EP0317452A1 - Composite diamond-abrasive product, process for manufacturing it and drilling or finishing tools provided therewith - Google Patents

Abstract

This abrasive product is of the type in which the active part consists of a sintered product comprising grains of diamond, each grain being linked directly to its neighbouring grains by bridging in order to have a polycrystalline structure, associated with a support essentially consisting of tungsten carbide. …<??>According to the invention, the tungsten carbide support comprises a chromium binder phase representing from 6 to 15% by volume of the carbide; the relative proportions by weight of nickel and chromium in the binder phase vary within a range from 60 to 90% and from 40 to 100%. …<??>The process for manufacturing this product consists:… - in placing in a crucible a layer of grains of diamond which is intended to constitute the active layer of the product;… - in placing on the layer thus formed a layer of tungsten carbide to which a nickel-chromium mixture is added, intended to constitute the support;… - in subjecting the layer arrangement thus formed to a temperature and a pressure which are sufficient to cause the plastic-phase sintering of the grains of diamond and to bind the compact thus obtained to the support. …<??>Drilling or machining tools equipped with the composite diamond- impregnated abrasive product according to the invention.

Description

The present invention relates to a composite diamond abrasive product, its preparation process and the drilling or machining tools which are equipped with it.

The present invention relates more particularly to abrasive composite products of the type having a part consisting of a "compact" containing diamond grains representing more than 80% by volume of the compact, each grain being bonded directly to its neighbors to present a rendered polycrystalline structure. integral with a hard and refractory support, consisting essentially of a refractory carbide such as tungsten carbide.

The term "compact" designates a sintered product consisting of grains linked together by bridges created by diffusion of material in the plastic state also called bridging. This plastic phase sintering is obtained at pressures and temperatures of the order of magnitude of the pressures and temperatures used for the synthesis of diamond grains.

The term "compact" does not cover abrasive products comprising a support made of silicon carbide and of polycrystalline diamond, unsintered since not subjected, during manufacture, to temperatures and pressures sufficient to allow inter-growth of the diamond grains between them; in these products, the voids between grains of the composite are occupied by a compound of silicon and a metal such as nickel (US-A-4,241,135). These products exhibit poor abrasion resistance due to the absence of sintering.

It does not also include composite abrasive products (US-A-4 124 401) comprising a mass of polycrystalline diamond cemented by a binder containing silicon associated with a carbide support whose cohesion is ensured by cobalt. The absence of catalyst and sintering during the manufacture of the diamond mass, however, prevents the formation of direct bridges between the diamond grains. We do not obtain a sintered compact having a skeleton of great rigidity, but a product which can be described as cemented by the binder. Such a product is sometimes called "cemented", according to terminology derived from English.

In some compacts of the type defined above (US-A-3,239,921) obtained at a temperature which may exceed 1,750 ° C., the voids of the compact are occupied by conversion catalyst, such as Co, Va, Ti, Zr, Cr, Si. These products have the disadvantage of degrading quickly (poor abrasion resistance) because the sintering is carried out in the absence of '' a sufficient amount of diamond grains

Products are known in which a compact is directly linked to a metal carbide support (tungsten carbide in general). FR-A-2 089 415 describes such a composite product consisting of a diamond compact on a tungsten carbide support; the compact and the carbide contain the same additive which can be cobalt, nickel or iron, this additive playing on the one hand the role of diamond catalyst solvent and on the other hand the role of carbide sintering binder. These products have the drawback of rapidly degrading when the active part is brought to a temperature exceeding about 700 ° C. due, on the one hand, to the stresses induced in the metal matrix as a result of the thermal expansion of this same matrix, and on the other hand, the tendency of the diamond in contact with the catalyst to return to the graphite state when it is brought to high temperature without at the same time being subjected to a high pressure. This graphitization affects the structural integrity of the composite.

Such a product with a cobalt binder, available on the market and commonly used, is therefore unusable for work which brings it to temperatures above 750 ° C.

The use of a nickel binder would partially solve these problems but the mechanical properties of tungsten carbide comprising such an additive are much lower than those of tungsten carbide with cobalt binder, which justifies that these products do not have so far encountered industrial applications.

