WO1999028276A1

WO1999028276A1 - Method for producing a sacrificial body for producing aluminal titanium aluminide composite bodies

Info

Publication number: WO1999028276A1
Application number: PCT/EP1998/007294
Authority: WO
Inventors: Tilmann Haug; Christoph Hesselmann; Steffen Rauscher; Michael Scheydecker
Original assignee: Daimlerchrysler Ag
Priority date: 1997-11-28
Filing date: 1998-11-14
Publication date: 1999-06-10
Also published as: JP2001524607A; EP1036050A1; CN1279659A; BR9815038A; DE19752775C1; CZ20001961A3; KR20010031873A

Abstract

The invention relates to a method for producing a sacrificial body from an initial mixture which is then used to produce a component consisting of an Al2O3/titanium aluminide composite substance. The invention also relates to an initial mixture and to a sacrificial body. In addition to titanium, preferably in oxide form, carbon and/or its intermediate products, fillers and binders are added to the initial mixture. A shaped body is then pressed from the initial mixture and subjected to heat treatment at a transition temperature in order to obtain a pressure-resistant sacrificial body. The filler and optionally, the binder are thermally removed during this process. The sacrificial body is provided under pressure for subsequent filling with aluminium and/or an aluminium alloy. The filling process takes place at a filling temperature which is higher than the transition temperature. The materials in the filled sacrificial body and the aluminium are reacted in a solids reaction below the filling temperature to form an Al2O3/titanium aluminide composite body.

Description

METHOD FOR THE PRODUCTION OF A SACRED BODY FOR THE PRODUCTION OF ALUMINUM / TITANIUM-ALUMINID COMPOSITE BODIES

The invention relates to a method for producing a sacrificial body from an initial batch for the later production of a component from an Al2θ ₃ / titanium aluminide composite material according to the preamble of claim 1, a starting batch for the sacrificial body according to the preamble of claim 16 and a sacrificial body according to the preamble of Claim 27, as everything emerges from the generic DE 196 05 858 AI as known.

DE 196 05 858 AI discloses a method for producing a component from an Al 2 O ₃ / italuminide composite material. The ceramic / metal composite combines the properties of the ceramic and the metallic phase and has high strength and high fracture toughness. In the process on which this 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 Al2O3. Among other things, Tiθ2 is mentioned as part of the initial batch. A near-net shape sacrificial body is produced from the initial batch, which is then infiltrated with AI. 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 arranged above the melting temperature of the aluminum and / or an aluminum alloy - hereinafter simply called 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. An SHS reaction (self propagating high temperature synthesis) is a reaction that takes place very quickly above its reaction temperature, is highly exothermic and is mostly 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 constituents of the sacrificial body to form an Al ₂ O 3 / titanium aluminide composite material.

However, the sacrificial body is usually only partially converted into the Al2θ ₃ / titanium aluminide composite. As can also be seen from DE 196 05 858 AI, a sacrificial body comprising TiO 2 can only be completely filled with aluminum in some cases. Furthermore, such a sacrificial body can also be completely provided with a continuous titanium aluminide hash only in exceptional cases.

From the unpublished DE-P 19710671.4 a method for producing a component from a metal / ceramic composite material is known, in which a sacrificial body made of ceramic materials is filled with thermally softened metal - in particular aluminum - and / or with a metallic alloy. 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 victim's body has been filled as completely as possible, the filled victim's 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 compound of the metal of the ceramic and the metal of the filling metal. By filling the victim's body with a metal softened by heating below a reaction temperature, during which an exchange reaction takes place between the filling metal and the material of the sacrificial body, the ceramic matrix is obtained during the filling and also during the subsequent exchange reaction between the introduced metal and the material of the sacrificial body. Ideally, the pores of the sacrificial body are filled completely, so that when the substances in question are stoichiometrically dimensioned, the component has reacted completely and without cracks or channels. The filling metal is preferably aluminum and the metal of the ceramic titanium, so that after the preferred exchange reaction the ceramic phase has TiB _x and / or TiC _y and / or TiCN and Al2O3, the intermetallic compound of the metallic phase being a high-temperature resistant titanium aluminide , in particular TiAl. The material properties of this metal / ceramic composite material are good. For example, a metal / ceramic composite 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 (metal matrix composites), but is only 42% of the density of comparable cast iron. Particularly in the preferred embodiment, 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. The metal / ceramic composite material produced is used in particular to produce friction rings for the friction surfaces of disc brakes. These friction rings are then attached to the brake disk cup using mechanical connection techniques such as screw connections, etc.

