Titanium nitride-based coated superhard tool and method of manufacture

Abstract

A kind of titanium nitride-based coating superhard cutter and its manufacturing method, it is related to coating cutter technical field, including cutter base body, Ti buffer layer, TiN-based hard layer, Ti buffer layer includes the initial titanium layer deposited on the cutter base body, and Ti / TiN mixed layer in the direction of initial titanium layer away from cutter base body;Ti / TiN mixed layer is loose titanium layer: located in the lower part un-nitrided loose titanium layer has vertical, the side wall of the cavity and / or crack is nitrided to form titanium nitride layer;Loose titanium layer in the upper part is nitrided to form titanium nitride layer, and it has vertical metal titanium inside.The present application first grows the Ti buffer layer of conventional thickness, guarantees titanium layer quality: whether initial titanium layer or loose titanium layer, since having sufficient incubation thickness, film layer quality is high, then Ti loose layer is nitrided to thin, reduce the thickness of final Ti buffer layer, improve the strength of Ti buffer layer.

Description

Technical Field

[0001] This invention relates to the field of coated cutting tool technology, specifically to a titanium nitride-based coated superhard cutting tool and its manufacturing method. Background Technology

[0002] Applying coatings to hard cutting tools such as PCBN can improve tool life and machining accuracy. Titanium nitride-based coatings are commonly used, including TiN, TiAlN, TiCN, and TiCrN. The following explanation uses TiN hard layers as an example, but it is understood that the same principles apply to TiAlN, TiCN, and TiCrN hard layers.

[0003] When depositing a titanium nitride-based coating on a PCBN cutting tool, one approach is to first deposit a Ti buffer layer on the tool. The buffer layer has the functions of improving the adhesion between the tool and the titanium nitride-based coating, and improving the deposition quality of the titanium nitride-based coating.

[0004] It is generally believed that when a Ti buffer layer is present, excessive impact loads on the coated tool during interrupted or heavy-duty machining are transferred from the TiN coating to the Ti layer, causing rapid coating failure, manifested as coating peeling. This is related to the fact that the strength of the Ti layer (below 10) is significantly lower than that of TiN (20-30). Appropriately reducing the thickness of the Ti buffer layer is beneficial to improving the strength of the coating on the tool. Reducing the thickness of the Ti buffer layer also facilitates the transfer of thermal stress generated in the TiN during cutting to the Ti layer. It is generally believed that when the buffer layer is thinner, it has high deformation capacity and can absorb the stress of the main coating above without cracking; while when the buffer layer is thicker, it has high strength, resists the intrusion of external stress, and is more prone to cracking under external stress.

[0005] However, the thickness of the Ti buffer layer has a lower limit and cannot be reduced excessively. It is generally not less than 300 nm. Otherwise, it will be difficult to completely cover the PCBN tool surface during deposition to form a continuous and reliable adhesion layer, which is not conducive to the growth of the subsequent nitride layer. Furthermore, the quality of the initially deposited Ti layer is poor, and it needs to go through a deposition incubation process of a certain thickness in order to grow a high-quality and high-strength Ti layer. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a titanium nitride-based coated superhard cutting tool and its manufacturing method. By improving the Ti buffer layer, the anti-stripping performance of the coating and the overall strength of the coating are enhanced.

[0007] The specific technical solution is as follows: it includes a tool substrate, a Ti buffer layer, and a TiN-based hard layer. The Ti buffer layer includes an initial titanium layer deposited on the tool substrate and a Ti / TiN hybrid layer located in the direction away from the tool substrate from the initial titanium layer.

[0008] The Ti / TiN mixed layer is a loose titanium layer: the lower part of the loose titanium layer has a vertical titanium nitride layer formed by nitriding the sidewalls of voids and / or cracks in the middle; the upper part of the loose titanium layer is nitrided to form a titanium nitride layer, which has vertical metallic titanium inside.

[0009] Preferably, the initial titanium layer has a thickness of 50-100 nm; the unnitrided porous titanium layer in the lower part has a thickness of 100-250 nm.

