DE10117394A1 - Metal-ceramic brake disk used for brakes comprises a matrix made from column and/or crystal-like silicon nitride infiltrated with an aluminum alloy in a squeeze-casting method - Google Patents

Abstract

Metal-ceramic brake disk comprises a matrix made from column and/or crystal-like silicon nitride having an open porosity of 35-65% and an average pore size of 0.5-10 mu m infiltrated with an aluminum alloy in a squeeze-casting method. The matrix has a 4 point bending strength of more than 150 MPa. An Independent claim is also included for a process for the production of a metal-ceramic brake disk. Preferred Features: The matrix is made from silicon aluminum oxynitride (SiAlON) or RBSN. The matrix is contained in the whole brake disk or only in the brake region.

Description

The invention relates to a method for producing metal-ceramic brake discs, in particular for axle or shaft disc brakes, a porous Si ₃ N ₄ pre-body being pressure-infiltrated with an Al alloy using the pressure or die-casting method.

Brake discs, e.g. B. for axle or shaft disc brakes are usually made of cast iron. However, the high weight of the moving masses has led to a number of new developments in the past few years, the main aim of which was to reduce the weight but also to achieve better high-temperature strength. CFC or other ceramic fiber-reinforced ceramic matrix brake discs are already used for unusual high-tech applications (e.g. Formula I), but these are unsuitable for mass use, including high-speed trains, for cost reasons. Aluminum-based composite materials with 20 ceramic additives (e.g. SiC, Al ₂ O ₃ , etc.), which are manufactured using very different processes, are currently being tested. Examples of this are the pressure-free infiltration of aluminum alloys into ceramic preforms (Primex, Primex-Cast, e.g. US Pat. No. 5,535,857), directed melt oxidation (DIMOX, e.g. US Pat. No. 5,268,339 and US Pat. No. 5,633,213), conventional Al Casting processes in which the melt contains ceramic particles (DurAlcan) or the infiltration of fiber preforms (on DE 41 12 693 A1; EP 0 496 935 A1, EP 0 335 692 or US Pat. No. 4,842,044). Wear-resistant, often hardened or ceramic-containing layers which are applied to brake disks are also examined (for example US Pat. No. 5,503,874 or WO 91/10840), but no weight saving is achieved.

The decisive disadvantages of these developments lie in the fact that in all cases in which a weight is saved compared to gray cast iron disks, low-melting aluminum alloys form the matrix without the ceramic phase having sufficient inherent strength. For this reason, the latest developments in brake discs aim to replace aluminum with similarly light aluminum-containing intermetallic phases. This is described, for example, in EP 0 800 495, in which reactive oxides, such as TiO ₂ , are mechanically alloyed with Al powder in such a way that reactions which lead to Al ₂ occur in the corresponding powder compacts even at temperatures around 450 ° C. Lead O ₃ aluminide composition. However, due to the very fine-particle Al powder (particle size usually <1 µm) required, these powder mixtures are so reactive that they are hardly manageable due to their very easy self-ignition. The same applies to developments in which reactive powder mixtures are infiltrated with liquid aluminum, so that an SHS reaction (SHS - Self-Propagating High Temperature Synthesis) is triggered, in which, however, neither the temperature control nor the microstructure can be precisely controlled, so that such bodies have high porosity and microcracks (e.g. U.S. Patent 4,033,400; U.S. Patent 4,585,618 or U.S. Patent 4,988,645). The latest developments are aimed at pressure infiltration, for example by die casting or die casting, of aluminum alloys in reactive preform in Al ₂ O ₃ and aluminides (e.g. JP 06192767, JP 08143990, EP 0 951 574, DE 197 06 925 A1 , DE 197 10 671 A1, DE 197 52 776 C1). In all of these cases, however, the desired goal, namely to achieve the complete or even partial reaction in one pressing operation, was not achieved. This makes a second heat treatment step necessary, in which the subsequent reaction of the only infiltrated brake disc takes place, but this leads to pore formation and thus to a decisive weakening of the structural part. All aluminothermic reactions in which no additional aluminum is added during the reaction are associated with a negative volume balance, ie the volume shrinks and the pore formation is often of the order of magnitude of more than 20%. Only gas pressure infiltration of aluminum into such pre-bodies enables a reaction during the infiltration, so that the wound does not appear in the human body (e.g. DE 196 05 858). However, gas pressure infiltration has the major disadvantage that it is not suitable for the production of brake discs, since the infiltration process takes too long and the technical requirements for mass production are not met. Another decisive disadvantage of the manufacture of brake discs by pressure infiltration into reactive preforms is that the overall strength of the brake discs is too low for critical use even in the case of a partial reaction.

