EP0277450B1 - Process for preparing metal-ceramic composite materials by using surface-active metals at the ceramic-metal interfaces - Google Patents

Abstract

It is known to produce ceramic-metal composites developed by powder metallurgy (or ceramic) technology from a ceramic powder and a metal powder. To improve the bonding between the ceramic phase and the metal phase, a surface-active additive of metal type, chosen from the group of the elements Ti, V, Sc, Zr, Y, Nb, Hf, La and rare earths, and Ta, is added to the mixture of the metal and ceramic powders, preferably in the form of a pulverulent compound capable of decomposing under the action of heat, the combination of the powders, after the usual treatment, being formed and sintered to obtain a coherent monolith, where the ceramic phase is predominant in volume, namely 50% to 95%, the metal phase is minor in volume, namely 50% to 5%, and where the surface-active metal provides the bonding at the interfaces of the phases with or without formation of a compound or alloy.

Description

The present invention relates to ceramic-metal composites and their production methods. It makes it possible to produce, by the methods of powder metallurgy and / or ceramic, a set of homogeneous polyphase materials, which have at least one ceramic phase and one metal phase.

Powder metallurgy technologies are now well known. They derive from ceramic art. Details of these can be found, in particular, in French patent 2,057,562. The constituents or materials to be formed are used in the form of powders, some of which may be pre-alloyed beforehand.

These powders are mixed and ground together, in a liquid medium, or dry. This mixing-grinding step is decisive for the rest of the process. It is on it, in fact, that homogeneity depends, hence the characteristics of the final product. It is carried out in grinders provided with grinding media. These grinding media are varied, by their nature: natural ceramic stones, alloys, cermets, etc., and by their shape: balls, rollers, cylinders, etc. The choice of these media, where economic considerations are not absent, is based on the risks of pollution, and the search for the type of particle size envisaged.

• le coulage en moule poreux ,
• l'épandage en feuille mince ,
• l'extrusion ,
• l'injection thermoplastique ,
• le pressage ,
• l'electrophorèse ,
  etc ...

The rest of the process is conditioned by the type of shaping used to make the desired article. Among the different possible types, it should be mentioned, although this is not limiting:

• pouring into a porous mold,
• thin sheet spreading,
• extrusion,
• thermoplastic injection,
• pressing,
• electrophoresis,
  etc ...

All these shaping methods can be applied within the framework of the invention, without departing from the invention. Those skilled in the art will understand that it is unnecessary to detail them all here. In the examples which follow, in order not to unnecessarily burden the description of the process which is the subject of the invention, we have limited ourselves to pressing.

For this shaping, the granulation of the mixture is most often carried out, following the mixture-grinding treatment. To this end, a temporary binder is generally added to the composition, in the form of an organic polymer. Its role is to gather the grains of powder into small quasi-spherical granules of similar size and provided with plasticity. The pressing dies are fed with this granule. It allows a reproducible filling. A pressure close to 1 T / cm2 (98 MPa) is then applied to the mold, using two punches, in the case of biaxial pressing. Under the effect of the pressure, the granules deform until they become practically contiguous while expelling residual air from the matrix. Compacts are thus obtained, the density of which can be greater than 70% of the theoretical density. The compacts are then transferred to ovens to be densified by the sintering operation, after purification of the organic binders. This sintering can be carried out with or without pressure at a sufficient temperature in the vast majority of cases, to achieve volume diffusion of the elements. During this heat treatment, the compacts evolve towards greater stability, on the one hand, by reducing their surface energy by elimination of the pores and crystal growth and, on the other hand, by forming the stable phases at the considered temperatures.

It is by this technology that industrial parts of large series are manufactured, more and more, and certain special alloys, in particular those described in French patents No. 1,473,618, No. 2,223,473, No. 2 095 826. These patents relate to alloys with ceramic dispersoids. The ceramic material in content generally less than 10%, does not intervene there for its intrinsic mechanical qualities, but as sites for anchoring dislocations and sites for blocking the propagation of dislocations. It has been found, in fact, that dispersions of fine particles, preferably in the form of oxides, of dimensions less than or close to a thousand Angstroms increased the hardness and the creep resistance of such compositions. The predominance of metallic mass, and the properties remain however such that the designation of alloys is better suited to these compositions than the term composites.