[0010] Preferably, the Ti buffer layer further includes an AlN / Ti cross structure in the direction away from the tool substrate of the Ti / TiN hybrid layer, wherein the starting layer of the AlN / Ti cross structure is an AlN layer and the ending layer is a Ti layer.

[0011] Preferably, the AlN layer in the AlN / Ti cross structure has a thickness of 20-50 nm and the Ti layer has a thickness of 5-20 nm, with the Ti layer thickness being less than the AlN layer thickness.

[0012] Preferably, the tool substrate is one of polycrystalline cubic boron nitride, polycrystalline diamond, and cemented carbide; the TiN-based hard layer is one or a combination of TiN, TiAlN, TiCN, and TiCrN.

[0013] Preferably, the Ti buffer layer further includes an AlN island-shaped film directly deposited on the Ti / TiN hybrid layer, the position of which is aligned with the top of the vertical titanium metal.

[0014] The preparation method of titanium nitride-based coated superhard cutting tools includes the following steps:

[0015] Step (1): Cleaning and drying the tool substrate;

[0016] Step (2): Deposition of the Ti buffer layer, including:

[0017] Step (2.1): First, deposit an initial titanium layer with a thickness of 50-100 nm;

[0018] Step (2.2): Deposit another loose titanium layer with a thickness of 200-500 nm;

[0019] Step (2.3): Deposit another layer of island-grown aluminum nitride with a thickness of 2nm-30nm. Annealing shrinks the island-grown aluminum nitride to further promote the island structure, i.e., AlN island film.

[0020] Step (2.4): Nitriding the porous titanium layer using island-shaped aluminum nitride as a mask;

[0021] Step (2.5): Deposit a continuous AlN layer with a thickness of 20-50 nm, and then deposit a thin Ti layer with a thickness of 5-20 nm; repeat the above steps 1-10 times;

[0022] Step (3): Deposit a TiN-based hard layer with a thickness of, for example, 0.8-6 μm.

[0023] Preferably, the annealing in step (2.3) also causes voids and / or cracks to form in the porous titanium layer.

[0024] Preferably, in step (2.4), the nitriding extends to more than half the depth of the loose titanium layer. That is, in the upper part of the original deposited loose titanium layer, the loose titanium layer not covered by the aluminum nitride mask is nitrided to form a titanium nitride layer, while the lower part of the loose titanium layer is an unnitrided loose titanium layer.

[0025] Preferably, in step (2.4), the titanium layer directly below the aluminum nitride island layer does not undergo nitriding, thereby retaining vertical metallic titanium in the nitrided titanium nitride layer, and the sidewalls of the voids and / or cracks in the remaining, unnitrided, porous titanium layer undergo nitriding to form voids and / or cracks in the nitrided titanium material.

[0026] This invention provides a titanium nitride-based coated superhard cutting tool and its manufacturing method, which has the following advantages compared with the prior art:

[0027] (1): The present invention first grows a Ti buffer layer of conventional thickness to ensure the quality of the titanium layer: whether it is the initial titanium layer or the loose titanium layer, the film quality is high due to the sufficient incubation thickness. Then, the loose Ti layer is nitrided to thin it, which reduces the final thickness of the Ti buffer layer and improves the strength of the Ti buffer layer.

[0028] (2): The Ti buffer layer of the present invention has a mixed layer of titanium layer and titanium nitride. This part has both high-strength titanium nitride and high-adhesion / flexibility titanium. The combination of the two further improves the overall strength and impact resistance of the Ti buffer layer (and thus the entire coating). Attached Figure Description

[0029] Figure 1 This is a layered side view of the tool substrate after a Ti buffer layer has been deposited in this invention.

[0030] Figure 2 : This is a diagram of the overall layered structure of the cutting tool of the present invention.

[0031] In the figure: 1-tool substrate, 2-initial titanium layer, 3-Ti / TiN mixed layer, 4-unnitrided porous titanium layer, 5-voids and / or cracks, 6-titanium nitride layer, 7-metallic titanium, 8-AlN layer, 9-Ti layer, 10-TiN-based hard layer, 30-AlN island film. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0034] Example: Figure 2 The invention relates to a titanium nitride-based coated superhard cutting tool, comprising a tool substrate 1, a Ti buffer layer, and a TiN-based hard layer; the Ti buffer layer comprises at least an initial titanium layer 2 and a Ti / TiN hybrid layer 3 located in the direction away from the tool substrate 1 of the initial titanium layer 2.

