FR3051186B1 - METHOD FOR MANUFACTURING A METAL-CERAMIC POWDER SUITABLE FOR THE PRODUCTION OF A HARD CERAMIC PIECE AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

------ PROCESS FOR MANUFACTURING A METAL-CERAMIC POWDER SUITABLE FOR THE MANUFACTURE OF A HARD CERAMIC PIECE AND CORRESPONDING MANUFACTURING METHOD The method for manufacturing a metal-ceramic powder comprises the following stages: preparation of 'A mechanically activated mixture of SiC, BN and B powders, a first fraction of aluminum powder, and at least one pulverulent dopant; mixing the mixture thus prepared and a binder; formation of primary billets by compacting the previous mixture; vacuum heat treatment of these primary billets; grinding of the primary billets thus treated; preparation of a mixture of the powder thus obtained and a second fraction of the aluminum powder; mixture of this mixture and a binder; secondary billet formation by compacting the mixture obtained; vacuum heat treatment of these secondary billets; and grinding of the secondary billets thus treated.

Description

PROCESS FOR THE PRODUCTION OF A METAL-CERAMIC POWDER APPROPRIATE FOR THE MANUFACTURE OF A CERAMIC PIECE AND METHOD OF MANUFACTURING THE SAME

The present invention relates to a process for producing a metal-ceramic powder suitable for the manufacture of a hard ceramic by selective melting. It also relates to a method of manufacturing a piece of hard ceramic with this powder.

Laser selective melting (Selective LaserMelting - SLM) is a unique process that provides the opportunity to manufacture units with very complex geometries. On the basis of the idea of a selective hardening of very thin layers (the size of which goes down to microns), this approach makes possible the production of internal cavities and channels of complex shape in the mass of the unit. At present, this technique is widely available for plastic materials - also known as 3D printing - covering a wide range of applications ranging from medical parts to the production of souvenirs.

The production of metal units by SLM is more expensive. However, it is irreplaceable for parts in aviation and the turbine industry. The idea of replacing metal with ceramics seems to be very attractive because ceramics, when compared to metals, have superior heat resistance, lower thermal conductivity, higher chemical resistance to oxygen / environments reagents, etc. However, to date, such production is impossible because it is not possible to produce ceramic units having the characteristics required by SLM.

Several attempts have been made to solve this problem. 1 - The use of ceramic powders covered by organic polymers The general idea is that each particle powder is covered by an ultrafine layer of an organic compound acting as an adhesive; under the effect of laser heating, this adhesive hardens and connects the particles. The advantage of this approach is that the curing process does not lead to changes in the geometry of the parts since no physical or chemical processes occur in the ceramic material of the particle itself. The disadvantage of the process is a very limited resistance of the final part; it can be improved by some tips with the polymer composition but it is still insufficient for industrial applications. Another point which renders this approach obsolete is the fact that all organic compounds burn at high temperatures, whereby the ceramic parts formed by such a technique have a very limited operating temperature range, even lower than for existing metal parts produced by SLM. 2 - The direct SLM of ceramic powder particles

This approach is based on the increase in laser heating power leading to a partial melting of the surface of the ceramic powder particles during the SLM process. Generally this technique can provide the necessary resistance and the necessary heat resistance of the ceramic parts produced, but it poses a certain number of problems: the nature of the SLM process does not ensure the appropriate cooling conditions which make it possible to eliminate the thermal stress defects occurring during fusion process, these constraints are necessarily transmitted to the mass of the partsynthetized, which in turn gives rise to an inevitable cracking in the mass of the part, leading to its partial or even complete destruction; - The dimensions of the particles are changedpectacularly during the surface fusion; it follows that a significant withdrawal takes place, rendering impossible the production of ceramic parts with the exact exact measurement required.

In conclusion, such an approach is not more appropriate for industrial applications. 3 - SLM ceramics from a slurry The general idea of this process is the evaporation of a liquid fraction from the laser boiling slurry; this results in the formation of solid ceramic. This technique also leads to strong shrinkage, the final gap of linear dimensions usually exceeding 30%. In addition, the mechanical strength is also very low.

