that the presence of rhenium and / or ruthenium leads to a somewhat tougher base body that can better absorb shocks.In this context, the proposed coating proves to be optimal in terms of direct bonding to a corresponding base body, eliminating the need for additional bonding layers. The proposed coating is extremely wear-resistant, but also adheres excellently to the base body, especially when the bottom layer is made of aluminum titanium nitride (AITiN). Thus, the special design of the base body and the coating system, on the one hand, as well as the interplay between the base body and the coating system, on the other, result in an optimized object.

[0014] The object is preferably designed such that the binder metal comprises a first binder metal portion selected from cobalt, nickel and / or iron, and a second binder metal portion selected from rhenium and / or ruthenium. Thus, conventional and inexpensive metals such as cobalt, nickel and / or iron can be used as binder metals, with rhenium and / or ruthenium additionally being present to adjust the properties of the base body. For this purpose, it is generally sufficient for the second binder metal portion to be lower than the first binder metal portion or, conversely, for the first binder metal portion to outweigh the second binder metal portion. A ratio of the first binder metal portion to the second binder metal portion can, for example, be in the range of 20:1 to 10:1, in particular 17:1 to 7:1, preferably 10:1 to 3:1.Within these ratio ranges, the desired property balance can be achieved with relatively low use of the expensive elements rhenium and / or ruthenium. Although the first binder metal component can be formed from the aforementioned elements cobalt, nickel, and / or iron, it is preferred that the first binder metal component be formed essentially from cobalt or consist of cobalt. This simplifies the binder mixture, especially since rhenium and / or ruthenium are already present.

[0015] Preferably, particularly when cobalt is used, the first binder metal portion contains 6 wt.% to 15 wt.%, preferably 7.5 wt.% to 14.5 wt.%, in particular 9 wt.% to 13.5 wt.%, of cobalt. In these ranges, the hard material particles can be effectively bound and, moreover, with increasing cobalt content, increased toughness is also achieved. This can be further optimized if the second binder metal portion comprises or consists of 0.3 wt.% to 2.5 wt.%, preferably 0.5 wt.% to 2.0 wt.%, in particular 1.25 wt.% to 1.75 wt.%, of rhenium and / or ruthenium.

[0016] In addition, chromium may be present in the binder metal, resulting in a chromium content of more than 0.0 wt.%. In a fine hard material grain (e.g., tungsten carbide with an average grain size of 2.5 pm or less), chromium acts as a grain growth inhibitor and also strengthens the binder metal. However, maximum chromium contents should not exceed 1.5 wt.%, preferably not more than 1.0 wt.%.

[0017] A metal carbide is preferably used as the hard material. The metal carbide can comprise one or more metals selected from the group consisting of tungsten, titanium, vanadium, tantalum, niobium, chromium and molybdenum. As a rule, the hard metal will consist only of particles with tungsten carbide, but mixtures of hard materials are also possible, in particular mixtures of tungsten carbide with titanium carbide, wherein the tungsten carbide preferably predominates by weight in relation to the titanium carbide. To coordinate special property profiles, other metal carbides such as tungsten carbide and / or molybdenum carbide can also be provided, preferably also in smaller weight proportions than tungsten carbide. In particular, chromium carbide in small proportions of up to about 1.5 wt.%, preferably about 1.0 wt.%, has proven particularly advantageous in synergistically matching the properties. It is preferred that the base body contains 80 wt.% to 95 wt.%, preferably 82 wt.-% to 90 wt.% tungsten carbide. A particularly favorable range is in the content range of 85 wt.% to 90 wt.%.

[0018] The coating can be a single layer, especially if it is a single layer of aluminum titanium nitride. However, a multi-layer coating is particularly preferred. A multi-layer coating with layers of aluminum titanium nitride and aluminum chromium nitride has proven particularly preferred. Especially in milling operations, such a coating, in conjunction with the specially designed base body, delivers excellent results in terms of extending the service life of a cutting insert.