Recently, there have been proposed (JP-A-56 164073; EP-A-0 198 653) diamond abrasive products, not associated with a tungsten carbide support, which are produced by direct sintering of diamond grains in the presence of a binder comprising nickel, for example nickel alloyed with chromium.

These products have the drawback of not being able to be soldered onto tools, which very seriously limits their applications and therefore their use.

There is therefore no composite abrasive product, that is to say consisting of a compact and a support which is integral with it, which simultaneously ensures the qualities of thermostability and resistance to abrasion desirable for current abrasives.

The object of the invention is to propose a diamond abrasive product on a brazable support which better meets those previously known than the requirements of the practice, in particular in that it comprises a compact in which the diamond grains are directly linked together by bridging, with increased thermostability.

The Applicant has been able to determine that the use as a sintering binder of the tungsten carbide support of a nickel-chromium binder made it possible to obtain a composite diamond abrasive product having, compared to a similar product with tungsten carbide support with cobalt binder, equivalent abrasion resistance, increased thermostability and better resistance to corrosion of the carbide support; the product is, moreover, endowed with non-magnetic properties.

The composite diamond abrasive product according to the invention, the active part of which consists of a sintered product comprising diamond grains, each grain being bonded directly to its neighbors by bridging to present a polycrystalline structure, associated with a support essentially consisting of tungsten carbide, is characterized in that the tungsten carbide support comprises a nickel-chromium binding phase.

The active part contains at least 80% by volume of diamond.

According to a preferred embodiment of the invention, the diamond catalyst binder is a nickel-chromium binder originating from the binder phase of the support.

The bonding phase of the support represents from 6 to 15% and preferably 10% by volume of the carbide.

The relative proportions by weight of nickel and chromium of the binding phase vary in the range from 60 to 90% for nickel and from 40 to 10% for chromium.

Apart from the advantages mentioned above, the new binding phase of the tungsten carbide support has the advantage of avoiding the oxidation problems which may arise at the support / active part interface during the diffusion of the binder in the diamond.

The process for manufacturing the diamond abrasive product according to the invention will now be described in detail.

In a cup of refractory protective metal (preferably molybdenum), the powder intended to constitute the active layer of the product is placed; it is a mixture of diamond grains with a grain size is chosen according to the application envisaged, this particle size being generally higher for drilling products than for machining products.

Thus, for products intended for machining, diamond powder can be used, the average grain size of which is between 0.5 and 30 microns; for products intended for drilling, an average grain size of 20 to 150 microns is preferred.

Then placed on the layer thus formed, a piece of tungsten carbide already sintered and containing, as sintering binder, a nickel-chromium binder. This piece, called a pawn, is generally cylindrical in shape. Its face in contact with the diamond mixture can be flat, hemispherical or grooved. The shape of this interface depends on the use of the composite.

The cup is crimped onto the carbide pin so as to ensure a good seal and to avoid any pollution of the active part.

According to another embodiment, the powdery components of the support are placed on the diamond powder layer, ie a tungsten carbide powder added with 6 to 15% of a nickel-chromium mixture, the relative proportions of nickel. and chromium which can vary in a range of 60 to 90% and 40 to 10%.

The assembly thus obtained is then surrounded by a pressure transmitting material which can be chosen from sodium chloride, hexagonal boron nitride, talc or any other suitable material.

The whole is placed in a metal or graphite resistor. The whole is surrounded by a material that transmits pressure and can form seals like pyrophyllite.

This "cell" is then introduced into a press which can develop ultra-high pressures as well as high temperatures.

US-A-3,913,280 describes a press of this type.

The pressure is first applied in order to place itself in the thermodynamic stability zone of the diamond, then the heating (by resistance).

The operating conditions are between 40 and 60 Kbars and 1,250 ° to 1,550 ° C for two to fifteen minutes; we prefer to work at 55 Kbars and 1400 ° C for three minutes.

It is obvious that the operating conditions may vary depending on the type of press and the type of cell used to obtain a good sintering. It is known to those skilled in the art that the optimum conditions for ensuring the sintering of the active part must be determined experimentally.

Under the operating conditions described above and with the help of the binding phase of the carbide support which diffuses by capillary action towards the layer of ultra-hard product, the diamond grains bond together and form a network of intergranular bridges, the voids between grains being filled by the binding phase.

