DE19752775C1 - Sacrificial body for aluminum oxide-titanium aluminide composite body production by molten aluminum filling - Google Patents

Abstract

A sacrificial body, for subsequent production of an alumina / titanium aluminide composite body, is formed by subjecting a starting mixture of titanium (especially as titanium oxide), carbon (precursor), filler and binder to pressing and heat treatment at below the subsequent aluminum filling temperature so that the filler and/or binder are decomposed before or during subsequent aluminum filling. Independent claims are also included for the following: (i) a starting mixture of titanium (especially as titanium oxide), carbon (precursor), filler and binder for use in the above process; and (ii) a sacrificial body, consisting of the above starting mixture in pressure stable pressed form, for production of an Al2O3/titanium aluminide composite body.

Description

The invention relates to a method for producing an Op ferkörpers from an initial batch for the later production of a component from an Al ₂ O ₃ / titanium aluminide composite material according to the preamble of claim 1, an initial batch for the sacrificial body according to the preamble of claim 16 and a sacrificial body according to the preamble of claim 27, as is apparent from the generic DE 196 05 858 A1.

DE 196 05 858 A1 discloses a method for producing a component from an Al ₂ O ₃ / titanium aluminide composite material. The ceramic / metal composite material combines the properties of the ceramic and the metallic phase and has high strength and high fracture toughness. In the process on which it is based, a starting mixture is formed which, inter alia, has an oxidic compound, which compound can be reduced by means of aluminum while simultaneously forming aluminide and Al ₂ O ₃ . Among other things, TiO ₂ is mentioned as part of the starting mixture. A near-net shape sacrificial body is produced from the initial batch, which is then infiltrated with Al. The sacrificial body is sintered for stabilization and in particular for filling with aluminum under pressure before the pressure infiltration. After sintering, the sacrificial body is tempered to a filling temperature which is above the melting temperature of the aluminum and / or an aluminum alloy - hereinafter referred to simply as aluminum. Furthermore, the filling temperature is arranged below a reaction temperature at which a so-called SHS reaction takes place between the aluminum and at least one of the starting materials. A SHS reaction (self propagating high temperature synthesis) is a reaction that takes place very quickly above its reaction temperature, is highly exothermic and is usually at least almost uncontrollable. At the filling temperature, the sacrificial body is filled with aluminum under pressure and heated again, an exchange reaction now taking place between the aluminum and the constituent parts of the sacrificial body, forming an Al ₂ O ₃ / titanium aluminide composite material.

However, the victim's body is usually only partially converted into the Al ₂ O ₃ / titanium aluminide composite. As can also be seen from DE 196 05 858 A1, a TiO ₂ with a sacrificial body pointing can only be completely filled with aluminum in some cases. Furthermore, such an op body can only be provided with a continuous titanium aluminide phase in exceptional cases.

From the unpublished DE-P 197 10 671.4, a method for producing a component from a metal / ceramic composite material is known in which a sacrificial body made of ceramic materials with thermally softened metal - in particular aluminum - and / or with a metallic one Alloys is filled. The filling temperature is arranged below a reaction temperature at which reaction temperature an exchange reaction takes place between a metal of the ceramic primary material and a metal of the filling metal. After the sacrificial body has been filled as completely as possible, the filled sacrificial body is heated to or above the reaction temperature, as a result of which the exchange reaction just mentioned then takes place. In this exchange reaction, a component is produced from the metal / ceramic composite material, which has a ceramic and a metallic phase with an intermetallic connection of the metal of the ceramic and the metal of the filling metal. By filling the Op ferkörpers with a metal softened by heating below a reaction temperature at which there is an exchange reaction between the filling metal and the material of the sacrificial body, the ceramic matrix is during the filling and also in the subsequent exchange reaction between the introduced metal and receive the material of the sacrificial body. Ideally, the pores of the sacrificial body are completely filled, so that when the stoichiometric measurement of the substances in question, the component is completely and free of cracks and channels. Preferably, the filling metal is aluminum and the metal of the ceramic titanium, so that after the preferred exchange reaction the ceramic phase TiB _x and / or TiC _y and / or TiCN and Al ₂ O ₃ has, the intermetallic compound the metallic phase is a high temperature resistant titanium aluminide, in particular TiAl. The material properties of this metal / ceramic composite are good. For example, a metal / ceramic composite material that is produced with aluminum as the filling metal and Ti as the metal of the ceramic sacrificial body has a density of 3.4 g / cm ³ , this density being slightly higher than that of the so-called MMCs However, (metal-matrix- omposits c), is iron only 42% of the density of comparable molding. In the preferred embodiment in particular, in which the high-temperature-resistant connection in the form of the intermetallic compound TiAl, the area of application of the component extends to at least 800 ° C., the values for gray cast iron being clearly exceeded. In particular, friction rings for the friction surfaces of disc brakes are produced from the metal / ceramic composite material produced. These friction rings are then attached to the brake disk cup using mechanical connection techniques such as screw connections, etc.

