EP0263427B1 - Metal-ceramic composite material and process for its manufacture - Google Patents

Abstract

A consolidated metal-ceramic composite comprises a first phase of particles of aluminum oxide or a solid solution based on aluminum oxide uniformly distributed in a second matrix phase wherein the second matrix phase is non-reactive with aluminum oxide and contains a sufficient amount of titanium carbide at the interface between the first and second phase to prevent a chemical reaction at the interface during consolidation at the liquidus temperature and which exhibits good mechanical properties with regard to strength and toughness at high temperatures up to about 1200 DEG C.

Description

The present invention relates to a ceramic-metallic composite material based on aluminum oxide and to a process for the manufacture of this material.

Aluminum oxide has the characteristics of excellent wear resistance. This material is used in cutting tools for metals or for wear-resistant surfaces. Aluminum oxide in the form of a coating on conventional carbide tools is formed by vapor deposition or by sputtering. It is known that the mechanical properties of aluminum oxide can be improved by forming solid solutions with other oxides such as chromium oxide, or by forming multiphase compositions with other oxides such as that of zirconium. . In addition, it is known to form cutting tools by sintering or by a hot pressing process. Aluminum oxide compositions may also include additives for fixing the grain boundaries, such as magnesium oxide, titanium oxide or titanium carbide. Aluminum oxide tools are too fragile for most steel cutting operations, and their use is limited to finishing cuts, due to their lack of ductility leading to an inability to resist loads or vibrations even averages between the tool and the workpiece without risk of breakage. Tests have been carried out to produce ceramic-metallic materials based on aluminum oxide for cutting tools, so far with very little success, this because of the difficulty of bonding aluminum oxide to metals. Thus, previous attempts to significantly increase the breaking strength of composite materials have not been successful.

Hot-pressed mixtures of aluminum oxide and titanium carbide, as well as aluminum oxide and silicon carbide whiskeys, are the strongest available oxide ceramics.

It has been proposed in US patent 4,217,113 to form metal compositions containing aluminum oxide intended to be used for cutting tools under conditions to form a reactive metal oxide phase at the interface of the aluminum oxide, which is formed from a metal derived from the metal phase, and aluminum oxide. However, since few oxides outperform aluminum oxide in terms of hardness and resistance at elevated temperatures, it has been found that defects in these compositions occur at the level of the metal oxide formed at the interface between aluminum oxide and metal. Hitherto, the prior art has focused on the formation of a reactive metal oxide interface between the metal matrix and the aluminum oxide in order to increase the tensile strength of the compositions. aluminum oxide.

The object of the present invention therefore consists in completely eliminating the interfacial oxide phases and thus in increasing the breaking strength. The ceramic-metallic composite material according to the present invention, aimed at achieving the goal mentioned above, has the characteristics mentioned in claim 1.

The second phase or matrix, preferably containing approximately 20% by weight of additional ingredients in addition to the metal and the titanium carbide, is therefore made non-reactive with respect to aluminum oxide by inclusion of a sufficient amount of titanium carbide at the interface between the aluminum oxide and this matrix, in order to prevent any chemical reaction at this interface between this matrix and the aluminum oxide particles, during the phase of consolidation at liquidus temperature, i.e. at sintering temperature. The structure obtained is characterized by the absence of brittle or weak resistance interfacial phase and by the absence of an interface made up of reaction compounds such as oxides.

When it is intended to be used as a cutting tool, the composite material according to the invention contains an amount of less than about 30% by volume of the matrix metal phase, and more particularly it contains between about 70 and 90% by volume of aluminum oxide. The material according to the invention is also useful for the manufacture of structural parts having good resistance to abrasion and to chemical wear, including to oxidation, and then contains the metallic phase in a concentration up to approximately 40% by volume, more particularly it contains between approximately 50 and 70% by volume of aluminum oxide.

Another object of the present invention consists in a process for manufacturing the ceremonial-metallic composite material defined above, which has the characteristics mentioned in the Claim 12. The sintering reaction of the constituent elements is therefore carried out by controlling the partial pressure of carbon monoxide, and preferably in a non-oxidizing atmosphere, for example under vacuum or under an inert atmosphere. It can be combined with hot pressing or with isostatic hot pressing.

According to a preferred form of the process, all the parts of titanium carbide present at the interface can be provided by coating the aluminum oxide component in the form of particles with titanium carbide, before the phase of consolidation of the particles by sintering. for the formation of an article.

