Patent Application
20160305018
The present invention pertains to a coated cutting insert, and especially a coated cutting insert coated via a chemical vapor deposition (CVD) technique, and which is useful in chipforming material removal applications such as, for example, machining, turning, and milling, as well as a method of making the same. More specifically, the present invention pertains to a CVD-coated cutting insert comprising a substrate with a coating scheme thereon and wherein the coating scheme includes a plurality of coating layers including a multi-layered coating scheme comprising a plurality of repeating coating sets. Each coating set comprises a coating layer of aluminum oxide and a coating layer of a nitrogen-containing material (e.g., titanium aluminum oxynitride or titanium nitride or zirconium nitride) whereby the coating scheme, which is applied by CVD, has higher toughness, good crack resistance, acceptable adhesion properties, acceptable abrasive wear resistance properties, and acceptable edge integrity, as well as a method of making the coated cutting insert.
Heretofore, coated bodies, such as, for example, coated cutting inserts, have been used in chipforming material removal applications. Such coated cutting inserts typically comprise a substrate of a cutting insert geometry and a coating scheme on the substrate. The coating layers that comprise the coating scheme typically comprise hard refractory materials that exhibit the property of wear resistance. One primary purpose of using a coating on a cutting insert has been to lengthen the useful life of the cutting insert in the material removal application. Exemplary ones of these coating schemes using hard refractory materials are described in the following documents: European Patent Application 1 245 698 B1 to Mitsubishi Materials Corp., European Patent Application No. 1 455 003 A2 to Sandvik A B, European Patent Application No. 1 980 649 B1 to Iscar Ltd., United States Published Patent Application No. US2012/0202032 to Tatsuoka et al., United States Published Patent Application No. US2013/0045057 to Kojima et al., U.S. Pat. No. 7,132,153 to Zackisson et al., U.S. Pat. No. 7,396,371 to Cedergren et al., U.S. Pat. No. 7,455,918 to Gates, Jr. et al., U.S. Pat. No. 7,470,296 to Londholm et al., U.S. Pat. No. 7,597,951 to Bjormander et al., U.S. Pat. No. 7,727,592 to Cedergren et al., U.S. Pat. No. 7,785,665 to Gates, Jr., et al., U.S. Pat. No. 8,080,312 to McNerny et al., U.S. Pat. No. 8,080,323 to Ban et al., U.S. Pat. No. 8,323,783 to Sottke et al., U.S. Pat. No. 8,557,406 to Ban et al., Chinchanikar et al., “Wear behavior of single-layer and multi-layer coated carbide inserts in high speed machining of hardened AISI 4340 steel”, Journal of Mechanical Science and Technology, 27 (5), (2013), pp. 1451-1459, and Halvarsson et al., “Microstructure and performance of CVD κ-Al2O3 multilayers”, Materials Science and Engineering, A209 (1996) pp. 337-344.
As is apparent from the above documents, many different coating schemes for a coated cutting insert have been used in the past. According to these documents, each one of these coating schemes is supposed to provide certain advantages. Even though there have been coating schemes that are supposed to provide certain advantages, there remains a need to provide coating scheme that lengthen the useful life of a coated cutting insert, as well as to improve the performance characteristics of a coated cutting insert in a material removal application. Further, there remains a need to provide an improved coated cutting insert wherein the coating scheme has a high toughness resulting in better edge integrity, especially during heavily interrupted turning and milling operations. Still further there remains a need to provide an improved coated cutting insert that has a coating scheme which includes a multi-layered coating scheme that better inhibits crack growth and propagation in the coating scheme whether due to mechanical stresses or thermal cycling. Yet further, there remains a need to provide an improved coated cutting insert that includes a transition coating layer that functions to promote better nucleation and adhesion of the multi-layered coating scheme.
Therefore, it would highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications. It would be highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert exhibits a lengthened tool life. It would be highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert exhibits improved performance characteristics.
It would be highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating scheme with a high toughness resulting in better edge integrity, especially during heavily interrupted turning and milling operations. It would be highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating scheme which includes a multi-layered coating scheme that better inhibits crack growth and propagation in the coating scheme whether due to mechanical stresses or thermal cycling. It would be highly desirable to provide an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating that includes a transition coating layer that functions to promote better nucleation and adhesion of the multi-layered coating scheme.
