Patent Grant
8329000
The present invention is directed to a workpiece having a body and a wear-resistant hard coating system on at least a part of its surface, further to a process for manufacturing such workpiece and to a method of manufacturing a device.
TiAlN is a coating which is widely used to machine hardened steel and is customarily applied by a PVD process.
We understand under a physical vapour deposition process (PVD) a vacuum deposition process, wherein a plasma is used and material is filled into the processing atmosphere from solid. Thereby, under this term of PVD e.g. cathodic arc evaporation, ion plating, sputtering, thereby magnetron sputtering, all the addressed processings reactive or non-reactive are members of the PVD processing category.
In opposition thereto CVD coating processes, chemical vapour deposition, and PECVD, plasma enhanced chemical vapour deposition provide coating out of gaseous phase.
TiAlN layers used as a single layer- or in multilayer-systems with sublayers of different Ti/Al/N stochiometries, can be used up to working temperatures of 900° C. at most for tooling application due to the incipient degradation of hardness at temperatures higher than 800 to 850° C. depending on the Aluminum/Titanium ratio.
Therefore, the US 2005-0003239 proposes to apply AlCrN coatings to workpieces so as to increase their oxidation resistance. This coating is known to have a good oxidation resistance and a hot hardness up to 1100° C. depending on the Aluminum/Chromium ratio. It is further referred to similar proposals in the WO 2006/005217, the WO 2006/084404 and the US 2006-0222893 trying to further improve oxidation resitance and/or hot hardness of the coatings by using different multilayers and/or by introducing other elements into the AlCrN matrix.
The US 2006-0269789 discloses a hard multilayer to cut high hardness material at a high speed. The hard multilayer comprises a first TiAlCrNX-based layer, wherein X stands for C or O. A second layer consists of a mixture of TiAlCrNX and of TiAl(SiC)NX or is a multilayer of layers of these alternative materials. A third outermost layer essentially consists of TiAl(SiC)NX.
Another coating to improve cutting of hardened steels is disclosed in the EP 1 690 959. There the coating comprises a two-layer system based on (TiAlSi)N of different Al and Si stochiometries.
In spite of the approaches as outlined above there is still a need to further improve hard coating systems on workpiece bodies with respect to wear and oxidation resistance, thereby further improving performance of such workpieces, especially used as cutting tools in machining of hard material, thereby especially of hardened steels.
It is thus an object of the present invention to further improve hard coatings with respect to wear resistance and oxidation resistance. To resolve such object there is proposed a workpiece having a body and a wear resistant hard coating system on at least a part of the surface of the body, wherein the system comprises at least one layer of the following composition:
(Al1-a-b-cCraBbZc)X, where
X is at least one of N, C, CN, NO, CO, CNO and
Z is at least one of W, Mo, Ta, Cb (also referred to as Nb) and wherein there is valid
0.2≦a≦0.5
0.01≦b≦0.2
0.001≦c≦0.04.
Astonishingly, the addressed object is achieved by generically adding boron (B) and at least one of the addressed Z elements to a matrix of AlCrX type by fulfilling the addressed conditions with respect to stochiometry. We address this layer as HL0.
In a preferred embodiment of the workpiece according to the invention the element Z is selected to be tungsten W and there is established
0.01≦b≦0.1 and
0.001≦c≦0.01
We address this layer as HL1.
We understand throughout the present description and claims under the term “coating system” or “coating subsystem” a system which consists of one single layer or of multiple, i.e. more than one layers.
The addressed at least one layers HL0 possibly HL1 may thereby be applied directly on the surface of the workpiece body. They further may be applied to form the outermost layer of the coating system. Clearly, if such coating system consists of one layer, then the addressed layer of HL-type resides directly on the surface of the body and is the outermost layer. The layer of HL0-type may further be the outermost layer of a multilayer system. It further may be embedded within a multilayer system between a first layer subsystem towards the surface of the workpiece body and a second layer subsystem towards the surface of the coated body. Still further, in a multilayer system more than one of the addressed HLo-type layers of equal or of varying stochiometry and/or material composition may be provided. Thereby, such layers of HLo-type may reside directly one upon the other with different stochiometry and/or material composition or may be separated by respective coating layer subsystems.
In one embodiment of the workpiece according to the present invention the at least one layer HL0 or HL1 resides outermost of the hard coating system.
In one embodiment of the workpiece according to the present invention the at least one layer of HL0-type resides directly on the surface of the body of said workpiece.