It can be emphasized that the main disadvantages of the above processes are due to the nature of the physical and chemical processes that occur during laser prototyping. Therefore, there is no real way to overcome them, tips are possible but only for a partial improvement.

Thus, at present, the above methods are not suitable for industrial applications and it is not seen how to make these processes industrially applicable in the future.

The present inventors have sought to solve this problem with the aim of proposing a method for producing, by SLM without shrinkage during the entire process - the final deviation of the dimensions generally having to be less than 0.5% - final ceramic pieces having a mechanical strength. typically greater than 40 MPa, which can be exploited in high temperature environments, exhibiting for this purpose a heat resistance, a high temperature resistance and a stability of the phase composition generally up to 1300 ° C.

The applications targeted for the ceramic parts obtained are very numerous in mechanics and precision mechanics, for example in the fields of the manufacture of engines for aviation, spacecraft, boats, automobiles and otherindustries. In particular, we can mention the design of a new generation of gas turbines, in particular ceramic microturbines.

The inventors then developed a process for manufacturing a metal-ceramic powder based on Al-SiC-BN-B system compositions, doped with In and Ga additions, for the production of hard ceramic parts having no withdrawal with cooking by SLM.

The present invention therefore firstly relates to a method for manufacturing a suitable metal-ceramic powder for the manufacture of a selective hard ceramic selective laser, characterized in that it comprises the following steps: a) preparation of a mechanically activated mixture of SiC, BN and B powders, a first aluminum powder fraction, and at least one pulverulent dopant; b) mixing the mixture prepared in step a) and a binder; c) forming primary billets by compacting the mixture of step b); d) vacuum heat treatment of the primary billetsprepared in step c); e) grinding the primary billets obtained in step d); f) preparing a mixture of the powder of step e) and a second fraction of the aluminum powder; g) mixing the mixture prepared in step f) and a binder; h) forming secondary billets by compacting the mixture of step g); i) vacuum heat treatment of the secondary billets prepared in step h); and j) grinding the secondary billets obtained in step i); the steps f to j can be repeated at least once, each time using a new aluminum fraction and starting each time with the preparation of a mixture of the powder obtained in the preceding step and the new powder fraction of aluminum. In step a), at least one dopant selected from indium and gallium can be used, said dopant being present in the form of an indium-gallium alloy. In step a), it is possible to use powders having a particle size of less than 40 μm. In step a), it is possible to mix a first mechanically activated mixture of SiC, BN and Bet with a second mechanically activated mixture of Al and the dopant (s).

The mechanical activation of a mixture can be effected by making this mixture in an agate mixing vessel containing agate beads at a speed of 300-500 rpm in 3-6 cycles for 18-48 hours.

The powders can be mixed in the following molar percentages:

SiC: 25-34 BN: 6-8 B: 9-11

Al: 50-55,

Ga (dopant): 0.50-0.75

In (dopant): 0.50-0.75 the total mass of the constituents representing 100%, Al being introduced in at least two fractions, namely the first fraction of step a) and the second fraction of step f), the fractions may be equal fractions.

In and Ga dopants can be used in the following percentages:

In: 10-90%

Ga: 90-10% the total mass of the dopants representing 100%. In step b) and in each step g), it is possible to use a binder formed of a synthetic rubber such as a styrene-butadiene rubber diluted in a solvent such as white spirit, in mass proportions. Synthetic rubber: solvent in particular 1 : 4 to 1: 7. In step c) and in each step h), compacting in pressureisostatic billets under 980.7 - 1471 MPa (10-15 tonnes / cm 2) can be carried out in molds for a period of 35-50 minutes.

After each of steps c) and h), the billets can be dried under the following conditions: ambient temperature for 20-30 hours; then - in a drying oven at 70-80 ° C for 20-30 hours and then at 105-120 ° C for 20-30 hours. In step d) and in each step i), the billets can be placed in a vacuum oven and heated at 1250-1500 ° C for 20-30 hours. In step e) and in each step j), the billets can be milled to a particle size of 40 μm, in particular using several steps: milling to the mill until a particle size smaller than 5 mm is obtained; At least one milling cycle until a granulometry of 3-5 mm is obtained; At least one abrasion cycle until a granulometry of 0.044-0.1 mm is obtained; Sieving in order to obtain a particle size of less than 40 μm. At each step f), aluminum powder may be used at a rate of 10-20% by weight relative to the total mass of the fraction obtained with the particle size below 40 μm.

