Coatings and coated cutting tools comprising said coatings

Abstract

The present invention discloses a coating and a coated cutting tool including the coating. The coating includes a layer having an alumina matrix and at least one of zirconia grains and hafnium dioxide grains in the alumina matrix. The average grain size of the at least one of the zirconia grains and the hafnium dioxide grains is 100 nm or less. A coated cutting tool includes a substrate and a coating bonded to the substrate. The substrate has a rake face, a flank face, and a cutting edge formed at an intersection of the rake face and the flank face.

Description

Technical Field

[0001] This application relates to the field of coatings, and more particularly, to coatings for cutting tools. Background Art

[0002] Cutting tools, including cemented carbide cutting tools, have been used for machining various metals and alloys in both coated and uncoated conditions. To improve the wear resistance, performance, and lifespan of cutting tools, one or more refractory layers have been applied to the cutting tool surface. For example, TiC, TiCN, TiN, and / or Al2O3 have been applied to a cemented carbide substrate by chemical vapor deposition (CVD) and physical vapor deposition (PVD). Although wear can be effectively inhibited and tool lifespan extended in various applications, refractory coatings based on single or multiple layer configurations of the aforementioned refractory materials have increasingly approached their performance limits, and thus there is a need to develop new coating structures for cutting tools. Summary of the Invention

[0003] In one embodiment, a coating includes a layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix. The average grain size of the at least one of the zirconia grains and the hafnia grains is 100 nm or less.

[0004] The average grain size of the at least one of the zirconia grains and the hafnia grains can be in the range of 1 nm to 80 nm.

[0005] The average grain size of the at least one of the zirconia grains and the hafnia grains can be in the range of 1 nm to 40 nm.

[0006] The average grain size of the at least one of the zirconia grains and the hafnia grains can be in the range of 40 nm to 80 nm.

[0007] The at least one of the zirconia grains and the hafnia grains can include grains having at least one of a tetragonal crystal structure, a monoclinic crystal structure, and an orthorhombic crystal structure.

[0008] The at least one of the zirconia grains and the hafnia grains can be mainly disposed within the grains of the alumina matrix.

[0009] The at least one of the zirconia grains and the hafnia grains can be mainly disposed at the grain boundaries of the alumina matrix.

[0010] The layer can have a thickness of 0.1 μm to 25 μm.

[0011] In another embodiment, a coated cutting tool includes a substrate and a coating bonded to the substrate. The substrate has a rake face, a flank face, and a cutting edge formed at the intersection of the rake face and the flank face. The coating includes a layer having an alumina matrix and at least one of zirconia grains and hafnium dioxide grains in the alumina matrix. The average grain size of at least one of the zirconia grains and the hafnium dioxide grains is 100 nm or less.

[0012] The average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 1 nm to 80 nm.

[0013] The average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 1 nm to 40 nm.

[0014] The average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 40 nm to 80 nm.

[0015] At least one of the zirconia grains and the hafnium dioxide grains can include grains having at least one of a tetragonal crystal structure, a monoclinic crystal structure, and an orthorhombic crystal structure.

[0016] In one aspect, at least one of the zirconia grains and the hafnium dioxide grains can be mainly disposed within the grains of the alumina matrix.

[0017] At least one of the zirconia grains and the hafnium dioxide grains can be mainly disposed at the grain boundaries of the alumina matrix.

[0018] The layer can have a thickness of 0.1 μm to 25 μm.

[0019] Other embodiments of the disclosed coatings and coated cutting tools will become apparent from the following detailed description, the drawings, and the appended claims. Description of the Drawings

[0020] Figure 1 A cutting insert substrate according to an example of the present specification is shown.

[0021] Figure 2A and 2B is a TEM image of the Al2O3-ZrO2 nanocomposite coating of the present specification.

[0022] Figure 3A 、 3B and 3C are SEM images of micron-sized ZrO2 formed by continuously introducing Zr into the coating system.

[0023] Figure 4A , 4B and 4C are SEM images of nanoscale ZrO2, which is formed by introducing Zr pulses into the coating system, and the formed ZrO2 preferably segregates at grain boundaries.