Before the sacrificial body with the metal or with the Alloy is filled, the raw materials of Op heated body, being between the materials a first exchange reaction takes place, in which the  Exchange materials high-quality and expensive materials bil the. After filling with the metal, it becomes expensive Materials and the metal the ceramic phase and me formed metallic phase, in turn to form a Exchange reaction, this time with the primary material and the filling metal is made.

Infiltration is also carried out in a further process ceramic sacrificial body with aluminum (US-A- 4,988,645). The ceramic body is Reaction established (SHS reaction: Self propagating high tem perature synthesis means the ignition of a reactive gemi where the reaction maintains itself and as Reaction products provides the desired ceramic matrix).

However, a component manufactured in this way sometimes has an unacceptable porosity, so that the rejection rate is high. In particular, the filling of sacrificial bodies with TiO ₂ as the primary material of the sacrificial body is very poor.

WO 84/02927 describes a method for producing fa server-strength die-cast parts with aluminum in the so-called squ eeze casting process known. When proceeding first one u. a. Starting mixture containing fibers a porous Green body pressed, which is then filled with aluminum becomes. To stabilize the porous green body and maintain it orientation of the fibers arranged in the green body, is de, starting mixture a binder added to the Filling the green body is removed thermally. By the The presence of the pores and the strength of the binder cannot be found ne or at most a negligible deformation of the green body instead. A chemical reaction between the filling Aluminum and the raw materials of the green body takes place does not take place here, so that the influence of such a reak tion on the structure and shape of the later die casting partly not known from this.  

Overall, all of the methods mentioned have high energy needs on the u. a. on the different thermal pro processes such as sintering, first exchange reaction, filling and on closing second exchange reaction in the opposite of the filling higher temperature. By the processes are expensive in view of this energy requirement.

The object of the invention is to provide the previously known method to further develop that the manufacture of components made of a metal / ceramic composite, easier, faster and in particular is cheaper and more energy efficient and that the composite body verver in terms of its volume casual and as far as possible provided with titanium aluminide that can.

This object is achieved with the underlying victim body with the characterizing features of claim 1. By using a pressure-stable and preferably reduced titanium oxide TiO _x with x = 1, 1.5, 1.67, or, in particular, carbon-reducible sacrificial body having TiO ₂ , which is preferably shaped and / or processed close to the final shape, the Al melt can even be spontaneously infiltrated and therefore particularly well pressure infiltrated.

The two previously known exchange reactions for converting the aluminum and the materials of the sacrificial body into an Al ₂ O ₃ / titanium aluminide composite material of the starting materials can be carried out in a single heating process.

This reaction temperature is preferably below the Be filling temperature, preferably below the melting temperature of aluminum and particularly preferably below 400 ° C arranges. As a result, the required energy requirement and also the reduced production time.

The sacrificial body is heated to fill the sacrificial body with aluminum or with an aluminum alloy. Therefore, it makes sense to use TiO ₂ and C to manufacture the sacrificial body, since u. U. TiO ₂ and C can then, among other things, form the reduced titanium oxide TiO _x (TiO, Ti ₂ O ₃ and / or Ti ₃ O ₅ ) during heating.

Surprisingly, however, no exchange reaction takes place during the pressure infiltration of the sacrificial body with aluminum, with the formation of Al ₂ O ₃ / titanium aluminide composite material. The formation of the Al ₂ O ₃ / titanium aluminide composite material takes place only through a solid-state reaction, the process temperature of which is below the melting temperature of the aluminum.