Still in a further embodiment the system comprises at least one interlayer of (TidAle)N. Thereby, in a further embodiment at least one of the addressed interlayers is interposed between the surface of the body and the addressed at least one HL0-type layer. We address this interlayer as IL1.
In a further embodiment of the workpiece the addressed interlayer resides directly on at least one of the surface of the workpiece and of the at least one layer of HLc-type.
Thus, in the embodiment wherein the interlayer is interposed between the surface of the body and the at least one HL0 or HL1, further interlayers of the addressed type may additionally be provided between the HL0 or HL1 and the surface of the system. Further, the addressed intermediate layer must not necessarily reside as the only layer between the surface of the body and the surface of the HL1 or HL0, additional layers may be provided therebetween, so that the interlayer is one layer of a multilayer subsystem between the surface of the body and HL0 or HL1. Nevertheless, in one embodiment the addressed intermediate coating directly resides upon at least one of the surface of the body and the HL0 or HL1. When applying the at least one interlayer of (TidAle)N in a further embodiment there is applied:
0.4≦d≦0.6 and
0.4≦e≦0.6.
In a further embodiment of the workpiece according to the present invention the hard coating system comprises at least one interlayer of (AlfCrg)N. We address this interlayer as IL2.
With respect to where such at least one interlayer may be provided the same prevails as was addressed above with respect to the (TidAle)N layer-IL1-, with the exception that for the (AlfCrg)N interlayer, in a further embodiment there is selected
0.4≦f≦0.7 and
0.3≦g≦0.6.
Further, both the addressed interlayers IL1 and IL2 may be provided in combination within the hard coating system.
Still in a further embodiment of the workpiece according to the present invention, the at least one layer, HL0 or HL1, exhibits a nanocrystalline glassy-like growth structure in the SEM cross-section and/or, as in a further embodiment, a relatively small fraction of AlN characterized by a crystal structure of the hexagonal type. Such hexagonal AlN phase in this embodiment resides with a percentage of Al of at least 70% within the metallic fraction of the HL0 or HL1 material, which fraction comprises all the elements but X of AlCrBZX or AlCrBWX.
Such hexagonal structure may be recognized by XRD analysis.
In a further embodiment of the workpiece according to the present invention the at least one HL0 or HL1 has a texture coefficient Q=I(200)/I(111) in the range of 0.1≦Q≦1. Such texture coefficient Q may be measured by X-ray diffraction analysis. As addressed, the term Q is defined as the ratio of the diffraction intensities I(200) to I(111) assigned respectively to the (200) and (111) planes in the X-ray diffraction of a material using a measuring setup as e.g. described in context with
Looking back to the addressed interlayers IL1, IL2 it should be mentioned that in respective embodiments these interlayers may exhibit a columnar growth structure, thereby giving to the overall coating system an excellent performance, especially if used on a cutting tool.
In a further embodiment of the workpiece according to the present invention the hard coating system comprises a multilayer of alternating layers of at least one of the addressed interlayers IL1, IL2 and of at least one of HL0 and HL1, thereby preferably of (AlCrBW)X, i.e. HL1.
Such a multilayer may e.g. comprise, departing from the surface of the body, a first of the addressed interlayers IL1, then possibly a second of the addressed interlayers IL2 of different type, then a first HL, i.e. HL0 or HL1, then again one or more than one of said interlayers IL1, IL2, a second HL0 or HL1 of same or of different material, a third HL0 or HL1 directly upon the former one, etc. etc. Thus, depending on the specific application there is a large variety of tailoring such multilayer hard coating system making use of the HL0 or HL1 and of the addressed intermediate layers IL1, IL2 in different combinations.
In a further embodiment of the workpiece according to the invention the body is of high speed steel, hardened steel, cemented carbide or of cubic boron nitride or in a further embodiment of a cermet or of ceramic material.
Still in a further embodiment the addressed workpiece according to the present invention is a cutting tool, thereby in a further embodiment an end mill, a drill, a cutting insert or a gear cutting tool.
A process according to the present invention for manufacturing a workpiece as was addressed, i.e. according to the present invention comprises providing such workpiece body in a plasma coating vacuum chamber, applying the hard coating system to the body by a physical vapour deposition process (PVD) during a processing time and thereby establishing a temperature of at least 550° C. to the surface of the coated body during at least a predominant part of processing time.
In one embodiment of such process the addressed temperature is selected to be at least 600° C.