However, before the sacrificial body is filled with the metal or the alloy, the starting materials of the sacrificial body must be heated, with a first exchange reaction taking place between the primary materials form high-quality and expensive raw materials for the exchange materials. After filling with the metal, the ceramic phase and the metallic phase are formed from these expensive primary materials and the metal, an exchange reaction being carried out again for this purpose, this time with the primary material and the filling metal.

In a further process, the infiltration of a ceramic sacrificial body with aluminum is also described (US Pat. No. 4,988,645). Here, the ceramic body is produced via an SHS reaction (SHS reaction: Seif propagating high temperature synthesis, means the ignition of a reactive mixture, the reaction maintaining itself and providing the desired ceramic matrix as reaction products).

However, a component produced 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 discloses a process for the production of fiber-reinforced die-cast parts with aluminum in the so-called sgueeze-casting process. In the process, a porous green body is first pressed from an initial mixture containing fibers, which is then filled with aluminum. In order to stabilize the porous green body and to maintain the orientation of the fibers arranged in the green body, a starting agent is added to the starting mixture, which is thermally removed when the green body is filled. Due to the presence of the pores and the strength of the binder, there is no or at most a negligible deformation of the green body. A chemical reaction between the filling aluminum and the starting materials of the green body does not take place here, so that the influence of such a reaction on the structure and shape of the later die-cast part is not known. Overall, all of the methods mentioned have a high energy requirement, which can be attributed, among other things, to the different thermal processes, such as sintering, first exchange reaction, filling and subsequent second exchange reaction at temperatures which are higher than the filling temperature. Because of this energy requirement, the processes are expensive.

The object of the invention is to further develop the previously known method in such a way that the production of components from a metal / ceramic composite material is simpler, faster and, in particular, cheaper and more economical in terms of energy technology, and that the volume of the composite body is reliable and as far as possible with titanium aluminum. can not be provided.

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 = l, 1.5, 1.67, or in particular carbon-reducible sacrificial body having iO 2, which is preferably shaped and / or processed close to the final shape, the Al melt can even infiltrate spontaneously and thus particularly well be pressure infiltrated.

The two previously known exchange reactions for converting the aluminum and the materials of the sacrificial body into an Al2θ3 / titanium aluminide composite of the starting materials can be carried out in a single heating process.

This reaction temperature is preferably below the filling temperature, preferably below the melting temperature of the aluminum and particularly preferably below 400 ° C. This reduces the energy requirement and also the production time required. The sacrificial body is heated to fill the sacrificial body with aluminum or with an aluminum alloy. Therefore, it makes sense to use for the production of, among other things Opferkorpers TiO 2 and C, as can be formed, inter alia, the reduced titanium oxide TiO _x (TiO, i2θ ₃ and / or Ti3Ü5) of TiO 2 and possibly C at heating then.

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 / italuminide composite material. The formation of the Al2θ 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 can be found in the corresponding further claims. Otherwise, the invention is explained in more detail with the aid of some examples listed below.

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

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., in particular burns out the filler and possibly also the binder under vacuum or protective gas, with a porous and non-sintered pressure-stable as well as ceramic sacrificial body.

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

Through the targeted addition of the fillers and the binder, a precisely defined porosity, pore structure and Fe- Stability can be set, whereby a pressure infiltration of the sacrificial body with aluminum is possible.