The process according to the invention may comprise an additional step after the last step: k) aging of the milled billets in a desiccator at room temperature for 10-14 days.

The present invention also relates to a method for manufacturing a hard ceramic selective laser perfusion part, characterized by the fact that it comprises the steps of: - building layer by layer the cermet piece selective laser perfusion from the powderobtained by the method as defined above; Subjecting the cermet piece thus obtained to vacuum calcination at a temperature of 1000 ° C. for 100 hours; Where appropriate, conducting at least one operation among diffusion welding of the workpiece to another workpiece obtained in the same way; inmation; and elasto-erosion treatment, and subjecting the resulting part to calcination in an oxygen-containing atmosphere, such as air, at a temperature of 1200-1250 ° C for a period of 100 hours.

These features make it possible to eliminate the possibility of formation of structural defects due to high temperature gradients and thermal shock.

As a result, the metal-ceramic preforms obtained by SLM are converted into ceramic parts with substantially no shrinkage, the deviation of the linear dimensions of the final ceramic part from the initial dimension of the metal-ceramic part being less than 0.5%.

According to the present invention: Because of the choice of the initial chemical composition of the powder and because of the mechanical activation of the powder in the steps of the powder preparation, it is possible to start laser-initiated heat-ignition processes. These reactions produce a significant heat emission which is the main driving force of the baking of the powder-metal-ceramic particles. 2 - The initial powder is a cermet (metal-ceramic); baking of the powder during the SLM process takes place while the powder is still a cermet. This fact ensures the absence of withdrawal at the procededitic stage. 3 - The piece produced by SLM is still a cermet and this gives the opportunity of a mechanical treatment of this intermediate piece - also called green piece - by conventional tools alloyed as opposed to conventional treatment of ceramics by diamond tools, treatment which is very expensive. 4 - The aluminothermic processes mentioned in paragraph 1 above are intentionally initiated at the powder preparation stage and then they are intentionally stopped. The laser impact during the SLM process resumes the aluminothermic processes but these are not completed at the SLM stage. The above reactions take place completely at the stage of vacuum calcination. This techniqueprovides the possibility of cooking without controlled removal of the ceramic unit. 5 - The mass of the workpiece after the vacuum calcination is characterized by a high porosity which is above 20%. This important feature of the method ensures the stability of the geometry of the piece (the absence of shrinkage). The final step of converting the cermet into the final ceramic is the leaching in an atmosphere containing oxygen, such as air; oxidation then occurs with a partial filling of the pores without any change in the dimensions of the part. In addition, a filling of pores hardens the mass of the part, which increases the mechanical strength. The following example illustrates the present inventionwithout limiting its scope.

Example 1 Manufacture of a Metal-Ceramic Powder

a) Preparation of a mechanically activated mixture of SiC, BN and B powders, a first fraction of aluminum powders and an In-Ga alloy powder as dopantal) Preparation of the SiC powder

Commercial SiC powder is sieved in order to separate the fraction of particles having a size smaller than 40 μπι.

The fraction of SiC powder thus obtained is cleaned in a rotary mill in an aqueous environment to eliminate physical pollution.

The fraction of SiC powder thus obtained is dried in a drying oven at 120 ° C. until complete evaporation of the water.

a2) Preparation of the BN powder

The procedure is as in al) replacing the SiC powder with BN powder.

a3) Preparation of the B powder

One proceeds as in al) by replacing the powder of SiC by powder of B.

a4) Preparation of a preliminary mixture of the SiC, BN and BA powders from the SiC, BN and B powders obtained in accordance with al), a2) and a3), using metering devices and a mixer of dry powders, the following mixture: - SiC powder 81% parts by weight - BN powder 12% parts by weight - B powder 7% parts by weight

