DE102011108088B4 - Tool with a nitridic hard material layer and method for its production - Google Patents

Abstract

Tool consisting of a tool substrate, which is coated with a nitridic hard material layer, in which aluminum is included, characterized in that in an edge region, the proportion of aluminum in the hard material layer compared to the proportion of aluminum at a distance of more than 500 microns from the edge region formed formed hard material layer is increased.

Description

The invention relates to a tool with a nitridic hard material layer and a method for its production. The tools are essentially tools for the machining of workpieces which have at least one edge, preferably a cutting edge. They can be used for cutting or for machining.

Such hard coatings are commonly formed on workpiece substrates by various known vacuum deposition techniques. However, since for many applications sharp transitions to edges also occur with the hard material layer, or at least on the basis of an edge already present on a tool substrate, no enlargement of the edge radius is desired there are problems with small edge radii, as is the case with cutting edges.

Up to now, an enlargement of the edge radius generally takes place during the coating process, starting from the original edge radius at the respective edge of a tool substrate on which the hard material layer is formed. This can only be countered by the fact that extremely thin layers of hard material are deposited, but which achieve a significantly limited life and effect.

Another possibility is the formation of very small edge radii on tool substrates, which are then provided with the hard material layer. For this purpose, however, the mechanical processing preparatory to the coating is very complex and the achievable very small edge radii smaller than 15 microns, as they are especially desired for cutting edges of tools, can not be prepared with a sufficient layer thickness. The rounding effect can not be avoided in this way. Only the effect with the smaller edge exit radius of a tool substrate can be reduced.

It is therefore an object of the invention to propose tools that are coated with a hard material layer and in edge areas a certain modifiable, preferably small edge radius, even taking into account the already existing on an edge region of a tool substrate edge radius, to comply or train.

According to the invention this object is achieved with a tool having the features of claim 1. It can be produced by a method according to claim 5. Advantageous developments can be realized with designated in subordinate claims characteristics.

A tool according to the invention is coated with a nitridic hard material layer in which aluminum is contained. In this case, the proportion of aluminum in the hard material layer is higher in an edge region than in the proportion of aluminum which is contained at a distance of at least 500 μm from the edge region formed hard material layer.

The proportion of aluminum which is contained at a distance of more than 500 microns from the edge region formed hard material layer should be increased by at least 5% than in the rest of the hard material layer.

Particularly advantageously, the edge radius, which is formed by the hard material layer in the edge region, should be smaller than the edge radius in the edge region of the uncoated tool substrate.

The edge radius in the edge region of the uncoated tool substrate should be less than 30 μm, preferably less than 15 μm.

Suitable materials for the hard material layer are AlCrN / TiN or AlCrSiN / TiN.

The production can be carried out with a PVD method in which a hard material layer formed on the tool substrate surface, which is formed with AlCrN / TiN or AlCrSiN / TiN, is maintained within a vacuum chamber in which a partial pressure of nitrogen> 2 Pa, preferably> 5 Pa, is maintained. is trained. In this case, at least one of the metallic elements in the hard material layer, and in a hard material layer in which silicon is also included, a silicon-containing evaporation source should be operated to form the hard material layer on the tool substrate surface. At least during the formation of the hard material layer, an electrically negative BIAS voltage of at least 100 V, preferably 500 V, is to be applied to the tool substrate to be coated.

In this case, the energy of the ions of the plasma is to be controlled or controlled taking into account a be formed on an edge region of the tool substrate edge radius of the hard material layer and the corresponding there edge radius of the tool substrate that a certain edge radius of the hard material layer is formed in the edge region and thereby the proportion of in the Hard material layer containing aluminum can be increased in the edge region.

The evaporator source (s) should preferably be a vacuum arc evaporator with a graphite anode or an anode formed predominantly with graphite. In the evaporator sources, the metallic components may be present in individual sources but also already in the form of an alloy of several metals.

The formation of the hard material layer should if possible be carried out so that the ions used for the formation have energies in the range of 0.3 keV to 1 keV.