[0024] Figure 5A , 5B and 5C are SEM images of nanoscale ZrO2, which is formed by introducing Zr pulses into the coating system, and the formed ZrO2 has an intragranular grain structure and the average grain size of ZrO2 is less than 100 nm. Detailed Description

[0025] The embodiments described herein can be more readily understood by reference to the following detailed description and examples, as well as its previous description and the following description. However, the elements, devices, and methods described herein are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments merely illustrate the principles of this specification. Many modifications and adaptations will be apparent to those skilled in the art without departing from the spirit and scope of this specification.

[0026] According to this specification, a coating comprises a layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix. The coating can be a single-layer coating on a substrate, or can be a multi-layer coating on a substrate, the coating comprising at least one layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix, and optionally one or more other layers.

[0027] Even at high temperatures, the alumina matrix has oxidation resistance. Pure alumina is prone to cracking. At least one of zirconia grains and hafnia grains in the alumina matrix is added to the alumina matrix to increase the crack growth resistance of the alumina matrix.

[0028] The average grain size of at least one of the zirconia grains and the hafnium dioxide grains is 100 nm or less. The small grain size of at least one of the zirconia grains and the hafnium dioxide grains can provide high hardness based on the Hall-Petch effect. At the same time, grain refinement can make the formed zirconia present a preferred phase, such as the tetragonal phase. Then, this phase may ultimately contribute to toughening the alumina matrix. Preferably, the average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 1 nm to 80 nm. For example, the average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 1 nm to 40 nm, or the average grain size of at least one of the zirconia grains and the hafnium dioxide grains can be in the range of 40 nm to 80 nm.

[0029] At least one of the zirconia grains and the hafnium dioxide grains may include grains having a tetragonal crystal structure, a monoclinic crystal structure, or an orthorhombic crystal structure. Zirconia grains or hafnium dioxide grains refined to the nanoscale tend to form a tetragonal crystal structure. The tetragonal phase is preferably more suitable for toughening the alumina matrix.

[0030] At least one of the zirconia grains and the hafnium dioxide grains may be mainly disposed within the grains of the alumina matrix, or at least one of the zirconia grains and the hafnium dioxide grains may be mainly disposed at the grain boundaries of the alumina matrix. Placing at least one of the zirconia grains and the hafnium dioxide grains within the grains of the alumina matrix is beneficial for toughening the alumina matrix to resist intragranular cracking. Placing at least one of the zirconia grains and the hafnium dioxide grains at the grain boundaries of the alumina matrix is beneficial for toughening the alumina matrix to resist intergranular cracking. The strengthening mechanism can be based on grain boundary strengthening caused by the dispersed nanoscale second phase of zirconia. The placement of at least one of the zirconia grains and the hafnium dioxide grains can be determined based on the overall structure of the coating. The placement of at least one of the zirconia grains and the hafnium dioxide grains can be selected by controlling the deposition conditions.

[0031] The average grain size of the alumina matrix is greater than the average grain size of at least one of the zirconia grains and the hafnium dioxide grains. In one aspect, the average grain size of the alumina matrix is 200 nm or greater. In another aspect, the average grain size of the alumina matrix is 500 nm or greater. In yet another aspect, the average grain size of the alumina matrix is 1 micron or greater. However, a small average grain size of the alumina matrix is preferred.

[0032] A layer having an alumina matrix and at least one of zirconia grains and hafnium dioxide grains in the alumina matrix can have any thickness consistent with the objective of the coating. For example, the layer can have a thickness of 0.1 μm to 25 μm.

[0033] A layer having an alumina matrix and at least one of zirconia grains and hafnium dioxide grains in the alumina matrix can be coated in any manner consistent with the objectives of this specification.

[0034] This specification provides the following method for preparing a layer using chemical vapor deposition (CVD).

[0035] By controlling the zirconium introduction method, the selection of the Al / Zr introduction ratio, and other processing conditions, uniformly distributed nanoscale ZrO2 grains (at least one dimension less than 100 nm) can be produced. In one case, the formed ZrO2 grains tend to precipitate / segregate at grain boundaries. In another case, under alternative deposition conditions, the formed ZrO2 grains can be uniformly incorporated in the Al2O3 matrix to form mixed Al2O3-ZrO2 composite grains. As Figure 2A and 2B shown, transmission electron microscopy (TEM) observations have determined that ZrO2 grains in the range of 50 nm to several tens of nm have been formed.

