EP1228261B1 - Metal-ceramic composite material body and method for producing the same - Google Patents

Abstract

The present invention relates to a method of fabrication and a product, which forms a composite body made of metal and a porous ceramic blank, which adjoins the metallic portion and is infiltrated by the metal, wherein a gradient in properties across the composite portion of the composite body is formed by a heat treatment that reduces some of the oxides across the thickness of the porous ceramic blank. In one embodiment, a gradient from substantial chemical reaction to incomplete chemical reaction of the reducible oxides of the blank with the infiltrated metal is formed inside the composite portion.

Description

The invention relates to a composite body made of metal and of an adjacent to the metallic part, infiltrated by the metal porous ceramic preform, are reducible by the metal reducible oxides of the precursor and the infiltrated metal to form intermetallic phases and metal oxides with each other or partially.

The infiltration of porous ceramic precursor body, so-called preform body, with metal alloy for the production of higher loadable components or surfaces is known. There are passive ceramics, such as alumina (Al ₂ O ₃ ), SiC or AlN and reducible metal oxide (oxides of Fe, Lr, Lo, Mu, Mo, Ti, Ni, Nb, Cu, Zr, V, W, Ta and other) comprehensive preform bodies are used, which are infiltrated with light alloy, especially aluminum alloy in die-casting or die-casting similar processes. It is also known that the above-mentioned chemical reaction between the metal penetrating into the pores and the metal oxides or generally oxidic substances of the preform body during the infiltration process, ie during the casting process, which takes less than 1 sec, for example in die-casting processes, runs only to a very small extent. It has therefore already been proposed to subject the composite bodies to be produced to a heat treatment at very high temperatures after the infiltration process. Carrying out such a heat treatment, which should preferably be carried out clearly above the solidus temperature of the metallic component, actually only makes sense in components in which the filter is infiltrated Porous ceramic preform 100% of the volume of the component makes, which therefore have no existing of the pure metal area, as this would deform at high temperatures or at least would be significantly affected.

With the DE 197 50 599 A1 It is proposed to cast a layer sequence of differently constructed porous ceramic precursor bodies with an encasing of pure metal alloy. The preforms are layered in such a way that the infiltrated preform which forms the surface of the composite body subjected to stress and wear is formed in the pores of the preform predominantly from intermetallic phases, specifically aluminides. Unreacted metal alloy, ie a mixture of intermetallic phases and metal alloy, is also present in layers facing away from the surface layer, the metal oxides previously contained in the preform being completely converted to intermetallic phases. In the examples of this document, after the infiltration process, either a thermal aftertreatment (annealing) is carried out to bring about the complete reduction of metal oxide present in the respective preform (Examples 1-4), or a single homogeneously constructed preform was placed in a die during an infiltration time of about 1/10 sec filled with metal alloy, whereby only a highly imperfect chemical reaction of the metal oxide and the metal of the encapsulation has been achieved.

The present invention is based on the object, starting from a composite body of the type mentioned, in which so an infiltrated precursor connects to a metallic part of the material body to improve so that a good connection of infiltrated precursor body and metal is reached, the highest loads withstand, and yet one only at high temperatures achievable over a correspondingly long time, very far-reaching reaction of the reducible constituents with the infiltrated metal takes place in those areas whose capacity is to be increased.

This object is achieved in a composite body of the generic type according to the invention that within the infiltrated region of the composite body, ie within the precursor, in the direction of the metallic part, a gradient of further chemical reaction to incomplete chemical reaction of the reducible oxides of the precursor with the infiltrated Metal is formed.

The invention thus proposes that a greater proportion of the reducible oxides is reduced by the infiltrated metal to be reinforced surface areas of the infiltrated preform, which is constructed as such, as in more distant from the surface closer to the metallic part (encapsulation) of the Composite body arranged areas.

If a gradient is mentioned above, below this is a stepless within the pre-body, i. understood in the mathematical sense continuous course of the proportion of chemical conversion.

Since the reaction infiltration of the preform by the formation of intermetallic phases leads to a hardness increase and generally to a higher load capacity of the mostly wear-stressed area of the composite body, a very extensive chemical reaction of the reducible metal oxides is provided at these near-surface areas. In regions close to the infiltrated preform, a more incomplete chemical reaction is provided according to the invention, so that there a greater proportion of unreacted metal of the encapsulation in the pores of the Pre-body is present. This leads to a better connection of the preform to the encapsulation, without having to use different layers of different preform materials and compositions.

Starting from the metal interface, preferably the incompletely responsive region extends 1/8 to 7/8 of the thickness of the composite body away from the interface.

If the preform is formed before the formation of the composite of eg alumina (Al ₂ O ₃ ) and from reducible metal oxides, these metal oxides are reduced during the heat treatment with the re-liquefied (previously infiltrated) aluminum alloy, ie the oxygen of the metal oxides forms with the aluminum Alumina, and the reduced metal of the metal oxides formed with the remaining aluminum alloy intermetallic phases in the form of aluminides.