The edge radius of the hard material layer in an edge region can be reduced by increasing the negative bias voltage. The reduction can lead so far that the edge radius at the surface of the hard material layer in the edge region is smaller than the edge radius of the original tool substrate in this region.

The properties of the material of the ready-made hard material layer and also edge radii can be influenced directly during the actual coating process. In this case, during the formation of the hard material layer at least one of the following parameters, namely the electrical bias voltage, the nitrogen partial pressure and / or the speed with which a tool substrate is moved, can be changed. When changing the speed, this may be the speed at which tool substrates to be coated or surface areas to be coated are moved past one or more evaporator sources. Due to the changing distances of the surface areas of a tool substrate to be coated, the respective proportions of the chemical elements with which the coating is formed at these times can vary. If multiple evaporator sources are used, their cathodes may have a different chemical composition.

As a result, the consistency of the formed hard material layer can be varied during the coating process. However, this takes place in such a way that as far as possible no boundary layer formation occurs within the hard material layer, but a very finely graded transition can be achieved during layer growth.

As the nitrogen partial pressure changes, the nitride content within the coating can be changed.

A change in the absolute amount of electrical bias voltage applied to the tool substrate may also contribute to affecting crystallite formation and layered stresses. However, the ions used for the formation of the hard material layer should have energies up to 1 keV. With these ion energies, a permanent removal of unstable phases from the surface of the hard material layer is already possible during the coating process, so that no or at least significantly fewer and smaller defects can occur.

The hard material layer produced according to the invention may have a hardness of at least 2500 HV. The residual stresses of the hard material layer are less than 2 GPa and a fine-crystalline structure with particle sizes smaller than 100 nm is maintained. Within the hard material layer, the proportions of the individual chemical elements forming the coating can vary, as has already been mentioned.

Thus, areas with an inhomogeneous distribution of the chemical elements can be achieved within the hard material layer. For example, areas of increased AlCrSiN may occur adjacent to areas of increased TiN. In particular, the proportion of Si may vary more, and there may even be areas where Si is absent. Predominantly, such regions can form superimposed very thin layers with thicknesses in the range 3 nm to 50 nm. The individual layers are not sharply separated in their consistency from each other, but there are formed mixing zones in which the proportions of the chemical elements differ only to a very small extent.

In the invention, a stabilization of the actual cubic AlN phase can be achieved by the titanium and thereby at least almost avoided formation of hexagonal AlN by a suitable composition of the cathodes used in the evaporator sources. If the proportion of titanium in the coating is maintained in the range of 10% by mass to 20% by mass, this has an advantageous effect with a reduction in the layer's residual stresses.

After fabrication, no sharpening of a cutting edge of a hard coated tool is required by grinding.

The hard material layers for the tools can be applied on different tool substrates made of different metals and alloys, ceramics or hard metals. Only a hard material layer formed with AlCrSiN / TiN should only be applied to temperature-resistant materials, eg. As carbide, are formed. This can be tungsten carbide or tungsten carbide with cobalt, in which are different, but common for hard metal portions of the chemical elements to be.

In the method according to the invention for coating the tools, a layer zone with a higher content of AlN, which is less electrically conductive, is formed in an edge region than in the remaining part of the coating, which is remote from the edge region. This leads to reduced ion bombardment in the edge region in comparison to the layer deposition processes of layers of higher electrical conductivity. The typically occurring in electrically conductive layers typical flattening of the formed coating in edge regions by geometrically induced electrical field increase can be compensated or overcompensated with the invention.

As the thickness of the hard material layer to be formed increases, the edge radius normally becomes larger. As a result, the thicknesses of hard material layers usually used are limited to 3 μm to 5 μm, which applies to the entire surface of the hard material layer. However, such a thin overall layer thickness has a negative effect because of the reduced service life. This can be counteracted with the invention.

With the targeted influence of the invention in the energy of the ions with which the hard material layer is formed, the original edge radius of the tool substrate can be maintained at least. However, it can also be reduced so that the edge radius on the surface of the hard material layer in the edge region is smaller than the edge radius of the tool substrate in this region.