In one form thereof, the invention is a coated cutting insert for use in a chipforming material removal operation. The coated cutting insert comprises a substrate and a coating scheme on the substrate. The coating scheme comprises a backing coating scheme deposited by chemical vapor deposition wherein the backing coating scheme is on the surface of the substrate. A transition coating layer is deposited by chemical vapor deposition on the surface of the backing coating scheme. A multi-layered coating scheme, which comprises a plurality of coating sets, is deposited by chemical vapor deposition on the surface of the transition coating layer. Each of the coating sets comprises an aluminum oxide coating layer that has an alpha aluminum oxide crystal structure, and a nitrogen-containing coating layer that has a nitrogen-containing coating crystal structure. The aluminum oxide crystal structure is distinct from the nitrogen-containing coating layer crystal structure whereby a distinct boundary is between adjacent aluminum oxide coating layers and the nitrogen-containing coating layers.
In still another form thereof the invention is a method of making a coated cutting insert comprising the steps of: providing a substrate; applying a transition coating layer by chemical vapor deposition; applying a multi-layered coating scheme to the transition coating layer by chemical vapor deposition wherein the multi-layered coating scheme comprises a plurality of coating sets, and wherein the steps to apply each coating set comprise: first applying an aluminum oxide coating layer without variation in coating deposition parameters wherein the aluminum oxide coating layer has an alpha aluminum oxide crystal structure; and interrupting the application of the aluminum oxide coating layer by applying a nitrogen-containing coating layer having a nitrogen-containing coating layer crystal structure wherein the nitrogen-containing coating layer crystal structure is distinct from the alpha aluminum oxide crystal structure thereby forming a distinct boundary between the aluminum oxide coating layer and the nitrogen-containing coating layer.
The following is a brief description of the drawings that form a part of this patent application:
The present invention pertains to a coated cutting insert useful for a chipforming material removal operation. In a chipforming material removal operation, the cutting insert engages a workpiece to remove material from a workpiece typically in the form of chips. A material removal operation that removes material from the workpiece in the form of chips typically is known by those skilled in the art as a chipforming material removal operation. The book Machine Shop Practice [Industrial Press Inc., New York, N.Y. (1981)] by Moltrecht presents at pages 199-204 a description, inter alia, of chip formation, as well as different kinds of chips (i.e., continuous chip, discontinuous chip, segmental chip). Moltrecht reads [in part] at pages 199-200, “When the cutting tool first makes contact with the metal, it compresses the metal ahead of the cutting edge. As the tool advances, the metal ahead of the cutting edge is stressed to the point where it will shear internally, causing the grains of the metal to deform and to flow plastically along a plane called the shear plane . . . . When the type of metal being cut is ductile, such as steel, the chip will come off in a continuous ribbon . . . ”. Moltrecht goes on to describe formation of a discontinuous chip and a segmented chip.
As another example, the text found at pages 302-315 of the ASTE Tool Engineers Handbook, McGraw Hill Book Co., New York, N.Y. (1949) provides a lengthy description of chip formation in the metal cutting process. At page 303, the ASTE Handbook makes the clear connection between chip formation and machining operations such as turning, milling and drilling. The following patent documents discuss the formation of chips in a material removal operation: U.S. Pat. No. 5,709,907 to Battaglia et al. (assigned to Kennametal Inc.), U.S. Pat. No. 5,722,803 to Battaglia et al. (assigned to Kennametal Inc.), and U.S. Pat. No. 6,161,990 to Oles et al. (assigned to Kennametal Inc.).
Referring to the drawings, there are shown a number of specific embodiments of a coated cutting insert. Referring to
Referring to the coating scheme shown in
There is a Ti+O+C+N transition coating layer 38 containing titanium and oxygen and carbon and nitrogen on the HT-TiCN coating layer 37. It is important to keep in mind that while applicants do not intend to be bound by any specific theory with respect to the function of the Ti+O+C+N transition coating layer, it is thought that the Ti+O+C+N transition coating layer functions to promote the nucleation and adherence of the coating layers of the multi-layered coating scheme.
The multi-layered coating scheme 49 is on the Ti+O+C+N transition coating layer 38 wherein the multi-layered coating scheme 49 comprises a plurality of coating sets (39, 43). Although
The composition of the coating layers that comprise the coating sets of the multi-layered coating scheme are selected so that the deposition of each coating layer is abruptly interrupted by the deposition of the following coating layer. The result is the complete interruption of the crystalline growth of the previous coating layer by the initiation of the following coating layer. This abrupt interruption can be caused by a change in coating composition or coating parameters resulting in the nucleation of a layer of distinct crystal structure. Such a change can result in different crystal structures between adjacent coating layers. These interruptions result in coating layers in which there is a distinct boundary between the adjacent coating layers so that there are no mixed phases of a composite within each coating layer.
