FR3051186A1 - 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

The process for producing a metal-ceramic powder comprises the steps of: preparing a mechanically activated mixture of SiC, BN and B powders, a first fraction of aluminum powder, and at least one dopant powdery; mixing the mixture thus prepared and a binder; forming primary billets by compacting the preceding mixture; vacuum heat treatment of these primary billets; grinding of the primary billets thus treated; preparing a mixture of the powder thus obtained and a second fraction of the aluminum powder; mixing this mixture and a binder; formation of secondary billets by compacting the resulting mixture; vacuum heat treatment of these secondary billets; and grinding the secondary billets thus treated.

Description

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

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

Selective Laser Melting (SLM) is a unique process that provides an opportunity to fabricate units with very complex geometry. Based on the idea of a selective hardening of very thin layers (whose size goes down to microns), this approach makes it possible to produce internal cavities and channels of complex shape in the mass of the unit. At present, this technique is widely available for plastics - 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, chemical resistance greater than 1 oxygen / to reactive environments, etc. However, to date, such production is impossible since there is no approach for the production of ceramic units having the characteristics required by SLM.

Several attempts have been made to solve this problem. 1 - The use of ceramic powders covered with organic polymers The general idea is that each particle of powder is covered by an ultrafine layer of an organic compound acting as an adhesive; under the effect of laser heating, this glue hardens and bonds the particles. The advantage of this approach is the fact that the curing process does not lead to changes in the geometry of the pieces 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 piece; it can be improved by some tips with the polymer composition but this is still insufficient for industrial applications. Another point which renders this approach obsolete is the fact that all the 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 that for existing metal parts produced by SLM. 2 - The direct SLM of ceramic powder particles

This approach is based on increasing the 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 strength and the necessary heat resistance of the produced ceramic parts but it poses a number of problems: - the nature of the SLM process does not provide the appropriate cooling conditions which make it possible to eliminate the defects thermal stress occurring during the melting process, these constraints are necessarily transmitted to the mass of the synthesized part, which in turn gives rise to an inevitable crack in the mass of the part, leading to its partial or even complete destruction; The particle dimensions are dramatically changed during surface melting; as a result, a significant shrinkage takes place, making it impossible to produce ceramic parts with the exact geometry required.

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

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

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

The present inventors have sought to solve this problem in order to propose a method for producing, by SLM without shrinkage during the entire process - the final gap of the dimensions generally to be less than 0.5% - final ceramic pieces having a mechanical strength generally 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 composition of phases generally up to 1300 ° vs.

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

The inventors then developed a method for manufacturing a metal-ceramic powder on the basis of Al-SiC-BN-B system compositions, doped with In and Ga additions, for the production of hard ceramic pieces. not showing shrinkage when cooked by SLM.

The present invention therefore firstly relates to a method for manufacturing a metal-ceramic powder suitable for the manufacture of a hard ceramic by selective laser melting, characterized in that it comprises the following steps: preparing a mechanically activated mixture of SiC, BN and B powders, a first fraction of aluminum powder, 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 billets prepared 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) formation of 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 using each time a new aluminum fraction and starting each time from the preparation of a mixture of the powder obtained in the previous step and the new fraction of aluminum powder. In step a), it is possible to use at least one dopant chosen from indium and gallium, said dopant possibly being in the form of an indium-gallium alloy. In step a), it is possible to use powders each 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 B and a second mechanically activated mixture of Al and the dopant (s).

The mechanical activation of a mixture can be effected by performing this mixing in an agate mixing vessel containing agate beads at a rate 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 the step a) and the second fraction of step f), the fractions being equal fractions.

In and Ga dopants can be used in the following mass 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 from 1: 4 to 1: 7. In step c) and in each step h), compacting in billets by isostatic pressure 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; 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 by proceeding in several steps: milling to the mill until a particle size of less than 5 mm is obtained ; At least one milling cycle until a particle size of 3-5 mm is obtained; At least one abrasion cycle until a particle size 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), an aluminum powder may be used in a proportion of 10-20% by weight relative to the total mass of the fraction obtained with the particle size of less than 40 μm.

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

The present invention also relates to a method of manufacturing a hard ceramic part by selective laser melting, characterized in that it comprises the steps of: - building layer by layer cermet piece by selective laser melting to from the powder obtained by the process 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 selected from diffusion welding of the workpiece to another workpiece obtained in the same way; machining; 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 forming structural defects due to high temperature gradients and thermal shock.

As a result, the metal-ceramic preforms obtained by SLM are converted into ceramic pieces with substantially no shrinkage, the deviation of the linear dimensions of the final ceramic piece from the initial dimension of the metal-ceramic piece being less than 0. , 5%.

