COMPOSITE OF A SUBSTRATE WITH A STRUCTURED COATING, CUTTING ELEMENT AND METHOD FOR PRODUCING A CUTTING ELEMENT

Abstract

The present invention relates to a cutting element formed from a composite of a substrate coated with a structured coating comprising a substrate with a surface in contact with the coating. The substrate has a plurality of substrate recesses at least in regions of the substrate surface. The coating extends into the recesses of the substrate, and the coating has an inner surface being in contact with the substrate and an outer surface opposite to the inner surface. The coating comprises at the outer surface a plurality of coating recesses being smaller than the recesses at the surface of the substrate resulting in a structured coating. Moreover, the present invention relates to a method for producing a cutting element.

Claims

1. A cutting element formed from a composite of a substrate with a structured coating, the cutting element comprising of a substrate with a surface in contact with a coating, wherein the substrate has a plurality of substrate recesses at least in regions of the substrate surface and the coating extends into the recesses of the substrate, and the coating has an inner surface being in contact with the substrate and a surface opposite to the inner surface, and the coating comprises at the surface a plurality of coating recesses being smaller than the recesses at the surface of the substrate resulting in a structured coating, wherein the surface of the structured coating has a total surface area A.sub.tot, a total recess area A.sub.r and a contact area A.sub.c=A.sub.totA.sub.r wherein Ac/A.sub.tot is in the range of 0.1 to 0.8.

2. The cutting element of claim 1, wherein the cutting element is characterized in that at least in regions of the composite the substrate is removed thereby exposing one or more protrusions, which preferably have the inverse shape of the recesses at the surface of the substrate.

3. The cutting element of any one of claims 1, wherein the substrate recesses have a width w.sub.sub in a range of 100 nm to 100 m, wherein the ratio w.sub.sub/d.sub.base is in the range from 0.20 to 25, and/or the coating recesses have a width w.sub.coat in a range of 100 nm to 100 m, preferably from 500 nm to 20 m, and a depth d.sub.coat, in a range 50 nm to 5 m, preferably from 100 nm to 2 m, wherein the ratio w.sub.coat/d.sub.coat is in the range from 0.25 to 25.

4. The cutting element of claim 3, wherein the cutting element is characterized in that d.sub.coat is smaller than d.sub.base.

5. The cutting element of claim 1, wherein the cutting element is characterized in that A.sub.c/A.sub.tot is in a range of 0.3 to 0.7.

6. The cutting element of claim 1, wherein the cutting element is characterized in that the substrate recesses are arranged such that the ratio s/d.sub.pair of the spacing s of any pair of two adjacent recesses to the average depth d.sub.pair of the same pair of two recesses is in the range from 0.25 to 20.

7. The cutting element of 1, wherein the cutting element is characterized in that the coating is a first coating deposited on the substrate at least in regions and on the first coating at least one further coating is deposited at least in regions.

8. The cutting element of claim 1, wherein the recesses have a circular or ellipsoidal or linear shape, wherein the recess has a recess opening perimeter which is a closed continuous line without any singularities.

9. The cutting element of claim 1, wherein the coating has a thickness T.sub.c of 100 nm to 50 m, and the substrate has a thickness T.sub.s of 20 to 2000 m and the composite has a total thickness T.sub.tot of 25 to 2050 m.

10. The cutting element of claim 1, wherein the ratio d.sub.base /T.sub.c of the depth d.sub.base of the substrate recesses to the thickness of the coating T.sub.c is in a range of 0.01 to 15 and the ratio d.sub.coat /T.sub.c of the depth d.sub.coat of the coating recesses to the thickness of the coating T.sub.c is in a range of 0.01 to 5.

11. The cutting element of claim 1, wherein the cutting element is selected from the group consisting of a knife blade, razor blade, scalpel, knife, machine knife in slitting- , burst- and crash cutting systems, scissors or shear cutting systems.

12. The cutting element of claim 11, wherein the regions of the composite in which the substrate is removed thereby exposing protrusions being the inverse structure of the recesses is the region of the cutting bevel.

13. The cutting element of claim 11, wherein the cutting element comprises a cutting bevel and a cutting element body whereby the cutting bevel is at least partially located in regions of the composite where the substrate is removed thereby exposing protrusions at the inner coating surface.