In the composites which are the subject of the present invention, it is sought to have the maximum of ceramic phases by volume so as to be able to benefit as much as possible from the intrinsic properties of ceramics, such as chemical and dimensional stability, in an aggressive medium. The metal is deliberately limited to the grain boundaries. We know, in fact, that in ceramics, it is the grain boundary which is fragile, and limits the resistance of ceramics to values much lower (about a factor of 10) than their theoretical resistances.

In such composites, it is generally sought to form a metallic binder phase, and one, or even several dispersed phases of the ceramic type. The binding phase has a continuity character: it coats the grains of the dispersed phase or phases, but generally remains a minority in volume; by way of example, it can be said that the binding phase occupies 30% + or - 10% of the volume. It is under these conditions that, in general, the best properties are obtained, without this being an absolute rule.

• Porosité ,
• Mauvaise dispersion des phases .

Until now, the production of such materials has encountered a major difficulty: the proper wetting of the two phases. Many systems have been studied; to illustrate this point, we will cite the nickel-alumina system, the copper-alumina system, on which there are relatively recent publications. The heterogeneities encountered in these systems, at the end of the production processes, such as sintering or infiltration, are of two types:

• Porosity,
• Poor phase dispersion.

• Nécessité d'accroître le pourcentage de phase liante pour obtenir une phase continue ,
• Affaiblissement de la majorité des caractéristiques ,
• Mauvaise reproductibilité dans l'élaboration du matériau et principalement de l'opération de frittage ou d'infiltration .

The following major drawbacks result:

• Need to increase the percentage of binding phase to obtain a continuous phase,
• Weakening of the majority of the characteristics,
• Poor reproducibility in the production of the material and mainly of the sintering or infiltration operation.

The presence of these two defects is due to the lack of "attraction", one could also say of "affinity", of the binding phase with the dispersed phase (s). This corresponds chemically to the absence or scarcity and / or weakness of the bonds of the atoms present. It follows that, in the processing of the material, the evolution of the system results in too little variation of Gibbs energy, to obtain a coating of the grains of the dispersed phase; in some cases, there would even be an increase in this energy.

• la cristallographie des phases en présence ,
• le rayon atomique des cations de la phase dispersée ,
• l'électronégativité telle que l'a définie L.PAULING , des éléments de la phase dispersée .

The use of certain addition elements, which we will call surface-active metals, makes it possible to resolve this difficulty. The choice of these elements is not arbitrary, but depends on the physico-chemical characteristics of the system, and, in particular on the metal of the binder phase and on the nature of the dispersed phase; we can quote on this subject:

• the crystallography of the phases present,
• the atomic radius of the cations of the dispersed phase,
• electronegativity as defined by L. Pauling, elements of the dispersed phase.

For a better understanding of what follows, we will briefly recall, very schematically, some notions of chemistry and crystallography.

The nature of the chemical bonds in the crystals: constituting the ceramic materials is mainly of the ionic and / or covalent type; in a large number of cases, there is hybridization of these two types of bond: one can cite as an example chromium oxide Cr₂O₃, alumina Al₂O₃. In such networks, we are used to considering that the anions (the O--, in the examples above), form a defined stacking, generally three-dimensional, quite often of compact type, as is the case with Cr₂O₃ and Al₂O₃. In the holes of this building, the cations are distributed (Al³⁺, or Cr³⁺, in the examples above). In networks with more marked covalence, for example Silicon Nitride Si₃N₄, the crystal structure is constructed as a function of the spatial distribution of the chemical bonds. It follows that atoms of the same nature are not necessarily equivalent, this is how in Si₃N₄ we distinguish two types of nitrogen sites.

In both cases, ionic bonds or covalent bonds, there is unsaturation of the surface atoms. It follows from this unsaturation that, in the expression giving the energy of GIBBS of the compound considered, a term should be added to take account of surface phenomena. As for the crystals, in the medium in which they are placed, they will modify their external structures, for example by adsorbing chemical species, to reach a higher level of stability, which corresponds to a lower GIBBS energy. In the case of the oxides mentioned above, it has been demonstrated by certain researchers the presence of superficial -OH groups, resulting from the capture of protons.