Still under a further aspect the present invention is directed on a method of manufacturing a device which has at least a part of a hard material. Such method comprises a cutting process of the hard material of the device using a cutting tool according to the present invention. Thereby, still in a further embodiment of the addressed device manufacturing method, the hard material has a Rockwell hardness of at least 52 HRC, thereby even of at least 55 HRC. Still in a further embodiment of the just addressed manufacturing method the hard material is hardened steel.
Cutting processes have been performed with cutting tools according to the present invention which showed on hard material results at least as good or even better than comparative examples performed with state of the art tools. However, cutting operation on hardened steel or other high hardness materials having a Rockwell hardness of HRC 50, especially of HRC 52 or higher, even of HRC higher than 55, the tools according to the present invention revealed a performance which was outstandingly good as will be shown below.
The present invention shall now be further described by means of examples and with the help of figures. The figures show:
In
According to the embodiment of
Thereby, the surface 7 of the resulting workpiece is formed by one surface of the addressed layer HL, which thus, as a good embodiment, forms the outermost surface of the workpiece.
In the embodiment of
As may be seen in the definition of the layers HL, and also HL1X, and in the case of HL, also Z may consist of different elements. According to the embodiment of
There may or may not follow further layers of the HL0 type and/or of the HL1 type up to surface 5 of the body 3.
Whereas at the embodiment of
In all the embodiments of
Nevertheless and e.g. with an eye on
In the embodiment according to
The alternating coating subsystems again may consist of one or more than one layers, at least one thereof being not of the HLo-type.
As exemplified by the embodiment according to
We have addressed in the introductory part of the description a first interlayer of (TidAle)N especially with d and e in specific ranges of values as IL1 and have addressed a second type of interlayer of (AlfCrg)N, with specific ranges for f and g as IL2.
With an eye on the embodiments of
Again, the skilled artisan recognizes from the addressed embodiments according to the
In the following some specific embodiments of the workpiece according to the present invention are exemplified. Cutting performance of workpieces according to the invention conceived as cutting tools were compared with such tools according to the state of the art, thereby equal cutting operations and cutting parameters were applied to the respective tools according to the present invention and to the comparative tools according to the state of the art, for valid comparison purpose.
The hard coating systems applied to the specimens in the following examples were deposited under the following conditions, if not specifically and differently specified, whereby the process for manufacturing the workpieces according to the present invention was applied.
Deposition technology: Cathodic arc evaporation
Total working pressure: 5.5 Pa of N2
Bias voltage of the body to be coated: −85V against ground potential for HL0 type layers and −100V against ground potential for IL1 and IL2 layers
Surface temperature of body being coated: 600° C.
Evaporation current: 200 A per evaporation target
The hard coating systems were deposited in a Balzers RCS coating machine in arc evaporation configuration. The cutting tool bodies were mounted on threefold rotating holders during the PVD deposition.
All the hard coating systems deposited on the cutting tool body had a total thickness between 2 and 2.5 μm, measured on the shank of the cutting tool.
A first series of mono-layered hard coating systems was compared with state of the art monolayer system of TiAlN and AlCrN.
Table 1 displays the hard coating system investigated under this example. To apply each of the addressed monolayer hard coating systems the coating machine was equipped with four identical arc evaporation cathodes, also called targets. The respective compositions of these targets are also listed in table 1. The resulting composition of the coating material was within 10% of the target composition for the main elements Al, Cr, Ti and was within about 20% of the target composition for the element B and W, Mo and Ta.
The performance of the hard coating systems was assessed in terms of wear resistance in a metal cutting operation. The amount of wear on the flank face, vbmax, was measured as a function of the length of the cut. The cutting test was a milling test under finishing conditions in a hardened cold work tool steel. The cutting conditions were the following:
The results of the cutting test are listed in Table 2.
It can be seen that the incorporation of B and W, Mo and Ta in AlCrN results in an improved wear protection compared with the wear protection of AlCrN and TiAlN according to the comparative specimens 1 to 3.
A series of double-layer hard coating systems was prepared. Table 3 lists the hard coating systems as investigated. The same tool bodies of the material as of Example 1 were coated. Thereby directly upon the surface of the tool body there was applied an interlayer IL1 and directly upon such interlayer a layer of HL1-type. The machine was equipped with two identical targets for the deposition of the interlayer and with four identical targets for the deposition of the outer layer of the HL1-type. The respective target material compositions are also listed in table 3.
