Polycrystalline Cubic Boron Nitride (PcBN) Body Made With Distinct Layers of PcBN

Abstract

A polycrystalline cubic boron nitride (PcBN) is fabricated using a process of overlaying layers of cubic boron nitride (cBN) powder, where the layers have cBN mixed with various concentrations of a ceramic. The process of fabricating the PcBN includes depositing, in a refractory capsule, a carbide, a cubic boron nitride (cBN), and a mixture of cBN and a ceramic, then applying a high pressure and high temperature (HPHT) to the content of the refractory capsule. During the depositing step of the process, the concentration of cBN in the mixture of the cBN and ceramic is lower than the concentration of cBN that is in the layer below it. Upon applying HPHT, the carbide first diffuses across the cBN layer, and then diffuses across the layer with the mixture of the cBN and ceramic. After HPHT ends and the content of the refractory capsule cools, the process yields a PcBN having layers with various concentrations of cBN, and at least one cBN layer with a ceramic material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of provisional application, No. 61/670,676, filed Jul. 12, 2012.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY

The present disclosure relates to a polycrystalline boron cubic nitride (PcBN) body. More specifically, the present disclosure relates to a PcBN body that is fabricated using a process of overlaying layers of cubic boron nitride (cBN) powder or pre-compacted disks, where the layers have cBN mixed with various concentrations of a ceramic.

BACKGROUND

In the discussion that follows, reference is made to certain structures and/or processes. However, the following references should not be construed as an admission that these structures and/or process constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or process do not qualify as prior art against the present invention.

In conventional polycrystalline cubic boron nitride fabrication processes, a substrate is adjacent to a PcBN layer that is made from a single grade (i.e., cBN is the primary material in the layer) in its entirety. Because of desired and often competing characteristics in the grade, optimizing for one characteristic, such as for example toughness, may result in the degradation of another characteristic, such as for example brazing stability or wear resistance.

Accordingly, there is a need for an improved PcBN fabrication process that produces a PcBN body with the desired characteristics, without degrading one or more of the desired characteristics in order to further another.

SUMMARY

This disclosure describes an improved PcBN fabrication process and the PcBN body created using the improved process.

In an embodiment, a process includes depositing, in a refractory capsule, the following: a substrate (e.g., with cobalt (Co)), cubic boron nitride (cBN), and a mixture of cBN and a ceramic. The deposited cBN and the mixture of cBN and ceramic may be a powder or a pre-compacted disk. The deposited substrate, cBN, and the mixture of cBN and ceramic being the content of the refractory capsule. During the depositing step, the concentration of cBN in the layer with the mixture of cBN and ceramic is lower than the concentration of cBN in the layer that is deposited below it. After depositing the content, a high pressure and high temperature (HPHT) is applied to the content of the refractory capsule. Upon applying HPHT, the Co, for example, of the substrate first diffuses across the cBN layer, i.e., the cBN layer is swept by the Co. In some embodiments, the Co may also sweep across the layer with a mixture of cBN and ceramic.

In some embodiments, the content is deposited in the reverse order, beginning with the mixture of cBN and a ceramic, the cBN, and the substrate (e.g., with cobalt (Co)). During the depositing step, the concentration of cBN in the layer with the mixture of cBN and ceramic is lower than the concentration of cBN in the layer that is deposited above it. After depositing the content in the reverse order, HPHT is applied to the content of the refractory capsule. Upon applying HPHT, the Co, for example, of the substrate sweeps across the cBN layer. In some embodiments, the Co may also sweep across the layer with a mixture of cBN and ceramic.

In a further embodiment, a polycrystalline cubic boron nitride (PcBN) body is prepared by a process that includes the following steps. Depositing, in a refractory capsule, a substrate (e.g., with cobalt (Co)), cubic boron nitride (cBN), and a mixture of cBN and a ceramic. The deposited cBN and the mixture of cBN and ceramic may be a powder or a pre-compacted disk. After depositing the content, then applying a high pressure and high temperature (HPHT) to the content of the refractory capsule. During the depositing step, the concentration of cBN in the layer with the mixture of cBN powder and ceramic powder is lower than the concentration of cBN in the layer that is deposited below it. Upon applying HPHT, the Co, for example, of the substrate diffuses across the cBN powder. In some embodiments, the Co may also sweep across the layer with a mixture of cBN and ceramic.

In some embodiments, the deposition of the content is applied in the reverse order, beginning with the mixture of cBN and a ceramic, the cBN, and the substrate (e.g., with cobalt (Co)).