[0035] The Ti / TiN mixed layer 3 is a loose titanium layer: the middle of the lower part of the unnitrided loose titanium layer 4 has a vertical titanium nitride layer formed by nitriding the sidewalls of voids and / or cracks 5; the upper part of the loose titanium layer is nitrided to form a titanium nitride layer 6, which has vertical metallic titanium 7 inside.

[0036] The initial titanium layer 2 has a thickness of 50-100 nm; the lower part of the unnitrided porous titanium layer 4 has a thickness of 100-250 nm.

[0037] The Ti buffer layer also includes an AlN / Ti cross structure in the direction away from the tool substrate 1 of the Ti / TiN hybrid layer 3. The starting layer of the AlN / Ti cross structure is the AlN layer 8, and it ends with the Ti layer 9.

[0038] In the AlN / Ti cross structure, the AlN layer 8 has a thickness of 20-50 nm, the Ti layer 9 has a thickness of 5-20 nm, and the thickness of the Ti layer 9 is less than that of the AlN layer 8.

[0039] The tool substrate 1 is one of polycrystalline cubic boron nitride, polycrystalline diamond, and cemented carbide, and the TiN-based hard layer 10 is one of TiN, TiAlN, TiCN, TiCrN, or a combination thereof.

[0040] The Ti buffer layer also includes an AlN island-shaped thin film 30 directly deposited on the Ti / TiN hybrid layer 3, which is aligned with the top of the vertical metallic titanium 7.

[0041] The preparation method of the above-mentioned titanium nitride-based coated superhard cutting tool includes the following steps:

[0042] Step (1): Clean and dry the tool substrate 1;

[0043] Step (2): The Ti buffer layer can be deposited by sputtering, ion plating, evaporation, etc.

[0044] The specific process is as follows:

[0045] Step (2.1): First, deposit an initial titanium layer 2 with a thickness of 50-100 nm;

[0046] Step (2.2): Deposit another loose titanium layer. The loose titanium layer is beneficial for absorbing the stress between the substrate and the titanium layer, and also facilitates the subsequent deep nitriding of this layer, reducing the thickness of the Ti buffer layer. The thickness of the loose titanium layer has a lower limit, generally not less than 200 nm, otherwise it is difficult to completely cover the PCBN tool surface and form a continuous and reliable adhesion layer. The preferred thickness of the loose titanium layer is 200-500 nm.

[0047] A porous titanium layer can be obtained by increasing the deposition rate, increasing the gas flow rate, and adjusting the sputtering pressure and power. These are conventional manufacturing processes in the field (see CN1808679A, CN105304510A, CN107359234A), and will not be described in detail here.

[0048] Step (2.3): Deposit another layer of island-shaped aluminum nitride, namely AlN island film 30. This is achieved by reducing the precursor energy reaching the growth surface, preventing it from moving laterally on the surface and instead causing it to grow in clusters. Reducing the energy reaching the surface can be achieved by increasing the deposition gas pressure or reducing power. The aluminum nitride layer thickness should not exceed 30 nm; otherwise, island growth will be difficult to maintain. The preferred thickness of the aluminum nitride layer is 2 nm to 30 nm. The aluminum nitride layer has good thermal stability, remaining stable at 2200℃, and also has high strength. The strength decreases very slowly with increasing temperature, making it suitable for use in high-speed cutting tools that generate high temperatures.

[0049] Island-like refers to a thin film that does not form a continuous layered structure, but rather a dispersed, fragmented shape.

[0050] Annealing causes the island-shaped aluminum nitride to shrink, further promoting the island structure. At the same time, annealing also causes the loose titanium layer to shrink laterally and become denser, releasing stress in the form of cracks and voids. This helps to reduce the overall stress of the tool coating, making the tool less prone to stress spalling during use after leaving the factory.