14. A method for producing a cutting element with the steps of: Providing a substrate with a surface, forming an etching mask with openings at the substrate surface, etching the substrate through the openings in the etching mask to form a plurality of substrate recesses at the substrate surface by reactive ion etching or wet chemical etching, removing the etching mask from the substrate, depositing a coating onto the substrate surface and into the plurality of recesses thereby transferring the substrate recesses into coating recesses at the coating surface which are smaller than the substrate recesses resulting in the structured coating, etching the substrate thereby exposing protrusions at the inner coating surface to form a cutting bevel of the cutting element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The present invention is further illustrated by the following figures and examples which show specific embodiments according to the present invention. However, these specific embodiments shall not be interpreted in any limiting way with respect to the present invention as described in the claims in the general part of the specification.

[0086] FIG. 1a-1c shows a top view, cross section and enlarged cross section of a recess, respectively.

[0087] FIG. 2 shows a cross section of a composite of the present invention.

[0088] FIG. 3 is a top view of a substrate onto the surface.

[0089] FIG. 4 is a cross-section of a substrate of the present invention.

[0090] FIG. 5a-5c are scanning electron microscopic (SEM) images of the substrate and the coating surface according to the present invention.

[0091] FIG. 6a-6b shows alternative recess shapes according to the present invention.

[0092] FIG. 7a-7e is a schematic illustration of the process steps of the method according to the present invention.

[0093] FIG. 8a-8d are schematic illustrations of the deposition of the coating layer onto a substrate material according to the present invention.

[0094] FIG. 9 shows schematic top and side views of a cutting element at different stages during the process according to the present invention.

[0095] FIG. 10a-10c shows schematic cross-sections of the formation of a cutting element in the hard-coating.

[0096] FIG. 11a-11c shows SEM photographs of perspectives of a cutting element with circular shaped recesses within different scales.

[0097] FIG. 12a-12b shows SEM photographs of perspectives of a cutting element with linear shaped recesses in different scales.

[0098] FIG. 13a-13b shows scanning electron photographs in different magnifications of a cross section in a perspective view of a cutting element.

REFERENCE SIGN LIST

[0099] 10 composite [0100] 110 interface [0101] 20 substrate (material) [0102] 200 substrate surface [0103] 205 substrate backside surface [0104] 210 photoresist [0105] 220 exposed photoresist regions [0106] 230 unprotected regions [0107] 240 region with recesses [0108] 250 region without recesses [0109] 30 coating (layer) [0110] 300 coating surface [0111] 305 coating inner surface [0112] 320 protrusion [0113] 330 coating recess [0114] 40, 40, 40, 40 recesses [0115] 410 recess opening [0116] 415 side wall [0117] 420 recess base [0118] 460 recess opening perimeter [0119] 462 recess maximum perimeter [0120] 470 largest inner circle [0121] 472 recess center [0122] 480 undercut [0123] 600 cutting element [0124] 610 cutting edge [0125] 620 cutting bevel [0126] 630 cutting element body

[0127] FIG. 1a shows the top view of a recess 40 in a substrate 20. The recess 40 has an opening 410 with an opening perimeter 460, both of which lie in the surface 200 of substrate 20. The opening perimeter 460 may be of arbitrary shape, but the preferred shape of the recess opening 410 has no corners, i.e., the recess opening perimeter 460 is a closed continuous line without any singularities. The width w.sub.sub of the recess is the diameter of the largest inner circle 470 that can be fitted fully within the perimeter 460 of the opening 410 as shown by the dotted line in FIG. 1a. The circumference of this largest inner circle 470 may coincide with the perimeter 460 of the recess opening 410 but may not exceed beyond the perimeter 460 of the recess opening 410. The centre of the largest inner circle 470 defines the recess centre 472 of the recess.

[0128] FIG. 1b shows the cross section of the recess 40 in a substrate 20 from FIG. 1a. The recess 40 comprises an opening located in the surface 200 of the substrate 20, and a base 420 and a side wall 415 located within the substrate 20. The opening has a width w.sub.sub as defined by the largest inner circle 470.

[0129] As can be seen from the enlargement of the side wall 415 on FIG. 1c, the side wall 415 has an undercut 480. This results in the recess 40 having a width at a depth below the substrate surface 200 that is greater than the width w.sub.sub of the opening of the recess 40 at the substrate surface 200. The width of the recess 40 at any depth below the substrate surface 200 is defined by the diameter of the largest inner circle that can be entirely placed within the perimeter of the recess at this depth below the substrate surface 200 whereby the perimeter lies within a plane parallel to the substrate surface at this depth.

