EP1975264A1 - Method of manufacturing a part comprising at least one block made from a dense material consisting of hard particles dispersed in a binding phase: application to cutting or drilling tools. - Google Patents

Abstract

Production of an element involves depositing coating material over at least part of block (1) surface having dense material constituted by hard particles dispersed in binder phase, leaving free at least one imbibition area of the surface; contacting imbibition area with imbibiting material (preferably pellet (2)) which locally enriches the block with binder phase; and subjecting resultant block to thermal cycle including heating, temperature maintenance and cooling, to bring some of imbibiting material and binder phase into liquid state. Production of an element involves depositing a coating material over at least part of a block (1) surface having dense material constituted by hard particles dispersed in a binder phase, leaving free at least one imbibition area of the surface; bringing the imbibition area into contact with an imbibiting material having properties which support locally enriching the block with binder phase; and subjecting the resultant block to a suitable thermal cycle, constituted by heating, temperature maintenance and cooling, which brings at least some of the imbibiting material and the binder phase of the block into the liquid state, so as to locally and gradually enrich the dense material block with binder phase by imbibition through the imbibition area. The coating material prevents migration of the imbibiting material through walls of the block on which it is deposited and modifies kinetics of migration of the binder phase into the block so as to create a gradual binder phase distribution. The method also involves depositing on one face of the block after imbibition a diamond table of either the polycrystalline diamond compact (PDC) or thermally stable polycrystalline diamond (TSP) type. An independent claim is included for a cutter comprising a block constituted by hard particles dispersed in a binder phase, and having a composition gradient of binder phase and a shape having a function of a tool; and with respect to the composition gradient, the block has a core, which is more rich in binder phase, and a surface with a low binder phase content of high hardness, with a continually varying binder phase gradient existing between it.

Description

The invention relates to the manufacture of parts comprising at least one block of dense material consisting of hard particles dispersed in a ductile binder phase, the dense material being capable of being locally enriched in the binder phase by imbibition.

The invention relates more particularly to the manufacture of ceramic-metal composite tools, also called cermet, and more particularly tools for oil drilling and / or mining.

By imbibition is meant a liquid enrichment of a perfectly dense solid / liquid system in which at least one solid phase is in the form of grains having the ability to adapt their shape by the absorption of liquid thus making the system more energetically stable . The enrichment in liquid is done under the effect of the driving force of the migration pressure existing in such systems.

The drilling tools consist of heads surmounted by cutters intended to cut or grind the rock. These cutting, active parts of the tool, are mainly based on carbide, extremely hard but fragile material. This fragility is particularly troublesome when such tools are used to drill geological layers made of rocks of different hardnesses, these heterogeneities being capable of causing shocks which can cause cracks in the cutters and thus lead to wear by peeling or to breaks in these cutters.

In order to reduce the risk of premature wear or breakage of these cutters, it has been envisaged to create cermet cutters whose core is more ductile than the outer surface, which is directly in contact with the rocks. Thus, the core of the cutter will be more resistant to shocks (zone enriched in the binder phase), while maintaining a good cutting capacity (poor zone in binder phase in contact with the rock).

In order to produce such cuttings, known as composition gradient or property gradient gradients, it has been proposed to produce porosity gradient non-dense cermets and to infiltrate them with a binder phase in order to improve the ductility of a product. area in the heart of the cermet. However, this method is poorly suited, in particular to WC-Co systems, because it leads to the partial destruction of the pre-existing carbide skeleton and, therefore, does not make it possible to obtain the properties desired for the cutting edge. . Infiltration is a liquid enrichment of a solid / liquid system that is not perfectly dense under the sole motive force of capillarity, also called capillary pressure. Infiltration involves a so-called non-condensed third phase (gas phase) in addition to the two condensed phases (solid, liquid).

It has also been proposed to produce composition gradient cermets having a hard outer surface and a ductile core, by natural sintering (without application of external pressure) in the solid phase of a multilayer part, each layer having a composition different. However, this method does not completely densify the material and must be followed by an expensive treatment of hot isostatic compaction. In addition, the preparation of the composition gradient cermet is complex since it requires the realization of a succession of elementary layers which fit into each other, each layer having a different composition. Finally, this process, which is complex and very expensive, does not make it possible to obtain a continuous gradient of composition. As a result, a cermet thus obtained comprises a succession of layers of hardness and expansion coefficients substantially different from each other, causing risks of delamination at the interface between two successive layers.