The performance of the tools according to this second series was investigated with the same cutting test as was applied to the example 1 tools. The results are listed in table 4.
Thereby, the interlayer IL1 of specimen No. 9 shows a stochiometry which is well within the range of
0.4≦d≦0.6
0.4<e≦0.6
of the (TiAle)N of the interlayer IL1, whereas the interlayer as applied in example No. 8 is just outside the addressed stochiometry range.
When applying a IL1 interlayer to the inventively provided HL-type layer especially tailored as HL1-type layer with X═N, provision of such interlayer most significantly improves wear resistance and even more if the addressed stochiometry ranges for the aluminum and titanium compounds are fulfilled.
A further series of workpieces, namely tools with a hard coating system according to the present invention consisting of two layers, was prepared, namely consisting of an interlayer TiAlN, IL1 directly between a tool body as was already used in the examples 1 and 2 and a HL1-type layer with X═N as already provided in specimens 8 and 9 of Table 3. Thereby, the temperature of a surface being coated was varied between 450° C. and 600° C. by varying heating time and/or power.
For the specimens 10, 11 and 12 as follow the same targets for the interlayer as well as for the outermost layer were used as specified for specimen No. 9.
Table 5 shows on one hand the addressed layers of the coating system and on the other hand the deposition temperatures.
The performance of the specimens was investigated with the same cutting conditions as Example 1. The results are listed in the following Table 6.
The results show on one hand that specimen No. 12 which was coated identically to specimen No. 9 of example 2 exhibits equal wear resistance compared with the addressed specimen 9. Further, specimen 10 reveals that even at lower temperatures of 450° C. the coating system according to the present invention is significantly superior to a comparable two-layer coating system coated at 600° C. as of specimen No. 7.
Further, it is evident from comparing the specimens 10 to 12 that wear resistance significantly increases with increasing deposition temperature and achieves best performance, as of specimen No. 12, at a maximum deposition temperature of 600° C. as investigated or more.
A fourth series of double-layered hard coating systems with an interlayer IL1 and a HL1-type layer of the specific embodiment with X═N was prepared.
As comparison specimens prior art single layer systems of TiAlN and AlCrN were selected. The following Table 7 lists the respective coating material and the target composition.
The performance of the resulting tools was assessed in terms of wear resistance in metal cutting application. The amount of wear on the flank face vbmax was measured in function of the length of the cut. The cutting tests were performed under the conditions of semi-finishing milling operation in a heat treated tool steel. The cutting conditions were the following:
Table 8 reveals the cutting test results.
A series of tools with double-layer coating systems, namely consisting of an IL1 interlayer and a HL1-type layer with X═N was prepared. They were compared with respective tools coated with state of the art double-layer coating systems, namely of TiN as interlayer and TiAlN as outermost layer or coated with AlCrN as interlayer and a TiSiN as outermost layer.
Table 9 shows the respective layer material and target material compositions.
The performance of the respectively coated tools was assessed in drilling operation on heat treated steel. The amount of wear on the flank face of the main cutting edge vbmax was used to assess the wear protection quality. The test conditions were the following:
The following table 10 displays the drilling results.
This example makes clear that the tools according to the present invention may not be the best choice for use in highly annealed steels and soft materials.
In the following examples No. 6 to 8 the hard coating systems were deposited again as was already addressed for the previous examples, but the total working pressure N2 was reduced from 5.5 Pa to 3.5 Pa and the substrate bias voltage against ground was increased from −85 V to −100 V for the deposition of the AlCrBWN outermost layer according to HL1 with X═N.
A sixth series of tools was prepared to establish the effect of an AlCrN interlayer IL2 instead of a TiAlN-interlayer IL1.
The Table 11 shows the respective layer materials and the target compositions.
Using tools coated as addressed, a cutting test with the following parameters was applied
The results are shown in Table 12.
From these results it may be seen that providing a IL1 or a IL2 interlayer leads substantially to the same good results.
By the seventh series of specimens it was the aim to establish for the effect of a different B and W content at a HL2-type layer with X═N. The following Table 13 lists the material of the interlayer as well as of the outer layer and the respective compositions of the target materials.
Using such tools, a cutting test with the same parameters as in example 6 was applied
The results are shown in Table 14
In the eighth series of specimens which were coated with a two-layer coating system as addressed in Table 15, prior to the cutting tests a brushing treatment was applied using a brushing machine according to the DE GM 20 2006 000 654.1 in order to adjust a state comparable to an initial homogeneous wear, which ensures afterwards a homogeneous progress of the wear during the cutting application.