The diffusion of at least Co, for example, across a first inter-diffusion layer (i.e., between the substrate and a first PcBN layer) and, in some embodiments, a second inter-diffusion layer (i.e., between the first PcBN layer and a second PcBN layer on top of it), during sintering results in fusion of the substrate to the PcBN layer adjacent to it, and to any additional PcBN layers that are adjacent. After the application of HPHT ends and the content of the refractory capsule cools, the process yields a PcBN body having layers with various concentrations of cBN and a ceramic material (i.e., distinct PcBN layers). The desired characteristics of the resulting PcBN body may be controlled by adjusting the concentration of the cBN and the ceramic material in each of the PcBN layers adjacent to the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:

FIG. 1 shows a cross-section, by a 60× scanning electron microscope (SEM), of an unpolished PcBN body fabricated using the disclosed process.

FIG. 2a shows a cross-section, by a 60×SEM, of a polished PcBN body fabricated using the disclosed process.

FIGS. 2b-e show multiple cross-sections, by a 1000×SEM, of various layers and inter-layer interfaces of a polished PcBN body fabricated using the disclosed process.

FIGS. 2f-g show refractory capsules (cups) that may be used to hold deposited content in accordance with some embodiments.

FIG. 3a shows a graph of Ti K fluorescent x-ray intensity generated using an energy dispersive x-ray (EDX) spectroscopy line-scan of a PcBN body fabricated using the disclosed process.

FIG. 3b shows a graph of Co K fluorescent x-ray intensity generated using an energy dispersive x-ray (EDX) spectroscopy line-scan of a PcBN body fabricated using the disclosed process.

FIG. 4 shows a flow diagram of steps of an improved process of fabricating a PcBN body.

FIG. 5 shows a flow diagram of steps of another improved process of fabricating a PcBN body.

DETAILED DESCRIPTION

It is an object of the embodiments described herein to illustrate a PcBN fabrication process, and a PcBN body manufactured by such process, where the resulting PcBN body has desired characteristics obtained without degrading one or more of the desired characteristics to further another.

Accordingly, embodiments are directed to a process for fabricating a polycrystalline cubic boron nitride (PcBN) body, that substantially obviates one or more problems due to limitations and disadvantages of the related art by improving brazing characteristics of the PcBN body using various concentrations of cBN powder and ceramic powder across different layers of the stack.

FIG. 1 shows an EDM cut cross-section of an unpolished PcBN body 101 fabricated using an improved process. The cross-section shows the resulting material after HPHT sintering. Next to a cemented carbide (WC/Co) substrate 102, there is a layer of cBN 103 (a high cBN material), and an adjacent mixture layer of cBN and ceramic 104 (a low cBN material). The layer of cBN 103 has a lower concentration of a ceramic than the low cBN layer 104.

The process for fabricating the unpolished PcBN body 101 includes depositing, in a refractory capsule, the following: a substrate 102, a cubic boron nitride (high cBN) powder, and a mixture layer of cBN and ceramic powders (low cBN), then applying a high pressure and high temperature (HPHT) to the content of the refractory capsule. Suitable examples of the substrate 102 include metallic cobalt (Co), cemented carbide (WC/Co), cermet ((W,Ti)(C,N)/(Co,Ni), silicon (Si), or nickel (Ni). In some embodiments, the deposited layer of the high cBN and the low cBN layers may be powders or pre-compacted disks.

In some embodiments, pre-compacted disks, also known as a pre-sintered bodies, may be made using the method(s) disclosed in U.S. Pat. No. 6,676,893 B2, “Porous Cubic Boron Nitride Based Material Suitable for Subsequent Production of Cutting Tools and Method for its Production,” issued on Jan. 13, 2004, which is incorporated herein by reference.

In some embodiments, the refractory capsule may be formed from a tantalum (Ta) or molybdenum (Mo) foil sheet/wrap, or any other grade IV-VI transition metal. Embodiments of a tantalum refractory capsule (cup) are shown in FIGS. 2f-g. FIG. 2f illustrates a tantalum metal container (cup) with a non-crimped top. FIG. 2g illustrates a tantalum refractory capsule (cup) with a crimped top.

In some embodiments, the concentration of cBN in the low cBN powder is lower than the concentration of the high cBN powder.

The ceramic powder may include, for example, titanium nitride (TiN) or aluminum oxide (Al₂O₃) or Ti₂AlN. Other ceramics may also be used without departing from the scope of the embodiments described. For example, ceramics such as AlN, TiC, TiCN, ZrN, ZrO₂, HfO₂, or any other grade IV-VI transition metal like Me (C,N,O) may be used.