[0130] FIG. 2 shows a cross-sectional view of a composite 10 comprising a substrate material 20 and a coating layer 30. The substrate material 20 is made of silicon. The substrate material 20 has a surface 200. The substrate material 20 comprises a plurality of recesses 40, which have been etched into the surface 200 according to the method described below and illustrated in FIG. 7. Each recess 40 has an opening at the surface 200 with a width w.sub.sub. Furthermore, each recess 40 has a maximum width w.sub.max at a depth d.sub.max below the surface 200. Adjacent recesses 40 are separated by a spacing s. The coating layer 30 consists of nanocrystalline diamond. The coating layer 30 is deposited onto the structured surface 200 of the substrate material 20 according to the method described below and illustrated in FIG. 7. The coating layer 30 has a coating thickness T.sub.c as measured from the substrate surface 200.

[0131] FIG. 3 shows a top view of the surface 200 of a substrate material 20. The substrate material 20 comprises a plurality of recesses 40, which have been etched into the surface 200 according to the method described below and illustrated in FIG. 7. Each recess 40 has an opening 410 at the surface 200 with a width w.sub.sub and a recess opening perimeter 460 around the opening 410 of recesses 40. Furthermore, each recess 40 has a maximum width w.sub.max at a maximum depth d.sub.max below the surface 200. Adjacent recesses 40 are separated by a spacing s.

[0132] FIG. 4 shows a cross sectional view of a substrate material 20. The substrate material 20 comprises a plurality of recesses 40, which have been etched into the surface 200 according to the method described below and illustrated in FIG. 7. Each recess 40 has an opening at the surface 200, a sidewall 415 and a base 420 at a depth d.sub.base below the surface 200.

[0133] As can be seen from the magnification of a sidewall 415 of a recess 40, an opening perimeter 460 is located around the opening of recesses 40. Furthermore, each recess 40 has a maximum perimeter 462 at a maximum depth d.sub.max below the surface 200. The largest inner circle that can be fully fitted into the opening perimeter 460 defines the surface width w.sub.sub and the largest inner circle that can be fully fitted into the maximum perimeter 462 defines the maximum width w.sub.max. The difference of w.sub.max minus w.sub.sub corresponds to the twice the width of the overhang h. The depth d.sub.max is greater than zero but less or equal than the depth d.sub.base of the recess 40, meaning that the maximum perimeter 462 and hence maximum width w.sub.max is located below the surface 200 of the substrate 20 to form and undercut 480. Adjacent recesses 40 are separated by a spacing s.

[0134] FIG. 5a shows a perspective scanning electron micrograph (SEM) of a surface 200 of a substrate material 20 comprising a plurality of circular recesses 40. As can be inferred from the scale bar, the opening width w.sub.sub of recesses 40 is approx. 10 m in this example.

[0135] FIG. 5b shows a cross section SEM of a substrate material 20 comprising a plurality of circular recesses 40 with undercuts 480. As can be seen from the scale bar and measurement, the opening width w.sub.sub of recesses 40 is approximately 10 m and the recess depth d.sub.base is approximately 1 m in this example.

[0136] FIG. 5c shows a perspective SEM of a composite 10 comprising a coating layer 30 and substrate material 20 with a plurality of recesses 40 where the coating layer has been partially removed. After depositing a coating layer onto a substrate surface that contains a plurality of recesses, these recesses transfer to the surface of the coating layer 300 and form a plurality of coating recesses 330.

[0137] FIG. 6a and 6b shows two alternative magnifications of sidewalls 415 of recesses 40.

[0138] As can be seen in FIG. 6a, the recess 40 has an undercut 480 with a straight sidewall 430 that increases the width of the recess from the opening towards the base 420. The opening perimeter 460 is located around the opening of recess 40, the maximum perimeter 462 is located at a maximum depth d.sub.max below the surface 200, which in this example equals the recess depth d.sub.base. The largest inner circle that fully fits into the opening perimeter 460 defines the surface width w.sub.sub and the largest inner circle that fully fits into the maximum perimeter 462 defines the maximum width w.sub.max 432. The difference of w.sub.max minus w.sub.sub corresponds to the twice the width of the overhang h.