Approaches to this problem are described in DE 43 22 113 A1 ben, on a cast iron support body a metal ceramic body either by sintering or by pressure-free pouring in a casting tool is applied. But here again the weight is problem not solved. If you make the support body from aluminum would, in turn, be the upper one for high-performance disc brakes Operating temperature is too low.

Another approach to solving the problem is in the German Applications DE 199 57 786 and DE 100 54 049 (or PCT / EP 00/11965) shown. Here is a ceramic aluminide body by reactive Hot pressing an Al powder-containing metal oxide mixture onto one Support body made of steel or titanium alloy applied. This process is however, time and cost intensive.  

The invention is therefore based on the object of a method for To provide manufacture, especially an uncooled brake disc, which has the disadvantages of being known to be particularly tribological did not claim previous metal-ceramic disc elements or only has to a significantly reduced extent. In particular, a Methods for producing such a brake disc are created which is much lighter than cast iron brake discs, which at the same time required strength with very good thermal conductivity, the can withstand higher temperatures than conventional ceramic particles containing aluminum alloys, and by a to Mass production process is available.

This object is achieved according to the invention by a method for producing a metal-ceramic brake disc, which is characterized in that an aluminum alloy is pressure or press infiltrated into a porous, stalk-shaped preform made of Si ₃ N ₄ ceramic or SiAlON.

The ceramic porous preform can be produced by methods known per se. An Si ₃ N ₄ ceramic preform is preferably used, which is obtained by adding a small amount of rare earth oxides and carbon to an α-Si ₃ N ₄ powder. After pressing and sintering such a powder mixture, β-Si ₃ N ₄ needles preferably grow without substantially reducing the porosity specified in the original pressing. Such porous Si ₃ N ₄ bodies have hitherto been used for filtering molten metals and also dirty water [see, for example, B. SEI Technical Review 49 (2000) 172; J. Mat. Sci. 34 (1999) 893; J. Ceram. Soc. Japan 106 (1998) 1135; Brochure Sumitomo Electric "Porous Silicon Nitride Filter PORECERAM ™ Module" (1999)].

Methods for producing such porous preforms have been documented in numerous publications [e.g. B. Ceramic Transactions 115 (2000) 481; J. Am. Ceram. Soc. 80 (1997) 2705; Ceramic Transactions (2001)]. Similarly, a highly porous RBSN material (Reaction Bonded Si ₃ N ₄ ) can be used, in the production of which also rare earth oxides (e.g. Y ₂ O ₃ , Yb ₂ O ₃ etc.) and possibly carbon in fine powder Form to be added to the Si powder before pressing and nitriding. It has already been shown that RBSN with an open porosity of 15 has more than 50% better strength and fracture toughness when it has been completely infiltrated with Al (J. Eur. Ceram. Soc. 9 (1992) 61). Sialones [(Si, Al) ₃ (O, N) ₄ ] with porosities <35% could also be used.

In order for the ceramic preform used according to the invention to withstand a large part of the load that is applied to an Al / Si ₃ N ₄ brake disc according to the invention, even at elevated temperature, such a preform itself must have a compressive and 4-point bending strength of <150 MPa. Such strengths are not achieved by Al ₂ O ₃ fiber scrims previously used with porosities of <25%.

The network-like preform is then placed in a brake disc die-casting mold and infiltrated with the Al alloy. The aluminum alloy should preferably contain Si, whereby a possible reaction of the Al with Si ₃ N _{4 is} suppressed. But in the commercial squeeze casting process, the duration of the hot Al alloy melts is so short (<1 s) that no AlN reactions can be expected even with Si-free alloys.

The die-cast metal-ceramic brake disk can either contain the porous Si ₃ N ₄ network in the entire disk area or the network can also only be present in the brake area. It is also possible to insert the Si ₃ N ₄ network body into the die casting mold in segments. This is advantageous when it comes to disks with diameters over 300 mm. In a preferred embodiment, the Al / Si ₃ N ₄ composite brake disc can also contain a support body made of a temperature-resistant metal alloy, for example made of steel, cast iron or titanium alloy, which is as perforated as possible. However, this support body should not make up more than 40% of the total weight of the brake disc. To produce this embodiment, one half of the ceramic network is expediently first placed in the die-casting mold. The support body is then placed on top of which the second half is finally placed. During the pressure infiltration, everything is then connected to one another with the aluminum alloy. Such a support body is described in PCT / EP 00/11965.