After sintering under high pressure and temperature, the heating is stopped; allowed to cool to about 100 ° C and then the pressure is canceled. The compact is recovered after removing the various materials surrounding it. The metal cup is sandblasted or chemically etched with acid. The compact is then ground and rectified. It can be cut into precise shapes by EDM or laser.

In an alternative embodiment, between 5 and 10% by volume of nickel-chromium mixture is added to the diamond grains of the active part.

In another alternative embodiment, a layer of nickel-chromium alloy is placed in contact with the diamond grains; this layer can be placed between the diamond powder and the support or on the upper part of the active part.

In a last variant, an intermediate layer (diffusion barrier) is placed between the active part and the support, consisting exclusively of diamond, tungsten carbide and / or nickel and chromium.

The characteristics of the product thus obtained were determined compared to the standard product only available on the market, in which the binder of the tungsten carbide support is a cobalt binder.

The wear and tear was studied as a function of the cutting speed both for the standard product and for the product according to the invention obtained under the conditions described in Example 4 below.

The cutting conditions are as follows:
a (depth of cut) = 0.5 mm
f (feed) = 0.7 mm / rev
Machined volume = 100 cm³ / pass
Machined material = dry granite

Examination of the results makes it possible to distinguish three distinct areas:
- the first zone (100 to 200 m / min) represents the wear of the tool mainly due to degradation by abrasion. Diamond grains are torn from the tool one after the other. Wear measures this tendency to "loosen", therefore the quality of the bridging of the diamond grains in the active part of the tool. The energy required for cutting is mainly used to remove material and to wear out the tool. In the present case, the standard product and the product according to the invention have an equivalent low speed abrasion resistance (equivalent wear);
- the second zone (200 to 250 m / min) is an intermediate zone between the first and the last zone described below;
- the third zone (greater than 250 m / min) represents the wear of the tool mainly due to thermal degradation. The energy required for cutting which is used to remove material and to wear the tool (as in the first zone) also serves to heat the tool. Indeed, the tool heats up a lot during work at these high speeds and the stresses due to this increase in temperature are preponderant: if the tool is not thermostable, thermochemical degradation is added to wear by abrasion: the expansion of the binder of the diamond part tends to weaken the intergranular bridging of the diamond and thus promote wear. In the present case, the product according to the invention has a significantly lower wear than the standard product and this indicates better temperature resistance of the product of the invention (increased thermostability). In fact, thermochemical degradation is nonexistent. All of the cutting energy is transformed into material removal and heat which reduces the amount of abrasive degradation.

The product according to the invention, unlike the standard product, can therefore be used for dry machining.

This characteristic is also very useful in the case of drilling tools: poor cooling of the drilling head is no longer a problem with the product according to the invention. This characteristic also allows the brazing of the tools according to a less restrictive operating process.

We have also carried out thermal damage tests on the product according to the invention and it has thus been found that this product retains its wear characteristics after heating to 850 ° C., whereas, under the same conditions, the standard product no longer cuts.

Impact resistance tests have also shown that the product according to the invention gives equivalent or slightly better results than those of the standard product.

To conclude, we can therefore say that, compared to the product standard, the product according to the invention has the following characteristics:
- equivalent abrasion resistance,
- improved impact resistance,
- increased thermostability,
- non-magnetic qualities,
- increased resistance to corrosion of the support.

The corrosion resistance as well as the non-magnetic characteristics of nickel-chromium allow applications (press anvils) using an induction heating for example that the standard product does not offer.

The invention also relates to tools equipped with the composite diamond abrasive product described above and, more specifically, tools intended for machining as well as drilling.

The following examples illustrate the invention without, however, limiting it.

Example 1

In a molybdenum cup, place in successive layers:
- a mixture constituting the active layer comprising 87% by weight of diamond grains having a semi-logarithmic distribution of maximum particle size 20 microns and 13% by weight of solvent-catalyst consisting of nickel and chromium powder with a particle size equivalent to that of diamond in a mass ratio of 80/20;
- a mixture constituting the diffusion barrier comprising 50% by volume of sintered tungsten carbide powder at 8% by weight of nickel with a particle size of 200/325 mesh (45 to 80 microns) and 50% by volume of diamond grains with a particle size 20 microns mixed with 13% by weight of nickel and chromium in a mass ratio of 40/60;
- a disc of tungsten carbide sintered to 10% by weight of binder phase consisting of nickel and chromium in a mass ratio of 80/20.