This preliminary mix is thoroughly milled in a planetary mixer having an agate-agate mixing vessel with agate beads, resulting in a mechanically-activated intimate mixture. a5) Preparation of a mixture of a first aluminum powder fraction and an In-Ga alloy powder From an aluminum powder and an In-Ga 0.10.9 alloy powder 0.9 / 0.1 each having a particle size of less than 40 μm, the following mixture is prepared using metering devices and a mixer of powder mixers: - aluminum powder 98.5% by weight - alloy powder In-Ga 1.5% by weight a6) Preparation of the mixture of the title of a)

The mixture obtained in a5) is added to the mixture obtained in a4). The resulting mixture is thoroughly milled in a planetary mixer having an agate mixing vessel with agate beads, resulting in a mechanically activated intimate mixture. b) Mixing of the mixture prepared in step a) and a binder bl) Preparation of a binder

Synthetic rubber and mineral spirit are mixed in a weight ratio of 10/90 to obtain a binder. b2) Preparation of the mixture of the title of b)

Binder as obtained in bl) is added to the mixture obtained in a) using a liquid mixing device at a proportion of 0.3 part by weight of the binder per 100 parts by weight of the mixture obtained in ), then mixed thoroughly in a mixer for dry mixes. c) Formation of primary billets by compacting the mixture of step b)

The mixture obtained in step b) is fed into billet molds. The mussels are placed on a table. Isostatic pressure is applied for 1 hour and the billets are removed from the molds.

The compacted billets are dried at room temperature for 24 hours, then in a drying oven at 80 ° C for 24 hours, and then at 1100 ° C for 24 hours. d) Vacuum heat treatment of the primary billetsprepared in step c)

Bricks of fireclay are cut from the storehouse to obtain plates made of fireclay bricks, which are stirred in a vacuum oven. The dried billets obtained in step c) are placed in the vacuum oven and subjected to a low pressure (vacuum) heat treatment for 24 hours at 1100 ° C, this time interval including loading / unloading, heating and cooling. e) Grinding of the primary billets obtained in step d)

In a grinding mill, the billets which have undergone heat treatment are ground into pieces having a maximum size of about 5 mm.

Then, a number of grinding cycles are conducted to obtain pieces having a size of less than 1 mm. Then a number of abrasion cycles are conducted to obtain a powder having a micrometric fraction.

The micrometric fraction is sieved by means of a sieve or gas separator to separate a fraction of size less than or equal to 40 μm, which is then used in the rest of the process. The fraction of the particles larger than 40 μm is returned to abrasion and sieved again. This procedure is repeated until 60% of the ground mass has a size less than or equal to 40 μm, the appropriate size for the rest of the process. f) Preparation of a mixture of the powder of step e) and a second fraction of the aluminum powder

In the agate container containing agate balls of a planetary mixer, powdery powder obtained in step e) is charged and aluminum powders are added at a rate of 13 parts by weight of powders. aluminum per 100 parts by weight of the powder obtained in step e). The mixture is ground in said planetary mixer. g) Mixture of the mixture prepared in f) and a binder

Binder (as obtained in b) is added to the mixture obtained in (f) using a liquid mixing device at a rate of 0.3 parts by weight of the binder for 100 parts by weight of the mixture obtained in (f). then mixed thoroughly in a blender for dry blends. h) Formation of secondary billets by compacting the mixture of step g

The procedure is as in step c) from the mixture of step g). i) Vacuum heat treatment of the secondary billets prepared in step h)

We proceed as in step d) from thebillettes obtained in h). j) Grinding of the secondary billets obtained in step i)

We proceed as in step e) from thebillettes obtained in i). k) Aging

The powder obtained in j) is placed in a drying rack for 10-14 days.

We will now describe as an example a method of manufacturing a piece of hard ceramic by SLM using the powder obtained in the previous example.