[0019] The coating is preferably deposited using a PVD process. This applies both to a single-layer coating, for example, made of aluminum titanium nitride, and to a coating system consisting of multiple layers, such as alternating layers of aluminum titanium nitride and aluminum chromium nitride. In both cases, no bonding layer to the base body is required; instead, the single layer or the first layer of several layers can be deposited directly onto the base body.

[0020] The coating preferably has a total layer thickness of 2 μm to 15 μm, preferably 3 μm to 10 μm, in particular 3.5 μm to 8.5 μm. A minimum layer thickness appears appropriate with regard to milling operations or other machining processes in order to achieve a certain service life. On the other hand, coating systems that are too thick provide no added value in use but require higher production costs. The aforementioned preferred total layer thicknesses result from the corresponding considerations.

[0021] The object according to the invention can be used in a variety of ways, particularly in various machining processes, but also in the field of metal forming. However, it is particularly preferred if the object is a cutting insert, in particular an indexable insert. In accordance with the advantages of an object described above, the further objective of the invention is achieved by using an object according to the invention for milling metallic materials, in particular for heavy-duty machining.

[0022] Further features, advantages, and effects of the invention will become apparent from the following exemplary embodiments. Reference is made to the drawings, which show:

[0023] Fig. 1 a secondary electron micrograph of a base body with a coating system applied thereon;

[0024] Fig. 2 is a picture showing different areas of the analysis of a chemical composition;

[0025] Fig. 3a to Fig. 3c Measurement results of the spectroscopic determination of individual elements in positions according to Fig. 2 in the marked areas;

[0026] Fig. 4a and Fig. 4b Measurement results for wear resistance due to impact stress.

[0027] Cutting inserts were created with geometries that are used in accordance with the state of the art for milling operations, in particular for machining crankshafts, strip edges of steel strips or similar heavy-duty machining tasks.

[0028] In a first variant, a base body was formed with 88.5 wt.% tungsten carbide (average grain size of the tungsten carbide particles of 2.5 pm), 10 wt.% cobalt, and 1.5 wt.% rhenium. Production was carried out by pressing and sintering corresponding blanks, as is familiar to those skilled in the art.

[0029] In a second variant, the base body was formed with 85 wt% tungsten, 13 wt% cobalt, 1.5 wt% rhenium and 0.5 wt% chromium carbide (C^Cs).

[0030] Furthermore, analogous substitutes were created for the first two variants, with the chromium being replaced with ruthenium in analogous proportions. The resulting cutting inserts, with their cemented carbide base bodies, were then coated. The coating was carried out exclusively using PVD processes. For coating layers made of aluminum titanium nitride, an AITi target with an approximate composition of 60 wt% aluminum and 40 wt% titanium was used. For coating layers made of aluminum chromium nitride, an AICr target consisting of 70 wt% aluminum and 30 wt% chromium was used.

[0031] The coating systems investigated on the individual substrates were single-layer coatings of aluminum titanium nitride and multi-layer coatings of alternating layers of aluminum titanium nitride and aluminum chromium nitride. A cross-sectional secondary electron micrograph of the latter coating system, formed with alternating coating layers, is shown in Fig. 1. The bottom of Fig. 1 shows the substrate, followed by the individual coating layers of aluminum titanium nitride and aluminum chromium nitride. Corresponding layer changes can be applied in any desired alternating sequence. It has been shown that approximately ten layer changes are appropriate. A higher number of layer changes, for example, 20 layer changes, does not lead to any improvement in the properties during use. Fig. 2 shows an image illustrating different measurement positions for a spectroscopic analysis of the chemical composition.The corresponding results are shown in Fig. 3a to Fig. 3c. The corresponding figures show that the coating system is composed of alternating layers of aluminum titanium nitride and aluminum chromium nitride, as intended. Cutting inserts of the first variant (88.5 wt.% tungsten carbide, 10 wt.% cobalt, and 1.5 wt.% rhenium), coated with ten layers of aluminum titanium nitride alternating with ten layers of aluminum chromium nitride, achieved a tool life of 2183 parts when machining crankshafts. In comparison, a conventional cutting insert with the same cutting insert geometry and composition (base body made of tungsten carbide and cobalt and coating made of aluminum titanium nitride) achieved a tool life of 750 to 800 parts.