[0036] To achieve a layer having an alumina matrix and at least one of zirconia grains and hafnium dioxide grains in the alumina matrix, a second phase beyond the matrix is introduced into the coating system. The introduction method of the second source material determines the final product. As Figure 3A 、 3B and 3C shown, by continuously introducing Zr into the coating system, an Al2O3 and ZrO2 composite can be formed at the micron scale together with ZrO2 grains.

[0037] To achieve refinement of the second phase of ZrO2, the Zr source is introduced in a pulsed mode, and the ratio between Al / Zr is selected to be 1.5 or greater. More preferably, the Al / Zr ratio can be greater than 2. Additionally, after introducing the Al / Zr mixture, a pure Al environment is used for ZrO2 grain refinement. The pure Al environment provides a pure Al2O3 deposition step, which refines ZrO2 grains by terminating the ZrO2 grains formed together with the Al / Zr mixture.

[0038] CVD deposition combines the temperature, gas flow, and partial pressure in the reactor, so the coating growth kinetics are also restricted by these factors. At 850 - 950 °C, ZrO2 grains are formed with an average grain size less than 100 nm, more favorably with an average grain size of 40 - 80 nm in the case of grain boundary segregation, as Figure 4A 、 4B and 4C shown.

[0039] As Figure 5A 、 5B, as shown in 5C, the structure of the grains within the nanoscale grains of the second-phase ZrO2 is directly introduced into the Al2O3 matrix by CVD. By controlling the deposition conditions, a high ZrO2 density of more than 300 per square micron and ZrO2 grains with an average grain size in the range of 40 - 100 nm are formed.

[0040] The pulse step size, the Al / Al + Zr ratio of the pure Al step size, the deposition duration, the temperature, the gas flow rate, and the introduction of other gas flows containing H2S and CO2 can play a role in the coating microstructure formation. A ratio of Al / Al + Zr and a short deposition time result in fine ZrO2 grains. The temperature can control atomic diffusion and segregation, and then cause grain boundary enrichment and alumina matrix inclusions. The CO2 flow controls the formation of H2O, thus determining the reaction kinetics. H2S is a crystal growth promoter and also affects the nucleation density and grain growth behavior.

[0041] Table 1 below describes exemplary non-limiting parameters for using CVD to deposit an alumina matrix and nanosized zirconia and hafnia grains in the alumina matrix.

[0042] Table 1

[0043]

[0044] According to the present specification, a coated cutting tool includes a substrate and a coating bonded to the substrate. The substrate of the coated cutting tool typically has a rake face, a flank face, and a cutting edge formed at the intersection of the rake face and the flank face.

[0045] In one aspect, a cutting tool is described that includes a refractory coating having a composite structure. In some embodiments, a cutting tool having such a refractory coating is suitable for high wear and / or abrasion applications, such as metal cutting operations.

[0046] Turning now to the specific components, the coated cutting tool includes a substrate. The coated article can include any substrate consistent with the objectives of the present specification. The cutting tool includes, but is not limited to, an indexable cutting insert, an end mill, a saw blade, or a drill bit.

[0047] The indexable cutting insert can have any desired ANSI standard geometry for milling or turning applications. The substrate of the coated article described herein can be formed of cemented carbide, carbide, polycrystalline diamond, polycrystalline cubic boron nitride, ceramic, cermet, steel, or other alloys.

[0048] In some embodiments, the cemented carbide substrate includes tungsten carbide (WC). WC can be present in the cutting tool substrate in any amount consistent with the objectives of this specification. For example, WC can be present in an amount of at least 70 wt%, at least 80 wt%, or at least 85 wt%. Additionally, the metallic binder of the cemented carbide can include cobalt or a cobalt alloy. For example, cobalt can be present in the cemented carbide substrate in an amount in the range of 1 wt% to 15 wt%. In some embodiments, cobalt is present in the cemented carbide substrate in an amount in the range of 5 wt% to 12 wt% or in the range of 6 wt% to 10 wt%. Further, the cemented carbide substrate can exhibit a binder enrichment region that begins at the surface of the substrate and extends inwardly from the surface of the substrate.

[0049] The cemented carbide substrate can further include one or more additives, such as one or more of the following elements and / or their compounds: titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium. In some embodiments, titanium, niobium, vanadium, tantalum, chromium, zirconium, and / or hafnium form a solid solution carbide with the WC of the substrate. In such embodiments, the substrate can include one or more solid solution carbides in an amount in the range of 0.1 wt% to 5 wt%. Additionally, the cemented carbide substrate can include nitrogen.