Further useful embodiments of the invention are the ent speaking further claims removable. Otherwise the Invention based on some examples listed below explained in more detail.

A powdery ceramic starting mixture with carbon and TiO ₂ and with a binder and with a filler is mixed and then pressed.

By a low-temperature treatment under vacuum or protective gas, in particular nitrogen or CO ₂ , between 350 ° C and 700 ° C, in particular at 400 ° C, the filler and possibly also the binder is burnt out under vacuum or protective gas, a porous and unsintered, pressure-stable and ceramic sacrificial body is created.

A thermogravimetric analysis is expediently carried out here (TG), which serves to demonstrate that the binder and if necessary, the filler is also completely removed.

Through the targeted addition of fillers and binders can have a precisely defined porosity, pore structure and strength speed can be set, whereby pressure infiltration of the Op body with aluminum is possible.  

One of the advantages of the invention is that in the whole Production of a component from such a metal / ceramic Composite material, i.e. starting with the manufacture of the victim body over the filling of the sacrificial body with aluminum up towards the formation of the composite material through the exchange raid tion no temperature steps above 800 ° C, especially above 700 ° C are required. On the other hand, this happens in a short time Time, especially filling by die casting.

Furthermore, the aluminum is converted into a high temperature resistant titanium aluminide. Continue to be very cheap raw materials used; the material price is currently at about 4 DM per kg.

To produce the starting batch, first of all, in particular Titanium dioxide and graphite in a defined stoichiometric Mixed relationship. Then the homogeneous Batch 1-3% by weight of binder, preferably polyvinyl alcohol PVA and / or polyethylene glycol PEG, added in aqueous solution knead and knead. After the binder, the mixture becomes a water-soluble powder and / or fibrous organic filling substance, preferably a celulose derivative, especially Celuloseace added and kneaded too.

The filler, which is preferably added in powder form, has in particular special an average grain size between 10 microns and 100 microns, be prefers 20 µm. The mixture is either dried or moist (residual moisture approx. 10-20% H2O) uniaxially with in particular 300 bar pressed. Optionally, the uniaxial pressing process follows further cold isostatic pressing.

The sacrificial body, which is preferably pressed close to the final shape, becomes mecha machined to final dimensions and for one at the manufacturer development of the component in the subsequent subsequent filling of the op body with liquid aluminum in a die casting mold sets.  

For the filling with aluminum in the die casting process are the Strength, the modulus of elasticity, the porosity and the pore structure of the victim's body.

These properties can be influenced by the choice of the binder, the fillers, the amount of filler and the pressing pressure. The particle sizes of the ceramic powders (TiO ₂ etc.) and the fillers are also included.

The relationships between influencing variables and target variables are in the following table 1 applied qualitatively.

Table 1:

Influence of the process parameters on the properties of the victim's body

Examples

Below are some examples of the initial batch for Op body specified.

Example 1:

3 mol TiO ₂ (average grain diameter d ₅₀ = 0.3 µm) are premixed with a mol C (d50 = 0.05 µm) in the kneader for approx. 10 min. 3% by weight of polyethylene glycol (in 20% aqueous solution) is added to this mixture and kneaded. 10% by weight of cellulose acetate (CA) (d ₅₀ = 20 μm) is again added to the moist mixture and mixed in a kneader. The powder is pressed uniaxially at 30 MPa. This is followed by cold isostatic pressing at a pressure of 200 MPa. The sacrificial body is heated at 700 ° C under nitrogen for 1 hour (holding time at 350 ° C, heating rate 1 K / min), whereby all organic additives burn out without residue. The sacrificial body has a compressive strength of 7 MPa and a porosity of 49%. The pore diameters have a bimodal distribution with a maximum of 0.1 µm and a maximum of 20 µm.

Example 2:

Like example 1, except that the molar ratio between TiO ₂ and C 3/2 is. Isostatic repressing at 300 MPa is required.

Example 3:

As example 1, except that the amount of celulose acetate is 20% by weight is.

Example 4:

As in Example 1, except that 10% by weight of water are added to the mixture of TiO ₂ / C / PEG / CA before uniaxial pressing.

