EP0591305A1

EP0591305A1 - Cermets based on transition metal borides, their production and use.

Info

Publication number: EP0591305A1
Application number: EP92912846A
Authority: EP
Inventors: Henri Pastor; Colette Allibert; Laurent Ottavi; Manuel Albajar; Francisco Castro-Fernandez
Original assignee: Sandvik Hard Materials SA
Current assignee: Sandvik Hard Materials SA
Priority date: 1991-06-28
Filing date: 1992-06-26
Publication date: 1994-04-13
Anticipated expiration: 2012-06-26
Also published as: WO1993000452A1; FR2678286B1; ATE130375T1; US5439499A; FR2678286A1; DE69206148T2; DE69206148D1; JPH06511516A; EP0591305B1; ES2081617T3

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

Cermets based on transition metal borides, their manufacture and their applications.

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 of 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.

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 transition metal borides, most often metal diborides. of transition and in particular of titanium diboride TiB2. These metals or alloys have in principle a double function:

- ensure the formation of a liquid fusible phase (most often with 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 toughness to the sintered cermet which is thus thus formed of a hard but fragile phase (the boride) and of a less hard but ductile metal 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 transforms S, at least partially, 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 TiB ₂ ^_ Fe cermets. To prepare these cermets, they mixed titanium diboride powder TiB ₂ (average grain diameter: 1 to a few μm) with iron powder (average grain diameter l 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 Fe ₂ B 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 attenuation of this. metallic binder.

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.

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 used in the composition of the transition metal boride constituting the hard phase, mainly present in this boride and a metal X chosen from aluminum and the metals of groups IIA and IIIB of the Classification. Periodical of the Elements, 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. The subject of the invention is therefore a cermet comprising:

1) a hard phase consisting 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 mainly transition metals of groups IVB to VIB of the Periodic Table of the Elements and

. x, x ', y and y' are whole or decimal numbers, preferably whole, identical or different numbers;

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, et. L 'is at least one metallic element of alloy for L, which does not substantially degrade its toughness, characterized in that it further comprises 3) a dispersion of 4th 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, and 4) a dispersion of oxide particles of a metal X chosen from aluminum and the metals of groups IIA and IIIB of the Periodic Table of the Elements, it being understood that the oxides forming the dispersions 3) and 4 ) can be combined as complex oxides. It is recalled that the transition metals of groups IVB to VIB (or 4 to 6) of the Periodic Table of the Elements are: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and.

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

The metals X of group IIA (2), or alkaline earth metals, preferably used according to the invention, are Mg and Ca.

The metals X of group IIIB (3), which comprises Se, Y, the lanthanides and the actinides, preferably used according to the invention, are Ce, Pr, Nd, Gd, Dy, Th, ϋ 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).

According to another aspect, the invention relates to a process for manufacturing the cermet defined above, characterized in that it essentially comprises: 1. the mixture with grinding:

- a hard phase powder consisting of a simple boride TxBy or a mixture of simple borides TxBy + T'x'By 'or a mixed boride (T, T') xBy, T, T ', x, x ', y and y' being defined as above, - of a metal powder binding pure L, or of a pre-alloy in which L is the majority,

- optionally at least one powder of a metallic element L 'of alloy for L which does not degrade substantially its tenacity,

- a powder of the transition metal T or T ', predominant in the hard phase powder, of the boride type, in the form of pure metal, of alloy and / or compound, and - of a powder of a metal X chosen from aluminum and the metals of groups IIA and IIIB of the Periodic Table of the Elements, 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 an alloy powder or a combination of these two elements,

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 of an XaLb or XcTd alloy, and / or of a corresponding mixed hydride (X, L) Hz or (X, T) Hz ′, and / or of a mixed boron XaLbBt (L preferably being 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. The mixture treated according to the invention for manufacturing cermets advantageously consists of:

- 50 to 97 I 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 the majority, - 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 one of its alloys and / or compounds and - 1 to 15% by weight of metal powder T or T 'or 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 10 ⁴ Pa of argon, or under pressure of 10 ^ Pa of hydrogen, or under vacuum of 10- 2 to 10 Pa, or by hot isostastic compression under 100 to 200 MPa of argon (HIF 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):

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 (FISHER average grain diameter: 4.3 μm), by grinding by attrition, under the following conditions: 200 g of mixture + 10 g of paraffin + 1750 g of beads steel (4 mm in diameter), for 4 hours, in the presence of 200 ml of acetone. The homogeneous mixture, crushed 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 10 ^ 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 X-ray crystallographic 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):

The following mixture is produced:

• 136.0 g of titanium diboride powder (BET specific surface: 0.52 m ^ / g; average FISHER grain diameter: 4.6 μm);

• 51.5 g of ex-carbonyl iron powder (FISHER average grain diameter: 2.0 μm); • 10.3 g of NdNis 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 the dewaxing are carried out as in Example 1. The sintering is carried out at 1500 ° C., under pressure of 10 ³ Pa of argon, for one hour. The total porosity measured on the sintered test pieces is

Metallographic and X-ray crystallographic examinations show that the binder consists essentially of an iron-nickel alloy. Note the presence of a fine dispersion of neodymium oxide particles ⁽ d2θ3 ⁾ , as well as titanium oxycarbonitride particles Ti (0, C, N).

The VICKERS hardness of the test pieces, under a load of 30 kg (294 N) is HV ₃₀ = 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. - • - • -

Table I: Compositions of the starting mixtures of the cermets studied

The FN, FNMo and FNW products (first three lines of the table) are typical of the prior art. The others correspond to cermets according to the invention.