Example 2: Manufacture of structural ceramic pieces

Cycle 1: Manufacture of a ceramic without structural shrinkage

This cycle comprises the following operations: 1.1 Introduction of filtered air into the operational space of an SLS machine; 1.2 Connecting the cylinder to the inert gas; 1.3 Switching on the SLS machine with start of the command program (start-up process test); 1.4 Mounting the baseline powder compartment in the initial lower position; 1.5 Transfer of activated base metal-ceramic powder, stored in the desiccator for no more than 7 days; 1.6 Sealing of metal-ceramic powder activated in the compartment; 1.7 Knurling of the activated metal-ceramic powder which is in the zero position; 1.8 Sealing the layer of metal-ceramic powder activated on the operating platform with a roller; 1.9 Loading the construction file of the ceramic-ceramic part without removal; 1.10 Process of the layer construction of the non-shrinkage ceramic-ceramic part by laser selective fusing technology with the continuous process layer control for the switched-mode system.

Cycle 2: Preliminary heat treatment (calcinationsous vacuum) of the metal-ceramic piece without shrinkage

This cycle comprises the following operations: 2.1 Cutting of the metal-ceramic part without removal of the operational aluminum platform, preferably by a mechanical process; 2.2 Mounting the non-shrinking metal-ceramic part on the ceramic base in the vacuum furnace; 2.3 Drying of the metal-ceramic piece without shrinkage by heating up to 300 ° C for 10 min; 2.4 Vacuuming the vacuum furnace to 10 ~ 3 atm; 2.5 Vacuum furnace heating up to 1100 ° C at the rate of 35 ° C per minute; 2.6 Exposure of the metal-ceramic piece to 1100 ° C and under a vacuum of 10 atm for one hour; 2.7 Cooling of the metal-ceramic part along the furnace.

Cycle 3: Diffusion welding of the metal-ceramic part without shrinking along the oven

This cycle comprises the following operations: 3.1 Grinding welded surfaces; 3.2 Placing a creamy mixture of the ceramic powder with the liquid glass on the welded surfaces of the metal-ceramic parts without shrinkage. 3.3 Placement of the ceramic-free ceramic parts joined to the ceramic base in the vacuum oven; 3.4 Drying of metal-ceramic pieces without shrinkageby heating them up to 300 ° C for 10 minutes; 3.5 Vacuum pumping in the vacuum furnace up to 1CT3 atm; 3.6 Heating in the vacuum furnace up to 1100 ° C at a rate of 35 ° C per minute; 3.7 Exposure of metal-ceramic parts without shrinkage at 1100 ° C and under a vacuum of 10 ~ 3 atm, for 1 hour; 3.8 Cooling of nonretrete metal-ceramic pieces joined along the furnace; 3.9 Removal from the vacuum furnace of the metal-ceramic piece without welded recess; 3.10 Visual inspection of the weld seam of the non-shrinkage ceramic-ceramic piece; 3.11 Cleaning the weld bead of the metal-ceramic part without shrinkage; 3.12 Verification of the geometry of the metal-ceramic part without shrinkage.

Cycle 4: Machining of the metal-ceramic part without shrinkage

This cycle comprises the following operations: 4.1 Fixing the metal-ceramic part without removal in a steel mandrel so that it would encompass -50% of the surface of the metal-ceramic part without shrinkage, for example its left half , leaving the right half free and easy to access, thus allowing the implementation of machining using conventional hard alloy cutting tools. It will be noted that for the manufacture of parts having relatively long elements of opposite direction the number of mandrels required is determined by the receiver; 4.2 Filling the surface in said mandrel with the solidified polymeric material at room temperature; 4.3 Machining in a special mode of the surface of the hard ceramic-ceramic element not found in said mandrel by means of a conventional hard alloy tool (cutting tool, grinder, drilling tool) having a special sharpening; 4.4 Heating of the mandrel along the surface of the metal-ceramic component without shrinkage in the furnace up to 500 ° C, the polymer material being converted into the phaseliquide at such a temperature; 4.5 Removal from said mandrel of a metal-ceramic part from; 4.6 Visual inspection of the metal-ceramic part withoutreterr; 4.7 Cleaning the surface of the metal-ceramic part without shrinkage; 4.8 Verification of the geometry of the metal-ceramic part without shrinkage; 4.9 Reiteration of operations 4.2 to 4.8 with fixation of half of the non-shrinking metal-ceramic part which has already undergone the required machining operation.