According to a preferred embodiment of the composite body according to the invention, a gradient of the thermal expansion coefficient of less than 12 × 10 ^-6 / K to more than 15 × 10 ^-6 / K is provided within the preform in the direction of the metallic part of the composite body. Preferably, the coefficient of thermal expansion in the claimed surface area is between 6 and 12 × 10 ^-6 / K and in the transition region to the metallic part of the composite body between 10 and 20, preferably between 12 and 20 × 10 ^-6 / K. In this way, a thermal expansion coefficient of the metallic part of the composite body is approached to a large extent approximated thermal expansion coefficient, whereby the connection to the metallic part of the composite body is inventively improved.

The invention also provides a method for producing a composite body of the type described above Art, wherein after infiltration of the preform, a thermal treatment of the infiltrated preform is made. The method is inventively characterized in that brought by intense local heat input areas of the infiltrated preform to temperatures above 500 ° C, especially about 650 ° C or above 700 ° C and held there for a short time and that by cooling the metallic part of the composite body whose temperature is kept below the solidus temperature of the metal. It is thus proposed according to the invention, where a very extensive reaction of the reducible metal oxides with the infiltrated metal is desired to provide the temperature required for this purpose. On the other hand, intensive cooling of the metallic part of the composite body ensures that the temperatures there do not rise above the heat treatment temperature permissible for the specific metal alloy, so that there is no impairment of the dimensional stability and microstructure of the metallic part of the composite body.

The local heating can be carried out, for example, inductively and / or by means of laser energy or a lamp focused on the surface (halogen lamp or arc lamp) or by means of arc plasma. Heating powers of more than 250 W / cm ² , preferably of more than 1000 W / cm ² , in particular more than 2000 W / cm ^2, are used for local heating of near-surface regions of the infiltrated part of the composite body. Depending on the reaction potential of the composite material and the heat dissipation through the component, the further chemical reaction can proceed automatically parallel to the surface and into the depth. With automatic progression it may be sufficient to introduce only the necessary high power density for ignition in one place only. If there is insufficient reactivity and too much heat dissipation through the rest of the component with the first or another heat source, the reaction is supported, so that the desired spatial Extension of the conversion zone and the degree of conversion can be set. Due to the temperature gradient thus achieved within the infiltrated part of the composite body, a stepless progression is achieved between completely / very largely reacted areas and non / incomplete reacted areas.

The cooling of the metallic part of the composite body takes place by the use of fluid coolants such as water, oil or other liquids. Less preferred is the use of gases, since the heat transfer resistances are too large.

Further features, details and advantages of the invention will become apparent from the claims and from the drawings and the following description of the invention.

Figur 1

eine schematische Darstellung eines keramischen Vorkörpers in einer Gießform;

Figur 2

eine schematische Darstellung des Verbundwerkstoffkörpers;

Figur 3

eine schematische Darstellung der lokalen Erhitzung und lokalen Kühlung des Verbundwerkstoffkörpers nebst angedeutetem Temperaturgradient und

Figur 4

eine schematische Darstellung des fertigen Verbundwerkstoffkörpers.

In the drawing shows:

FIG. 1

a schematic representation of a ceramic preform in a mold;

FIG. 2

a schematic representation of the composite body;

FIG. 3

a schematic representation of the local heating and local cooling of the composite body together with the indicated temperature gradient and

FIG. 4

a schematic representation of the finished composite body.

FIG. 1 schematically shows a ceramic preform 2, which is formed from metal oxides and, for example. Alumina (Al ₂ O ₃ ) as a filler. The preform is inserted into a mold 4. When the mold with technical die-cast aluminum alloy 6 is filled while the porous ceramic body 2 is infiltrated (6), this leads, albeit to a slight extent, to the conversion of the preform into a composite body of Al ₂ O ₃ and intermetallic compounds. Namely, the infiltrated metal in the form of the aluminum die casting alloy leads to the reduction of the metal oxides, forming intermetallic phases and further alumina. Due to the chemical reaction, locally special properties can be set that differ greatly from those of the aluminum alloy (eg tribological, mechanical, physical or chemical). In the case of reaction-containing precursors, the chemical reaction does not take place during the infiltration process or only to a very small extent. For a more complete chemical reaction, a thermal aftertreatment at temperatures above 500 ° C would be required. However, these temperatures are above the allowable heat treatment temperature of die-cast aluminum components. If composite castings, in which the ceramic preform occupies only a small volume fraction, are heated to temperatures above 450.degree., Then the gases dissolved in the aluminum encapsulation precipitate to form bubbles. Further, when heated above the solidus point of the aluminum alloy, the dimensional stability of the composite body is impaired. Such a heat treatment is therefore limited to the composite body in which the ceramic preform occupies almost the entire volume of the composite body.