Although not shown in
Table 1 below sets forth the ranges of the thicknesses of the coating schemes and coating layers for the coated cutting insert 30 illustrated in
up to 2
up to 1
Table 2 below sets forth the deposition parameters for the deposition of the coating scheme 32A of the coated cutting insert 30 of
Referring to the coating scheme shown in
There is a Ti+O+C+N transition coating layer 60 containing titanium and oxygen and carbon and nitrogen on the TiCN coating layer 59. It is important to keep in mind that while applicants do not intend to be bound by any specific theory with respect to the function of the Ti+O+C+N transition coating layer, it is thought that the Ti+O+C+N transition coating layer functions to promote the nucleation and adherence of the coating layers of the multi-layered coating scheme.
The multi-layered coating scheme 69 is on the Ti+O+C+N transition coating layer 60 wherein the multi-layered coating scheme 69 comprises a plurality of coating sets (64, 70). Coating set 64 comprises an aluminum oxide coating layer 66 and a TiN coating layer 68, and coating set 70 comprises an aluminum oxide coating layer 72 and a TiN coating layer 74. Although not shown in
Table 3 below sets forth the ranges of the thicknesses of the coating schemes and coating layers for the coated cutting insert 30 illustrated in
Table 4 below sets forth the deposition parameters for the deposition of the coating scheme 52A of the coated cutting insert 50 of
Referring to the microstructure of the coated cutting insert shown in the photomicrograph
Referring to the coating scheme shown in
There is a Ti+O+C+N transition coating layer 139 containing titanium and oxygen and carbon and nitrogen on the TiCN coating layer 140. It is important to keep in mind that while applicants do not intend to be bound by any specific theory with respect to the function of the Ti+O+C+N transition coating layer, it is thought that the Ti+O+C+N transition coating layer functions to promote the nucleation and adherence of the coating layers of the multi-layered coating scheme.
A multi-layered coating scheme 141 is on the Ti+O+C+N transition coating layer 139 wherein the multi-layered coating scheme 141 comprises a plurality of coating sets (146, 152, 158). Coating set 146 comprises an aluminum oxide coating layer 148 and a TiAlOCN coating layer 150. Coating set 152 comprises an aluminum oxide coating layer 154 and a TiAlOCN coating layer 156. Coating set 158 comprises an aluminum oxide coating layer 160 and a TiAlOCN coating layer 162. In one embodiment of the invention, the outermost repeating layer is exposed. In another embodiment of the invention, there is an optional outer coating layer scheme that can be applied via CVD to the surface of the outermost layer of the repeating set. The specific embodiment of
up to 2
up to 1
Table 6 below sets forth the deposition parameters for the deposition of the coating scheme 133 of the coated cutting insert 130 of
5-20.
1-4.5
1-1.5
1-5.5
1-1.5
Cutting tests were conducted to evaluate the performance of the coated cutting inserts of the invention as compared to standard conventional coated cutting inserts. Tables 7 and 8 sets forth test results as measured in number of passes using the following wear criteria: The tests were conducted under the following parameters: cutting insert geometry CNMG432RN (straight cutting edge style); lead angle 0°/90°; cutter diameter=2.48 inches; maximum tool diameter=2.48 inches; length of pass=12 inches; MMR=1.95 inches3/minute; cutting speed=820 surface feet per minute; revolutions per minute=1263; program chip load (fz)=0.008 ipt; feed rate (Vf)=10.104 ipm; axial depth of cut (Ap)=0.098 inch; radial depth of cut (Ae)=1.969 inch; machine=Mazak AJV; coolant=dry; and work material DCI 80-55-06.