One of the advantages of the invention is that in the entire production of a component from such a metal / ceramic composite material, that is to say starting from the production of the sacrificial body through the filling of the sacrificial body with aluminum up to the formation of the composite material by the exchange reaction, no temperature steps over 800 ° C, especially above 700 ° C are required. On the other hand, this happens in a short time, especially the filling by die casting.

In addition, the aluminum is converted to a high-temperature-resistant titanium aluminide. Very cheap raw materials are also used; the material price is currently around 4 DM per kg.

To produce the starting batch, titanium dioxide and graphite in particular are first mixed with one another in a defined stoichiometric ratio. Subsequently, 1-3% by weight of binder, preferably polyvinyl alcohol PVA and / or polyethylene glycol PEG, is added to the homogeneous mixture in aqueous solution and kneaded. After the binder, a water-soluble powder and / or fibrous organic filler, preferably a celulose derivative, in particular celulose acetate, is added to the mixture and likewise kneaded.

The filler, which is preferably added in powder form, has in particular an average grain size between 10 μm and 100 μm, preferably 20 μm. The mixture is either dried or moist (residual moisture approx. 10-20% H20) uniaxially pressed at in particular 300 bar. The uniaxial pressing process is optionally followed by a further cold isostatic pressing process.

The sacrificial body, which is preferably pressed close to the final shape, is mechanically machined to the final dimension and is used for a Position of the component in the subsequent filling of the sacrificial body with liquid aluminum placed in a die-casting mold.

The strength, the modulus of elasticity, the porosity and the pore structure of the sacrificial body are important for filling with aluminum using the die casting process.

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

The relationships between influencing variables and target variables are plotted qualitatively in Table 1 below.

Table 1: Influence of the process parameters on the properties of the sacrificial body

Influencing variables- »

Target type of filler FS- -Quantity PressParticle sizes -i print size

GK strength + + +++ +

E-module + + +++ +

Porosity + ++ ++ ++

Pore structure ++ ++ + +++

+ = little influence; ++ = medium influence; +++ = great influence

Examples

Below are some examples of starting batches for sacrificial bodies.

Bf.1 πpi ei 1 • 3 mol TiO ₂ (average grain diameter d ₅₀ = 0.3 μm) are premixed with a mol C (d50 = 0.05 μm) in a kneader (eg from Eirich) for approx. 10 min. 3% by weight of polyethylene glycol (in 20% aqueous solution) is added to this mixture and kneaded. The damp mixture is again 10 wt .-% cellulose acetate (CA) (d _so = 20 microns) was added 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 in which a maximum is 0.1 μm and a maximum is 20 μm.

Example 7. ^■

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

Example ^ -

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

Rice ipl 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.

At spi P! •

As in Example 1, except that 1% by weight of methyl cellulose is added to the mixture of Ti0 ₂ / C / PEG / CA before uniaxial pressing. BeiπpieJ & _--

Like example 1, except that short fibers of constantan wire or of C fibers are added to the mixture of TiO 2 / C / PEG / CA. This increases the elongation at break.

Rei πpi ei 7 _--

As example 1, except that the grain size of TiO 2 has an average diameter of 15 μm. 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, as a result of which a component is made of composite material, which has, in particular, homogeneously distributed TiC, Al2O3 and _G A ^ Ti.

It must be pointed out here in particular that a solid-state reaction takes place during the subsequent temperature treatment to produce the composite material. Therefore, this reaction can take place below the melting point of the aluminum. The preferably homogeneous composite material is resistant to high temperatures and wear.

The method according to the invention and thus also the starting mixture according to the invention or the sacrificial body according to the invention are particularly suitable for producing friction surfaces, tribological systems or engine components and / or vehicle components and / or brake discs and / or friction surfaces for brake discs. In addition to brake disks, tribological systems are preferably to be understood as meaning structural components in jet engines and engines, in particular plain bearings, cutting materials.