The quantities of powder used are such that the thicknesses in the final sintered product are 0.7 mm for the active layer and 0.2 mm for the diffusion barrier. The tungsten carbide support is 0.9 mm thick.

The cup is crimped onto the carbide pin, then the assembly is placed in a cell. This is subjected to a pressure of 60 kbar approximately and a temperature of 1500 ° C for three minutes. After cooling, the pressure is removed. The composite product recovered is then freed from its cup by chemical attack and then lapped on both sides. Shapes were then cut by electroerosion in this part and then mounted by brazing on a cutting tool support. After sharpening and polishing, the tools thus obtained were used for dry machining of tungsten deposition on cathodes for X-ray tubes. The results concerning the service life were two to three times greater than those obtained with conventional tools with cobalt bond.

Example 2

In a molybdenum cup, place in successive layers:
- A mixture constituting the active layer of composition identical to that of Example 1 with the exception of the maximum particle size which is 8 microns;
a mixture constituting the diffusion barrier comprising 50% by volume of sintered tungsten carbide powder at 8% by weight of nickel with a particle size of 325 mesh (80 microns) and 50% by volume of diamond powder with a particle size of 20 microns mixed with 13% by weight of nickel and chromium in a mass ratio of 90/10;
a disc of tungsten carbide sintered to 10% by weight of binding phase consisting of nickel and chromium in a mass ratio of 80/20 covered on its part in contact with the powder with a coating of 20 microns of chromium obtained by PVD (Physical Vapor Deposition).

The thicknesses of the various layers are identical to those of Example 1.

The cup is crimped on the pin, then the whole is placed in a cell. This is subjected to a pressure of approximately 60 kbar and a temperature of 1500 ° C. for three minutes. After cooling, the pressure is removed. The composite product is treated in an identical manner to that of Example 1. The cutting tools manufactured were used for the machining of agglomerated wood panels. The performance obtained was 10% higher than that of a part with a cobalt binder.

Example 3

In a molybdenum cup, place in successive layers:
- the powder constituting the active layer comprising 100% of diamond grains with a particle size between 20 and 60 microns;
- the mixture constituting the diffusion barrier comprising 50% by volume of powdered tungsten carbide powder 325 mesh (80 microns) and 50% by volume of diamond powder with particle size 60 microns;
- a cylinder of tungsten carbide sintered to 11% by weight of binder phase consisting of nickel and chromium in a mass ratio of 85/15.

The quantities of powder used are such that the thicknesses in the final sintered product are 0.7 mm for the active layer and 0.15 mm for the diffusion barrier. The tungsten carbide support is 7.4 mm thick.

After crimping the cup onto the carbide pin, the assembly is placed in a subjected cell, after reaching a pressure of 55 kbar, at a temperature of 1400 ° C. for 3.5 minutes. After cooling, the pressure is removed. The composite product (picot) is then rid of its cup by sandblasting. It is then prowled on both sides and then ground to the standard diameter. It was then brazed on a drilling tool head. The pins placed on the periphery of the head, the area most stressed in temperature, were significantly less used than those of the standard product with Cobalt binder.

Example 4

In a molybdenum cup, place in successive layers:
- The powder constituting the active layer comprising 100% of diamond grains with a particle size between 20 and 60 microns in sufficient quantity to form a sintered layer of 0.7 mm;
- a cylinder of tunsgtene carbide sintered to 11% by weight of binder phase consisting of nickel and chromium in a mass ratio of 85/15.

The thickness of this support is 3.2 mm.

The manufacturing cycle was identical to that of the previous example.

The manufactured pins made it possible to carry out comparative tests with the standard product with cobalt binder.