The high cBN powder has a high cBN content of approximately 90%, for example. The layer 103 contains approximately 90% cBN and approximately 10% of some other material(s), which may include the ceramic. In some embodiments, the cBN layer 103 may also include a relatively low concentration of approximately 10%, for example, of a ceramic such as TiN or Al₂O₃. Moreover, the low cBN layer 104 may have a cBN content of approximately 50%, for example. The layer 104 may also include a relatively high concentration of approximately 50%, for example, of a ceramic such as TiN or Al₂O₃.

Upon applying HPHT to the content 102-104 of the refractory capsule, to commence sintering, the Co of the substrate 102 first diffuses across the cBN powder layer 103, and then, in some embodiments, diffuses across the mixture of cBN powder and ceramic powder layer 104. As a consequence, in some embodiments, two inter-diffusion layers may be formed. A first inter-diffusion layer between the substrate 102 and high cBN layer 103, and a second inter-diffusion layer between the high cBN layer 103 and the low cBN layer 104. The diffusion of substrate material (e.g., Co) across the two inter-diffusion layers, for example, results in fusion of the substrate layer 102 to the high cBN layer 103 next to it, and any additional PcBN layer(s) adjacent to the cBN layer 103 such as, for example, the low cBN layer 104.

After HPHT ends and the content of the refractory capsule cools, the process yields a PcBN body having layers with various concentrations of cBN and a ceramic material (i.e., distinct PcBN layers). The desired characteristics of the resulting PcBN body may be controlled by adjusting the concentration of the cBN and the ceramic material in each of the PcBN layers adjacent to the substrate layer 102. In some embodiments, the high cBN layer 103 has an approximately 86-99% volume of cBN, and an 88-96% volume of cBN, as well as a metallic binder with a ceramic content of approximately 2-8%. In some embodiments, the low cBN layer 104 has an approximately 35-85% volume of cBN, and a binder of ceramic character after HPHT.

In the cross-section of an unpolished PcBN body 101 fabricated using an improved process, a first amount corresponding to a thickness of a layer of a substrate 102 may be, for example, approximately between 0.0 and 8 mm. A second amount corresponding to a thickness of a high cBN layer 103 may be, for example, approximately between 0.3 and 3.2 mm, and between approximately 0.5 and 1.0 mm. A third amount corresponding to a thickness of a low cBN layer 104 may be, for example, approximately between 0.2 and 3.2 mm, and between 0.3 and 1.0 mm.

FIG. 2a shows a cross-section, using a scanning electron microscope (SEM) at 60×, of a polished PcBN body 201 fabricated using the improved process. The polished PcBN body 201, as shown, has a first WC/Co cemented carbide substrate layer 202, a second high cBN layer 203, and a third low cBN layer 204. In this example the carbide substrate layer 202 (not shown in its entirety) has a thickness of approximately 4 mm. The second layer of cBN powder 203 has a thickness of approximately 0.6 mm. The third low cBN layer 204 has a thickness of approximately 0.4 mm. The polished PcBN body 201 was fabricated using the process described earlier. After HPHT the body 201 was EDM cut, and the cross section polished in order to enhance microscopy. Polishing was accomplished by using standard metallographic methods.

FIGS. 2b-e show multiple cross-sections, at a higher magnification of 1000× in the SEM, of various layers and inter-layer interfaces of a PcBN body 201 fabricated using the improved process. In particular, FIG. 2b shows the substrate 202—high cBN layer 203 interface 205; FIG. 2c shows the second layer 203 at higher magnification 206; FIG. 2d shows the high cBN layer 203—low cBN layer 204 interface 207; and, FIG. 2e shows the low cBN layer 204 at higher magnification 208.

At 1000× magnification it is easy to see the grain structure of the carbide, the Co (metallic binder), and the light gray ceramic binder (cBN grains appear dark). The substrate 202 has a visible light contrast (see FIG. 2b), which is due to its WC and Co content. The second layer 203 is shown in higher magnification 206 in FIG. 2e. The dark grains are cBN and the light contrast in the binder phase is due to interdiffused Co from the substrate, also known as sweep. The third layer 204 is shown in higher magnification 208. Dark grains are cBN and the gray phase is the ceramic binder with no Co interdiffusion. Both the substrate layer 202 to second layer 203 interface 205, and second layer 203 to third layer 204 interface 207 are rather abrupt (see FIGS. 2b, and 2d). No cracks or pores appear in the PcBN body (see FIGS. 2b-e), which implies good bonding characteristic.

