EP0591305B1 - Cermets based on transition metal borides, their production and use - Google Patents

Abstract

PCT No. PCT/FR92/00595 Sec. 371 Date Feb. 26, 1993 Sec. 102(e) Date Feb. 26, 1993 PCT Filed Jun. 26, 1992 PCT Pub. No. WO93/00452 PCT Pub. Date Jan. 7, 1993.A cermet useful in the fabrication of metal cutting, rockdrilling and mineral tools, as well as wear parts. The cermet comprises (i) a hard phase of a simple boride of a transition metal, a mixture of simple borides of transition metals, or a mixed boride of transition metals; (ii) a binder phase of Fe, Ni, Co, Cr, or alloys thereof; (iii) a dispersion of particles of oxides of transition metals in which the oxygen can be replaced by nitrogen and/or carbon; and (iv) a dispersion of oxides of metals chosen from aluminum and Group IIA and IIIA metals.

Description

The subject of the invention is cermets based on borides of transition metals, in particular titanium diboride, having in particular improved toughness.

Cermets are hard materials used in particular to make cutting or drilling tools and wearing parts. They generally consist, as their name suggests, of a predominantly hard but fragile ceramic phase and a much less hard but tenacious metallic binder phase, which gives them an interesting and rare combination of hardness and tenacity. The term ceramic is taken here in the broad sense, including in particular the oxides, nitrides, carbides and borides of the transition metals, or even their combinations.

• assurer la formation d'une phase fusible liquide (le plus souvent avec dissolution d'une certaine quantité de borure dans le métal liquide) mouillant aussi parfaitement que possible le composant solide ce qui, en principe, facilite le frittage et permet une densification totale ;
• apporter une certaine ténacité au cermet fritté qui est donc ainsi formé d'une phase dure mais fragile (le borure) et d'un liant métallique moins dur mais ductile (le métal ou alliage liant).

It is known that certain metals (iron, nickel, cobalt, chromium, copper, etc.) or their alloys have been used as binders in the manufacture of cermets based on borides of transition metals, most often diborides of transition metals and in particular of titanium diboride TiB₂. These metals or alloys have in principle a double function:

• ensuring the formation of a liquid fusible phase (most often with the dissolution of a certain amount of boride in the liquid metal) wetting the solid component as perfectly as possible which, in principle, facilitates sintering and allows total densification;
• bring a certain tenacity to the sintered cermet which is thus thus formed of a hard but fragile phase (the boride) and of a less hard but ductile metallic binder (the metal or alloy binder).

In reality, a review of the literature shows that experimentally densification by sintering in the presence of the liquid phase of such cermets is not perfect and even often insufficient: the open porosity remains high (from 4 to 30% by volume) and the metallic binder most often, at least partially, transforms into boride by chemical reaction with the hard phase; this results in a considerable drop in the toughness of the cermet, which restricts its field of application.

The inventors have observed these facts experimentally, for example on TiB₂-Fe cermets. To prepare these cermets, they mixed titanium diboride powder TiB₂ (average grain diameter: 1 to a few µm) with iron powder (average grain diameter 1 to a few µm) by conventional means (mixer, ball mill, attrition mill, etc.). The mixture was then compressed under 100 to 200 MPa of pressure. The sintering was carried out for 1 to 4 hours, at a temperature between 1450 and 1550 ° C., depending on the volume iron content of the cermet (10 to 20% by volume). They then found that the densification was very poor (the residual porosity varying between 10 and 20%) and that the major part of the iron-binding metal had transformed into boride Fe₂B or / and fragile FeB, thus causing a drop in toughness , which makes the use of such a material practically impossible in the envisaged applications.

In conclusion, obtaining a hard and tenacious boride-metal (or alloy) cermet appears practically impracticable due to the interaction, during sintering, of the metal binder with the hard boride, with at least partial concomitant boriding of this binder. metallic.

The object of the present invention is to find conditions making it possible to manufacture cermets based on transition metal borides which do not have the drawbacks of cermets of the same type obtained according to the prior art and allowing their use in the envisaged applications, in particular due to their high tenacity.

Patent application DE-A-28 46 889 relates to an alloy powder, its preparation and its use for manufacturing sintered parts.

The alloy powder consists essentially of a boride or a complex boride phase as a support for hardness and a metal or an alloy as a binding phase.