[0032] Furthermore, variants with rhenium and ruthenium were subjected to a bolt impact test. For this test, a bolt made of tempered steel DIN 1.7225 was used with V2 = 250 m / min and a p= 3 mm repeatedly brought into contact with cutting inserts. This is intended to simulate an intermittent cut, as occurs particularly when machining crankshafts. Corresponding test results are shown in Fig. 4a and Fig. 4b. As can be seen from Fig. 4a, those cemented carbide grades containing rhenium or ruthenium produce significantly better results compared to an otherwise identically designed cutting insert. From Fig. 4b it can be seen that results for ruthenium are advantageous compared to the mere addition of chromium, but the addition of chromium also leads to a significant increase in performance through the formation of chromium carbide.

[0033] In further tests, a comparison was conducted between coating systems made of aluminum titanium nitride and a combined coating system with aluminum titanium nitride and aluminum chromium nitride, using the same insert geometry and base body composition. The former system showed a tool life extension of 111%, whereas the coating system with alternative layers achieved a tool life increase of 122%.

[0034] In summary, the special combination of the design of the base body in terms of material chemistry together with the coating system ensures a maximized service life.

[0035] The coating systems can, in principle, be applied in any thickness, but for heavy-duty machining processes, a layer thickness of approximately 7 pm to approximately 10 pm is appropriate. For standard milling operations with lower operating stresses, layer thicknesses of up to 5 pm, for example, 2.5 pm to 4.5 pm, may be sufficient.

Claims

Patent claims 1. Object, in particular a cutting tool such as a cutting plate, comprising a base body and a coating applied thereto, wherein the base body is formed from a hard metal, characterized in that - the base body is formed with a metal carbide and a binder metal comprising rhenium and / or ruthenium, and - the coating is formed with at least one layer of aluminium titanium nitride and / or aluminium chromium nitride.

2. Object according to claim 1, characterized in that the binder metal comprises a first binder metal portion selected from cobalt, nickel and / or iron, and a second binder metal portion selected from rhenium and / or ruthenium.

3. Object according to claim 2, characterized in that the first binder metal portion predominates over the second binder metal portion.

4. Object according to one of claims 1 to 3, characterized in that the first binder metal portion is formed essentially from cobalt or consists of cobalt.

5. Object according to one of claims 1 to 4, characterized in that the first binder metal portion comprises 6 wt.% to 15 wt.%, preferably 7.5 wt.% to 14.5 wt.%, in particular 9 wt.% to 13.5 wt.%, of cobalt.

6. Object according to one of claims 1 to 5, characterized in that the second binder metal content is 0.3 wt.% to 2.5 wt.%, preferably 0.5 wt.% to 2.0 wt.%, in particular 1.25 wt.% to 1.75 wt.%, of rhenium and / or ruthenium.

7. Object according to one of claims 1 to 6, characterized in that the metal carbide comprises one or more metals selected from the group consisting of tungsten, titanium, vanadium, tantalum, niobium, chromium and molybdenum.

8. Object according to one of claims 1 to 7, characterized in that the base body comprises 80 wt.% to 95 wt.%, preferably 82 wt.% to 90 wt.%, tungsten carbide.

9. Object according to one of claims 1 to 8, characterized in that the coating is formed in multiple layers with layers of aluminum titanium nitride and aluminum chromium nitride.

10. Object according to one of claims 1 to 8, characterized in that the coating is deposited using a PVD process.

11. Object according to one of claims 1 to 9, characterized in that the coating has a total layer thickness of 2 pm to 15 pm, preferably 3 pm to 10 pm, in particular 3.5 pm to 8.5 pm.

11. Object according to one of claims 1 to 10, characterized in that the object is a cutting insert, in particular an indexable insert.

12. Use of an object according to one of claims 1 to 11 for milling metallic materials, in particular for heavy machining.

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