According to the present invention: 1 - Due to the choice of the initial chemical composition of the powder and because of the mechanical activation of the powder in the steps of the preparation of the powder, it is possible to start aluminothermic processes initiated by laser impact. These reactions produce a significant heat emission which is the main driving force of the firing of the metal-ceramic powder particles. 2 - The initial powder is a cermet (metal-ceramic); the baking of the powder during the SLM process takes place while the powder is still a cermet. This fact ensures the absence of shrinkage at the critical process step. 3 - The piece produced by SLM is still a cermet and this gives the opportunity of a mechanical treatment of this intermediate part - also called green part - by the usual high-alloyed tools as opposed to the conventional treatment of ceramics by tools diamond, treatment that is very expensive. 4 - The aluminothermic processes mentioned in paragraph 1 above are intentionally initiated at the powder preparation stage and then 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 proceed completely to the vacuum calcination step. This technique provides the possibility of baking without controlled shrinkage of the ceramic unit. The mass of the workpiece after vacuum calcination is characterized by a high porosity which is greater than 20%. This important feature of the process ensures the stability of the geometry of the part (the absence of shrinkage). The final step of converting the cermet into the final ceramic is calcination in an atmosphere containing oxygen, such as air; oxidation then takes place with partial filling of the pores without changing the dimensions of the part. In addition, such a pore filling harden the mass of the part, which increases the mechanical strength. The following example illustrates the present invention without 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 alloy powder Ga as dopant

al) Preparation of the SiC powder

Commercial SiC powder is sieved to separate the fraction of particles having a size of less than 40 μm.

The fraction of SiC powder thus obtained is cleaned in a rotary mill in a water-based environment to eliminate physical pollution.

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

a2) Preparation of the BN powder

The procedure is as in (a) by replacing the SiC powder with BN powder.

a3) Preparation of the B powder

The procedure is as in (a) by replacing the SiC powder with B powder.

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

This preliminary mixture is thoroughly milled in a planetary mixer having an agate mixing agate container with agate beads, resulting in a mechanically-activated intimate mixture. a5) Preparation of a blend of a first fraction of aluminum powder and an In-Ga alloy powder from an aluminum powder and an In-Ga 0.10 alloy powder. 9 in 0.9 / 0.1 each having a particle size of less than 40 μm, the following mixture is prepared using dosing devices and a dry powder mixer: - aluminum powder 98.5% by weight - In-Ga alloy powder 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 spirits 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 b1) is added to the mixture obtained in a), using a metering device for liquid mixtures, at a proportion of 0.3 part by weight of the binder per 100 parts by weight of the mixture obtained. in a), 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, then at 1100 ° C for 24 hours. d) Vacuum heat treatment of the primary billets prepared in step c)

Commercial fireclay bricks are cut to obtain fireclay brick plates that are available in a vacuum furnace. 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 the loading operations. unloading, heating and cooling. e) Grinding of the primary billets obtained in step d)

In a mill, the heat-treated billets are milled into pieces having a maximum dimension of about 5 mm.

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

The micrometric fraction is sieved by means of a screen or gas separator to separate a fraction of size less than or equal to 40 μm, which will be used in the following process. The fraction of particles larger than 40 μm is returned to the abrasion stage and sieved again. This procedure is repeated until 60% of the ground mass has a size less than or equal to 40 μm, which is appropriate 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 vessel containing agate balls of a planetary mixer, powder as obtained in step e) is charged and aluminum powder is added at a rate of 13 parts by weight. of aluminum powder 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 bl) is added to the mixture obtained in f), using a metering device for liquid mixtures, at a proportion of 0.3 part by weight of the binder per 100 parts by weight of the mixture obtained in f), and then thoroughly mixed in a mixer for dry mixes. 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)

The procedure is as in step d) from the billets obtained in h). j) Grinding of the secondary billets obtained in step i)

The procedure is as in step e) from the billets obtained in i). k) Aging

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

An example of a process for manufacturing a piece of hard ceramic by SLM using the powder obtained in the preceding example will now be described by way of example.

Example 2: Manufacture of structural ceramic pieces

Cycle 1: Manufacture of ceramic without structural shrinkage

This cycle comprises the following operations: 1.1 Introduction of filtered air into the operating 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 control program (test of the start-up process); 1.4 Mounting the baseline powder compartment in the initial lower position; 1.5 Pouring of activated baseline metal-ceramic powder, stored in the desiccator for no more than 7 days; 1.6 Sealing of activated metal-ceramic powder in the compartment; 1.7 Knurling of the activated metal-ceramic powder which is in the zero position; 1.8 Sealing of the layer of activated metal-ceramic powder on the operating platform by means of a roller; 1.9 Loading the construction file of the metal-ceramic part without removal; 1.10 Process of the layer construction of the non-shrinking metal-ceramic part by selective laser melting technology with continuous layer-based process control for the switched display system.