It follows from the preamble and the statement of the aim pursued that the invention described in this document relates to the partial replacement of iron in the hard phase of boride type according to the prior art by other elements forming borides.

In fact, in the hardness support the iron boride is partially replaced by at least one boride of another metal such as for example a transition metal (see, for example, page 5, lines 16 to 24).

The borides used in Example 3 contain 70.32% by weight of iron for the boride of structure MB which is used in an amount of 43% by weight to form the sintered product, and 76.77% by weight of iron for the boride of structure M₂B which is used at a rate of 16% by weight to form the sintered product.

Comparable proportions of iron-based borides are used in the other examples. The sintered products disclosed in patent application DE-A-28 46 889 therefore all contain a high proportion of iron boride. However, the object of the present invention is to avoid the presence of metal boride of the binder phase (iron in particular).

Furthermore, patent application DE-A-28 46 889 teaches that the presence of aluminum as an impurity in the alloy powder plays an unfavorable role, which should have dissuaded the person skilled in the art from adding this item.

Patent application FR-A-2 514 788 teaches a sintered hard alloy very similar to that taught by document DE-A-28 46 889, in which the hard phase composed of "multiple borides" contains at least 10% by weight of iron, which goes against the object pursued according to the present invention.

Thanks to extensive research, the inventors have found that the interaction between the hard transition metal boride and the metal binder which causes a drop in toughness, can be prevented or at least greatly reduced by adding certain elements to the binder. of metal type, in the form of simple or compound bodies, during the preparation of the mixture of the boride and the metal binder, that is to say before the sintering of this mixture.

The elements in question are essentially the transition metal entering into the composition of the transition metal boride constituting the hard phase, mainly present in this boride and a metal X chosen from aluminum, alkaline earth metals, Sc, Y, lanthanides, actinides and alloys consisting of iron and ceric metals, or a mixture of at least two of these metals X.

During sintering, the added transition metal is transformed into oxide in which part of the oxygen can be replaced by nitrogen and / or carbon and the metal X is transformed into oxide. These oxides precipitate in the form of dispersions of separate oxide particles, or combined in the form of complex oxides.

The carbon possibly present in the oxide of the transition metal is due to the presence of this element, as an impurity, in the boride of the hard phase.

• 1) une phase dure de type borure ;
• 2) une phase liante constituée d'un métal liant pur L, ou d'un alliage d'au moins deux métaux (L,L'...) où :
  • . L est un métal choisi dans le groupe constitué par Fe, Ni, Co et Cr, et
  • . L' est au moins un élément métallique d'alliage pour L, qui ne dégrade pas substantiellement sa ténacité, caractérisé en ce que la phase dure 1) est constituée d'un borure simple TxBy, d'un mélange de borures simples TxBy + T'x'By' ou d'un borure mixte (T,T')xBy où :
  • . T et T' sont des métaux de transition choisis dans le groupe constitué par Ti, Zr, Hf, V, Nb, Ta, Cr, Mo et W, et
  • . x, x', y et y' sont des nombres entiers ou décimaux, de préférence des nombres entiers, identiques ou différents ;
  et en ce que ledit cermet comprend en outre :
• 3) une fine dispersion de particules d'oxyde du métal de transition T ou T', majoritaire dans la composition de la phase dure 1), oxyde dans lequel une partie de l'oxygène peut être remplacée par de l'azote et/ou du carbone, cet oxyde étant notamment un oxycarbonitrure, et
• 4) une fine dispersion de particules d'oxyde d'un métal X choisi dans le groupe constitué par l'aluminium, les métaux alcalino-terreux, Sc, Y, les lanthanides, les actinides et les alliages constitués de fer et de métaux cériques,
  étant entendu que les oxydes formant les fines dispersions 3) et 4) peuvent être combinés sous forme d'oxydes complexes.

The subject of the invention is therefore a cermet comprising:

• 1) a hard phase of boride type;
• 2) a binder phase consisting of a pure binder metal L, or an alloy of at least two metals (L, L '...) where:
  • . L is a metal chosen from the group consisting of Fe, Ni, Co and Cr, and
  • . L 'is at least one metallic element of alloy for L, which does not substantially degrade its toughness, characterized in that the hard phase 1) consists of a simple boride TxBy, of a mixture of simple borides TxBy + T 'x'By' or a mixed boride (T, T ') xBy where:
  • . T and T 'are transition metals selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, and
  • . x, x ', y and y' are whole or decimal numbers, preferably whole, identical or different numbers;
  and in that said cermet further comprises:
• 3) a fine dispersion of oxide particles of the transition metal T or T ', predominant in the composition of the hard phase 1), oxide in which part of the oxygen can be replaced by nitrogen and / or carbon, this oxide being in particular an oxycarbonitride, and
• 4) a fine dispersion of oxide particles of a metal X chosen from the group consisting of aluminum, alkaline earth metals, Sc, Y, lanthanides, actinides and alloys consisting of iron and ceric metals ,
  it being understood that the oxides forming the fine dispersions 3) and 4) can be combined in the form of complex oxides.