[0050] The cutting tool substrate generally includes one or more cutting edges formed at the junction of the rake face of the substrate and at least one flank face. Figure 1 A cutting insert substrate according to an example described herein is shown. As Figure 1 shown, the substrate 10 has a cutting edge 12 formed at the junction of the rake face 14 and the flank face 16 of the substrate. The substrate 10 further includes a hole 18 for securing the substrate 10 to a tool holder. The substrate 10 has various geometries and configurations, for example, with or without a chip breaker, mounting holes, or positive or negative rake angles.

[0051] A layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix can be directly deposited on the substrate surface. Alternatively, a multi-layer coating having at least one layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix can further include one or more inner layers between the substrate and the layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix.

[0052] In some embodiments, one or more inner layers may include one or more metal elements selected from the group consisting of aluminum and the metal elements of Groups IVB, VB, and VIB of the periodic table, and one or more non-metal elements selected from Groups IIIA, IVA, VA, and VIA of the periodic table. More specifically, one or more inner layers may include carbides, nitrides, carbonitrides, oxycarbonitrides, oxides, or borides of one or more metal elements selected from the group consisting of aluminum and the metal elements of Groups IVB, VB, and VIB of the periodic table.

[0053] For example, one or more inner layers may be selected from the group consisting of titanium nitride, titanium carbonitride, titanium oxycarbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, zirconium oxycarbonitride, zirconium carbide, hafnium nitride, and hafnium carbonitride. Additionally, a titanium oxycarbonitride layer may be employed as an adhesion layer between one or more inner layers and a layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix.

[0054] One or more inner layers of the coating may have any thickness consistent with the objectives of the present specification. For example, a single inner layer may have a thickness of at least 1.5 μm. Alternatively, multiple inner layers may together achieve a thickness of at least 1.5 μm.

[0055] Table 2 below describes exemplary parameters for depositing exemplary inner layers using CVD.

[0056] Table 2

[0057]

[0058] A layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix may be the outermost layer of the coating. Alternatively, the coatings described herein may include one or more outer layers over a layer having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix. One or more outer layers may include one or more metal elements selected from the group consisting of aluminum and the metal elements of Groups IVB, VB, and VIB of the periodic table, and one or more non-metal elements selected from Groups IIIA, IVA, VA, and VIA of the periodic table. More specifically, one or more outer layers may include carbides, nitrides, carbonitrides, oxycarbonitrides, oxides, or borides of one or more metal elements selected from the group consisting of aluminum and the metal elements of Groups IVB, VB, and VIB of the periodic table. For example, one or more outer layers may be selected from the group consisting of titanium nitride, titanium carbonitride, titanium oxycarbonitride, titanium carbide, zirconium nitride, zirconium carbonitride, hafnium nitride, hafnium carbonitride, and alumina and mixtures thereof.

[0059] One or more outer layers as described herein can have any thickness consistent with the objectives of this specification. In some embodiments, the coating outer layer can have a thickness in the range of 0.2 μm to 5 μm.

[0060] The coatings described herein can undergo post - coating treatments. The coatings can, for example, be sand - blasted with various wet and / or dry particle compositions. The post - coating sand - blasting can be applied in any desired manner. In some embodiments, the post - coating sand - blasting includes shot - peening or pressure sand - blasting. The pressure sand - blasting can be applied in various forms, including compressed air sand - blasting, wet compressed air sand - blasting, pressure liquid sand - blasting, wet sand - blasting, and steam sand - blasting. For example, wet sand - blasting is achieved using a slurry of inorganic and / or ceramic particles such as alumina and water. The particle slurry can be pneumatically sprayed onto the surface of the coated cutting tool body to impact the surface of the coating. The size of the inorganic and / or ceramic particles generally can be in the range between 20 μm and 100 μm.

[0061] The sand - blasting parameters include pressure, impact angle, distance from the component surface, and duration. In some embodiments, the impact angle can be in the range of 5° to 90°, i.e., the particles impact the coating surface at an angle in the range of 5° to 90°. At a distance of 1 - 6 inches from the coated surface, a suitable pressure can be in the range of 30 - 55 pounds per square inch (psi). Additionally, the duration of the sand - blasting can generally be in the range of 1 - 10 seconds or longer. The sand - blasting can be applied generally over the surface area of the coating or can be applied to selected locations, such as the workpiece contact area of a cutting tool. The workpiece contact area can be the honing area of a cutting tool.