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

This cycle comprises the following operations: 2.1 Cutting of the metal-ceramic piece without removal of the operational aluminum platform, preferably using 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 a rate of 35 ° C per minute; 2.6 Exposure of the metal-ceramic piece at 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 shrinkage 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 non-shrinking metal-ceramic parts joined to the ceramic base in the vacuum furnace; 3.4 Drying of non-shrinking metal-ceramic parts united by heating 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 the non-shrinking metal-ceramic pieces together at 1100 ° C and under a vacuum of 1 cc atm for 1 hour; 3.8 Cooling of non-shrinking metal-ceramic parts joined together along the furnace; 3.9 Removal from the vacuum furnace of the metal-ceramic piece without welded recess; 3.10 Visual examination of the weld bead of the metal-ceramic piece without shrinkage; 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 the metal-ceramic part without shrinkage

This cycle comprises the following operations: 4.1 Fixing the non-shrinking metal-ceramic piece in a steel mandrel so that it would encompass ~ 50% of the surface of the metal-ceramic piece without shrinkage, for example its half left, leaving the right half free and easy to access, allowing the implementation of machining using conventional hard alloy cutting tools. Note that for the manufacture of parts having relatively long elements of opposite direction, the number of mandrels required is determined by the designer; 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 metal-ceramic part which is not in said mandrel by means of a conventional hard alloy tool (cutting tool, grinder, drilling tool) having a special sharpening; 4.4 Heating the mandrel along the surface of the metal-ceramic piece without shrinking in the oven up to 500 ° C, the polymer material being converted into the liquid phase at such a temperature; 4.5 Removal from said mandrel of a hard metal-ceramic piece from; 4.6 Visual examination of the metal-ceramic part without shrinkage; 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 attachment of half of the non-shrinking metal-ceramic part that 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 shrinkage not placed in the mandrel; 5.3 Fixing a conventional wire tool (0 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 part without removal; 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 fixing of half of the non-shrinking metal-ceramic piece which has already undergone the required treatment in the mandrel.

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

This cycle comprises the following operations: 6.1 Cleaning the metal-ceramic part without shrinkage; 6.2 Drying of the hard metal-ceramic part in a ventilated cabinet at 50 ° C for one hour; 6.3 Mounting the hard metal-ceramic part in an oxidation furnace 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 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 equivalent of the channels and holes necessary for the subsequent operation of the hard ceramic pieces; (b) Impregnation of structural ceramic parts without shrinkage with tetraethoxysilane until complete filling of the open pores; (c) Alkaline hydrolysis of tetraethoxysilane with aqueous ammonia with formation of a silica gel; (d) Placing the treated portion of the structural ceramic without shrinkage in an aqueous solution of ammonium nitrate; (e) Drying of the structural ceramic pieces without shrinkage in the air at room temperature, placing the structural ceramic piece without shrinkage in a flame in air at 200 ° C followed by calcination in a flame in air at 900-950 ° C; (f) Reiterating at least three times 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 strength of the structural ceramic piece without shrinkage; (g) In order to eliminate the porosity of the surface, the structural ceramic piece without shrinkage is placed in the polysilicic acid sol for the time necessary to fill the surface pores without diffusion into the bulk of the structural ceramic piece without withdrawal; (h) Drying the structural ceramic piece without shrinkage at room temperature, placing the part in a flame in air at 200 ° C and calcining it at 900-950 ° C ; (i) repeating steps (g) and (h) at least three times to remove the porosity surfaces of the structural ceramic piece without shrinkage; (j) Surface treatment of the ceramic part by a suspension 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 (15)

1 - Process for producing a metal-ceramic powder suitable for the manufacture of a hard ceramic by selective laser melting, characterized in that it comprises the following steps: a) preparation of a mechanically activated mixture of powders SiC, BN and B, a first fraction of aluminum powder, 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 billets prepared 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) formation of 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 using each time a new aluminum fraction and starting each time from the preparation of a mixture of the powder obtained in the previous step and the new fraction of aluminum powder. 2 - Process according to claim 1, characterized in that in step a), at least one dopant chosen from indium and gallium is used, said dopant being in the form of an indium-aluminum alloy. gallium. 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), is carried out mixing a first mechanically activated mixture formed of SiC, BN and B and a second mixture mechanically activated Al and dopants. 5 - Process according to one of claims 1 to 4, characterized in that one carries out the mechanical activation of a mixture by performing this mixture in an agate mixing container containing agate balls at a speed 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: 25-34 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 the step a) and the second fraction of step f), the fractions being equal fractions. 7 - Process according to one of claims 2 to 6, characterized in that the dopants In and Ga are used in the following percentages by weight: In: 10-90% Ga: 90-10% the total mass of the dopants representing 100%. 8 - Process according to one of claims 1 to 7, characterized in that in step b) and in each step g), is used a binder formed of a synthetic rubber such as a styrene-butadiene rubber diluted in a solvent such as white spirit, in proportions by mass synthetic rubber: solvent in particular from 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 isostatic pressure 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; 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 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 each step j), the billets are milled to a particle size of 40 pm, including several steps steps: - milling to the mill until a particle size less than 5 mm; At least one milling cycle until a particle size of 3-5 mm is obtained; At least one abrasion cycle until a particle size of 0.044-0.100 mm is obtained; Sieving in order to obtain a particle size of less than 40 μm. 13 - Method according to one of claims 1 to 12, characterized in that in each step f), is used an aluminum powder in a proportion of 10-20% by weight relative to the total mass of the fraction obtained with the particle size less than 40 μm. 14 - Method according to one of claims 1 to 13, characterized in that it comprises an additional step 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 cermet piece by selective laser melting from the powder obtained 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 selected from diffusion welding of the workpiece to another workpiece obtained in the same way; machining; 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.