The bonds between atoms in the metallic phases are different: certain peripheral electrons of the atoms are delocalized in the Brillouin zones; so that one can schematize a metal phase by a defined three-dimensional stack of cations in an electron cloud. In reality, to explain all of the physical characteristics and particularly in the case of refractory transition metals, it is necessary to design a more complex model, in which hybridizations between atoms of the external electronic orbitals occur (This is particularly marked for column VIB of the periodic table). A metallic covalent bond can therefore be superimposed on this metallic bond.

It can be seen from the above that it is difficult to link a ceramic phase and a metal phase together: the nature of the forces between opposite faces being rather repulsive in nature. The modification of the surface films of the grains generally results in an increase in the energy of GIBBS.

The role of the surfactants will be to serve as an intermediary between the dispersed and metal phases, and to lower the energy of GIBBS of the whole. It has been found that certain metals which have a certain affinity for the metal phase and an affinity for the ceramic phase, particularly by forming compounds of very negative free enthalpy, could play this role. This is particularly the case when the surfactant element has an isotype (or even isomorphic) compound, or a structure close to that of the ceramic phase.

• Ti , V , Sc ,
• Y , Nb ,
• Hf , La et Terres rares.

Among the elements that could be used as surfactants, we found that the following elements were particularly effective:

• Ti, V, Sc,
• Y, Nb,
• Hf, La and Rare earths.

These surface-active elements are particularly reactive, and especially with respect to oxygen; this is the reason why, rather than using them directly in metal form, one will preferably use one of their compounds, easily decomposable to heat, such as hydrides. These compounds, generators of surface-active elements, are introduced in pulverulent form, before mixing-grinding of the other constituents, with a suitable particle size, so as to obtain an intimate mixture and of homogeneous particle size of the whole.

JP-A-60 169 533 describes high hardness products comprising a hard phase CBN and / or WBN; a hard TiC phase; an alloy or compound of Al; Mo and / or Nb; Co and / or Ni; and Ti, Zr and / or Hf, in the form of hydrides; the manufacturing process for these products using temperatures of 1200 ° C to 1500 ° C and very high pressures of 50 to 65 Kbars, or pressures of 5000 to 6500 MPa.

The method according to the invention is in accordance with the claim.

The composites which are the subject of the invention contain a metallic part, which is a minority in volume, ie from 50% to 5%, and a ceramic part, ie from 50% to 95%; this metallic part, contains, in addition, the surface-active metals, which ensure the connection and the transition between the metallic and ceramic phases, possibly by the formation of compounds, during the sintering process.

• composés de type corindon : Al2O3 , Cr2O3 ,Ti2O3 , Y2O3 ,etc...,
• nitrure de silicium , nitrure de bore ,
• diborure de titane ,
• carbure de silicium , carbure de bore .

For the manufacture of such composites, the ceramic material is chosen from the following compounds:

• corundum type compounds: Al2O3, Cr2O3, Ti2O3, Y2O3, etc ...,
• silicon nitride, boron nitride,
• titanium diboride,
• silicon carbide, boron carbide.

• nickel , nickel-aluminium
• alliages réfractaires au Ni , Cr , Co , Fe ( type de produit connu sous le nom de marque Refractaloy ),
• alliages à dilatation controlée à base de fer et de nickel, connus sous les noms de marque Invar , ADR , N42 , N56 , Dilver , ou Platinite,
• aluminium ,
• alliage utilisé en frottement tel que le bronze au plomb, à l'étain à l'aluminium au silicium .

The metal part is chosen from the metals and alloys below

• nickel, nickel-aluminum
• alloys refractory to Ni, Cr, Co, Fe (type of product known under the brand name Refractaloy),
• alloys with controlled expansion based on iron and nickel, known under the brand names Invar, ADR, N42, N56, Dilver, or Platinite,
• aluminum,
• alloy used in friction such as lead bronze, tin aluminum silicon.