More particularly, the material according to the invention is prepared by consolidation or sintering of a mixture of microscopic homogeneous powders with an aluminum oxide and / or of a solid solution containing one or more constituents of aluminum oxide and (b) a matrix phase. This matrix phase comprises a metal capable of retaining relatively high concentrations of titanium and carbon and a source of titanium and carbon. The relative concentrations of titanium and carbon should be such that they can form titanium carbide in an amount sufficient to prevent reaction at the interface between the matrix phase and the aluminum oxide phase. Such a reaction must be eliminated, since it results in the formation of interface compositions which may be harmful. Suitable temperatures for consolidation by sintering the homogeneous mixture to form an article are between the minimum temperature at which the metallic component forms a liquid with the appropriate concentration of titanium and carbon up to the temperature of the melting point of aluminum oxide. Preferably, this temperature is between approximately 1300 and approximately 1600 ° C. The mixture is subjected to an elevated temperature for a period sufficient for the titanium and carbon constituents to dissolve in the metal matrix, so that the titanium and carbon are retained in this matrix in the form of a liquid solution. It is believed that the presence of titanium carbide at the interface delays or prevents a reaction at the interface of the metal matrix and aluminum oxide.

For the production of cutting tools or other wear-resistant surfaces, the compositions prepared by the process according to the invention contain between approximately 70 and 90% by volume of aluminum oxide. For the production of abrasion resistant articles such as valves, fuel pump components, structural parts of engines, or the like, the composite material according to the present invention contains more than about 50% by volume. aluminum oxide, preferably between about 50 and 70% by volume.

${\text{Al₂O₃ + 3 TiC = 5(Al}}_{\text{0,4}}{\text{Ti}}_{\text{0,6}}\text{) + 3CO↑ (2)}$

$$\frac{\text{x}}{\text{2}}{\text{Al₂O₃ + (a+y) TiC = Al}}_{\text{x}}{\text{Ti}}_{\text{y}}{\text{+ Ti}}_{\text{a}}{\text{O}}_{\text{b}}\text{+ (a+y)CO↑ (3)}$$

où

$\text{b =[1,5 x - (a+y)]}$

The possible reactions of Al₂O₃ and TiC can be represented by the following three equations:

$\text{2Al₂O₃ + 3TiC = Al₄C₃ + 3 TiO₂ (1)}$

${\text{Al₂O₃ + 3 TiC = 5 (Al}}_{\text{0.4}}{\text{Ti}}_{\text{0.6}}\text{) + 3CO ↑ (2)}$

$$\frac{\text{x}}{\text{2}}{\text{Al₂O₃ + (a + y) TiC = Al}}_{\text{x}}{\text{Ti}}_{\text{y}}{\text{+ Ti}}_{\text{at}}{\text{O}}_{\text{b}}\text{+ (a + y) CO ↑ (3)}$$

or

$\text{b = [1.5 x - (a + y)]}$

In order to ensure that the above reaction (2) occurs in preference to the other two, and thus to suppress the formation of unwanted titanium oxide, it is important that the partial pressure of CO during sintering is maintained in a range of about 10⁻⁵ to 10⁻² Torr (1.33.10⁻³ to 1.33 Pa), and preferably about 10⁻⁴ to 10⁻³ Torr (1.33.10⁻² to 1, 33.10⁻¹ Pa).

The composite material according to the invention is characterized by a microstructure which is substantially composed of a ceramic phase of aluminum oxide separated and agglomerated by a ductile metallic matrix phase. The interface between the aluminum oxide phase and the metallic matrix phase is mainly composed of titanium carbide. This composite material has a breaking strength (or stress intensity factor K _IC ) of 8 to 15 MN / m³ / 2, therefore much higher in comparison with the 4 to 5 MN / m³ / 2 of the compositions based commercially available alumina. Preferably, the various constituents intended to form the composite material according to the invention are mixed and ground by techniques such as ball milling, air milling, or the like, before subjecting the mixture to a temperature and a pressure. high.