Example 5

In a cup with a hemispherical molybdenum bottom, we successively place it in a uniformly distributed half-sphere:
a layer constituting the active part comprising 87% by weight of diamond grains with a particle size of 0.5 - 8 microns and 13% by weight of solvent-catalyst consisting of nickel and chromium powder with a particle size equivalent to that of diamond in a mass ratio of 85/15;
- A layer consisting of 80% by volume of the above mixture and 20% by volume of tungsten carbide sintered to 8% nickel with a particle size 200/325 mesh (45 to 80 microns);
- a layer made up of the same components as the previous one but where the volume ratios are 40/60 instead of 80/20;
- a cylindrical pin terminated on one side by a half-sphere made of sintered tungsten carbide with 6% of Ni / Cr binding phase in a mass ratio of 85/15.

The quantities of powder used are such that the respective thicknesses of the layers in the final sintered product are 0.3 mm, 0.4 mm and 0.5 mm on the support with a total height of 16 mm.

After crimping the cup onto the carbide pin, the assembly is placed in a subjected cell, after reaching a pressure of 55 kbar, at a temperature of 1450 ° C. for four minutes. After cooling, the pressure is removed. The composite product thus produced (dome) is then freed from its cup by sandblasting. It is then rectified to the nominal diameter and then bevelled into a cone on the rear face.

This product, by its shape and its intermediate layers which act as a shock absorber, is particularly well suited to work involving shocks. It was mounted on a percussion tool. The results were 1.2 times better than the performance usually achieved with products having a cobalt binder.

Example 6

The product identical to that obtained under the conditions of Example 5 was used at the periphery of the cones on the drill heads in tricones. The results were equivalent to those of the product of the prior art with a cobalt binder.

Claims (17)

1- Composite diamond abrasive product, the active part of which consists of a sintered product comprising diamond grains, each grain being linked directly to its neighbors by bridging to present a polycrystalline structure, associated with a support essentially consisting of tungsten carbide, characterized in that the tungsten carbide support comprises a nickel-chromium binding phase. 2- Product according to claim 1, characterized in that the active part comprises at least 80% by volume of diamond. 3- Product according to claim 1 and claim 2, characterized in that the binding phase of the support represents from 6 to 15% by volume of the carbide. 4- Product according to claim 3, characterized in that the binding phase of the support represents 10% by volume of the carbide. 5- Product according to one of claims 1 to 4, characterized in that the relative proportions by weight of nickel and chromium of the binder phase vary in a range from 60 to 90% and from 40 to 10%. 6- Product according to one of claims 1 to 5, characterized in that the diamond catalyst binder is nickel-chromium from the binder phase of the support. 7- Method of manufacturing a thermostable diamond abrasive product, characterized in that it consists:
- placing in a cup a layer of diamond grains intended to constitute the active layer of the product;
- Place on the layer thus formed a layer of tungsten carbide added with a nickel-chromium mixture, intended to constitute the support;
- Subjecting the stack thus produced to a temperature and a pressure sufficient to cause sintering in the plastic phase of the diamond grains between them and ensuring the bonding of the compact thus obtained on the support. 8- A method according to claim 7, characterized in that the active layer of the product contains at least 80% by volume of diamond. 9- A method according to claims 7 and 8, characterized in that the layer intended to constitute the support is a part of tungsten carbide already sintered containing 6 to 15% by volume of nickel-chromium binder phase. 10- A method according to claims 7 and 8, characterized in that the layer intended to constitute the support is a tungsten carbide powder containing 6 to 15% of a powdery mixture of nickel-chromium. 11- A method according to any one of claims 7 to 10, characterized in that added to the diamond grains of the active part between 5 and 15% by weight of a nickel-chromium mixture. 12- Method according to one of claims 7 to 11, characterized in that the relative proportions by weight of nickel and chromium are respectively in a range of 60 to 90% and 40 to 10%. 13- Method according to any one of claims 7 to 10 and 12, characterized in that a layer of nickel-chromium alloy is placed in contact with the diamond grains. 14- A method according to any one of claims 7 to 13, characterized in that an intermediate layer consisting exclusively of diamond and tungsten carbide is placed between the active part and the support. 15- Method according to claim 14, characterized in that the intermediate layer further comprises a nickel-chromium mixture. 16. A machining tool equipped with the composite diamond abrasive product according to any one of claims 1 to 6. 17- A drilling tool equipped with the composite diamond abrasive product according to any one of claims 1 to 6.