In order to overcome the disadvantages of solid phase sintering, it has been proposed to produce such materials by natural sintering in the liquid phase, which makes it possible to obtain very quickly and in a single step, a completely dense graded structure material. But, this process presents the disadvantage of mitigating rather strongly the composition gradient due to the migration of liquid between thin layers. In addition, and against all odds, the composition gradient remains discontinuous when the duration of maintenance in the liquid state remains below a critical time beyond which there is a complete homogenization of the cermet.

For these various reasons, the three methods that have been proposed in the past are unsuited to the industrial manufacture of drilling tools, having satisfactory use properties, both surface wear resistance and ductility. or tenacity at heart.

Moreover, in order to improve the service life of cutting tools, it has been proposed to deposit on the surface of cermets hard nitride, carbonitride, oxide or boride coatings. Such methods have been described, for example, in patents US 4,548,786 or US 4,610,931 . However, these methods have the disadvantage of only improving the resistance to abrasive wear of the cermet, and only on small thicknesses (a few microns). Furthermore, since the coating is different in nature from that of the cutter, delamination or peeling of this layer can occur following a thermomechanical stressing of the cutter.

It has also been proposed to improve both the wear resistance of the surface and the impact resistance of cermets of the WC-Co type by contacting a dense cermet under stoichiometric carbon with a gas phase rich in carbon dioxide. carbon (methane). Under the effect of the temperature, the carbon of the gaseous phase diffuses in the cermet under stoichiometric and reacts with the phase η, according to the chemical reaction 2C + CO ₃ W ₃ C (phase η) → 3WC + 3Co leading to a release cobalt that migrates to areas poorer in cobalt. This method described for example in the patent US 4,743,515 , however, has the drawback of leading to a cobalt-rich binder phase gradient over one or two millimeters, while retaining the heart of the fragile cermet, since it consists of the n phase, which can easily crack during repeated shocks.

Finally, it has been proposed to make cutting tools having particular structures, in particular honeycomb structures, the advantage of which is to combine both good wear resistance and good toughness. These functional microstructure cermets have a compromise of ductile / fragile properties of interest but remain insufficient for the desired application. This composite material is the subject of the patent US 5,880,382 .

The object of the present invention is to overcome these disadvantages by providing a means for manufacturing under satisfactory industrial conditions blocks of dense material based on cermet for cutting or drilling tools having both a very good resistance surface wear and good tenacity at heart so as to have an improved life compared to that of conventional tools.

For this purpose, the subject of the invention is a process for manufacturing a part comprising at least one block of dense material consisting of hard particles dispersed in a binder phase, the dense material being capable of being locally enriched in the binder phase by imbibition of an imbibition material.

According to this method, a protective material is deposited on all or part of the block surface capable of preventing the migration of the imbibition material through the walls on which it is deposited and possibly modifying the kinetics of migration of the phase. binder in the block, leaving free at least one imbibition area of a surface of the block, the imbibition area is placed in contact with an imbibition material capable of locally enriching the block in the binder phase, and then subjecting the dense block to a suitable thermal cycle consisting of heating, temperature maintenance and cooling, so as to partially or completely pass the imbibition material and the liquid phase in the liquid state. binding the block so that the binder phase enrichment is done only through the impregnation area.

Preferably, the thermal cycle is carried out, so that in the assembly formed by the dense material block and the imbibition material, a temperature gradient such that the minimum imbibition temperature is reached the interface between the block and the imbibition material, and such that, in the block, the temperature is higher than the minimum imbibition temperature and, in the imbibition material, at least in the vicinity of the interface, the temperature is below the minimum imbibition temperature.

The thermal cycle can also be carried out so that the time spent in the liquid state and the holding temperature generate a liquid volume of the imbibition material just sufficient for the desired enrichment.

The imbibing material is, for example, a pellet consisting of a compact of compacted powdered powder under heat, one side of which is in contact with a surface of the block made of dense material. It preferably has a local change in the composition of its binder phase following a rise in temperature in a crucible leading to a non-collapse of the imbibition material.

The imbibition material may also be in the form of a paste (a mixture of a powder and an aqueous cement) deposited on a surface of the block made of dense material, for example with a brush, or in the form of a projected coating by plasma or laser. The advantage of such conditioning of the imbibition material is that it can adapt to all block geometries.

Preferably, the block in contact with the imbibing material is placed in a refractory crucible chemically inert with respect to the imbibition material, for example alumina or graphite, and heated in an oven under a controlled atmosphere or under vacuum.