Representative sources of titanium are metallic titanium and titanium carbide. Representative sources of carbon are carbon, as well as titanium carbides, molybdenum, tungsten, vanadium, carbide, chromium, tantalum, niobium, zirconium, and hafnium. The first suitable metal components which are relatively non-reactive by compared to aluminum oxide, titanium and titanium carbide, include nickel, iron, cobalt or mixtures thereof. The solubility of titanium and carbon in the metallic matrix phase can be increased by adding a third component in an amount generally between about 5 and 30% by weight, relative to the weight of said first metallic component, such as carbide molybdenum, chromium carbide, tantalum carbide, and niobium carbide, tungsten carbide, vanadium carbide, ruthenium, rhodium, rhenium and osmium, as well as mixtures and alloys of those -this.

Any available form of alumina can be used in the present invention, including a powder of particles between about 0.1 and 100 micrometers in diameter, whiskers, fibers or other solid forms. The present invention can also be used to bond solid aluminum oxide components to each other or to metallic components.

According to a preferred variant of the invention, the aluminum oxide particles are pre-coated with titanium carbide, titanium oxi-carbides or titanium, before being mixed with the metallic matrix phase. Suitable coating techniques include chemical vapor deposition, simple or combined with plasma or laser technique, sputtering, physical vapor deposition, vacuum evaporation or reduction of titanium oxide coating on the surface of the aluminum oxide particles.

The above-mentioned coating methods can be carried out in a reaction chamber which is surrounded by an induction coil electrically connected to a radio frequency oscillator. The room is equipped with inputs and outputs at radio. The chamber is provided with inlets and outlets at its axial ends for the flow of the gaseous medium. The untreated powder is placed in the reaction chamber and subjected to the desired coating temperatures by use of the radio frequency oscillator.

For example, titanium carbide layers are formed on aluminum oxide particles in the reaction chamber by entraining the particles in a gaseous mixture of titanium tetrachloride, from a source of carbon gas, such as than methane, and hydrogen, and by heating the particles to a temperature between about 800 and about 1800 ° C, preferably around 1000 ° C. The reaction can be described by the following equation, although hydrogen is often added to ensure that the reaction takes place in a reducing environment:



TiCl₄ + CH₄ → TiC + 4 HCl ↑

The mixture containing the particles is kept at the reaction temperature until the desired coating thickness is obtained. A routine test is carried out to determine the value of the growth in thickness of the coating at a particular value of the gas flow rate and at a determined temperature. Typical preferred coatings are on the order of 100-1000 ångströms, and preferably 200-500 ångströms (1 ångström (Å) = 0.1 nm).

The present invention will now be described in more detail with reference to the following illustrative example:

Example

Alumina powders were placed in pyrex glass tubes for chromatography having a tapered end to which a porous sintered glass plate has been attached. Argon was introduced into the tubes and passed through the sintered glass and the powder bed. By precisely controlling the gas flow, by means of a micrometric valve, only fine particles were entrained in the gas stream and introduced into the reaction chamber either at the bottom of the latter in the gas inlet or directly in plasma by attaching an elongated alumina tube to the normal gas and powder inlet. The powder was collected by reducing the speed of the gas stream in an enlarged chamber and by filtering the gas through stainless steel filters. After the generator was operated at full power, argon was introduced into the reaction chamber until a flow rate of 750 ml / min was obtained. At this time, the gas mixture of TiCl₄ + CH₄ + H₂ was introduced. After a plasma composed of the reagent was brought to the desired flow parameter, argon gas was slowly introduced through the powder bed. Then the gas flow was increased until it can be seen that fine powder leaves the fluidization chamber and enters the plasma chamber.

After a sufficient amount of coated powder was obtained, six samples were prepared, and three additional commercial ceramic composites were also prepared for comparison. The chemical composition of the different samples prepared for the experiment is described in Table I.

The powders were ground for 24 hours in containers containing about 1.3 cm alumina beads as a means of grinding. The powder mixtures were then placed in a mold and pressed uniaxially at around 100 Kpsi (700 MPa) to form compact samples. These compact samples were sintered under vacuum for one hour at 1370 ° C. The sintered samples based on alumina were encapsulated in steel containers and isostatically pressed at 45 Kpsi (310MPa) and 1370 ° C for samples 1 and 4, and at 35 Kpsi (242MPa) and at 1315 ° C for samples 2,3,5 and 6. These samples thus treated were cut by means of diamond blades, polished and mounted so as to examine their microstructure.

In compositions 1, 2 and 3, the alumina phase is aggregated and continuous, and the metal phase is distributed in bags isolated by the alumina phase, indicating that the incomplete wetting results in apparent sintering in the solid state of the powders. alumina.