[0051] Step (2.4): Using the island-shaped aluminum nitride layer as a mask, the porous titanium layer is nitrided, for example, by ammonia plasma treatment. Conventional plasma nitriding typically only reaches a depth of tens of nanometers, as nitrogen plasma has difficulty penetrating the dense, thick titanium nitride layer and the underlying titanium to continue the reaction. However, since this layer is a porous titanium layer during deposition, nitriding can penetrate to more than half the depth of the porous titanium layer, meaning the thickness of the porous titanium layer undergoing nitriding is at least 100-250 nm. Of course, the titanium layer directly below the aluminum nitride layer does not undergo nitriding; that is, the island-shaped aluminum nitride layer acts as a mask for the nitriding process, thus retaining vertically oriented metallic titanium 7, such as columnar structures, in the nitrided titanium nitride layer. The remaining lower part is an unnitrided loose titanium layer 4. Although it is not nitrided as a whole, the cracks and voids caused by annealing are generally penetrating and extend to the bottom of the loose titanium layer. The cracks and voids allow nitrogen plasma to reach without obstruction, which leads to the nitriding of the voids and / or cracks 5 sidewalls in the bottom unnitrided loose titanium layer 4.

[0052] After the loose titanium layer is nitrided, the following coating structure is formed ( Figure 1 The initial titanium layer 2 remains unchanged. Above it is a loose, unnitrided titanium layer 4 with a thickness of no more than 100-250 nm (e.g., 100 nm, 150 nm, 200 nm), containing vertically penetrating titanium nitride sidewalls. This layer is entirely composed of metallic titanium 7, exhibiting good toughness, and contains high-strength titanium nitride material voids and / or cracks 5 as sidewalls. Above this is a titanium nitride layer 6 (formed by nitriding the loose titanium layer), containing vertical metallic titanium 7 (below the aluminum nitride layer). This layer is entirely composed of titanium nitride, exhibiting high strength, and contains metallic titanium with good toughness. Above this is an island-shaped aluminum nitride layer, i.e., an AlN island-shaped thin film 30. For ease of expression, the unnitrided loose titanium layer (with high-strength titanium nitride material voids and / or cracks 5 as sidewalls) and the titanium nitride layer 6 (with metallic titanium 7 as sidewalls) are collectively referred to as the Ti / TiN mixed layer 3. Vertical titanium refers to titanium that penetrates the vertical thickness of the layer it is in, not that titanium must be in a vertical direction; the same applies to vertical titanium nitride sidewalls.

[0053] Step (2.5): Deposit a continuous AlN layer 8 with a thickness of 20-50 nm, and then deposit a thin Ti layer 9 with a thickness of 5-20 nm; repeat steps 1 to 10 times; starting with AlN layer 9 and ending with Ti layer 8. The total thickness of the AlN / Ti cross structure does not exceed 200 nm.

[0054] In the AlN / Ti cross-structure, each titanium layer is very thin, which is beneficial for absorbing the stress of the upper TiN-based hard layer. The thin layer thickness also allows for good deformability, facilitating stress release through layer extension (under tensile stress) or contraction (under compressive stress) without cracking. Furthermore, high-strength AlN layers, thicker than the Ti layers, are inserted between the Ti layers, forming the main material of the cross-structure. This results in high overall strength of the cross-structure, making it less prone to coating peeling from this point. The structure ends with a thin Ti layer, which promotes adhesion to the upper TiN-based hard layer. This multi-periodic structure facilitates the gradual, multi-stage release of stress, preventing stress concentration in a single layer (to avoid cracking of that layer) and absorbing more stress.

[0055] The multi-periodic AlN / Ti / AlN… / Ti structure is beneficial for improving the impact resistance of the Ti buffer layer. Compared to existing technologies, the Ti buffer layer in this application is thinner, thus increasing its strength, particularly its resistance to lateral slippage parallel to the film direction. However, the toughness perpendicular to the film direction (compared to the thicker Ti layers in existing technologies) is slightly reduced. To compensate, the AlN / Ti multi-periodic structure can absorb impacts perpendicular to the film direction. In other words, the AlN / Ti / AlN… / Ti multi-periodic structure works in conjunction with the structures of the initial titanium layer and the Ti / TiN hybrid layer.