With the invention it is now proposed, locally and for a limited time (in the range of a few seconds) to enter a very high thermal power density in those regions for initiating the conversion reaction in which a very substantial change in properties, ie usually a gain or hardening of the material to be achieved , This is preferably carried out in an inductive manner. By suitable design of induction coils 10 and adjusting the frequency of the alternating current, the Penetration depth of the induced alternating field and thus influenced or adjusted by heating the composite body. To avoid overheating in the metallic part 12 of the composite body (to prevent blistering and fusing), the metallic part 12 of the composite body is intensively cooled, eg by water, oil or other fluid coolants. At least in principle, cooling by means of moving gases is also possible. In targeted control of heating (registered heat quantity Q _a) and cooling (dissipated heat amount Q _ab) arises in the component, a stationary temperature gradient T (x), which leads in infiltierten region 14 of the composite body to a steady course in the proportion of the chemical reaction, that is, the proportion of further converted areas (ceramics, intermetallic compounds) to less converted areas (ceramics, reducible oxide components, infiltrated metal).

The transformed infiltrated region 18 of the composite body is characterized, for example, by high tribological, mechanical, thermal and chemical resistance or by a coefficient of thermal expansion adapted to the metallic encapsulation. The unconverted infiltrated region 20 is characterized, for example, by a high thermal conductivity and a thermal expansion coefficient adapted to the encapsulation. Especially a continuous transition of the thermal expansion behavior from a coefficient of thermal expansion by 10 · 10 ^-6 / K in the largely converted part of the composite body to values around 15 · 10 ^-6 / K in the low converted or unconverted region can be expected for cyclic, thermal and highly stressed composite castings the thus reduced thermal stresses at the interface of preform to casting (coefficient of thermal expansion 20 - 25 10 ^-6 / K) life be determined.

FIG. 4 indicates such a course of the extensive chemical reaction in the region 18 of the surface 16 up to very low conversion in the boundary region 20 of the preform to the metallic part 6 of the composite body.

Claims (16)

1. Composite material body comprising metal (6) and a porous ceramic precursor body (2), which adjoins the metallic part and has been infiltrated by the metal, wherein oxides of the precursor body that can be reduced by the metal and the infiltrated metal have partially reacted to form intermetallic phases, characterized in that within the precursor body (2) a gradient from a more extensive chemical reaction to a less complete chemical reaction between the reducible oxides of the precursor body and the infiltrated metal has formed in the direction of the metallic part.
2. Composite material body according to Claim 1, characterized in that substantially no chemical reaction has taken place between the material of the precursor body (2) and the infiltrated metal (6) in the transition zone between the metal and the infiltrated precursor body.
3. Composite material body according to Claim 2, characterized in that starting from the metal boundary surface the region in which only an incomplete chemical reaction between the material of the precursor body and the infiltrated metal has taken place extends 1/8 to 7/8 of the cast body thickness into the precursor body from the metal boundary surface.
4. Composite material body according to Claim 1, 2 or 3, characterized in that the metal is an aluminium alloy.
5. Composite material body according to Claim 4, characterized in that the metal is an aluminium die-casting alloy.
6. Composite material body according to one of the preceding claims, characterized in that prior to the formation of the composite material the precursor body (2) is formed from aluminium oxide (Al₂O₃), SiC, AlN or combinations thereof and metal oxides.
7. Composite material body according to one of the preceding claims, characterized in that within the precursor body (2) a gradient of the coefficient of thermal expansion ranging from below 12 · 10^-6/K to over 15·10^-6/K is provided in the direction of the metallic part of the composite material body.
8. Composite material body according to Claim 7, characterized in that a coefficient of thermal expansion of 6-12·10^-6/K has been formed in the extensively reacted region of the infiltrated precursor body.
9. Composite material body according to one of the preceding claims, characterized in that a coefficient of thermal expansion of 10-20·10^-6/K, in particular of 12-20·10^-6/K, has formed in the less extensively reacted region of the infiltrated precursor body.
10. Composite material body according to Claim 7, 8 or 9, characterized in that the transition in coefficient of thermal expansion between the infiltrated precursor body and the metal is less than 5·10^-6/K.
11. Process for producing a composite material body comprising metal (6) and a porous ceramic precursor body (2) which adjoins the metal and has been infiltrated by the metal according to one or more of the preceding claims, wherein after the infiltration of the precursor body a heat treatment is carried out, characterized in that through intensive local introduction of heat (Q_in) regions of the infiltrated precursor body (2) are brought to temperatures of over 500°C and are held there briefly, and in that by cooling (Q_out) the metallic part of the composite material body its temperature is kept below the solidus temperature of the metal.
12. Process according to Claim 11, characterized in that the local heating is carried out inductively.
13. Process according to Claim 11, characterized in that the local heating is carried out by means of laser energy.
14. Process according to Claim 11, characterized in that the local heating is generated by arc means.
15. Process according to Claim 11, 12, 13 or 14, characterized in that heating powers of over 250 W/cm², preferably over 1000 W/cm², in particular over 2000 W/cm², are introduced into the surface of the composite material body.
16. Process according to one of Claims 11 to 15, characterized in that a temperature gradient of between 2 K/mm and 50 K/mm is set within the infiltrated precursor body by means of the local heating and the cooling of the metallic part of the composite material body.

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