Claims

Pa entanπpr-nehe

1. A process for producing a sacrificial body from a starting batch for the later production of an Al 2 O ₃ / titanium aluminide composite body, in which process the titanium, in particular as an oxide, is added to the starting batch and a molded body is pressed from the starting batch, the molded body at a transfer temperature of a temperature treatment for formation is subjected to the sacrificial body, the sacrificial body for filling with aluminum and / or an aluminum alloy - hereinafter referred to simply as aluminum - is provided under pressure, and the materials of the sacrificial body and the aluminum are reacted to form an Al 2 O ₃ / titanium aluminide composite body, characterized that carbon and / or its precursors, fillers and binders are added to the starting mixture, that the molded body is pressed from this starting mixture, that the individual constituents of the starting mixture are mixed with the binder at least in regions It is pressure-stabilized that the decomposition temperature of the filler and preferably also of the binder is selected to be equal to or less than the filling temperature, so that the filler or the binder is removed during or before the subsequent filling of the molded body from the starting materials with the aluminum , and that the transfer temperature is arranged below the filling temperature, so that the molded body is converted into the sacrificial body during the heating to the filling temperature for later pressure filling.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the molded and unsintered sacrificial body is provided for filling with the aluminum.

3. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the sacrificial body is produced close to the final shape.

4. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the sacrificial body is pressed and then machined close to the final shape.

5. The method according to claim 1, characterized in that TiO and / or Ti ₂ θ3 and / or Ti ₃ 0 ₅ and / or preferably Tiθ2 is used as the oxide of titanium.

6. The method according to claim 1, characterized in that the oxide of titanium TiÜ _{2 is} used, that TiÜ2 is reduced by the carbon and that the preferably effective thermal removal of the fillers and / or the binder, the reducing carbon is formed as the end product and in The victim's body remains.

7. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the fillers are evaporated below the filling temperature and / or converted into carbon.

8. The method according to claim 1, characterized in that the binder evaporates below the filling temperature and / or are converted into carbon.

9. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that as the filler organic material preferably thermoplastic or thermosetting material, and particularly preferably starch and / or flour and / or a cellulose derivative, in particular cellulose acetate and / or is selected.

10. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the starting materials of the starting batch are distributed homogeneously.

11. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that 1 - 3 wt .-% (wt .-%) binder are added to the starting batch.

12. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that polyvenyl alcohol (PVA) and / or polyethylene glycol (PEG) is preferably chosen as a binder in aqueous solution.

13. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that a powder with a preferred grain size between 10 microns and 100 microns, particularly preferably about 20 microns is selected as the filler.

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, d a d u r c h g e k e n n z e i c h n e t that fibers, in particular from mineral and / or ceramic materials, are added to the starting mixture.

16. Starting batch for producing a sacrificial body, the sacrificial body being produced by a temperature treatment at a transfer temperature from a shaped body, which shaped body itself is molded from titanium, preferably as an starting batch comprising oxide, the sacrificial body being filled at a filling temperature with aluminum and / or an aluminum alloy - hereinafter referred to simply as aluminum - and is provided for a reaction with the materials of the sacrificial body with aluminum, and wherein in the reaction a component is formed from an Al2θ3 / titanium aluminide composite material, characterized in that the starting mixture of carbon and / or its Intermediate products, fillers and binders have that the individual constituents of the starting batch are at least partially connected to one another in a pressure-stabilizing manner with the binder, that the decomposition temperature of the filler and especially The binder may also be equal to or less than the filling temperature, so that they can be removed with or before the filling of the molded and unsintered sacrificial body with the aluminum from the starting materials, and that the transfer temperature is below or equal to the filling temperature, so that the Conversion of the molded body into the sacrificial body takes place during the heating to the filling temperature.

17. Starting mixture according to claim 16, characterized in that the oxide of titanium is TiO and / or Ti ₂ 0 ₃ and / or Ti ₃ 0 ₅ and / or TiO 2 with reducing carbon.

18. Starting mixture according to claim 16, characterized in that the oxide of titanium is iO ₂ , that the carbon has a reducing action with respect to iO ₂ and that the carbon is an end product formed in the removal of the binder and / or the fillers.