[0056] Step (3): Deposit a TiN-based hard layer 10. The deposition method can be sputtering, ion plating, evaporation, etc. The thickness of the TiN-based hard layer is, for example, 0.8-6 μm. The TiN-based hard layer includes one or a combination of TiN, TiAlN, TiCN, and TiCrN. Using two or more hard layers at the same time can further optimize the performance of the hard layer. For example, a high-strength layer such as TiAlN can be used as the lower layer and TiN can be used as the surface layer to improve the lubricity of the coating.

[0057] Example 1: The preparation method of the above-mentioned titanium nitride-based coated superhard cutting tool includes the following steps:

[0058] Step (1): Clean and dry the cubic boron nitride (PCBN) tool substrate 1;

[0059] Step (2): Deposition of the Ti buffer layer;

[0060] The specific process is as follows:

[0061] Step (2.1): First, deposit an initial titanium layer with a thickness of 50 nm;

[0062] Step (2.2): Deposit another loose titanium layer with a thickness of 200 nm;

[0063] Step (2.3): Deposit another layer of island-grown aluminum nitride, with a thickness of 2-5 nm;

[0064] Island-like refers to a thin film that does not form a continuous layered structure, but rather a dispersed, fragmented shape.

[0065] Annealing causes the island-shaped aluminum nitride to shrink, further promoting the island structure. At the same time, annealing also causes the loose titanium layer to shrink laterally and become denser, releasing stress in the form of cracks and voids.

[0066] Step (2.4): Using island-shaped aluminum nitride as a mask, the porous titanium layer is nitrided. The nitriding can penetrate to more than half the depth of the porous titanium layer, that is, the thickness of the nitrided porous titanium layer is at least 100-250 nm. Of course, the titanium layer directly below the aluminum nitride layer is not nitrided, thus retaining vertically oriented metallic titanium in the nitrided titanium nitride layer. The remaining, unnitrided bottom porous titanium layer, the voids and / or cracks 5 in the lower part of the unnitrided porous titanium layer will be nitrided.

[0067] Step (2.5): Deposit a continuous AlN layer with a thickness of 20-50 nm, then deposit a thin Ti layer with a thickness of 5-20 nm; repeat steps 1 to 10 times; start with an AlN layer and end with a Ti layer. The total thickness of the AlN / Ti cross structure does not exceed 200 nm.

[0068] Step (3): Deposit TiN-based hard layer 10 with a thickness of 0.8-6 μm.

[0069] Example 2: The difference from Example 1 is that the initial titanium layer thickness is 80nm, the loose titanium layer thickness is 300nm, the aluminum nitride layer thickness is 5-10nm, and the TiN-based hard layer is TiAlN.

[0070] Example 3: The difference from Example 1 is that the initial titanium layer thickness is 100 nm, the loose titanium layer thickness is 500 nm, the aluminum nitride layer thickness is 10-15 nm, and the TiN-based hard layer is TiCN.

[0071] Comparative Example 1: The difference from Example 1 is that in step (2.5): a continuous AlN layer with a thickness of 20-50 nm is deposited, and then a thin Ti layer with a thickness of 5-20 nm is deposited; the above steps 1 to 10 times are repeated; starting with an AlN layer and ending with an AlN layer.

[0072] Comparative Example 2: The difference from Example 1 is that step (2.5) is missing, i.e., there is no AlN / Ti cross structure.

[0073] Comparative Example 3: The difference from Example 1 is that the initial titanium layer thickness is 500 nm, and there is no Ti / TiN mixed layer 3.

[0074] For the cutting tools of Examples 1-3 and Comparative Examples 1-3, 10 tools from each example were selected for coating quality testing. The test involved cutting a hardened steel workpiece with dimensions of Φ110mm × 300mm at a cutting speed of 100m / min. The average time for the crater wear of the cutting tool to spread to the negative chamfer of the tool was used as the comparison standard for coating quality.

[0075] Table 1 shows the average time for the crater wear to spread to the negative chamfer of the tool.

[0076] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Time / min 18 23 21 16.3 14 10.6

[0077] As can be seen, this application significantly improves the tool life by reducing the thickness of the Ti buffer layer, introducing a suitable Ti / TiN hybrid buffer layer, and cooperating with the AlN / Ti cross structure.