The constituent phases of the block of dense material generally comprise at least hard particles of one or more metal carbides, and a ductile metallic binder phase, which preferably forms a temperature eutectic with the metal carbide (s). The block may further consist of other hard particles such as diamond particles.

The imbibing material preferably has a composition close to that of the binder phase of the dense material block. In particular, above the imbibition temperature, the composition of the imbibition material is close to that of the liquid binder phase of the dense material block. For example, it consists, for at least 85% by weight, of a eutectic formed between the metal carbide (s) of the block and the metal binder phase, whose melting temperature is less than or equal to slightly greater than the melting temperature of the blocking phase of the block, the metallic binder phase of the imbibition material consisting of one or more metal elements taken from Co, Fe, Ni, and at most 15% by weight, of one or more metal elements selected from Cu, Si, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, the remainder being impurities.

The imbibition temperature is, in general, the eutectic temperature Te of the imbibition material and corresponds, in general, to the melting temperature of the binder phase of the dense block.

Preferably, the thermal cycle comprises a rise in temperature at a holding temperature Tm greater than or equal to the eutectic temperature Te of the imbibition material, preferably less than Te + 200 ° C, and better, less than Te + 100 ° C, followed preferably by a short hold at the temperature Tm, then a rapid cooling (about 50 ° C / min) at a temperature below Te, and, finally, a slower cooling (10 to 5 ° C / min) up to room temperature.

The material of which the block made of dense material is made can be a cermet of the WC-Co or WC- [Co and / or Ni and / or Fe] type, to which diamond particles have optionally been added, and the imbibition material is a eutectic of the WC-M type, M being one or more metals taken from Co, Ni and Fe.

The cermet of which the block made of dense material is made may in particular be of the WC-Co type and comprise at most 35% by weight of cobalt, and the imbibition material may in particular be a eutectic of the WC-Co type, comprising at most 65 % by weight of cobalt.

When a protective layer is deposited on the surface of the block of dense material, this protective layer may consist in particular of boron nitride, but also possibly of graphite or alumina.

The block of dense material is for example a bit of drill bit, and after the imbibition treatment can be reported on one side of the block a PDC (Polycrystalline Diamond Compact) diamond-shaped insert ("compact of pollycrystalline diamond"). or TSP (Thermally Stable Polycrystalline diamond: "thermally stable polycrystalline diamond").

The diamond plate can be directly reported by HPHT (High Pressure - High Temperature) process on the block of dense material previously treated by imbibition. The diamond wafer may also be attached to another homogeneous dense cermet support block which is then imbibed together on the first imbibed treated block.

The invention also relates to a drill bit for cutting and / or grinding rocks, such as a drill bit, a mine pick, a tricone, an impregnated tool, comprising a block of dispersed hard particles (s). ) in a binder phase, in particular of the WC-Co type, optionally added with diamonds, which comprises, over a distance greater than 0.5 mm, a continuous compositional gradient so as to constitute a tenacious core opening onto a face, surrounded by a hard layer on the surface.

The cutter may, in addition, be surmounted by a PDC or TSP type diamond wafer on one face of the block.

Finally, the invention relates to a grinding tool and / or rock cutting comprising at least one cutting according to the invention.

• la figure 1 est un schéma de fabrication par imbibition d'un bloc en cermet dense ayant une surface extérieure dure et un coeur tenace ;
• la figure 2 est un schéma d'un cycle thermique d'imbibition d'un bloc en cermet dense ayant une surface extérieure dure et un coeur tenace ;
• la figure 3 est un schéma en coupe transverse suivant la hauteur h d'un cermet dense dont le coeur a été rendu plus tenace par imbibition ;
• la figure 4 est un schéma du profil de répartition en phase liante le long de la hauteur h de la face inférieure à la face supérieure du cermet dense dont le coeur a été rendu plus tenace par imbibition, représenté à la figure 3 ;
• la figure 5 est une vue en coupe transverse d'un taillant pour outil de forage constitué d'un bloc en cermet dense dont le coeur a été rendu plus tenace, et sur lequel une plaquette de diamant a été rapportée;
• la figure 6 est une vue en coupe transverse d'un taillant pour outil de forage, comprenant un premier bloc en cermet dense dont le coeur a été rendu tenace, et sur lequel a été assemblé par imbibition un second bloc en matériau dense surmonté d'une plaquette de diamant.