Advantageously, the ratios x / y and x '/ y', identical or different, are equal to 1/2 or 2/5, or close to these values.

The alkaline earth metals X preferably used according to the invention are Mg and Ca.

The other metals X preferably used according to the invention are Ce, Pr, Nd, Gd, Dy, Th, U as well as an alloy, consisting of iron and ceric metals, such as for example that known under the name of Mischmetall ®.

According to a preferred embodiment, the cermet according to the invention comprises between 20 and 99%, preferably between 50 and 97% by weight of hard phase 1).

• 1. le mélange avec broyage :
  • d'une poudre de phase dure de type borure,
  • d'une poudre de métal liant L défini comme ci-dessus, pur et/ou d'un préalliage dans lequel L est majoritaire,
  • éventuellement d'au moins une poudre d'un élément métallique L' d'alliage pour L ou d'un alliage de L' qui ne dégrade pas susbstantiellement la ténacité de L, et
  • d'une poudre de métal de transition T ou T', sous forme de métal pur, d'alliage et/ou de composé, caractérisé en ce que la phase dure de type borure est constituée d'un borure simple TxBy, d'un mélange de borures simples TxBy + T'x'By' ou d'un borure mixte (T,T')xBy, T,T', x, x', y et y' étant définis comme ci-dessus, le métal de transition T ou T' est le métal majoritaire dans la poudre de la phase dure de type borure, et on mélange simultanément avec broyage :
  • une poudre d'un métal X choisi dans le groupe constitué par l'aluminium, les métaux alcalino-terreux, Sc, Y, les lanthanides, les actinides et les alliages constitués de fer et de métaux cériques, sous forme élémentaire, d'alliage et/ou de composé,
    étant entendu que le métal de transition T ou T' et le métal X peuvent être introduits sous forme d'une poudre d'un alliage ou d'une combinaison de ces deux éléments, ce procédé étant en outre caractérisé en ce qu'il comprend de plus :
• 2. la granulation du mélange obtenu en 1.,
• 3. la compression des granulés obtenus en 2.,
• 4. le frittage et/ou le frittage sous pression gazeuse modérée (sinter-HiP) et/ou la compression isostatique à chaud (HIP) du produit comprimé obtenu en 3.

According to another aspect, the invention relates to a process for manufacturing the cermet defined above, comprising:

• 1. mixing with grinding:
  • a hard phase powder of boride type,
  • of a powder of metal binder L defined as above, pure and / or of a pre-alloy in which L is predominant,
  • optionally at least one powder of a metallic element L ′ of alloy for L or of an alloy of L ′ which does not significantly degrade the toughness of L, and
  • a transition metal powder T or T ', in the form of pure metal, of alloy and / or of compound, characterized in that the hard phase of boride type consists of a simple boride TxBy, of a mixture of simple borides TxBy + T'x'By 'or of a mixed boride (T, T ') xBy, T, T', x, x ', y and y' being defined as above, the transition metal T or T 'is the majority metal in the powder of the hard phase of boride type, and the following are mixed simultaneously with grinding:
  • a powder of a metal X chosen from the group consisting of aluminum, alkaline earth metals, Sc, Y, lanthanides, actinides and alloys consisting of iron and ceric metals, in elementary form, of alloy and / or compound,
    it being understood that the transition metal T or T ′ and the metal X can be introduced in the form of a powder of an alloy or of a combination of these two elements, this method being further characterized in that it comprises Furthermore :
• 2. the granulation of the mixture obtained in 1.,
• 3. compression of the granules obtained in 2.,
• 4. sintering and / or sintering under moderate gas pressure (sinter-HiP) and / or hot isostatic compression (HIP) of the compressed product obtained in 3.