19. Starting mixture according to claim 16, d a d u r c h g e k e n n z e i c h n e t that the fillers and possibly the binder at or below the filling temperature is evaporable and / or convertible into carbon.

20. Starting mixture according to claim 16, so that the filler is organically preferably thermoplastic or thermoset, and particularly preferably starch and / or flour and / or a cellulose derivative, in particular a cellulose derivative.

21. Starting batch according to claim 16, so that the starting materials of the starting batch are homogeneously distributed before being pressed into the sacrificial body.

22. Starting batch according to claim 16, so that the starting batch has 1 - 3 percent by weight (% by weight) of binder.

23. Starting batch according to claim 16, characterized in that the binder polyvinyl alcohol (PVA) and / or polyethylene glycol (PEG) is preferably in aqueous solution.

24. Starting mixture according to claim 16, so that the filler is a powder with a preferred particle 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 at the filling temperature of the sacrificial body has non-volatile additives, in particular TiC and / or SiC and / or BaC and / or TiB ₂ .

26. Starting batch according to claim 16, d a d u r c h g e k e n n z e i c h n e t that the starting batch has fibers, in particular from mineral and / or ceramic materials.

27. sacrificial body for producing a component from an Al2θ ₃ / titanium aluminide composite material, which sacrificial body has titanium in particular as an oxide and which sacrificial body for filling with aluminum and / or an aluminum alloy - hereinafter simply called aluminum - and for reacting with the materials of the sacrificial body the aluminum is provided, the component being formed from the Al2θ ₃ / titanium aluminide composite material during the reaction, the sacrificial body itself being produced by heat treatment at a transfer temperature from a molded body which is pressed from an initial batch, characterized in that the unsintered one Victim body is pressure stable against overpressure, that the sacrificial body has carbon and / or its precursors, fillers and binders, that the binder connects the individual components of the sacrificial body to one another at least in areas to stabilize the pressure, that the decay Resetting temperature of the filler and preferably also of the binder is equal to or less than the filling temperature, so that it during or before filling of the molded and unsintered sacrificial body with the aluminum are removable and that the transfer temperature is less than or equal to the filling temperature.

28. sacrificial body according to claim 27, characterized in that the oxide of titanium is TiO and / or Ti ₂ θ3 and / or Ti ₃ 0 ₅ and / or Tiθ2.

29. sacrificial body according to claim 27, characterized in that the oxide of titanium is Ti0 ₂ , that the carbon with respect to the Tiθ2 has a reducing effect carbon and that the carbon is an end product formed in the removal of the binder and / or the fillers.

30. Victim body according to claim 27, that the filler and optionally the binder can be vaporized and / or converted to carbon at or below the filling temperature.

31. Victim body according to claim 27, that the filler is organically preferably thermoplastic or thermosetting, and particularly preferably starch and / or flour and / or a cellulose derivative, in particular a cellulose derivative.

32. sacrificial body according to claim 27, characterized in that the starting materials are homogeneously distributed in the sacrificial body.

33. Victim body according to claim 27, so that the sacrificial body has 1-3% by weight (wt.%) Binder.

34. Victim body according to claim 27, that the binder polyvenyl alcohol (PVA) and / or polyethylene glycol (PEG) is preferably in aqueous solution.

35. Victim body according to claim 27, so that the filler is a powder with a preferred grain size between 10 μm and 100 μm, particularly preferably about 20 μm.

36. sacrificial 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. Victim body according to claim 27, so that the sacrificial body has fibers, in particular from mineral and / or ceramic materials.

38. Use of a method according to claim 1 for the production of friction surfaces of tribological systems or of engine components and / or of vehicle components and / or of brake discs and / or of friction surfaces for brake discs.

39. Use of an initial batch 16 for the production of friction surfaces of tribological systems or of engine components and / or of vehicle components and / or of brake discs and / or of friction surfaces for brake discs.

40. Use of a sacrificial body 27 for the production of friction surfaces of tribological systems or of engine components and / or of vehicle components and / or of brake discs and / or of friction surfaces for brake discs.