Cycle 5: Elasto-erosion treatment of the metal-ceramic part without shrinkage

This cycle involves the following operations: 5.1 Filling of the elasto-erosion machine with kerosene; 5.2 Immersion of the surface of the metal-ceramic part without removal in the mandrel; 5.3 Fixing of a conventional wire tool (0.2 mm brass wire, 0 0.1 mm tungsten wire); 5.4 Elasto erosion treatment using a special program; 5.5 Removal from the kerosene bath of the non-shrinking metal-ceramic piece; 5.6 Drying of the surface of the metal-ceramic part which has already undergone the elasto-erosion treatment operation; 5.7 Removal from the mandrel of the metal-ceramic piece without shrinkage; 5.8 Visual examination of the metal-ceramic piece; 5.9 Verification of the geometry of the metal-ceramic part without shrinkage; 5.10 Reiteration of operations 5.2. at 5.9. with fixation of half of the non-shrinking metal-ceramic piece which has already undergone the required treatment in the mandrel.

Cycle 6: Final sintering of the metal-ceramic parts without shrinking in an oxidation furnace after machining (calcination in an atmosphere containing oxygen)

This cycle comprises the following operations: 6.1 Cleaning the metal-ceramic part withoutretraitrait; 6.2 Drying of the hard metal-ceramic part in a ventilated storage at 50 ° C for one hour; 6.3 Mounting the hard metal-ceramic part in an oxidation process on a ceramic base; 6.4 Increasing the temperature in the oven to 1000 ° C at the rate of 5 ° C per minute; 6.5 Exposure for 20 hours in the oven at 1000 ° C; 6.6 Increase in oven temperature up to 1200 ° C at a rate of 5 ° C per minute; 6.7 Exposure for 100 hours in the oven at 1200 ° C; 6.8 Oven cooling for the ceramic finished product without structural shrinkage up to 20 ° C; 6.9 Oven removal of ceramic product without structural shrinkage, visual inspection, cleaning, geometry verification.

Example 3: Reduction of the porosity and increase of the mechanical strength of the hard ceramic pieces

The following operations were carried out on the structural ceramic pieces: (a) Filling with paraffin or an equivalent of the channels and holes necessary for the subsequent operation of the ceramic ceramic pieces; (b) Impregnation of the structural ceramic parts without tetraethoxysilane removal until complete filling of the open pores; (c) Alkaline hydrolysis of tetraethoxysilane by aqueous ammonia with desilicating gel formation; (d) Placing the treated part of the structural ceramics without removal in an aqueous solution of ammonium nitrate; (e) Drying structural ceramic parts without shrinking in air at room temperature, setting up the structural ceramic piece without shrinking in a flame in the air at 200 ° C forcing followed by calcination in a flame in the air at 900-950 ° C; (f) Reiteration at least three times of steps (b) to (e) for germination of cordierite crystals which were generated in this procedure within the internal volume of the open pores, thereby increasing the mechanical resistance of structural ceramic part without shrinkage; (g) In order to eliminate the porosity of the surface, the non-shrinking structural ceramic part is placed in the polysilicic acid sol for the time necessary to fill the surface pores without diffusion into the bulk of the non-shrinking structural ceramic part; (h) Drying the structural ceramic piece without shrinking in air at room temperature, placing the part in a flame in air at 200 ° C and calcining it at 900-950 ° C; (i) reiterating steps (g) and (h) at least three times to remove non-shrink structural ceramic porosity surfaces; (j) surface treatment of the ceramic piece with an upright containing, equally distributed, zinc, aluminum, magnesium and phosphate; (k) Drying in air at room temperature, placing the part in the flame in air at 200 ° C and calcining in air at 1000 ° C.

