TixSi1-xN layers and their production

Abstract

A workpiece having a coating, said coating comprising at least one Ti.sub.XSi.sub.1-xN layer, characterized in that x≦0.85 and the Ti.sub.xSi.sub.1-xN layer contains nanocrystals, the nanocrystals present having an average grain size of not more than 15 nm and having a (200) texture. The invention also relates to a process for producing the aforementioned layer, characterized in that the layer is produced using a sputtering process, in which current densities of greater than 0.2 A/cm.sup.2 arise on the target surface of the sputtering target, and the target is a Ti.sub.XSi.sub.1-xN target, where x≦0.85. An intermediate layer containing TiAlN or CrAlN is preferably provided between the Ti.sub.xSi.sub.1-xN layer and the substrate body of the workpiece.

Claims

1. A method for coating a workpiece having a coating comprising at least one Ti.sub.xSi.sub.1-xN layer, wherein x≦0.85 and the Ti.sub.xSi.sub.1-xN layer contains nanocrystals and the nanocrystals present have an average grain size of not more than 15 nm, wherein x is the concentration of Ti expressed in at % when only metallic elements are taken into consideration, the method comprising: using a sputtering process to produce the Ti.sub.xSi.sub.1-xN layer as a nanocrystalline layer, wherein in the sputtering process a power source constantly outputs high power, and in which a plurality of sputtering cathodes are used, wherein a full power of the power source and thus a high power density is initially only applied to a first sputtering cathode, and subsequently a second sputtering cathode is connected to an output of the power source, and wherein TiSi targets are operated as sputtering cathodes, wherein current densities of at least 0.2 A/cm.sup.2 arise on the target surface of the sputtering target, and wherein the TiSi targets which are operated for producing the nanocrystalline layer have a silicon content of equal to or greater than 15 at %.

2. The method for coating a workpiece according to claim 1, further comprising providing an intermediate layer containing TiAlN between the Ti.sub.xSi.sub.1-xN layer and the substrate body of the workpiece.

3. The method for coating a workpiece according to claim 2, further comprising providing a transition layer containing both TiAlN and Ti.sub.xSi.sub.1-xN between the intermediate layer and the Ti.sub.xSi.sub.1-xN layer.

4. The method for coating a workpiece according to claim 3, wherein the transition layer is a graded layer having a silicon content that increases as distance from the substrate surface increases.

5. The method for coating a workpiece according to claim 1, further comprising providing an intermediate layer containing Cr.sub.yAl.sub.1-yN between the Ti.sub.xSi.sub.1-xN layer and the substrate body of the workpiece, wherein y indicates the Cr concentration expressed in at %, when only the metallic elements are taken into consideration.

6. The method for coating a workpiece according to claim 5, further comprising providing a transition layer containing both Cr.sub.yAl.sub.1-yN and Ti.sub.xSi.sub.1-xN between the intermediate layer and the Ti.sub.xSi.sub.1-xN layer.

7. The method for coating a workpiece according to claim 6, wherein the transition layer is a graded layer having a silicon content that increases as distance from the substrate surface increases.

8. The method for coating a workpiece according to claim 1, further comprising producing a transition layer between an intermediate layer and the Ti.sub.xSi.sub.1-xN layer by co-sputtering.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a correlation between Si concentration and average grain size of the nanocrystals.

(2) FIG. 2 shows how the concentration conditions in the target used for coating are almost directly reflected in the coated layer.

(3) FIG. 3 shows that the grain sizes of layers, which were coated at different positions on a rotating carousel, were maintained.

(4) FIG. 4 shows that as the silicon content increases, the layers have increased hardness and reduced E-modulus.

(5) FIG. 5 shows a series of two-layer structures according to the present invention, wherein different targets are used for coating the Ti.sub.xSi.sub.1-x layers.

(6) FIG. 6 shows that pulse duration directly influences the position of the corresponding maxima.

(7) FIG. 7 shows that as soon as a target having a certain Si concentration is selected, the grain size can be finely adjusted by means of the nitrogen consumption.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) A plurality of sputtering cathodes are used herein. Unlike the conventional HiPIMS method, a pulse generator is not used, but rather the full power of the power source and thus a high power density is initially only applied to a first sputtering cathode. Subsequently, a second sputtering cathode is connected to the outputs of the power source. At first, relatively little happens, since the impedance of the second sputtering cathode at this time is substantially higher than the impedance of the first sputtering cathode. Only when the first sputtering cathode is separated from the outputs of the power source is the power substantially output via the second sputtering cathode. The corresponding high-power magnetron sputtering method is more closely described in WO2013060415. Typically, the power source is operated in the order of 60 kW. Typical powers, to which the sputtering cathodes are exposed in the temporal mean, are in the order of 8 kW.