The treatment of the coated tool was conducted with rotary brushes according to the addressed document.
Alternatively or even additionally a similar honing treatment by brush, blast, grinding operations or the like can be applied before the coating process as a pretreatment.
With the tool coated according to Table 15
cutting tests were performed with the following cutting parameters:
From the examples as shown above it becomes clear that tools wherein the hard coating systems comprise the HL0 layer in the specific form of HL1 with X═N as in a single layer system or, and especially in connection with the addressed IL1 and/or IL2 interlayer, provide for an astonishing increase of wear resistance compared with state of the art coating systems e.g. with outermost TiAlN or AlCrN coating systems.
Despite the fact that the addressed HL1 with X═N coating is applied through all the examples as the outermost layer of the coating system, it is evident to the skilled artisan that for some applications additional layers may be provided upon the addressed layer as e.g. a lubricating layer.
Further, throughout the examples the addressed HL1 layer is, considered towards the tool body, applied either directly on the tool body or separate there from by a IL1 or IL2 interlayer.
Nevertheless, for some applications it is evident to the skilled artisan that such multilayer systems with the inventively proposed HL-type and IL-type layers may be conceived in a huge variety depending upon the specific needs.
Moreover, the above examples have been conducted specifically on the HL1 layers, wherein X═N. Nevertheless, it is perfectly clear to the skilled artisan that replacing N by C, CN, NO, CO or CNO will lead to layers HL1 with similar wear resistance qualities.
The same is valid if in the HL1 type layer the element W is replaced by Mo, Ta, Cb (Nb).
Still further, the tools whereupon the examples have been performed have a tool body of tungsten carbide.
Nevertheless, with respect to the material of the tool body or more generic workpiece body, it is perfectly clear to the skilled artisan that the targeted increase of wear resistance by the coating system according to the present invention will also be achieved on workpiece bodies of high speed steel, cemented carbide or cubic boron nitride or of a cermet or of a ceramic material. The addressed improvement of wear resistance may be highly desirable not only for tools like cutting tools such as for end mills, drills, cutting inserts, gear cutting tools but also for other workpieces than tools.
By the method of manufacturing a device which is at least in part of a hard material, thereby especially with a hardness of at least HRC 52, comprising a cutting process of the addressed hard material using the cutting tool according to the present invention, device manufacturing becomes faster, thus throughput higher and manufacturing costs are lowered.
In
The type HL1 outer layer exhibits the same glassy-like growth structure as specimen No. 4 of Example 1 (see
As expected for an AlxCr1-xN hard coating having an x≦0.7, there is no hexagonal AlN phase in such hard coating. The AlCrBWN hard coating exhibits diffraction peaks which are assigned to the <111>, <200> and <220> planes of AlCrN as well. However AlxCrBWN hard coatings, having the same x of 0.7, show a remarkable contribution of hcp—(hexagonal closed packed) AlN. Peaks at around 33.1°, 49.5° and 58.9° point out signals attributed to that phase. Peaks at around 31.5°, 35.7°, 48.3°, 64.1° and 65.9° derive from the WC—Co body of the carbide substrate.
Measurement was performed using the setup as was described in context with
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/EP2007/059070 | Aug 2007 | WO | international |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6824601 | Yamamoto et al. | Nov 2004 | B2 |
| 7226670 | Derflinger et al. | Jun 2007 | B2 |
| 7348074 | Derflinger | Mar 2008 | B2 |
| 7498089 | Omori et al. | Mar 2009 | B2 |
| 7504149 | Toihara et al. | Mar 2009 | B2 |
| 7510761 | Kondo et al. | Mar 2009 | B2 |
| 7521131 | Yamamoto | Apr 2009 | B2 |
| 20050003239 | Derflinger | Jan 2005 | A1 |
| 20060222893 | Derflinger | Oct 2006 | A1 |
| 20060269789 | Toihara | Nov 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 1219723 | Jul 2002 | EP |
| 1690959 | Aug 2006 | EP |
| 2004059030 | Jul 2004 | WO |
| 2006005217 | Jan 2006 | WO |
| 2006084404 | Aug 2006 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20120234143 A1 | Sep 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60826943 | Sep 2006 | US | |
| 60909559 | Apr 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11858362 | Sep 2007 | US |
| Child | 13484384 | US |