Example 5:

As in Example 1, except that 1% by weight of methyl cellulose is added to the mixture of TiO ₂ / C / PEG / CA before uniaxial pressing.

Example 6:

As in Example 1, except that the mixture of TiO ₂ / C / PEG / CA short fibers made from constanta wire or from C fibers is added. This increases the elongation at break.

Example 7:

As example 1, except that the grain size of the TiO _{2 has} an average diameter of 15 microns. this causes the porosity to drop to 47%. The compressive strength increases to 7.5 MPa.

The sacrificial bodies are intended for subsequent pressure filling with aluminum. After filling, they are subjected to a temperature treatment below the melting point of the aluminum, whereby a component made of composite material is made of, in particular, homogeneously distributed TiC, Al ₂ O ₃ and Al ₃ Ti.

It must be pointed out here in particular that the subsequent heat treatment to produce the Ver solid material reaction takes place. Therefore this reaction below the melting point of the aluminum occur. The preferably homogeneous composite is resistant to high temperatures and wear.

The inventive method and thus also the Invention appropriate starting batch or the victim body according to the invention are especially for the production of friction surfaces, by tribolo systems or engine components and / or driving components and / or brake discs and / or friction surfaces suitable for brake discs. Under tribological systems In addition to brake discs, structural components are preferred in Jet engines and engines, especially plain bearings, Understand cutting materials.

Claims (38)