The invention will now be described in a more precise but nonlimiting manner with reference to the appended figures, in which:

• the figure 1 is an imbibition manufacturing scheme of a dense cermet block having a hard outer surface and a stubborn core;
• the figure 2 is a diagram of a thermal imbibition cycle of a dense cermet block having a hard outer surface and a stubborn core;
• the figure 3 is a diagram in transverse section along the height h of a dense cermet whose heart has been made more tenacious by imbibition;
• the figure 4 is a diagram of the binder phase distribution profile along the height h of the lower face to the upper face of the dense cermet whose core has been made more tenacious by imbibition, shown in FIG. figure 3 ;
• the figure 5 is a cross-sectional view of a drill tool cutter made of a dense cermet block whose core has been made more tenacious, and on which a diamond plate has been reported;
• the figure 6 is a cross-sectional view of a drill tool cutter, comprising a first dense cermet block whose core has been made tenacious, and on which a second block of dense material surmounted by a wafer has been assembled by imbibition; diamond.

In general, cutters for a drilling tool, or more generally for a cutting tool, are parts comprising blocks of generally parallelepipedal or cylindrical shape, obtained by powder metallurgy, made of a material whose structure comprises on the one hand hard particles such as metal carbides, and in particular tungsten carbides, and on the other hand a binder phase consisting of a metal or metal alloy which, in contact with the carbides, can form, in temperature , a eutectic having a melting point lower than both the melting temperature of the carbides and the melting temperature of the metal or metal alloy. This metal or metal alloy is for example cobalt, but may also be iron, or nickel, or a mixture of these metals. In addition, the binding phase may contain addition metals whose sum content may be up to 15% by weight, but in general does not exceed 1% by weight. These addition metals may be copper to improve the electrical conductivity, or silicon which has a surfactant effect with respect to the system consisting of carbide and the binder phase, or which may still be carburigenic elements that can form mixed carbides or carbides of the type M _x C _y other than tungsten carbide. These various elements are in particular manganese, chromium, molybdenum, vanadium, niobium, tantalum, titanium, zirconium and hafnium.

In addition to these main elements, the composition of the binder phase may include addition elements which are usually encountered in such materials and which modify the shape and / or inhibit the magnification of the hard particles. The skilled person knows these elements. Finally, the chemical composition of these materials includes unavoidable impurities that result from the processes of making. The person skilled in the art knows these impurities.

For certain applications, in order to reinforce the wear resistance of the cutters, diamond particles are added. These diamond particles are added to the powder mixture which is used to manufacture the block by sintering.

In general, after sintering, the block is dense and consists of hard particles dispersed in a binder phase. Thus the block is made of a dense material.

In the case of the WC-Co system, the temperature-forming composition of the eutectic has a cobalt content of about 65% by weight. Of course, the blocking properties obtained thus depend in particular on the relative proportions of carbide (s) and metal or metal alloy. In the case of drilling materials, its binder phase content is generally much lower than that of the eutectic and even substantially less than 35% by weight. Indeed, the lower the binder phase content, the higher the hardness, and therefore the wear resistance of the material. However, the lower the binder phase content, the lower the cermet toughness. These properties of these materials, called cermets, are well known to those skilled in the art.

In addition, the properties of the cermet also depend on the size and shape of the carbide grains.

In order to improve the properties of the blocks considered in accordance with the invention, a method for enriching the binder phase of a part of the block and possibly modifying its composition, by imbibition, from a dense sintered cermet is used. preferably having a homogeneous composition.

The phenomenon of imbibition is possible in two-phase systems (hard particles constituting the solid phase - binder phase constituting the liquid phase at the imbibition temperature) fulfilling certain conditions. Thus, at the imbibition temperature (T≥Te), the binder phase which is liquid, must wet the hard particles, these same hard particles must be partially soluble in the liquid binder phase and the system must have Ostwald ripening. with modification of the shape of the hard particles without necessarily a magnification of these particles by the phenomenon of dissolution - reprecipitation.

To perform the imbibition, it is necessary to contact a dense cermet having a binder phase content below a critical content (35% by weight in the case of the WC-Co system) with an imbibition material of suitable composition and carry all at a temperature sufficient for the imbibition material and the binder phase to be liquid or at least partially liquid. When these conditions are realized, there is transfer of binder phase inside the cermet and thus, enrichment thereof in the binder phase. In general, the imbibing material preferably has a composition that is identical to or similar to that of the eutectic of the cermet considered at the imbibition temperature. In this case, the imbibition increases the content of the cermet in the binder phase without modifying the chemical composition of this material. This phenomenon can continue until there is saturation in the binding phase of the cermet. For a cermet of the tungsten carbide / cobalt type with an imbibing material of the same kind, the saturation is obtained for a cobalt content of about 35% by weight in the cermet.