The transition metal T or T '(added according to the invention) can be added in elementary form, that is to say not combined with the mixture of the other powders. However, to facilitate its introduction into this mixture, it is advantageously used in the form of its THz type hydride, z being an integer or decimal, or one of its alloys of type (T, L), L being l '' one of the binding metals used according to the invention, namely Fe, Ni, Co or Cr, or one of its mixed hydrides of type (T, L) Hz, z being an integer or decimal number, because these compounds or alloys are generally more easily grindable than pure metal.

The metal X can also be added in elementary form, that is to say not combined, to the mixture of the other powders. However, to facilitate its introduction into this mixture, it is advantageously used in the form an alloy XaLb or XcTd, and / or a corresponding mixed hydride (X, L) Hz or (X, T) Hz ', and / or a mixed boride XaLbBt (L being preferably Fe, Ni or Co) because these alloys, hydrides or borides are generally more easily grindable and less reactive with respect to the environment than pure metal X. In these alloys or compounds of the metal X, a, b, c, d, t, z and z 'are numbers whole or decimal.

One can also advantageously use its grounded hydride XHz, in which z is an integer or decimal.

• 50 à 97 % en poids de poudre de type borure,
• 3 à 50 % en poids de poudre de métal liant L pur, ou d'un préalliage dans lequel L est majoritaire,
• 0 à 25 % en poids de poudre d'au moins un élément métallique L' d'alliage pour L qui ne dégrade pas substantiellement sa ténacité,
• 0,1 à 20 % en poids de poudre de métal X ou de l'un de ses alliages et/ou composés et
• 1 à 15 % en poids de poudre du métal T ou T' ou de l'un de ses alliages et/ou composés.

The mixture treated according to the invention for manufacturing cermets advantageously consists of:

• 50 to 97% by weight of boride type powder,
• 3 to 50% by weight of metal powder binding pure L, or of a pre-alloy in which L is predominant,
• 0 to 25% by weight of powder of at least one metallic element L 'of alloy for L which does not substantially degrade its toughness,
• 0.1 to 20% by weight of metal powder X or of one of its alloys and / or compounds and
• 1 to 15% by weight of powder of the metal T or T 'or of one of its alloys and / or compounds.

Mixing with grinding can be carried out according to any process known to those skilled in the art. It is advantageously carried out by attrition in a ball mill.

The duration of the grinding is preferably from 2 to 48 hours.

The compression is advantageously carried out under a pressure of 50 to 300 MPa.

The sintering is advantageously carried out at a temperature of 1300 to 1700 ° C, for 1 to 3 hours, under pressure of 1 to 10⁴ Pa of argon, or under pressure of 10⁵ Pa of hydrogen, or under vacuum of 10⁻² to 10 Pa, or by hot isostastic compression under 100 to 200 MPa of argon (HIP press: ASEA Q1H-6 for example). One can also practice in the same oven, in a single operation (sinter-HIP), sintering followed by hot isostatic compression under moderate pressure (for example 5 to 10 MPa of argon).

Given their remarkable properties, in particular their toughness, the cermets obtained according to the invention can be used in particular for manufacturing cutting tools, drilling tools or Wear parts.

The invention is explained in more detail and its advantages are highlighted in the nonlimiting examples which follow.

Example 1 (comparative) :

• · 139,2 g de poudre de diborure de titane (surface spécifique BET : 1,5 m²/g ; diamètre de grain moyen FISHER : 4,3µm) ;
• · 60,8 g de poudre de fer ex-carbonyle (diamètre de grain moyen FISHER : 4,3 µm),

par broyage par attrition, dans les conditions suivantes : 200 g de mélange + 10 g de paraffine + 1750 g de billes d'acier (4 mm de diamètre), pendant 4 heures, en présence de 200 ml d'acétone. Le mélange homogène, broyé et séché est comprimé sous forme d'éprouvettes parallélépipédiques ISO B (Norme ISO 3327) en matrice et poinçons, sous 200 MPa, en compression uniaxiale bidirectionnelle. Après déparaffinage, le frittage des éprouvettes est effectué à 1450°C, sous pression de 10³ Pa d'argon, pendant 1 heure. La porosité ouverte, mesurée sur les éprouvettes frittées, est de 20 %. Elle peut être ramenée à 12 % par frittage d'une heure à 1520°C.The following mixture is produced:

• 139.2 g of titanium diboride powder (BET specific surface: 1.5 m² / g; average FISHER grain diameter: 4.3 µm);
• 60.8 g of ex-carbonyl iron powder (average FISHER grain diameter: 4.3 µm),

by grinding by attrition, under the following conditions: 200 g of mixture + 10 g of paraffin + 1750 g of steel balls (4 mm in diameter), for 4 hours, in the presence of 200 ml of acetone. The homogeneous mixture, ground and dried, is compressed in the form of ISO B parallelepipedic test pieces (Standard ISO 3327) in matrix and punches, at 200 MPa, in bidirectional uniaxial compression. After dewaxing, the sintering of the test pieces is carried out at 1450 ° C, under pressure of 10³ Pa of argon, for 1 hour. The open porosity, measured on the sintered test pieces, is 20%. It can be reduced to 12% by sintering for one hour at 1520 ° C.

Metallographic and radiocrystallographic examinations show that the binder consists essentially of iron borides Fe₂B and FeB.

Since Example 1 can be considered typical of the prior art, in order to concretize the improvements linked to the invention, the inventors have carried out Example 2 which follows.

Example 2 (according to the invention) :

• · 136,0 g de poudre de diborure de titane (surface spécifique BET : 0,52 m²/g ; diamètre de grain moyen FISHER : 4,6 µm) ;
• · 51,5 g de poudre de fer ex-carbonyle (diamètre de grain moyen FISHER : 2,0 µm) ;
• · 10,3 g de poudre d'alliage NdNi₅ ;
• · 2,2 g de poudre d'alliage TiFe₂.

The following mixture is produced:

• 136.0 g of titanium diboride powder (BET specific surface: 0.52 m² / g; FISHER average grain diameter: 4.6 µm);
• 51.5 g of ex-carbonyl iron powder (average FISHER grain diameter: 2.0 µm);
• · 10.3 g of NdNi₅ alloy powder;
• 2.2 g of TiFe₂ alloy powder.

The grinding is carried out as in Example 1, with the only difference that the grinding time is reduced to 2 hours. The compression and dewaxing are carried out as in Example 1. The sintering is carried out at 1500 ° C., under pressure of 10³Pa of argon, for one hour. The total porosity measured on the sintered test pieces is 2%.

Metallographic and radiocrystallographic examinations show that the binder consists essentially of an iron-nickel alloy. We note the presence of a fine dispersion of neodymium oxide particles (Nd₃0₃), as well as titanium oxycarbonitride particles Ti (O, C, N).

The VICKERS hardness of the test pieces, under a load of 30 kg (294 N) is HV₃₀ = 14000 ± 500 MPa.

Example 3 (according to the invention) :

A whole series of cermets has been produced. The compositions of the starting mixtures are given in Table I which follows.

• · conteneur en polyéthylène de 500 cm³
• · billes en acier inoxydable austénitique (100 cm³) de 5 mm (30 cm³) et 20 mm (70 cm³)
• · vitesse de rotation : 45 tr/min
• · durée de broyage : 48 h

For each product, the mixture of powders (with a total weight of 50 g) is produced by grinding in a ball mill, with the following operating characteristics:

• · 500 cm³ polyethylene container
• · Austenitic stainless steel balls (100 cm³) of 5 mm (30 cm³) and 20 mm (70 cm³)
• · Rotation speed: 45 rpm
• · Grinding time: 48 h

The ground mixture is separated from the beads by sieving.

The compression of test pieces (5 g per test piece) is carried out at 70 MPa, the matrix (in hardened steel) being lubricated with zinc stearate.

The test pieces are encapsulated and sintered by hot isostatic compression (HIP ASEA Q1H-6 press) according to the following cycle: TEMPERATURE (° C) PRESSURE (Argon MPa) BEGINNING END SPEED ° C / min BEGINNING END SPEED MPa / min Min duration 20 430 10 empty* empty* - 43 450 450 - empty* empty* - 30 450 820 10 empty* empty* - 37 820 820 - empty* 0.5 - 0.017 820 1000 10 0.5 0.5 - 18 1000 1350 8.75 0.5 150 3.75 40 1350 1350 - 150 150 - 30 1350 300 - 35 150 70 - 2.7 30 300 270 - 15 70 1 - 35 2 * empty: 1 Pa

The characteristics measured on the densified specimens are recorded in Table II.