FIGS. 2f-g show refractory capsules (cups) 210 that may be used to hold deposited content in accordance with some embodiments. FIG. 2f illustrates a refractory capsule 210 made of tantalum and having a non-crimped top. FIG. 2g illustrates a refractory capsule made of tantalum and having a crimped top. Other refractory capsule types than FIG. 2f or FIG. 2g may be used without departing from the scope of the embodiments.

FIG. 3a shows a graph of Ti K fluorescent x-ray intensity generated using energy dispersive x-ray (EDX) spectroscopy of a PcBN body fabricated using the disclosed process. The graph 301 is a line-scan (along the white line 302) of the PcBN body qualitatively illustrating the concentration of Ti across the depth of the PcBN body. The line-scan 301 was taken from the top to the bottom along the white line 302. Ti, which may be bound as ceramic TiN, does not show any evidence of diffusing, as the second-to-third layer interface 303 corresponds to the open arrow on the graph 301. The presence of TiN in the third layer 204, which is towards the top/intended working surface of the PcBN body, is for increasing the PcBN layer's chemical stability and strengthening the PcBN body for its use, for example, as a cutting tool in hard part turning applications. The higher cBN content in the second layer 203 gives the material higher toughness and hardness.

FIG. 3b shows a graph 305 of Co K fluorescent x-ray intensity generated using energy dispersive x-ray (EDX) spectroscopy of a PcBN body fabricated using the disclosed process. The graph 305 is a line-scan of the PcBN qualitatively illustrating the concentration of cobalt (Co), across the depth of the PcBN body. The line-scan 306 is taken from the top to the bottom along the white line 305.

The line-scans of the PcBN body were obtained in a scanning electron microscope in which the electron probe generates characteristic x-ray fluorescence that is proportional to the concentration of Co in the PcBN body. In this example Co metal from the substrate 202 has enriched at the first interface 308 between the substrate layer and the second layer, and diffused through the second layer 203 across the interface 308 but not past the second interface 307 into the third layer 204.

FIG. 4 shows a flow diagram 400 of steps 401-404 of an improved process of fabricating a polycrystalline cubic boron nitride (PcBN body). The process includes: depositing, in a refractory capsule, a first amount of a substrate 401; depositing, in the refractory capsule, a second amount of at least cubic boron nitride (cBN) 402; depositing, in the refractory capsule, a third amount of a mixture of cBN and ceramic 403; and applying a high pressure and high temperature (HPHT) to a content of the refractory capsule 404, where a first concentration of cBN in the third amount is lower than a second concentration of cBN in the second amount, and where, upon applying HPHT, Co of the substrate first diffuses across the second amount of at least the cBN, and then diffuses across the third amount of the mixture of cBN and ceramic.

One or more steps may be inserted in between or substituted for each of the foregoing steps 401-404 without departing from the scope of this disclosure.

FIG. 5 shows a flow diagram 500 of steps 501-504 of another improved process of fabricating a PcBN body. The process includes: depositing, in a refractory capsule, a first amount of a mixture of cubic boron nitride (cBN) and ceramic 501; depositing, in the refractory capsule, a second amount of at least cBN 502; depositing, in the refractory capsule, a third amount of a substrate 503; applying a high pressure and high temperature (HPHT) to a content of the refractory capsule, where a first concentration of cBN in the first amount is lower than a second concentration of cBN in the second amount, and where, upon applying HPHT, Co of the substrate first diffuses across the second amount of at least the cBN, and then diffuses across the first amount of the mixture of cBN and ceramic 504. The advantage here is that the refractory capsule does not require an extra tantalum (Ta) layer as a lid.

One or more steps may be inserted in between or substituted for each of the foregoing steps 501-504 without departing from the scope of this disclosure.

Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A process of fabricating a polycrystalline cubic boron nitride (PcBN) cutting tool, comprising:

depositing: a first amount of a substrate; a second amount of at least a cubic boron nitride (cBN); a third amount of a mixture of cBN and ceramic; and

applying a high pressure and high temperature (HPHT).

2. The process of claim 1, wherein the substrate comprises at least one of a metal and silicon.

3. The process of claim 1, wherein the depositing is into a refractory capsule formed from a foil sheet or wrap of tantalum (Ta), molybdenum (Mo), or a grade IV-VI transition metal.

4. The process of claim 1, wherein the substrate includes carbide.

5. The process of claim 1, wherein the ceramic includes at least one from a group consisting of: TiN, Al2O3, AlN, TiC, TiCN, ZrN, ZrO2, and HfO2.

6. The process of claim 3, wherein the refractory capsule includes: (1) the substrate, (2) the cBN, and (3) the mixture of cBN powder and ceramic.