The imbibing material may have a composition different from that of the binding phase of the dense cermet. In this case, there is not only enrichment of the cermet in the binder phase, but also modification of the chemical composition of the binder phase and possibly the carbide phase.

The imbibition phenomenon is thermally activated and its kinetics is therefore related to the temperature but also to the initial binding phase content of the cermet, as well as to the size and shape of the hard particles.

The imbibition is usually used to enrich dense binder-phase cermet blocks by dipping one of their ends in a liquid having the eutectic composition of the cermet considered. This method has the disadvantage that the liquid imbibing material migrates not only into the cermet through (s) zone (s) of contact but also through the faces adjacent to this (these) zone (s) of contact, making the shape of the gradient is difficult to control.

Also, to obtain the desired result which is the opposite of the result usually obtained by dipping, the inventors have imagined to proceed as will now be explained.

As represented in figure 1 , there is a block 1 to be treated, a dense material consisting of hard particles embedded in a binder phase, in contact with a pellet 2 made of an imbibition material capable of migrating, starting from a certain temperature, by imbibition inside the block 1. The block 1 is generally cylindrical or parallelepipedal shape and has a lower face 3, one or more side faces 5 and an upper face 6. The wafer 2 imbibition material is in contact of the lower face 3 of the block 1, and the contact area 4 of the pellet 2 of imbibition material and of the block 1, also called imbibition area, is of surface substantially lower than the surface of the lower face 3 of the block 1. It is in particular the positioning and extent of the imbibition area with respect to the lower face 3 of the dense cermet which determine the shape of the gradient. The face or the lateral faces 5 and the upper face 6 of the block 1 are covered with a layer 7 of protective material. This protective material, which is, for example, boron nitride, is intended on the one hand to prevent the transfer of imbibition material through this protective layer and, on the other hand, to modify the kinetics of migration of the binder phase. in the block. The assembly constituted by the block 1 with its protective layer 7 and by the wafer 2 of imbibition material, is placed in a crucible inert chemically at the temperatures of the heat treatment, for example alumina or graphite 8 placed in a furnace 9 under a controlled atmosphere which may be a vacuum oven or an oven under a nitrogen or argon atmosphere. This oven must be capable of reaching a sufficient temperature, so that the imbibing material and the binder phase of the block are partially or completely in the liquid state, for example 1350 ° C, or even 1320 ° C, for the case of a WC-Co block, with high heating and cooling rates in order to be able to control and in particular to minimize the time that the assembly will pass above the eutectic temperature of the treated system which is the temperature at from which the imbibition occurs and which for cermets of the WC-Co type is of the order of 1300 ° C. This oven can be a resistance furnace, an induction furnace, a microwave oven or a SPS (Spark Plasma Sintering) installation.

The block 1 of dense material is then subjected to a thermal cycle which first comprises heating to a temperature greater than or equal to the temperature at which at least the contact zone 4 between the pellet 2 of imbibition material and the lower surface 3 of the block 1 goes into the liquid state. The heating is carried out so that the temperature inside the block is greater than the melting temperature Te of the block eutectic.

Preferably, the natural temperature gradient of the furnace is used so that the heating is carried out so that the temperature inside at least a portion of the pellet 2 remains below the melting temperature of the material of the furnace. imbibing.

By doing so, at the imbibition temperature, the imbibing material migrates into the interior of the dense material block at the contact zone between the imbibition material pellet and the lower surface of the block, for example. against, it does not migrate by the outer side walls 5, nor by the upper wall 6 of the block. Thus, the enrichment material imbibition block dense material is essentially in an inner zone opening on the bottom wall 3 and extending towards the inside of the block.

More specifically, the heat treatment comprises, as shown in FIG. figure 2 , a heating phase up to the melting temperature Te of the eutectic, then a phase 16 in which the temperature is maintained above the temperature Te to a holding temperature T _m at which the block is maintained for a holding time t _m , then a phase 17 in which the block 1 is cooled very rapidly to a temperature below the temperature Te and, finally, a cooling phase 18 slower to room temperature.

During the heating phase, below the temperature Te, the imbibition material consolidates and shrinks. Beyond the temperature Te, a eutectic liquid is formed at the contact surface.