In this case, a dielectric component is specifically incorporated in the hard material layer. This is usually but at least predominantly AlN. In edge regions with small edge radii, the electrically conductive component, with which the hard material layer is actually formed, can be removed in a larger amount by the field elevation in conjunction with the increased ion energies. It comes to a segregation, which in turn leads to an increase in electrical resistance per area. This results in increasing electrical shielding of this zone associated with decreasing ion bombardment. As a result, the hard material layer grows over the entire surface, ie also in edge regions, at the same coating rate, whereby the usual edge rounding can be avoided. By further increasing the electrical bias voltage applied to the tool substrate, the edge radius can even be reduced.

With the invention, tools can be made available that have sharp edges / cutting edges, without the need for time-consuming subsequent or pre-processing.

This can only be achieved by targeted adaptation of the coating parameters. This also a targeted adjustment of edge radii is possible.

The invention will be explained in more detail by way of example in the following.

Showing:

1 a diagram of the metallic components contained in a hard material layer as a function of the distance from an edge

Example 1:

For the production of cutting tools with a small cutting edge radius, which should be formed of tungsten carbide cobalt as a hard metal and coated with a 4 micron hard layer of AlCrSiN / TiN, the procedure was as follows:
The tools were placed in a bath containing an alkaline detergent prior to coating and cleaned by ultrasound. Thereafter, the components were rinsed clear and dried.

The material had the composition 90 mass% tungsten carbide and 10 mass% cobalt. The thus pre-cleaned components were placed in a vacuum chamber in which the internal pressure was reduced to <0.01 Pa. The tools were inserted into a rotatable component carrier. In the vacuum chamber, they were heated to a temperature of 300 ° C in order to remove possibly remaining organic residues from the surface. For this purpose, a radiant heater was used. Following this preheating, the surface to be coated was finely cleaned by ion bombardment. The following parameters were observed: an argon partial pressure 5 Pa, BIAS voltage -1 kV and t = 20 min.

First, an approximately 100 nm thick adhesion promoter layer of TiN was applied to the surface. Here, a vacuum arc evaporator source in which the cathode was made of pure titanium was operated by electric arc discharge. During the electric arc discharge, the electric voltage was kept at 20 V and the electric arc current at 100 A. A negative BIAS electrical voltage of -500 V was applied to the tools. The nitrogen partial pressure was set to 1 Pa and the tools were moved past the evaporator source by means of a carrier. Following the formation of this primer layer, all other things being equal, a second evaporator source was set up in which the cathode was formed of AlCrSi (60:30:10 at%). After ignition of the electric arc discharge of this evaporator source, in which the anode was a graphite electrode, the tools were rotated by the carrier at the two evaporator sources over. The electric arc discharge of the second evaporator source was maintained at a voltage of 20 V and an electric arc current of 100 A. As a result, and in conjunction with the BIAS voltage applied to the tools, it was possible to achieve an ion bombardment with an energy of 0.5 keV and a coating rate of 15 μm / h to 20 μm / h. The coating process was operated for about 12 minutes. After a cooling phase of 30 minutes, the tools provided with the hard coating could be removed. With the 4 μm thick hard coating of AlCrSi / TiN a hardness of the hard material coating of 2900 HV was achieved.

• – vor der Beschichtung: 9 μm Kantenradius und
• – nach der Beschichtung: 5 μm Kantenradius.

Measurements of the edge radii were carried out on the cutting edges of the tools before and after the coating, resulting in the following values for the edge radii:

• - before coating: 9 μm edge radius and
• - after coating: 5 μm edge radius.

Example 2:

For the production of cutting tools with a small cutting edge radius, which should be formed of tungsten carbide cobalt as hard metal and coated with a 50 micron hard material layer of AlCrN / TiN, the procedure was as follows.

The carbide tools were placed in a bath containing an alkaline detergent prior to coating and cleaned by ultrasound. Thereafter, the components were rinsed clear and dried.