[0139] As can be seen in FIG. 6b, recess 40 has an undercut 480 with a sidewall 415 of varying shape. The opening perimeter 460 is located around the opening of recess 40, the maximum perimeter 462 is located at a maximum depth d.sub.max below the surface 200. The depth d.sub.max is greater than zero but less or equal than the depth d.sub.base of the recess 40, meaning that the maximum perimeter 462 and hence maximum width w.sub.max is located between the substrate surface 200 and the recess base 420.

[0140] The largest inner circle that fully fits into the opening perimeter 460 defines the surface width w.sub.sub and the largest inner circle that fully fits into the maximum perimeter 462 defines the maximum width w.sub.max. The difference of w.sub.max minus w.sub.sub corresponds to the twice the width of the overhang h.

[0141] To form an undercut 480, the sidewall 415 of recess 40 can have any shape if a depth d.sub.max exists at which the width w.sub.max of the recess is greater than the width w.sub.sub at the opening of the recess, i.e., an overhang h exists that is greater than zero.

EXAMPLE

[0142] The inventive process for producing a composite of a substrate with a structured coating is shown in the diagram of FIG. 7 and explained in detail in the following.

[0143] Process step a) shows the starting point, providing a single crystal silicon wafer as the substrate.

[0144] After cleaning the substrate surface 200 carefully in step b) a photoresist 210 providing a reasonable selectivity against the reactant etch gas composition is deposited by spin coating or spraying to achieve a reasonable thickness (e.g., 1 to 2 m) and homogeneity. To obtain a reasonable resolution and selectivity, standard photoresists for semiconductor fabrication are recommended.

[0145] The photoresist is dried/prebaked according to the recommended parameters provided by the photoresist manufacturer. To pattern the photoresist, a photolithographic mask and an UV Exposure apparatus are needed. The photoresist is exposed through the photoresist mask and the exposed photoresist regions 220 are developed according to the recommended parameters provided by the photoresist manufacturer.

[0146] After development, a post bake may be recommended to increase the selectivity of the following etching process. Processing of the photoresist is schematically shown in process steps b).

[0147] The recesses 40 are formed by isotropic etching of the unprotected regions 230 on the substrate, utilizing the photoresist 210 as mask with sufficient stability against the reactants. If a small recess depth is required, it is advantageous to utilize dry etching processes such as (D)RIE or ICP. In case of a silicon substrate, advantage can be taken from DRIE adapted processes, alternating side wall passivation and isotropic etching steps. Details can be found e.g., in M.D. Henry, ICP Etching of silicon for micro and nanoscale devices, Thesis California Institute of Technology, May 19, 2010. Such steps allow for a precise control of a desired shape of the sidewall 415 and an undercut 480. This process is shown in process step c).

[0148] After recess 40 formation, the photoresist 210 is removed utilizing the recommended solutions by the photoresist manufacturer, shown in process step d).

[0149] A coating process is performed using a planar silicon substrate (e.g., wafer) coated with a 10 m thick nanocrystalline diamond CVD film. As the diamond growth or deposition, respectively, does not spontaneous start on a clean silicon surface, a nucleation step (not shown) must be performed in advance. Here, a water-based nucleation slurry containing purified diamond particles (seeds) are used. The size of the seeds should be much smaller than the recess depth d.sub.base to enable a high nucleation density. The nucleation process is performed by dipping the Silicon wafer into the slurry and followed by a water-based rinsing and a drying step.

[0150] After nucleation, the wafer is placed e.g., in a hot filament CVD system and the growth process is started. The hot filament CVD growth of diamond is known to be rather isotropic as no ion bombardment is involved. Thus, the recessed silicon surface is overgrown or covered, respectively, and the residual diamond growth surface smoothens out with increasing diamond film thickness as seen in the cross-sectional SEM pictures of FIG. 5c. Process step e) shows schematically, the final result.