The bearing temperature should not be too far from the temperature Te, but enough to generate enough liquid and allow the wetting and migration of a liquid in chemical equilibrium with the dense cermet to be soaked. This temperature difference is for example at most 200 ° C or better 100 ° C, and preferably less than 50 ° C.

The total time tt above the minimum imbibition temperature Te, generally less than 15 min, as well as the holding temperature T _m and the holding time t _m , are chosen to ensure adapted distribution of the imbibition material inside the dense material block. The skilled person knows how to choose these parameters.

The cooling between the bearing temperature and the eutectic imbibition temperature is carried out rapidly, so as to avoid uncontrolled migration of the imbibing material.

For this, it is desirable that the rapid cooling rate is greater than 40 ° C / min, more preferably greater than 50 ° C / min and more preferably greater than 60 ° C / min. However, in order to avoid generating excessive stresses in the dense material block, it is preferable that the cooling rate remains below 100 ° C./min.

Below the eutectic temperature, the migration of the imbibition material being blocked, the cooling is done at a substantially lower speed so as to avoid generating excessive residual stresses inside the block of dense material.

By doing so, we obtain dense blocks such as the one shown in section at figure 3 and which has a core having a high binder phase content and an outer zone 21 having a low binder phase content. Due to its low binder phase content, the outer zone 21 has a very high hardness, so a very high wear resistance but low toughness. On the other hand, because of its high binder phase content, the inner zone 20 has a very good toughness.

By the imbibition process which has just been described and which corresponds to a gradual enrichment of the dense cermet in the binder phase, the evolution of the binder phase content is done continuously decreasing from the core to the active sides of the block. This is schematically represented in the figure 3 by bonding phase isotment lines 22a, 22b, 22c, 22d and at the figure 4 by a binder phase distribution profile along the height h of the lower face to the upper face of the dense cermet.

When the dense cermet block is of the tungsten carbide / cobalt type, the latter must have a cobalt content of less than 35% by weight. weight. Indeed, beyond this content, the imbibition process is impossible. To enrich such a block in its own binder, this block is brought into contact with an imbibition material consisting of a mixture of tungsten carbide / cobalt whose cobalt content can vary between 35% and 65% by weight. Preferably, for the WC-Co system, the mixture has the eutectic composition corresponding to 65% by weight of cobalt. This mixture of tungsten carbide / cobalt is homogenized, for example dry or wet, preferably in a turbula, for several hours. The mixture is then compacted, for example cold in a single-action mold or is mixed with an aqueous cement. When the imbibition material is compacted cold, it is in the form of a pellet which is brought into contact with the block that is to be treated. When the imbibition material consists of a powder mixed with an aqueous cement, it can be deposited on the block with a brush on a defined area which can have any shape. It can also be deposited by plasma projection or laser projection techniques. The technique of brush or spray application has the advantage of allowing to deposit the imbibition material on any area of a block whose shape may be more complex than that of a parallelepiped or a cylinder.

It will be noted that for each block of dense material to be treated, the size and shape of the imbibition area must be adapted to the shape of the gradient that is to be generated inside the block. The skilled person knows how to make these adaptations.

Moreover, the inventors have found quite unexpectedly that the presence of the protective layer on the outer surface of the dense material block had a significant effect on the migration of the imbibition material inside the block.

In particular, they found that the protective layer made it possible to obtain a steeper binder phase gradient and consequently a much greater hardness gradient than is possible to obtain. in the absence of this protective material. In addition, the binder phase gradient may be domed.

This effect is illustrated by the following two examples, both of which concern the treatment of a dense block of tungsten carbide / cobalt whose cobalt content before treatment is 13% by weight, the imbibition material consisting of a pellet of tungsten carbide / cobalt eutectic composition, that is to say about 65% by weight of cobalt. The size of the WC grains is, for example, approximately 1 μm corresponding to an initial hardness of 1230 HV. In both cases, the assembly is placed in an alumina crucible inside a resistance furnace and heated to a temperature of 1350 ° C. (sample temperature) for 3 minutes.

In the first example, the outer walls of the dense block which were not intended to be in contact with the imbibing material, were coated with a protective material consisting of boron nitride. After treatment, the hardness in the vicinity of the outer surface of the block was of the order of 1370 HV, while the minimum hardness inside the core of the block was 890 HV only, a difference in hardness of the order of 480 HV, the variation of hardness being able to take place on distances of the order of 5mm.