In order to generate dust when handling the porous preforms can prevent the disc-shaped network value before insertion into the Die casting mold with a die that is easy to break and close in die casting volatilizing film are wrapped. This film can for example consist of gelatin or a similar substance.

The advantage of the metal-ceramic brake disc according to the invention lies in the fact that it can be produced in one process, usually in less than 1 minute, by die casting or die casting. On the other hand, this aluminum matrix composite brake disc has a better temperature resistance than other aluminum-based brake discs (such as those made of PRIMEX or Duralcan) because the Si ₃ N ₄ ceramic network is coherent and despite the high Porosity is very firm. This improves both the rigidity and the bending and compressive strength at elevated temperatures compared to the previous aluminum-ceramic composite brake discs. Compared to composite brake discs of this type which contain aluminides, the composite brake discs according to the invention have a higher thermal conductivity, so that a lower temperature overall occurs with the same energy dissipation during the braking process. Another advantage over the Al ₂ O ₃ / aluminide brake discs is that the corresponding brake pads for aluminum-ceramic composite brake discs have been developed and tested positively. The stem-shaped or crystalline Si ₃ N ₄ network can also be replaced by corresponding SiC or Al ₂ O ₃ networks, the simple production method and the high strength, which is also present with large porosities, preferably Si ₃ N ₄ ceramic network. As an alternative to an Si ₃ N ₄ ceramic network, one made of SiAlON or RBSN can also be used.

Embodiments of the brake disc according to the invention are shown in Figure 1. The areas hatched to the top right contain the cast-in Si ₃ N ₄ ceramic network and are marked with A, the areas hatched to the top left consist of the Al alloy without ceramic insert (B). 1 is an example of a brake disk with brake pot made of Al alloy, ie only the braking area contains the ceramic network; 2 represents a simple disc, which also contains the ceramic network only in the braking area, and 3 a simple disc, which consists entirely of the network filled with Al alloy.

The method according to the invention is illustrated by the following example in Connection explained with the drawing:

example

Porous Si ₃ N ₄ preforms with porosities between 43 and 62% and approximate dimensions 40 × 40 × 10 mm, by Sumitomo Electric, Itami (Poreceram) and the NIRIN research institute in Nagoya (Dr. Yang) according to the previously cited Sintering processes were produced and all had a 4-point bending strength of <150 Mpa, were with a Si-containing Al alloy [German Standard No. 231, Al Sil2 (Cu)] at a melting temperature of 750 ° C and a pressure of 39 MPa within about 1 s in the squeeze casting process. All samples made therefrom were completely infiltrated with aluminum and no AlN formation was found. Samples made from such plates had 4-point bending strengths of over 600 MPa and fracture toughness of over 10 MPa √m (measured in the ICL method). Maximum bending strengths of <800 MPa were measured.

Claims (7)

1. Metal-ceramic brake disc with a 4-point bending strength of at least 600 MPa and a fracture toughness of <8 MPa m, characterized in that it has a matrix of stem and / or crystallite Si ₃ N ₄ with an open porosity between 35 and 65% and has an average pore size of 0.5 to 10 µm, which is pressure infiltrated with an aluminum alloy in the squeeze casting process, the matrix alone having a 4-point bending strength of <150 MPa. 2. Brake disc according to claim 1, characterized, that the matrix is made of SiAlON. 3. Brake disc according to claim 1, characterized, that the matrix consists of RBSN. 4. Brake disc according to claim 1, characterized, that the ceramic matrix is contained in the entire brake disc. 5. Brake disc according to claim 1, characterized, that the ceramic matrix is only contained in the braking area. 6. Brake disc according to one of claims 1 to 5, characterized,  that they are a ring-shaped corset made of an Fe or Ti alloy contains less than 40% of the total weight of the brake disc accounts. 7. A process for producing a metal-ceramic brake disc by pressure infiltration of a porous, matrix-forming ceramic preform, characterized in that a stem and / or krisatllite-shaped network made of Si ₃ N ₄ , SiAlON or RBSN with a 4-point bending strength of <150 MPa and one open porosity between 35 and 65% and an average pore size of 0.5 to 10 µm with an aluminum alloy in a brake disc die casting mold in the squeeze casting process.