[0151] FIGS. 8a to 8d illustrate the stages of the deposition of a coating layer onto a structured substrate 20 that contains a plurality of recesses (40, 40, 40, 40) with different widths to illustrate the importance to choose the correct recess width w.sub.sub and ratio w.sub.sub/d.sub.base. It has been found that the deposition rate strongly depends on this ratio w.sub.sub/d.sub.base and that the deposition rate at the recess base 420 is in general lower than the growth rate at the coating surface 300 resulting in different coating thicknesses T.sub.c-surf and T.sub.c-base (see FIG. 8a). With increasing coating thickness (FIGS. 8b, 8c, 8d), the coating layer at the coating surface 300 may form a continuous layer before the recesses have been filled with the coating material which leads to the formation of cavities 340 in the coating layer 30. These cavities are undesirable because they reduce the adhesion between the substrate material 20 and the coating layer 30. Knowledge of the deposition rates makes it possible to choose the correct ratio of the recess width to the recess depth w.sub.sub/d.sub.base. For the CVD growth of nanocrystalline diamond a ratio w.sub.sub/d.sub.base in the range of 1 to 20 is preferred. The finally formed recesses have a width w.sub.coat and a depth d.sub.coat depending on the substrate width w.sub.sub, the depth d.sub.base and the thickness of the coating T.sub.c.

[0152] FIG. 9 shows a schematic top view and cross sections of a cutting element at different stages during the composite and cutting element making process. The cutting element 600 with a cutting edge 610 and a cutting element body 620 are produced from the layered composite 10, whereby the coating layer 30 comprises a hard-coating from the selection of materials disclosed above. Cutting edges 610 may be produced by partially removing the substrate material 20 until only the coating layer 30 remains and subsequently forming a cutting edge 610 in the portion of the coating layer that is unsupported by substrate material. If the substrate material 20 contains recesses 40 on the surface 200, the coating layer 30 contains protrusions 320 that were formed during the coating process when the coating materials filled the recesses 40 in the substrate material 20. These protrusions 320 mirror the shape and distribution of the recesses 40 that were created in the surface 200 of the substrate material 20 prior to depositing the coating layer 30. However, in the case of cutting edges 610 formed in the unsupported coating layer 30 by partially removing the substrate material 20, it is desirable not to have protrusions 320 on the cutting edges 610. Protrusions 320 on the cutting edge 610 may cause the cutting edge 610 to be ragged and the cutting bevel 620 to be rough which may lead to poor cutting performance and instability of the cutting blade 600. It is therefore desirable to avoid protrusions 320 at the cutting edge 610, which requires that recesses 40 must not be created on the surface 200 of the substrate 20 in regions where the substrate 20 will be removed after the coating process to form cutting bevels 620 with cutting edges 610.

[0153] FIG. 10a-10c shows the optional cutting edge formation process on a substrate surface 200 that has been structured to contain a plurality of recesses 40 so that a cutting element 600 with a cutting bevel 620 containing protrusions 320 and a cutting element body 630 with a coating surface 300 containing coating recesses 330 can be achieved.

[0154] The initial stage a) in FIG. 10 corresponds to step e) in FIG. 7, where a coating 30 with thickness T.sub.c has been deposited onto a substrate 20 with thickness T.sub.s and a plurality of recesses 40. The coating 30 comprises a plurality of coating recesses 330 at the coating surface 300 that have been transferred from the plurality of recesses 40 on the surface 200 of the substrate 20 and will reduce the contact area of the coating surface to tailor the friction properties. Furthermore, the coating 30 comprising protrusions 320 at the inner coating surface 305 that fill the recesses 40 in the substrate 20.

[0155] FIG. 11a-11c shows an electron microscopy image of a cutting element 600 at 3 different magnifications. The inner coating surface 305 has been exposed on the cutting bevel 620 formed in the coating layer 30 after removing substrate material 20. A plurality of circular protrusions 320 can be seen on the inner coating surface 305 of the cutting bevel 620.

[0156] FIG. 12a-12b shows an electron microscopy image of a cutting element 600 at 2 different magnifications. The inner coating surface 305 has been exposed on the cutting bevel 620 formed in the coating layer 30 after removing substrate material 20. In this case, a plurality of linear protrusions 320 can be seen on the inner coating surface 305 of the cutting bevel 620.

[0157] FIG. 13a-13b shows scanning electron photographs in different magnifications of a cross section in a perspective view of a cutting element according to the present invention. The width of the circular shaped recesses 40 w.sub.sub is approx. 10 m, the spacing s is 15 m, the depth d.sub.max of recesses is approx. 1 m. Recesses 330 and protrusions 320 are originated in the recesses 40.