In the cermets according to the invention, it is found that the theoretical density is practically reached and the metallographic and radiocrystallographic examinations show that the binder phase is essentially iron: there does not appear any boride phase Fe₂B or FeB, while this phase is predominant in the FN, FNMo and FNW alloys developed according to the prior art. This absence of iron boride phase in the alloys according to the invention is confirmed by the increase in ductility of the binder phase, quantified by the measurement of the stress intensity factor K _IC by the PALMQVIST indentation method.

On metallographic examination, the alloys according to the invention exhibit a fine dispersion of alumina particles (Al₂O₃).

Example 4 (according to the invention) :

A series of cermets has been produced. The compositions of the starting mixtures are given in Table III below.

For each composition, the mixture of powders is produced in a ball mill (of stainless steel) under the conditions described in Example 3.

The crude mixture is separated from the beads by sieving.

The compression of test pieces is done under 100 MPa, in a hardened steel matrix, lubricated with zinc stearate.

The test pieces are encapsulated and sintered by hot isostatic compression (HIP ASEA Q1H-6 press), according to the cycle described in Example 3.

The characteristics measured on the fully densified test pieces are given in the following table:

On metallographic examination, the alloys according to the invention, with the addition of TiAl₃, exhibit, in addition to the hard phase TiB₂ and the binder Fe / Ni / Cr or stainless steel 316L, a fine dispersion of alumina and oxycarbonitride particles of titanium. Note the influence of the addition of TiAl₃ in alloys with 316L stainless steel binder: the hardness decreases only by 3% while the toughness increases by around 40%.

Example 5 (according to the invention) :

• · 129,2 g de poudre de diborure de titane (surface spécifique BET : 0,52 m²/g ; diamètre de grain moyen FISHER : 4,6 µm)
• · 6,8 g de poudre de diborure de chrome (diamètre de grain moyen FISHER : 4 µm)
• · 51,5 g de poudre de fer ex-carbonyle (diamètre de grain moyen FISHER : 2,0 µm)
• · 10,3 g de poudre d'allïage NdNi₅
• · 2,2 g de poudre d'alliage TiFe₂.

The following mixture is produced:

• 129.2 g of titanium diboride powder (BET specific surface: 0.52 m² / g; FISHER average grain diameter: 4.6 µm)
• 6.8 g chromium diboride powder (FISHER medium grain diameter: 4 µm)
• 51.5 g of ex-carbonyl iron powder (FISHER average grain diameter: 2.0 µm)
• 10.3 g of NdNi₅ alloy powder
• 2.2 g of TiFe₂ alloy powder.

The grinding is carried out as in Example 2. The compression and the dewaxing are carried out as in Example 1. The sintering is carried out at 1600 ° C. under argon pressure of 10³Pa, for two hours. The total porosity measured on the sintered test pieces is less than 0.5%.

Metallographic and radiocrystallographic examinations show that the hard phase consists of the solid solution (Ti, Cr) B₂ and the binder is essentially an Fe / Ni alloy. Note the presence of a fine dispersion of particles of neodymium oxide (Nd₂O₃) and titanium oxycarbonitride [Ti (O, C, N)].

The VICKERS hardness under load of 30 kg (294 N) of the sintered test pieces is 14,900 ± 500 MPa, i.e. 6% higher than that of the test pieces of Example 2 (without substitution of TiB₂ by CrB₂) which is 14000 ± 500 MPa.

Claims (13)

1. Cermet including:

   1) a hard phase of boride type:

   2) a binding phase consisting of a pure binding metal L or of an alloy of at least two metals (L, L'), where:

   - L is a metal chosen from the group consisting of Fe, Ni, Co and Cr, and

   - L' is at least one metallic element alloying with L, which does not substantially damage its toughness, characterized in that the hard phase 1) consists of a simple boride TxBy, of a mixture of simple borides TxBy + T'x'By' or of a mixed boride (T, T')xBy, where:

   - T and T' are transition metals chosen from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, and

   - x, x', y and y' are integral or decimal numbers, preferably integral numbers, which are identical or different,
   and in that the said cermet additionally includes:

   3) a fine dispersion of particles of oxide of the transition metal T or T', predominant in the composition of the hard phase 1), in which oxide a proportion of the oxygen may be replaced with nitrogen and/or carbon, this oxide being especially an oxycarbonitride, and