In the alumina compositions coated with TiC, namely samples 4, 5 and 6 with a high metal content, the alumina phase is surrounded by the metal phase which appears to be continuous. The size distribution of the alumina particles appears to be similar, but the TiC coated alumina particles are more uniformly dispersed in the metal binder than the uncoated alumina particles.

The results of the hardness H _v and the resistance to cracking W are given in table II, as well as the modulus of elasticity and the stress intensity factor K _IC and the values of the propagation energy of the G _IC cracks calculated. The values of K _IC and G _IC were determined using the so-called Palmquist technique.

Claims (17)

1. Ceramo-metallic composite material comprising a ceramic phase, including particules of aluminium oxide or of an aluminium oxide-based solid solution, which are uniformly distributed in a matrix, said matrix being non-reactive with aluminium oxide and comprising a metal selected among Ni, Co, Fe and the mixtures thereof, as well as titanium carbide, and in which the content of titanium carbide present at the interface between the ceramic phase and the matrix is such that it prevents the chemical reaction between them at the sintering temperature.
2. Composite material according to claim 1, characterized by the fact that the aluminium oxide particles are under the form of a powder with grains having a diameter of 0.1 to 100 micrometers.
3. Composite material according to claim 1, characterized by the fact that the aluminium oxide particles are under the form of whiskers or filaments.
4. Composite material according to one of the claims 1 to 3, characterized by the fact that the aluminium oxide particles are coated with titanium carbide, titanium oxicarbide or titanium.
5. Composite material according to claim 4, characterized by the fact that the thickness of the coating is of 100 to 1000 A.
6. Composite material according to claim 5, characterized by the fact that the thickness of the coating is of 200 to 500 A.
7. Ceramo-metallic composite material comprising a ceramic phase, including particles of aluminium oxide or of an aluminium oxide-based solid solution, which are uniformly distributed in a matrix, said matrix being non-reactive with aluminium oxide and comprising a metal selected among Ni, Co, Fe and the mixtures thereof, as well as titanium carbide, and a third component in an amount lower than 30% by weight, said third component being selected in such a way that it makes the titanium carbide more soluble in said first metal, and the content of titanium carbide present at the interface between the ceramic phase and the matrix being such that it prevents the chemical reaction between these phases at the sintering temperature.
8. Composite material according to claim 7, characterized by the fact that the third component is selected from the group comprising the carbides of Mo, Cr, W, V, Ta and Nb, and the metals Ru, Rh, Re and Os, as well as the mixtures and alloys thereof.
9. Composite material according to claim 7, characterized by the fact that the third component is Mo, Mo₂C or a combination thereof.
10. Composite material according to one of claim 1 to 9 for the realization of abrasion resisting articles, characterized by the fact that it contains between about 50 and 70 vol. % of aluminium oxide particles, or of aluminium oxide-based solid solution.
11. Composite material according to one of claims 1 to 9 for the realization of wear resisting articles such as cutting tools, characterized by the fact that it contains between about 70 and 90 vol. % of aluminium oxide particles, or of aluminium oxide-based solid solution.
12. Process for the manufacture of the ceramo-metallic composite material according to one of the claims 1 to 11, characterized by the fact that the various components are sintered under such conditions that the partial pressure of the formed CO is comprised between 1.33.10⁻³ and 1.33 Pa.
13. Process according to claim 12, characterized by the fact that the sintering is carried out under partial vacuum or in inert atmosphere, at a temperature comprised between 1300 and 1600°C and by maintaining the partiel pressure of CO between 1.33.10⁻² and 1.33.10⁻¹ Pa.
14. Process according to claim 13, characterized by the fact that the material is uniaxially pressed at about 700 MPa before sintering.
15. Process according to claim 13, characterized by the fact that the material is pressed in an isostatic manner between 242 and 310 MPa before sintering.
16. Process according to one of claim 12 to 15 for the manufacture of a composite material according to claim 4, characterized by the fact that a coating of titanium carbide or oxicarbide or of metal titanium is deposited on the aluminium oxide particles prior to the sintering.
17. Process according to claim 16, characterized by the fact that the coating is carried out by chemical reduction in vapor phase of TiCl₄ by hydrogen in presence of a carbon source, for example methane, at a temperature comprised between 800 and 1200°C.