All of the constituents: ceramics, metals, compounds generating surface-active metals, are used in the form of powders. These powders are used by the methods of powder metallurgy (or ceramic), methods well known to those skilled in the art, for the production of objects, obtained in the green state, in an intermediate stage. These objects are then densified in a secondary vacuum furnace preferably working under load although the load is not necessary). The sintering temperature is located near the melting temperature of the metal alloy used (for example more or less 100 ° C). During the heat treatment, the surface-active metal or metals diffuse and provide the bond at the interfaces, with possible formation of compounds or alloys.

The examples below will make it possible to better understand the process for manufacturing these composites, which are the subject of the invention.

1 / CHROME-NICKEL-TITANIUM OXIDE COMPOSITE.

• 312 g d'oxyde de chrome Cr2O3 en poudre (de surface spécifique , méthode Blaine , 25 000 cm2/g par exemple sans que cela soit une nécessité.)
• 313 g de poudre de nickel (S.S. Blaine: 5 000 cm2/g, environ ).
• 50 g de poudre d'hydrure de titane ( S.S. Blaine: 3000 cm2/g environ.) - 130 g de trifluoretrichoroéthane, type flugène 113 par exemple,
• 50 g de camphre.

Poured into a jar, a cylindrical container, made of stainless steel with a capacity of approximately 1 liter, containing 2.5 kg of stainless steel balls with a diameter of approximately 1 cm:

• 312 g of chromium oxide Cr2O3 powder (specific surface area, Blaine method, 25,000 cm2 / g for example without this being a necessity.)
• 313 g of nickel powder (SS Blaine: 5,000 cm2 / g, approximately).
• 50 g of titanium hydride powder (SS Blaine: 3000 cm2 / g approximately.) 130 g of trifluoretrichoroethane, flugene type 113 for example,
• 50 g of camphor.

Then, in the jar, an argon sweep is carried out, with a flow rate of 1 l / min. approximately, for 2 min., in order to expel most of the air. Then we close the jar quickly. The jar is placed on a jar turner, speed of the order of 90 revolutions per minute, and it is rotated for approximately 8 hours. The purpose of this operation is to homogenize and grind the different constituents.

At the end of the treatment, the suspension of beads is separated, then it is dried with stirring to avoid demixing of the constituents, optionally under reduced pressure, preferably in a granulator.

The powder is then compacted in the press in the form of test tubes, and the residual camphor is sublimed. The test pieces are then treated in a sintering oven under load, working under secondary vacuum.

One operates under a vacuum of 10⁻⁵ torre and under a load corresponding to a pressure of 10 MPa. The heat treatment includes a level of decomposition of hydrides between 300 ° C and 500 ° C and a sintering level of 30 min. at 1200 ° C, the temperature rise being carried out in 2 hours.

A pellet of density 6.02 is obtained.

The duration and the temperature of the sintering stage depend on the pressure exerted: without pressure they can be brought to 2 hours and 1450 ° C, respectively.

Ceramic-metal composites are thus obtained, corresponding to the invention.

2 / ALUMINUM-ALUMINUM-NICKEL-TITANIUM OXIDE COMPOSITE

• 362 g de poudre d'alumine alpha de surface spécifique , méthode Blaine , 5000 cm2/g .
• 86,5 g de poudre d'hydrure de titane .
• 70,2 g de poudre d'aluminium diamètre moyen des particules de l'ordre du micron .
• 153,7 g de poudre de nickel .

We operate as before according to the following formula:

• 362 g of alpha surface alumina powder, Blaine method, 5000 cm2 / g.
• 86.5 g of titanium hydride powder.
• 70.2 g of aluminum powder, mean particle diameter on the order of a micron.
• 153.7 g of nickel powder.

Sintering is carried out under the following conditions:
Temperature rise of 1000 ° C, linearly in 75 min. , under vacuum of 10⁻⁵ torre without pressure; progressive loading up to a pressure of 10 MPa reached in 15 min. and maintaining the pressure until the end of the heat treatment; rise to 1350 ° C in 1 hour and step of 40 min. at this temperature.

A composite pellet of density 5.15 is obtained.