Claims (12)

1 - A method of manufacturing a metal-ceramic powder suitable for the manufacture of a ceramic by selective melting laser, characterized in that it comprises the following steps: a) preparation of a mechanically activated mixture of SiC powders, BN and B, a first aluminum powder fraction, and at least one pulverulent dopant; b) mixing the mixture prepared in step a) and a binder; c) forming primary billets by compacting the mixture of step b); d) vacuum heat treatment of the primary billetsprepared in step c); e) grinding the primary billets obtained in step d); f) preparing a mixture of the powder of step e) and a second fraction of the aluminum powder; g) mixing the mixture prepared in step f) and a binder; h) forming secondary billets by compacting the mixture of step g); i) vacuum heat treatment of the secondary billets prepared in step h); and j) grinding the secondary billets obtained in step i); the steps f to j can be repeated at least once, each time using a new aluminum fraction and starting each time with the preparation of a mixture of the powder obtained in the preceding step and the new powder fraction of aluminum. 2 - Process according to claim 1, characterized in that in step a), at least one dopantchoisi among indium and gallium, said dopant can be present in the form of an indium-gallium alloy. 3 - Process according to one of claims 1 and 2, characterized in that in step a), powders each having a particle size less than 40 microns. 4 - Process according to one of claims 1 to 3, characterized in that in step a), the mixture is mixed with a first mechanically activated mixture of SiC, BN and B and a second mechanically-activated activated mixture Al and the dopant (s). 5 - Process according to one of claims 1 to 4, characterized in that one carries out theMechanical activation of a mixture by performing this mixture in an agate mixing container containing agate beads at a rate of 300- 500 rpm in 3-6 cycles for 18-48 hours. 6 - Process according to one of claims 1 to 5, characterized in that the powders are mixed in the following molar percentages: SiC: 25-34BN: 6-8 B: 9-11 Al: 50-55 Ga ( dopant): 0.50-0.75 In (dopant): 0.50-0.75 the total mass of the constituents representing 100%, Al being introduced in at least two fractions, namely the first fraction of step a) and the second fraction of step f), the fractions being equal fractions. 7 - Method according to one of claims 2 to 6, characterized in that the dopants In andGa are used in the following percentages by weight: In: 10-90% Ga: 90-10% the total mass of the doping agents representing 100%. 8 - Method according to one of claims 1 to 7, characterized in that in step b) and in each step g), a binder is used consisting of a synthetic rubber that a styrene-butadiene rubber diluted in a solvent such as white spirit, in classical proportions synthetic rubber: solvent in particular 1: 4 to 1: 7. 9 - Process according to one of claims 1 to 8, characterized in that in step c) and in each step h), the compaction is carried out in billets by pressureisostatic under 980.7 - 1471 MPa (10- 15 tons / cm2) in molds for a period of 35-50 minutes. 10 - Process according to one of claims 1 to 9, characterized in that after each of the steps c) and h), the billets are dried under the following conditions: - ambient temperature for 20-30 hours; then - in a drying oven at 70-80 ° C for 20-30 hours and then at 105-120 ° C for 20-30 hours. 11 - Process according to one of claims 1 to 10, characterized in that in step d) and in each step i), the billets are placed in a vacuum oven and heated to 1250-1500 ° C for 20-30 hours. 12 - Process according to one of claims 1 to 11, characterized in that in step e) and inétape step j), the billets are milled to a particle size of 40 pm, proceeding in particular in several steps: Grinding to the mill until a particle size less than 5 mm is obtained; At least one milling cycle until a granulometry of 3-5 mm is obtained; At least one abrasion cycle until a granulometry of 0.044-0.100 mm is obtained; Sieving in order to obtain a particle size of less than 40 μm. 13 - Process according to claim 12, characterized in that each step f) ,Use aluminum powder at a rate of 10-20% by weight relative to the total mass of the fraction obtained with agglomerometry less than 40 pm. 14 - Method according to one of claims 1 to 13, characterized in that it comprises an additional steps after the last step: k) aging milled billets in a desiccator at room temperature for 10-14 days. 15 - Process for manufacturing a hard ceramic part by selective laser melting, characterized in that it comprises the steps of: - building layer by layer the selective cermet piece laser selective from the powderobtained by the process as defined in one of Claims 1 to 14; Subjecting the cermet piece thus obtained to vacuum calcination at a temperature of 1000 ° C. for 100 hours; Where appropriate, conducting at least one operation among diffusion welding of the workpiece to another workpiece obtained in the same way; inmation; and elasto-erosion treatment; and - subjecting the obtained part to calcination in an atmosphere containing oxygen, such as air, at a temperature of 1200-1250 ° C for a period of 100 hours.