In the second example, given for comparison, the outer walls of the dense block have not been coated with a protective layer. The maximum hardness observed was 1200 HV at the outer surface of the block, and the minimum hardness at the heart of the 1010 HV block, which corresponds to a difference of only 190 HV.

The difference between the two results may have different explanations. In particular, it can be thought that the protective material increases the interfacial energy between the binder phase and the carbide phase, and thus affects the migration of the binder phase within the block.

The method which has just been described and which makes it possible to obtain dense blocks intended to constitute cutting tools has the advantage of making it possible to obtain blocks whose external part is hard and the part Central is tenacious. This variation of hardness is done over millimeter distances. In particular, the variation in hardness is over a distance greater than 0.5 mm, preferably greater than 1 mm, even greater than 2 mm, or even 3 mm, but preferably less than 30 mm, better still less than 8 mm. mm, even less than 6 mm.

In addition, the inventors have found that after imbibition of the dense block, it is possible to deposit on the upper face of the block, a synthetic diamond wafer, while maintaining in part the gradient obtained by the imbibition treatment. This relatively thick diamond layer, preferably greater than 0.5 mm, can be set up by pressing a graphite powder by HPHT (High Pressure - High Temperature) process. We then obtain a cutting as shown in section at figure 5 which consists of a dense cermet support block 40 whose core 41 has been enriched in binder phase by imbibition to be more tenacious, and a diamond plate 42 attached to a face 43 of the support block.

When the diamond wafer has been reported on a block of dense material which has been treated with a protective layer as just described, the amplitude of the hardness gradient inside the support block is no longer than 350 HV instead of 480 HV, but the maximum hardness at the periphery of the sample is 1550 HV instead of 1370 HV and the minimum hardness is 1200 HV at the bottom of the block instead of 890 HV, ie a block support harder on the surface, but a little less tenacious at heart compared to the same treated block, before HPHT operation.

This change in hardness results from the diamond pressing operation, which affects the cobalt gradient and thus the hardness of the diamond platelet support.

To deposit a diamond layer on a dense cermet support block, it is also possible to proceed according to a second method which is illustrated in FIG. figure 6 .

According to this second method, a dense cermet block 50 is used which has been treated according to one or the other of the imbibition methods indicated above in order to give it a core 51 whose toughness has been improved by increasing the the binder phase content. On this cermet is assembled by imbibition through a surface 55 a cutting 52 consisting of a support block 53 in dense and homogeneous cermet on which has previously been reported a diamond plate 54.

The compositions of the blocks 53 and 50 are chosen so that, when they are brought into contact and brought to a temperature greater than or equal to the eutectic temperature, there is a binder phase migration of one of the blocks to the other, so as to ensure the perfect assembly of these two blocks. To obtain this result, it is appropriate to choose, for blocks 53 and 50, cermets having compositions and / or sizes and / or hard particle shapes such that the migration pressures are different. These migration pressures depend in particular on the size and shape of the carbide particles and the binder phase content. The skilled person knows how to choose these cermet structures.

The method that has just been described makes it possible to manufacture cutters for drill tool heads such as tricones, PDC or TSP tools, impregnated tools for oil drilling, or even cutters for felling tools. or fragmentation of rocks or drilling, in the field of mining, civil engineering, or tools for machining materials.

These cutters are pieces which comprise at least one block of dense material obtained by the method according to the invention or which consist of such a block. These blocks can have very different shapes, adapted to the case for which they are intended. They can thus constitute blades.

These cutters can be installed on any type of tool for oil drilling or mining drilling or in the field of civil engineering, especially on any ground or subsoil excavation machine. These applications include peaks used on mining machines of the type "point attack" or type "continuous minor" or type "shearing" or tunneling soft rocks. These applications can also be knobs used on machines including full section such as tunnel boring machines or drills, or rotary drill bit or rotary-percussion drilling.

This method can also be used to fabricate metal working tool elements for which a very hard active surface is desired on a more tenacious body.