(9) The inventors have now discovered to their surprise that if operated with TiSi targets having a silicon content of equal to or greater than 15 at %, such a method is capable of producing nanocrystalline layers having very good mechanical properties in a reproducible manner. What is particularly interesting is that with an Si concentration in the target of 15 at % or more, the nanocrystals have an average grain size of less than 15 nm as shown in FIG. 1. FIG. 2 shows how the concentration conditions in the target used for coating are almost directly reflected in the coated layer. It should be noted that as soon as a target having a certain Si concentration is selected, the grain size can be finely adjusted by means of the nitrogen consumption, as shown in FIG. 7.

(10) This is a highly robust phenomenon, as can be seen from FIG. 3. The grain sizes of layers were measured, which were coated at different positions on a rotating carousel. The series of readings with the black filled-in circles refers to a Ti.sub.95Si.sub.5 target. The series of readings with the white filled-in circles refers to a Ti.sub.90Si.sub.10 target. The series of readings with the black filled-in squares refers to a Ti.sub.85Si.sub.15 target. The series of readings with the white filled-in triangles refers to a Ti.sub.80Si.sub.20 target. The series of readings with the black filled-in triangles refers to a Ti.sub.75Si.sub.15 target. Clearly, the grain size is maintained over the entire coating height of the chamber.

(11) As the silicon content increases, the layers have increased hardness and reduced E-modulus, as shown in FIG. 4. This does not show the concentration ratios within the layers, but the Ti to Si concentration ratio in the targets used for producing the layers.

(12) According to a further embodiment of the present invention, the Ti.sub.xSi.sub.1-xN layer with an Si content of at least 15 at % of the metallic component is not applied directly on the substrates to be coated, but rather a TiAlN layer is provided as an intermediate layer between the substrate and the layer according to the present invention. This intermediate layer has the advantage, among others, that it functions as a transition with respect to the stress anchor pressure conditions between the less brittle substrate and the extremely hard Ti.sub.xSi.sub.1-xN layer having extremely high residual stresses. Flaking off is thus greatly reduced, and the layer adhesion is correspondingly improved.

(13) FIG. 5 shows a series of such two-layer structures according to the present invention, wherein, as already discussed, different targets are used for coating the Ti.sub.XSi.sub.1-x layers as indicated in the figure. The different structures of the Ti.sub.XSi.sub.1-x layers in the series are clearly visible, which become increasingly finer as the Si content increases. In the present example, a target was used for producing the intermediate layer, which comprises 40 at % titanium and 60 at % aluminum. It was established that it was particularly advantageous if the two layers TiAlN and TiSiN have a (200) texture.

(14) Such double layers with different Si content were tested on tools. The machining tests were performed under the following conditions: workpiece steel DIN 1.2344 hardened to 45HRC, tool diameter 10 mm, solid cemented-carbide milling cutter, cutting speed 220 m/mm, feed per tooth 0.1 mm, axial infeed 10 mm, radial infeed 0.5 mm. It was measured how many meters a corresponding tool can machine, without being damaged. Tools coated with the usual commercially available coating survive for just over 200 m. A tool coated with the above-described double layer survives about the same distance, when the outer layer contains only 5% silicon. In contrast, the tests show that the tool can survive for more than 500 m if the outer layer contains at least 15% silicon. Table I shows the wear values measured on the tool after 140 m cutting distance. It can be seen quite clearly that wear is lowest with the coating containing 30% silicon.

(15) According to a further advantageous embodiment, a transition layer is provided between the TiAlN intermediate layer and the Ti.sub.XSi.sub.1-x layer, the transition layer being produced by means of co-sputtering. With the above-described sputtering method, co-sputtering can be reliably performed in such a way that, for example, the pulse widths for the different targets are selected in such a way that the maxima of the reactive gas consumption curves as a function of the pressure present in the coating chamber essentially overlie each other. This is possible because the pulse duration directly influences the position of the corresponding maxima. This is shown, for example, in FIG. 6, where three different pulse durations (0.05 ms, 0.2 ms and 2 ms) were used for sputtering. In this way it is possible to optimally operate both targets at the same pressure present in the chamber and under the same gas flow conditions.

(16) According to a further embodiment of the present invention, the transition layer is implemented as a graded layer, having a decreasing content in TiAlN and an increasing content of Ti.sub.XSi.sub.1-xN as the distance from the substrate snake increases.

(17) According to a further embodiment of the present invention, the final Ti.sub.XSi.sub.1-xN layer is not a pure Ti.sub.XSi.sub.1-xN layer but also contains a certain proportion of TiAlN.

(18) According to a further embodiment of the present invention, a first Ti.sub.xSi.sub.1-x target and a second Ti.sub.xSi.sub.1-z target are used for coating, wherein 0≦x≦1 and 0≦z≦1, but z≠x, i.e. the first and second targets differ in their compositions and (x+z)/2≦0.85, so that further layers having an Si concentration of ≧15 at % can be produced. In the method, both targets can be operated according to the above-described co-sputtering method. This allows the Si concentration to be varied during coating, i.e. to implement an Si concentration gradient.