7. The process of claim 6, wherein the ceramic includes at least one from a group consisting of: TiN, Al2O3, AlN, Ti2AlN, TiC, TiCN, ZrN, ZrO2, and HfO2.

8. The process of claim 1, further comprising the step of ending application of HPHT.

9. The process of claim 1, wherein a first concentration of cBN in the third amount is lower than a second concentration of cBN in the second amount.

10. The process of claim 4, wherein upon applying the HPHT, carbide of the substrate first diffuses across the second amount of at least the cBN, and then diffuses across the third amount of the mixture of the cBN and ceramic.

11. The process of claim 1, wherein the first amount is a thickness of approximately 0.0 to 8 mm.

12. The process of claim 1, wherein the second amount or third amount is a thickness of approximately 0.3 to 3.2 mm.

13. The process of claim 1, wherein the second amount is a thickness of approximately 0.5 to 1.0 mm.

14. The process of claim 1, wherein the third amount is a thickness of approximately 0.3 to 1.0 mm.

15. The process of claim 1, wherein the second amount comprises at least one from the group consisting of: TiN, Al2O3, AlN, TiC, Ti2AlN, TiCN, ZrN, ZrO2, and HfO2.

16. The process of claim 15, wherein in the second amount the second concentration of cBN is greater than a concentration of at least one from the group consisting of: TiN, Al2O3, AlN, Ti2AlN, TiC, TiCN, ZrN, ZrO2, and HfO2.

17. The process of claim 15, wherein a first concentration of TiN or Al2O3 in the second amount is less than a second concentration of TiN or Al2O3 in the third amount.

18. The process of claim 1, wherein the deposited second amount or third amount is in the form of a pre-compacted disk.

19. The process of claim 1, wherein the deposited second amount or third amount is in the form of a powder.

20. The process of claim 1, wherein the substrate includes metal carbo nitrides of the form Me (C,N).

21. A polycrystalline cubic boron nitride (PcBN) cutting tool, comprising:

in a content to which high pressure and high temperature (HPHT) is applied: a first amount of a substrate; a second amount of at least a cubic boron nitride (cBN); and a third amount of a mixture of cBN and ceramic.

22. The PcBN of claim 21, wherein the substrate comprises at least one of a metal and silicon.

23. The PcBN of claim 21, wherein the content is contained in a refractory capsule formed from a foil sheet or wrap of tantalum (Ta), molybdenum (Mo), or a grade IV-VI transition metal.

24. The PcBN of claim 21, wherein the substrate includes carbide.

25. The PcBN of claim 21, wherein the ceramic includes at least one from a group consisting of: TiN, Al2O3, AlN, TiC, TiCN, ZrN, ZrO2, and HfO2.

26. The PcBN of claim 21, wherein a first concentration of cBN in the third amount is lower than a second concentration of cBN in the second amount,

27. The PcBN of claim 24, wherein upon applying the HPHT, carbide of the substrate first diffuses across the second amount of at least the cBN, and then diffuses across the third amount of the mixture of the cBN and ceramic.

28. The PcBN of claim 21, wherein the first amount is a thickness of approximately 0.0 to 8 mm.

29. The PcBN of claim 21, wherein the second amount or third amount is a thickness of approximately 0.3 to 3.2 mm.

30. The PcBN of claim 21, wherein the second amount is a thickness of approximately 0.5 to 1.0 mm.

31. The PcBN of claim 21, wherein the third amount is a thickness of approximately 0.3 to 1.0 mm.

32. The PcBN of claim 21, wherein the second amount comprises at least one from the group consisting of: TiN, Al2O3, AlN, TiC, Ti2AlN, TiCN, ZrN, ZrO2, and HfO2.

33. The PcBN of claim 25, wherein in the second amount the second concentration of cBN is greater than a concentration of at least one from the group consisting of: TiN, Al2O3, AlN, Ti2AlN, TiC, TiCN, ZrN, ZrO2, and HfO2.

34. The PcBN of claim 25, wherein a first concentration of TiN or Al2O3 in the second amount is less than a second concentration of TiN or Al2O3 in the third amount.

35. The PcBN of claim 21, wherein the second amount or third amount of the content is in the form of a pre-compacted disk.

36. The PcBN of claim 21, wherein the second amount or third amount of the content is in the form of a powder.

37. The PcBN of claim 21, wherein the substrate includes metal carbo nitrides of the form Me (C,N).

38. A process of fabricating a polycrystalline cubic boron nitride (PcBN) cutting tool, comprising:

depositing: a first amount of a mixture of a cubic boron nitride (cBN) and ceramic; a second amount of at least cBN; a third amount of a substrate; and

applying a high pressure and high temperature (HPHT).