   4) a fine dispersion of particles of oxide of a metal X chosen from the group consisting of aluminium, alkaline-earth metals, Sc, Y, the lanthanides, the actinides and the alloys consisting of iron and of ceric metals,
   it being understood that the oxides forming the fine dispersions 3) and 4) may be combined in the form of complex oxides.
2. Cermet according to Claim 1, in which the ratios x/y and x'/y', which are identical or different, are equal to 1/2 or 2/5 or close to these values.
3. Cermet according to Claim 1 or 2, characterized in that the alkaline-earth metal is Mg or Ca.
4. Cermet according to Claim 1 or 2, characterized in that the metal X is chosen from the group consisting of Ce, Pr, Nd, Gd, Dy, Th, U and the alloys consisting of iron and of ceric metals.
5. Cermet according to any one of Claims 1 to 4, characterized in that it includes between 20 and 99 %, preferably between 50 and 97 % by weight of hard phase 1).
6. Process for the manufacture of the cermet according to any one of Claims 1 to 5, including:

   1. mixing with grinding:

   - of a powder of hard phase of boride type,

   - of a powder of binding metal L defined as in Claim 1, pure, and/or of a prealloy in which L is predominant,

   - optionally of at least one powder of a metallic element L' alloying with L or of an alloy of L' which does not substantially damage the toughness of L, and

   - of a powder of transition metal T or T', in the form of pure metal, of alloy and/or of compound,

   characterized in that the hard phase of boride type consists of a simple boride TxBy, of a mixture of simple borides TxBy + T'x'By' or of a mixed boride (T, T')xBy, T, T', x, x', y and y' being defined as in Claim 1, the transition metal T or T' is the predominant metal in the powder of the hard phase of boride type, and the following is mixed simultaneously with grinding:

   - a powder of a metal X chosen from the group consisting of aluminium, alkaline-earth metals, Sc, Y, the lanthanides, the actinides and the alloys consisting of iron and of ceric metals, in the form of element, of alloy and/or of compound,

   it being understood that the transition metal T or T' and the metal X may be introduced in the form of a powder of an alloy or of a combination of these two elements, this process being moreover characterized in that it additionally includes:

   2. the granulation of the mixture obtained in 1.,

   3. the compression of the granules obtained in 2.,

   4. the sintering and/or the sintering under moderate gas pressure (HiP-sinter) and/or the isostatic compression with heating (HIP) of the compressed product obtained in 3.
7. Process according to Claim 6, characterized in that the transition metal T or T', added in the form of powder, is in the form of its hydride of THz type, z being an integral or decimal number, or of one of its alloys of (T, L) type, L being Fe, Ni, Co or Cr, or of one of its mixed hydrides of (T, L)Hz type, z being an integral or decimal number.
8. Process according to Claim 6 or 7, characterized in that the metal X is added in the form of an alloy XaLb or XcTd and/or of a corresponding mixed hydride (X, L)Hz or (X, T)Hz' and/or of a mixed boride XaLbBt in which L is preferably Fe, Ni or Co, and/or of its hydride XHz, a, b, c, d, t, z and z' being integral or decimal numbers.
9. Process according to any one of Claims 6 to 8, characterized in that the treated mixture consists of:

   - 50 to 97 % by weight of powder of boride type,

   - 3 to 50 % by weight of powder of pure binding metal L or of a prealloy in which L is predominant,

   - 0 to 25 % by weight of powder of at least one metallic element L' alloying with L which does not substantially damage its toughness,

   - 0.1 to 20 % by weight of powder of metal X or of one of its alloys and/or compounds and

   - 1 to 15 % by weight of powder of the metal T or T' or of one of its alloys and/or compounds.
10. Process according to any one of Claims 6 to 9, characterized in that the duration of the grinding is from 2 to 48 hours.
11. Process according to any one of Claims 6 to 10, characterized in that the compression is performed at a pressure of 50 to 300 MPa.
12. Process according to any one of Claims 6 to 11, characterized in that the sintering is performed at a temperature of 1300 to 1700°C, for 1 to 3 hours, at a pressure of 1 to 10⁴ Pa of argon or at a pressure of 10⁵ Pa of hydrogen or in a vacuum of 10⁻² to 10 Pa, or by isostatic compression with heating at 100 to 200 MPa of argon, or, in the same furnace, in a single operation, by sintering followed by an isostatic compression with heating at moderate pressure (HIP-sinter).
13. Use of the cermet according to any one of Claims 1 to 5, or such as obtained by making use of the process according to any one of Claims 6 to 12, for manufacturing cutting tools, drilling tools or wear components.