A key characteristic in the failure mode of a coating structure described in this invention is the wear mechanism exhibited during a heavily interrupted chip forming process. In interrupted cutting operations, the coating experiences an impact every time it engages with the workpiece material. Successive impacts can result in fatigue failure of the coating resulting in flaking through one or more layers in conventional coatings. In the inventive coating described herein, failure of a single coating layer unit does not compromise the integrity of the entire coating scheme because a crack is dissipated between coating layer units (e.g., pair of coating layers comprising Al2O3—Ti-containing layer). In other words, the present inventive coating scheme limits the extent of damage to a specific single coating layer step (or Al2O3—Ti-containing coating layer pair) thereby preventing the propagation of a crack(s) throughout the entire coating scheme. The failure of a single coating layer step (or Al2O3—Ti-containing coating layer pair) does not compromise the integrity of the overall coating scheme including the underlying Al2O3—Ti-containing coating layer pairs. This feature is shown in
The coating scheme of
The conventional coating scheme of a conventional tool is shown in
The substrate for each one of the specific embodiments can be selected from the same group of materials. In this regard, suitable materials for the substrate include cemented carbides (e.g., tungsten carbide-cobalt materials). Another preferred substrate material is based on cobalt cemented tungsten carbide that comprises between about 0.1 weight percent and about 20 weight percent cobalt and the balance tungsten carbide. It is possible that such a cobalt cemented tungsten carbide may include additives like titanium, tantalum, niobium, zirconium, hafnium, vanadium, and chromium either alone or in any combination wherein these additives may be in the form of carbides and/or nitrides and/or carbonitrides, as well as other additives typically added to cemented carbides. In still another composition, the substrate comprises a cemented tungsten carbide comprising: between about 89.8 weight percent and about 92.3 weight percent tungsten carbide, between about 5.7 weight percent and about 11.5 weight percent cobalt, up to about 3.0 weight percent tantalum, up to about 2 weight percent titanium, up to about 2.4 weight percent niobium, and up to about 0.80 weight percent chromium.
Applicants also contemplate that the substrate could exhibit gradient compositions, especially in the binder concentration, the carbonitride concentration and the carbide concentration. Exemplary substrates could include a cemented carbide substrate that presents a surface zone of binder enrichment or a cemented carbide substrate that exhibits a surface zone of binder depletion of solid solution carbide enrichment.
For each one of the specific embodiments, it should be appreciated that prior to the deposition of the coating scheme the surface of the substrate may be treated so as to improve the adhesion of the coating scheme to the substrate. Exemplary pre-treatments include a process to remove or reduce the level of binder at the surface of the substrate. In the case of the cobalt cemented tungsten carbide substrate such a pre-treatment would remove cobalt from the surface of the substrate or treat the surface to improve the coating adhesion. Another exemplary pre-treatment would be a process that mechanically works the surface of the substrate so as to roughen the surface of the substrate making it ready to produce good coating adhesion.
It should be appreciated that in some instances the surface of the coating scheme may be subjected to a post-deposition treatment so as to improve performance by smoothening and producing a stress altering effect on the coating. One exemplary treatment is the removal of asperities from the surface of the coating scheme so as to reduce or minimize any stress riser sites. Another exemplary treatment is to preferentially remove the coating (or a part of the coating layer) from selected areas of the cutting insert. A surface treatment typically reduces the tensile stresses or increases the compressive stresses in the coating layer(s). For example, PCT Patent Publication No. WO 02/077312 to Widia GmbH discloses shot blasting a coating (PVD or PCVD or CVD) to increase internal pressure stress or reduce internal tension stress in the outer coating layers.
Furthermore, it should be appreciated that to improve adhesion of the coating layers there may be provided microscopically rough interfaces between each of the coating layers. These microscopically rough interfaces can be generated by controlling the CVD (or moderate temperature chemical vapor deposition [MT-CVD]) parameters so as to promote high growth rates for the coating layers. High growth rates in CVD (including MT-CVD processes) processes may occur by the use of relatively high deposition temperatures and/or relatively high pressures. As another alternative to improve adhesion between coating layers, in the deposition process the composition can be gradually changed between adjacent layers so as to reduce the existence of a sharp compositional interface between adjacent coating layers.
In view of the above, it can be appreciated that there is provided an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating scheme with a high toughness resulting in better edge integrity, especially during heavily interrupted turning and milling operations. There is provided an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating scheme which includes a multi-layered coating scheme that better inhibits crack growth and propagation in the coating scheme whether due to mechanical stresses or thermal cycling. There is provided an improved coated cutting insert, and a method of making the same, wherein the cutting insert is useful in material removal applications wherein the coated cutting insert has a coating that includes a transition coating layer that functions to promote better nucleation and adhesion of the multi-layered coating scheme.
The patents and other documents identified herein are hereby incorporated by reference herein. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or a practice of the invention disclosed herein. It is intended that the specification and examples are illustrative only and are not intended to be limiting on the scope of the invention. The true scope and spirit of the invention is indicated by the following claims.