[0062] In other embodiments, the coating undergoes post - coating polishing treatment. The polishing can be applied using a paste having an appropriate diamond or ceramic grit size. In some embodiments, the grit size of the paste is in the range of 1 μm to 10 μm. In one embodiment, the coating is polished using a diamond grit paste with a size of 5 - 10 μm. Additionally, the grit paste can be applied to the coating by any device consistent with the objectives of this specification, such as a brush. In one embodiment, for example, a flat brush is used to apply the grit paste to the coating in the workpiece contact area of a cutting tool.

[0063] The coatings described herein can be sand - blasted or polished for a period of time sufficient to achieve a desired surface roughness and / or other parameters such as reducing the residual tensile stress of the coating.

[0064] In addition, in some embodiments, the post - coating treatment does not remove one or more outer layers of the coating, such as the outer layers of TiN, TiCN, TiOCN, TiC, ZrN, ZrC, ZrCN, ZrOCN, HaN, HaC, HaCN, and / or HaOCN. Alternatively, the post - coating treatment may remove or partially remove one or more outer layers.

[0065] Table 3 below describes exemplary properties of coatings including a layer having an alumina matrix and at least one of zirconia grains and hafnia grains with an average grain size of 100 nm or less in the alumina matrix.

[0066] Table 3

[0067]

[0068] Example A shows the case of grain - boundary segregation, while Example B shows the case of second - phase inclusion into the Al2O3 matrix.

[0069] Although various embodiments of the disclosed coatings and coated cutting inserts have been shown and described, those skilled in the art can make modifications after reading the specification. This application encompasses such modifications and is limited only by the scope of the claims.

Claims

1. A coating, comprising: A layer deposited by chemical vapor deposition having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix, wherein an average grain size of the at least one of the zirconia grains and the hafnia grains is 100 nm or less.

2. The coating according to claim 1, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 1 nm to 80 nm.

3. The coating according to claim 1, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 1 nm to 40 nm.

4. The coating according to claim 1, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 40 nm to 80 nm.

5. The coating according to claim 1, wherein the at least one of the zirconia grains and the hafnia grains comprises grains having at least one of a tetragonal crystal structure, a monoclinic crystal structure, and an orthorhombic crystal structure.

6. The coating according to claim 1, wherein the at least one of the zirconia grains and the hafnia grains is mainly disposed within grains of the alumina matrix.

7. The coating according to claim 1, wherein the at least one of the zirconia grains and the hafnia grains is mainly disposed at grain boundaries of the alumina matrix.

8. The coating according to claim 1, wherein the layer has a thickness of 0.1 μm to 25 μm.

9. A coated cutting tool, comprising: A substrate (10) having a rake face (14), a flank face (16), and a cutting edge (12) formed at an intersection of the rake face (14) and the flank face (16); and A coating bonded to the substrate (10), the coating comprising a layer deposited by chemical vapor deposition having an alumina matrix and at least one of zirconia grains and hafnia grains in the alumina matrix, wherein an average grain size of the at least one of the zirconia grains and the hafnia grains is 100 nm or less.

10. The coated cutting tool according to claim 9, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 1 nm to 80 nm.

11. The coated cutting tool according to claim 9, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 1 nm to 40 nm.

12. The coated cutting tool according to claim 9, wherein the average grain size of the at least one of the zirconia grains and the hafnia grains is in a range of 40 nm to 80 nm.

13. The coated cutting tool according to claim 9, wherein at least one of the zirconia grains and the hafnium dioxide grains comprises grains having at least one of a tetragonal crystal structure, a monoclinic crystal structure, and an orthorhombic crystal structure.

14. The coated cutting tool according to claim 9, wherein at least one of the zirconia grains and the hafnium dioxide grains is mainly disposed within the grains of the alumina matrix.

15. The coated cutting tool according to claim 9, wherein at least one of the zirconia grains and the hafnium dioxide grains is mainly disposed at the grain boundaries of the alumina matrix.

16. The coated cutting tool according to claim 9, wherein the layer has a thickness of 0.1 μm to 25 μm.

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