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:

empty: 1 Pa

The characteristics measured on the densified test pieces are shown in Table II

-d

Table II: Characteristics of fried cermets

HV10: VICKERS hardness under load of 10 kg (98 N)

Kic: stress intensity factor determined by indentation (PALMQVIST method)

In the cermets according to the invention, it is found that the theoretical density is practically reached and metallographic and radiocrystallographic examinations show that the binder phase is essentially iron: there does not appear any boride phase Fe ₂ B or FeB, whereas 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 binding phase, quantified by the measurement of the stress intensity factor K ^ c psr the PALMQVIST indentation method. On metal • laougraphic examination, the alloys according to the invention exhibit a fine dispersion of alumina particles (AI ₂ O ₃ ).

Example 4 (according to the invention): a series of cermets was produced. The compositions of the starting mixtures are given in Table III below.

Table III: Compositions of the starting mixtures of the cermets studied

* pre-alloyed stainless steel powder (grade 316 L)

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: -

HV ₁₀ : VICKERS hardness under load of 10 kg (98N)

Kic: stress intensity factor determined by indentation (PALMQVIST method)

Of: flexural strength (4 points)

E: modulus of elasticity nd: not determined

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 TiAl ₃ in the 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): The following mixture is produced:

• 129.2 g of titanium diboride powder (BET specific surface: 0.52 m ² / g; average FISHER grain diameter: 4.6 μm)

• 6.8 g of 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 powder of all ^•, IAGE NdNis

• 2.2 g of TiFe ₂ 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 10 ³ Pa, 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) B ₂ and the binder is essentially an Fe / Ni alloy. Note the presence of a fine dispersion of particles of neodymium oxide (Nd2θ3) and titanium oxycarbonitride [Ti (0, C, N)]. The VICKERS hardness under load of 30 kg (294 N) of the sintered test pieces is 14,900 1,500 MPa, i.e. 6% higher than that of the test pieces of Example 2 (without substitution of iB ₂ with CrB ₂ ) which is 14,000 ± 500 MPa.

Claims

^••

1.- Cermet including:

1) a hard phase consisting of a single 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 mainly transition metals from groups IVB to VIB of the Periodic Table of the Elements and. x, x ', y and y ¹ are whole or decimal numbers, preferably whole, identical or different numbers;

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 it further comprises 3) a dispersion of oxide particles of the transition metal T or T', predominant in the composition of the hard phase 1), an oxide in which part of the oxygen can be replaced by nitrogen and / or carbon, and

4) a dispersion of oxide particles of a metal X chosen from aluminum and the metals of groups IIA and IIIB of the Periodic Table of the Elements, it being understood that the oxides forming the dispersions 3) and 4) can be combined in the form of complex oxides.

2.- Cermet according to claim 1, in which the ratios x / y and x '/ y', 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 metal X of group IIA (2) is Mg or Ca. 4.- Cermet according to claim 1 or 2, characterized in that the metal of group IIIB ( 3) is chosen from the group consisting of Ce, Pr, Nd, Gd, Dy, Th, U and the alloys consisting of iron and ceric metals. 5.- Cermet according to any one of claims 1 to 4, characterized in that it comprises between 20 and 99%, preferably between 50 and 97% by weight of hard phase 1). 6. A method of manufacturing the cermet according to any one of claims 1 to 5, characterized in that it essentially comprises:

1. mixing with grinding:

- a hard phase powder consisting of a simple boron TxBy or 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,

- a pure metal powder binding L, or a pre-alloy in which L is the majority, - optionally at least one powder of a metallic element L 'of alloy for L which does not substantially degrade its toughness,

a powder of the transition metal T or T 'predominant in the hard phase powder, of the boride type in the form of pure metal, of alloy and / or of compound, and

- a powder of a metal X chosen from aluminum and the metals of groups IIA and IIIB of the Periodic Table of the Elements, 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,

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.. - Method according to claim 6, characterized in that the transition metal T or T ', added in powder form, is in the form of its hydride of the THz type, z being an integer or decimal number, or one of its alloys of type (T, L), L being Fe, Ni, Co or Cr, or one of its mixed hydrides of type (T, L) Hz, z being an integer or decimal. 7 '

8.- Method 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 a corresponding mixed hydride (X, L) Hz or (X, T) Hz 'and / or a mixed boride XaLbBt in which L is preferably Fe, Ni or Co, and / or its hydride XHz, a, b, c, d, t, z and z' being whole numbers or decimals.

9.- Method according to any one of claims 6 to 8, characterized in that the treated mixture consists of:

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

- 3 to 50% by weight of pure binder metal powder 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 ¹ of alloy for L which does not substantially degrade its toughness,

- 0.1 to 20% by weight of metal powder X or 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.- Method according to any one of claims 6 to 9, characterized in that the duration of the grinding is from 2 to 48 hours.

11.- Method according to any one of claims 6 to 10, characterized in that the compression is carried out under a pressure of 50 to 300 MPa.

12.- Method according to any one of claims 6 to 11, characterized in that the sintering is carried out at a temperature of 1300 to 1700 ° C, for 1 to 3 hours, under pressure of 1 to 10 ⁴ Pa of argon or under pressure of 105 p _a of hydrogen, or under vacuum of 10-2 to 10 Pa, or by hot isostatic compression under 100 to 200 MPa of argon, or, in the same oven, in a single operation, by sintering followed by hot isostatic compression under moderate pressure (sinter-HIP). 13.- Use of the cermet according to any one of claims 1 to 5, or as obtained by implementing the method according to any one of the claims

6 to 12, for manufacturing cutting tools, drilling tools or wearing parts.