3 / CHROME-NICKEL-COBALT-YTTRIUM OXIDE COMPOSITE.

• 438 g d'oxyde de chrome
• 236 g d'alliage MCrAlY . La composition de MCrAlY est en pourcentage : Ni 10 , Co 52 , Cr 25 , Al 7 , Ti 5 , Y 0,75 . Sa granulométrie moyenne est de l'ordre de 25 microns .

The procedure is as in Example 1, with a heat treatment of 1 hour at 1360 ° C, according to the following formula:

• 438 g of chromium oxide
• 236 g of MCrAlY alloy. The composition of MCrAlY is in percentage: Ni 10, Co 52, Cr 25, Al 7, Ti 5, Y 0.75. Its average particle size is around 25 microns.

At the end of the heat treatment, a composite with a density of 5.45 is obtained.

4 / OTHER EXAMPLES.

• 41 / In the above examples, the proportion of metallic phase can be varied from 5% to 50% by volume.
• 42 / In the above examples, the content of surfactant metal is modified, so as to vary it from 2% to 50 atomic% of the metal phase.
• 43 / In the examples above, the nickel powder is replaced by powder of refractory alloy with Ni, Cr, Co, Fe, type Refractaloy.
• 44 / In the above examples, the nickel powder is replaced by alloys with determined expansion, type Invar A D R, or N42 or N58 or Dilver or Platinite.
• 45 / In the above examples, the ceramic powder is replaced by silicon nitride, silicon carbide, boron carbide, boron nitride (HBN or CBN) powder.
• 46 / In the examples above, the other surface-active metals listed above are used.
• 47 / As metallic powder, aluminum powder is used, as ceramic powder is titanium diboride powder TiB2 (60% by volume), with one of the surface-active metals mentioned above, and in particular, titanium ( due to 25 atomic% relative to the metallic mass). After sintering under load corresponding to a pressure of 10 MPa for 1 hour at 1380 ° C., a composite with a density close to 4.05 is obtained.
• 48 / A friction alloy powder such as lead, tin, aluminum or silicon bronze is used as the metal powder, and boron nitride ceramic powder.

• La réalisation de pièces de structure , et en particulier dans les machines thermiques .
• La réalisation de pièces de frottement .
• La réalisation de pièces de contact dans l'électrotechnique .
• La réalisation d'outils de coupe, de meule, d'organes soumis à l'abrasion et à la corrosion .
• La réalisation d'électrodes .
• La réalisation de prothèses médicales.

The applications of such composites are extremely numerous and depend of course on the composites produced. We can cite in this regard:

• The production of structural parts, and in particular in thermal machines.
• The production of friction parts.
• The production of contact parts in electrical engineering.
• The production of cutting tools, grinding wheels, organs subject to abrasion and corrosion.
• The production of electrodes.
• The production of medical prostheses.

Claims (1)

1. Process for the production of a ceramic-metal composite prepared by powder metallurgy technology or by ceramic technology, from a ceramic powder, a metal powder and a metal-type or metal hydride-type powdered additive which may be decomposed under the action of heat, the whole of the said powders and the said additive, after the usual treatment, being shaped and sintered to obtain the said ceramic-metal composite in which the ceramic phase represents 50 to 95 % by volume, the metal phase represents 50 to 5 % by volume and the said additive represents 2 to 50 atomic % of the said metal phase, a process according to which the additive consists of an element chosen from the group comprising Ti, V, Sc, Y, Nb, La, the rare earths and the hydrides of these elements, this additive ensuring a bond between the ceramic-metal interfaces, with or without the formation of a compound or alloy, the ceramic powder consisting of corundum, an isomorph of corundum, titanium diboride or at least one component from the group comprising silicon nitride, silicon carbide, boron carbide and boron nitride, the metal powder consisting of one or more compounds chosen from the group comprising nickel, a nickel-aluminium alloy, aluminium, a refractory alloy or an alloy with a controlled expansion based on iron, nickel, chromium and/or cobalt, and a friction alloy such as a bronze based on lead, tin, aluminium or silicon, sintering being carried out at a pressure of not more than 10 MPa and a temperature of 1200 to 1450 °C.