[0078] Although the present invention has been specifically shown and described in conjunction with preferred embodiments, there are many methods and approaches to implement this technical solution. The above description is only a preferred embodiment of the present invention. However, those skilled in the art should understand that various changes in form and detail can be made to the present invention without departing from the spirit and scope of the present invention as defined in the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. A superhard tool comprising a tool substrate (1), a Ti buffer layer, a TiN-based hard layer (10) in that order, characterised in that, The Ti buffer layer comprises an initial titanium layer (2) deposited on the tool base body (1), and a Ti / TiN mixed layer (3) deposited on the initial titanium layer (2); The Ti / TiN mixed layer (3) is a loose titanium layer: a vertical titanium nitride layer is formed in the middle of the lower part of the un-nitrided loose titanium layer (4) to nitride the side walls of the cavities and / or cracks (5); the upper part of the loose titanium layer is nitrided to form a titanium nitride layer (6) with vertical metallic titanium (7) inside; The Ti / TiN mixed layer (3) further comprises an AlN / Ti cross structure away from the tool base body (1), the initial layer of the AlN / Ti cross structure is an AlN layer (8), and the end layer is a Ti layer (9).

2. The titanium nitride-based coated superhard cutter of claim 1, wherein, The initial titanium layer (2) has a thickness of 50-100 nm; the un-nitrided loose titanium layer (4) in the lower part has a thickness of 100-250 nm.

3. The titanium nitride-based coated superhard cutter of claim 1, wherein, The AlN layer (8) in the AlN / Ti cross structure has a thickness of 20-50 nm, and the Ti layer (9) has a thickness of 5-20 nm, and the thickness of the Ti layer (9) is less than that of the AlN layer (8).

4. The titanium nitride-based coated superhard cutter of claim 1, wherein, The tool base body (1) is one of polycrystalline cubic boron nitride, polycrystalline diamond, and cemented carbide; the TiN-based hard layer (10) is one of TiN, TiAlN, TiCN, TiCrN, or a combination thereof.

5. The titanium nitride-based coated superhard cutter of claim 1, wherein, The Ti buffer layer further comprises an AlN island film (30) deposited directly on the Ti / TiN mixed layer (3), which is aligned with the top of the vertical metallic titanium (7).

6. The method of making a superhard tool with a titanium nitride-based coating as claimed in claim 1, wherein, The method comprises the following steps: Step (1): cleaning and drying the tool base body (1); Step (2): depositing the Ti buffer layer, comprising: Step (2.1): first depositing an initial titanium layer (2) with a thickness of 50-100 nm; Step (2.2): then depositing a loose titanium layer with a thickness of 200-500 nm; Step (2.3): then depositing an island-shaped aluminum nitride layer, i.e. an AlN island film (30), with a thickness of 2-30 nm; annealing the island-shaped aluminum nitride to shrink and further promote the island structure; Step (2.4): using the island-shaped aluminum nitride layer as a mask to nitride the loose titanium layer; Step (2.5): depositing a continuous AlN layer (8) with a thickness of 20-50 nm, and then depositing a thin Ti layer (9) with a thickness of 5-20 nm; repeating the above steps 1-10 times; Step (3): depositing a TiN-based hard layer (10) with a thickness of 0.8-6 μm.

7. The method of claim 6, wherein the method further comprises the step of: The annealing in step (2.3) also forms cavities and / or cracks (5) in the loose titanium layer. ​ 8. The method of claim 7, wherein the method further comprises the step of: In step (2.4), the nitriding is carried out to a depth of more than half of the loose titanium layer, i.e. the upper part of the originally deposited loose titanium layer is nitrided to form a titanium nitride layer (6), while the lower part of the loose titanium layer is un-nitrided as a whole.

9. The method of claim 8, wherein the method further comprises the step of: The titanium layer just below the island-shaped layer of aluminum nitride in step (2.4) is not nitrided, so that the vertical metal titanium (7) is retained in the titanium nitride layer (6) formed by nitriding, and the sidewalls of the cavities and / or cracks in the remaining lower part of the loose titanium layer (4) which is not nitrided are nitrided to form cavities and / or cracks (5) of titanium nitride material.

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