1. A method for producing a sacrificial body for the later production of an Al ₂ O ₃ / titanium aluminide composite body, the sacrificial body being produced from an initial mixture of titanium, in particular as titanium oxide, carbon and / or its precursors, fillers and binders , a molded body is pressed therefrom and the molded body is subjected to a temperature treatment which is chosen below the subsequent filling temperature with Al, so that the filler and / or the binder is decomposed before or during the subsequent filling with Al. 2. The method according to claim 1, characterized, that for filling with the aluminum the molded and un sintered sacrificial body is provided. 3. The method according to claim 1, characterized, that the sacrificial body is produced close to the final shape. 4. The method according to claim 1, characterized, that the sacrificial body is pressed and then machined end is processed form-fitting. 5. The method according to claim 1, characterized in that TiO and / or Ti ₂ O ₃ and / or Ti ₃ O ₅ and / or preferably TiO _{2 is} used as the oxide of titanium. 6. The method according to claim 1, characterized in that TiO _{2 is} used as the oxide of titanium, that TiO ₂ is reduced by the carbon and that the reducing effective carbon is formed as the end product in the preferably thermal removal of the fillers and / or the binder and remains in the victim's body. 7. The method according to claim 1, characterized, that the fillers evaporate below the filling temperature and / or converted to carbon. 8. The method according to claim 1, characterized, that the binder ver below the filling temperature vapors and / or be converted into carbon. 9. The method according to claim 1, characterized, that as filler organic material is preferably thermoplastic sches or thermosetting material, and particularly preferred Starch and / or flour and / or a cellulose derivative, in particular re cellulose acetate is selected. 10. The method according to claim 1, characterized, that the starting materials of the starting batch homogeneously ver be shared. 11. The method according to claim 1, characterized, that the initial batch 1-3 weight percent (wt .-%) bandage medium can be added. 12. The method according to claim 1,  characterized, that as a binder polyvinyl alcohol (PVA) and / or polyethylene lenglycol (PEG) is preferably chosen in aqueous solution. 13. The method according to claim 1, characterized, that as a filler, a powder with a preferred grain size between 10 µm and 100 µm, particularly preferably about 20 µm is chosen. 14. The method according to claim 1, characterized in that non-volatile additives, in particular TiC and / or SiC and / or BaC and / or TiB _{2, are} added to the starting mixture at the filling temperature. 15. The method according to claim 1, characterized, that the initial batch fibers, in particular from mineral and / or ceramic materials are added. 16. Starting batch for producing a sacrificial body for the later production of an Al ₂ O ₃ / titanium aluminide composite body for a method according to at least one of claims 1 to 15, wherein the starting batch in addition to titanium, in particular titanium oxide, carbon and / or its precursors, fillers and Binding agent has, with the binder Be the individual constituents of the starting batch are at least partially connectable with each other pressure stabilizing, and wherein the decomposition temperature of the filler and preferably also that of the binder is equal to or less than a later filling temperature of the sacrificial body with Al. 17. Starting mixture according to claim 16, characterized in that the oxide of titanium is TiO and / or Ti ₂ O ₃ and / or Ti ₃ O ₅ and / or TiO ₂ with reducing carbon. 18. Starting mixture according to claim 16, characterized in that the oxide of titanium is TiO ₂ , that the carbon has a reducing effect with regard to the TiO ₂ and that the carbon is an end product formed in the removal of the binder and / or the fillers. 19. starting batch according to claim 16, characterized, that the fillers and possibly the binder at or below the filling temperature to evaporate and / or in carbon is changeable. 20. starting batch according to claim 16, characterized, that the filler organically preferred thermoplastic or you plastic, and particularly preferably starch and / or flour and / or a cellulose derivative, in particular a cellulose acetate is. 21. starting batch according to claim 16, characterized, that the starting materials of the starting batch before the Pres sen are homogeneously distributed to the victim's body. 22. starting batch according to claim 16, characterized, that the starting batch 1-3 weight percent (wt .-%) bandage medium. 23. starting batch according to claim 16, characterized by that the binder polyvinyl alcohol (PVA) and / or polyethylene Lenglycol (PEG) is preferred in aqueous solution. 24. starting batch according to claim 16,  characterized, that the filler is a powder with a preferred grain size between 10 µm and 100 µm, particularly preferably about 20 µm. 25. Starting batch according to claim 16, characterized in that the starting batch has non-volatile additives, in particular TiC and / or SiC and / or BaC and / or TiB ₂ , at the filling temperature of the sacrificial body. 26. starting batch according to claim 16, characterized, that the initial batch of fibers, especially mineral and / or ceramic materials. 27. sacrificial body from a pressed starting mixture for the later production of a component from an Al ₂ O ₃ / titanium aluminide composite material, which sacrificial body has titanium in particular as an oxide, for a method according to at least one of claims 1 to 15, the unsintered sacrificial body being opposite Overpressure is pressure-stable, the sacrificial body having carbon and / or its precursors, fillers and binders, and wherein the binder connects the individual constituents of the sacrificial body to one another at least in a pressure-stabilizing manner, the decomposition temperature of the filler and preferably also of the binder being the same or small ner than a later filling temperature of the sacrificial body with Al. 28. sacrificial body according to claim 27, characterized in that the oxide of titanium is TiO and / or Ti ₂ O ₃ and / or Ti ₃ O ₅ and / or TiO ₂ . 29. sacrificial body according to claim 27, characterized in that the oxide of titanium is TiO ₂ , that the carbon with regard to the TiO _{2 is} reducing effective carbon and that the carbon is an end product formed in the removal of the binder and / or the fillers. 30. sacrificial body according to claim 27, characterized, that the filler and possibly the binder at or below the filling temperature to evaporate and / or in is changeable. 31. sacrificial body according to claim 27, characterized, that the filler organically preferred thermoplastic or you plastic, and particularly preferably starch and / or flour and / or a cellulose derivative, in particular a cellulose acetate is. 32. sacrificial body according to claim 27, characterized, that the starting materials are homogeneously distributed in the sacrificial body are. 33. victim body according to claim 27, characterized, that the sacrificial body 1-3% by weight (wt .-%) bindemite tel. 34. sacrificial body according to claim 27, characterized, that the binder polyvinyl alcohol (PVA) and / or polyethylene Lenglycol (PEG) is preferred in aqueous solution. 35. sacrificial body according to claim 27, characterized, that the filler is a powder with a preferred grain size between 10 µm and 100 µm, particularly preferably about 20 µm.   36. Victim body according to claim 27, characterized in that the sacrificial body has non-volatile additives at the filling temperature, in particular TiC and / or SiC and / or BaC and / or TiB ₂ . 37. sacrificial body according to claim 27, characterized, that the sacrificial body fibers, especially from mineral and / or ceramic materials. 38. Use of the sacrificial body according to one of claims 27 to 37 for the subsequent pressure filling with aluminum for forming a component made of an Al ₂ O ₃ / titanium aluminide composite material for friction surfaces of tribological systems or engine components and / or vehicle components and / or of brake discs and / or of friction surfaces for brake discs.