(19) Furthermore, the inventors established that surprisingly excellent layer performances can be achieved with the layers deposited according to the present invention by the use of a Cr.sub.yAl.sub.1-yN layer as an intermediate layer. Accordingly, further preferred embodiments of the present invention will be described in the following, which comprise Cr.sub.yAl.sub.1-yN layers as intermediate layers.

(20) According to a further embodiment of the present invention, the Ti.sub.xSi.sub.1-xN layer having an Si content of at least 15 at % of the metallic, components is not applied directly on the substrate to be coated, but rather a Cr.sub.yAl.sub.1-yN layer is provided as an intermediate layer between the substrate and the layer according to the present invention. A chromium percentage of 40 at % and an aluminum content of 60 at % has proved itself to be advantageous. This intermediate layer has the advantage, among others, that it functions as a transition with respect to the stress and/or pressure conditions between the less brittle substrate and the extremely hard Ti.sub.xSi.sub.1-xN layer having extremely high residual stresses. Flaking off is thus greatly reduced, and the layer adhesion is correspondingly improved.

(21) In the preceding section and the following description, x is the concentration of Ti expressed in at % and y is the Cr concentration expressed in at %, when only the metallic elements are taken into consideration.

(22) Such double layers having different Si contents were tested on tools, it was measured how many meters a corresponding tool can machine without being significantly damaged. The machining tests were carried out under the following conditions: workpiece steel DIN 1.2379, hardened to 69HRC, tool diameter 2 mm solid cemented-carbide spherical-head milling cutter, cutting speed 110 m/min, feed per tooth 0.04 mm, axial infeed 0.1 mm, radial infeed 0.04 mm. Tools coated with the usual commercially available coating survived for just over 60 m. In contrast, tools coated with the above-described double layer, wherein the outer layer contains at least 10% silicon, survived for more than 100 m. The interesting fact is that the CrAlN layer should be kept relatively thin. This seems to indicate that the CrAlN layer essentially takes on the role of an adhesive layer.

(23) According to a further advantageous embodiment, a transition layer is provided between the CrAlN intermediate layer and the Ti.sub.xSi.sub.1-x layer, the transition layer being produced by means of co-sputtering. With the above-described sputtering method, co-sputtering can be reliably performed in such a way that, for example, the pulse widths for the different targets are selected in such a way that the maxima of the reactive gas consumption curves as a function of the pressure present in the coating chamber essentially overlie each other. This is possible because the pulse duration directly influences the position of the corresponding maxima. This is shown, for example, in FIG. 6, where three different pulse durations (0.05 ms, 0.2 ms and 2 ms) were used for sputtering. In this way it is possible to optimally operate both targets at the same pressure present in the chamber and under the same gas flow conditions.

(24) According to a further embodiment of the present invention, the transition layer is implemented as a graded layer, having a decreasing content of CrAlN and an increasing content of Ti.sub.XSi.sub.1-xN as the distance from the substrate suffice increases.

(25) According to a further embodiment of the present invention, the final Ti.sub.XSi.sub.1-xN layer is not a pure Ti.sub.XSi.sub.1-xN layer but also contains a certain proportion of CrAlN.

(26) The invention also specifically refers to a workpiece having a coating, said coating comprising at least one Ti.sub.XSi.sub.1-xN layer, characterized in that x≦0.85 and the Ti.sub.xSi.sub.1-xN layer contains nanocrystals and the nanocrystals present have an average grain size of not more than 15 nm and preferably have a (200) texture. The invention also relates to a method for coating a workpiece with a coating comprising at least the above-mentioned Ti.sub.XSi.sub.1-xN layer, wherein the method used for producing the Ti.sub.xSi.sub.1-xN layer is a sputtering method, in which at least one Ti.sub.xSi.sub.1-x target is used as a sputtering target, wherein x≦0.85 in at % and wherein current densities of at least 0.2 A/cm.sup.2, preferably more than 0.2 A/cm.sup.2, arise on the target surface of the sputtering target. Preferably an intermediate layer containing TiAlN or CrAlN or TiAlN and CrAlN is provided between the Ti.sub.xSi.sub.1-xN layer and the substrate body of the workpiece.

(27) According to a preferred embodiment of a method for coating a workpiece according to the present invention, in which a transition layer is to be deposited, the transition layer is produced by means of co-sputtering.

(28) If it is advantageous for certain applications, the Ti.sub.xSi.sub.1-xN layer according to the present invention can also contain TiAlN or CrAlN or TiAlN and CrAlN percentages.

(29) Depending on the application, it is also possible to use other metal nitride or metal nitride-based materials for coating in the above mentioned embodiments of the present invention instead of TiAlN or CrAlN, in order to achieve the desired layer properties.