The material had the composition 90% by mass of tungsten carbide and 10% by mass of cobalt. The thus pre-cleaned components were placed in a vacuum chamber in which the internal pressure was reduced to <0.01 Pa. The components were inserted into a rotatable carrier. In the vacuum chamber, the tools were heated to a temperature of 300 ° C in order to remove possibly remaining organic residues from the surface. For this purpose, a radiant heater was used. Following this preheating, the surface to be coated was finely cleaned by ion bombardment. The following parameters were observed: Argon partial pressure 5 Pa, BIAS voltage -1 kV and t = 20 min.

First, an approximately 100 nm thick adhesion promoter layer of TiN was applied to the surface. In this case, an evaporator source, wherein the cathode was made of pure titanium, operated by means of electrical arc discharge. During the electric arc discharge, the electric voltage was kept at 20 V and the electric arc current at 100 A. A negative BIAS electrical voltage of -500 V was applied to the tools. The nitrogen partial pressure was set to 1 Pa and the tools were moved past the evaporator source by means of the carrier. Following the formation of this primer layer, all other things being equal, a second evaporator source was put into operation, in which the cathode was formed of AlCr (70:30 at%). After ignition of the electric arc discharge of this evaporator source, in which the anode was a graphite electrode, the tools were rotated by the carrier at the two evaporator sources over. The electric arc discharge of the second evaporator source was maintained at a voltage of 20 V and an electric arc current of 100 A.

As a result of this, and in conjunction with the BIAS voltage of 300 V applied to the tools, bombardment with ions whose energy was 0.3 keV and a coating rate of 15 μm / h to 20 μm / h could be achieved. The coating process was operated for 11 minutes.

After a cooling phase of 30 minutes, the tools provided with the hard coating could be removed. With the 4 μm thick hard coating of AlCrN / TiN a hardness of the hard material coating of 2500 HV was achieved.

• – vor der Beschichtung: 11 μm Kantenradius und
• – nach der Beschichtung: 3 μm Kantenradius.

Measurements of the edge radii were carried out on the cutting edges of the tools before and after the coating, resulting in the following values for the edge radii:

• - before coating: 11 μm edge radius and
• - after coating: 3 μm edge radius.

Claims (8)

Tool consisting of a tool substrate, which is coated with a nitridic hard material layer, in which aluminum is included, characterized in that in an edge region, the proportion of aluminum in the hard material layer compared to the proportion of aluminum at a distance of more than 500 microns from the edge region formed formed hard material layer is increased. Tool according to claim 1, characterized in that the edge radius of the hard material layer in the edge region is smaller than the edge radius in the edge region of the uncoated tool substrate. Tool according to one of the preceding claims, characterized in that the edge radius in the edge region of the uncoated tool substrate is less than 30 microns. Tool according to one of the preceding claims, characterized in that the hard material layer with AlCrN / TiN or AlCrSiN / TiN is formed. Method for producing a tool according to one of the preceding claims, in which a hard material layer of AlCrN / TiN or AlCrSiN is applied to the tool substrate surface. This is done with a PVD method within a vacuum chamber at a nitrogen partial pressure of> 2 Pa, preferably> 5 Pa and using an evaporator source containing the metallic components or the metallic components and silicon. During the formation of the hard material layer, an electrically negative bias voltage of at least 100 V is applied to the tool substrate to be coated. The bias voltage and the energy of the ions of the plasma are controlled or controlled taking into account an edge radius of the hard material layer to be formed on an edge region of the tool substrate and the edge radius of the tool substrate there, so that a certain edge radius of the hard material layer is formed in the edge region, wherein a reduction the edge radius of the hard material layer is achieved by increasing the BIAS voltage. The proportion of aluminum contained in the hard material layer is thereby increased in the edge region. A method according to claim 5, characterized in that is used as an evaporator source or for a plurality of evaporator sources, a vacuum arc evaporator with a graphite anode or an anode formed predominantly with graphite. A method according to claim 5 or 6, characterized in that the formation of the hard material layer is carried out so that the ions used for the formation have energies in the range 0.3 keV to 1 keV. Method according to one of claims 5 to 7, characterized in that tools are produced with cutting edges.

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