Claims (20)

Process for manufacturing a part comprising at least one block of dense material (1, 40, 50) consisting of hard particles, of identical or different nature, dispersed in a binder phase, the dense material being capable of being locally enriched in the binder phase by imbibing an imbibition material, characterized in that it is deposited on all or part of the surface of the block leaving at least one imbibition area (4) of a surface (3) of the block free a material protection device (7) capable of preventing the migration of the imbibition material through the walls on which it is deposited and possibly modifying the kinetics of migration of the binder phase in the block, the imbibition area is set ( 4) of the surface (3) of the block (1) in contact with an imbibition material (2), and then subjecting the dense block in contact with the imbibition material to a suitable thermal cycle consisting of heating, of a temperature maintenance and a cooling, of partially or completely converting the blocking phase of the block into the liquid state, so that the binder phase enrichment takes place only through the impregnation area. Process according to Claim 1, characterized in that the thermal cycle is carried out so that in the group consisting of the dense block and the imbibition material a temperature gradient such as the minimum temperature of imbibition is achieved at the interface between the block and the imbibition material and such that, in the block, at least in the vicinity of the interface, the temperature is higher than the minimum imbibition temperature and, in the material imbibition, at least in the vicinity of the interface, the temperature is below the minimum imbibition temperature. Process according to any one of Claims 1 to 2, characterized in that the imbibition material is a pellet (2) consisting of a mixture of agglomerated powder, one side of which is in contact with a surface of the block. Process according to any one of claims 1 to 2, characterized in that the imbibing material is in the form of a coating on a surface of the block deposited for example by brush, by plasma spraying or by laser projection. Process according to any one of Claims 1 to 4, characterized in that the block (1) in contact with the imbibition material (2) is heated in an oven (9) under a controlled atmosphere or under vacuum. Process according to any one of Claims 1 to 5, characterized in that the solid particles of which the block material consists comprise at least particles of hard metal carbides, and in that the binder phase is of a metallic nature. Process according to Claim 6, characterized in that the block contains, in addition, natural or synthetic diamond particles up to 1 mm in diameter. Process according to Claim 6 or Claim 7, characterized in that the imbibition material consists of hard particles dispersed in a binder phase, these particles and this binder phase being of the same or different nature as those of the block, and in the same proportions or not as those of the block, including the proportion corresponding to the eutectic composition, if the system presents a eutectic. Process according to Claims 6 to 8, characterized in that the chemical composition of the imbibing material consists, for at least 85% by weight, of a eutectic formed between the metal carbide (s) of the block and the metal binder phase, such that the difference between the melting temperature of the binder phase of the imbibition material and the binder phase of the block is less than 200 ° C, and at most 15%, by weight, of one or more metallic elements selected from Cu, Si, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, the remainder being impurities. Process according to Claim 8 or Claim 9, characterized in that the imbibition temperature is the melting temperature Te of the eutectic of the imbibition material. Process according to Claim 10, characterized in that the thermal cycle undergone by the block in contact with the imbibition material consists of a rise in temperature up to a holding temperature Tm, within a range [eutectic temperature of the material of imbibition Te; Te + 200 ° C], during a holding time tm, fixed as a function of the geometry of the block and the geometry of the desired composition gradient, from 0 to 15 min, followed by a first rapid cooling ( above 40 ° C / min) to a temperature below Te, and finally, slower cooling (below 10 ° C / min) to room temperature. Process according to any one of Claims 6 to 11, characterized in that the material of which the block is made is a dense cermet of the WC-Co or WC- [Co and / or Ni and / or Fe] type, to which optionally added diamond particles, and in that the imbibition material is of the WC-M type, M being composed of one or more metals selected from Co, Ni and Fe. Process according to Claim 12, characterized in that the cermet of which the block is made is of the WC-Co type and comprises at most 35% by weight of cobalt, and in that the imbibition material comprises a cobalt content of 35% by weight. at 65% by weight. Process according to any one of Claims 1 to 13, characterized in that the protective layer consists of boron nitride, graphite or alumina. A method according to any one of claims 1 to 14, characterized in that the block (40, 50) is a drill bit holder and in that after the block imbibition treatment is deposited on a face of the block a diamond insert (42, 54) PDC (Polycrystalline Diamond Compact) or TSP (Thermally Stable Polycrystalline diamond). Process according to Claim 15, characterized in that the diamond pellet (42) is attached by HPHT directly to the block (40). A method according to claim 15, characterized in that the diamond wafer (54) is carried by a cermet (53) which is imbibed on the block (50). Cutter for a rock size tool, such as a block consisting of hard particles dispersed in a binder phase, in particular of the WC-Co type, optionally with added diamond particles, characterized in that it comprises a distance greater than 0 , 5 mm, a strong gradient of continuous composition in binder phase, of shape defined by the functions of the tool, so as to obtain a tenacious core, rich in binder phase, and a surface poor in binder phase, high hardness. Cutter according to claim 18, characterized in that it is surmounted by a PDC or TSP diamond-shaped wafer. A rock size tool comprising at least one cutter or blade according to claim 18 or claim 19.

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