WO1993022258A1

WO1993022258A1 - A ceramic composite, particularly for use at temperatures above 1400 °c

Info

Publication number: WO1993022258A1
Application number: PCT/SE1992/000297
Authority: WO
Inventors: Lars Pejryd; Robert Lundberg; Edwin Butler
Original assignee: Volvo Flygmotor Ab; Rolls Royce Plc
Priority date: 1992-05-07
Filing date: 1992-05-07
Publication date: 1993-11-11
Also published as: CA2135061C; CA2135061A1; ES2098522T3

Abstract

A ceramic composite material comprises matrix and possibly reinforcing materials and intermediate weak interface material and is particularly intended for being used at temperatures above 1400 °C and in an oxidizing environment, the matrix and possibly reinforcing materials consisting of the same or different ceramic oxides having a melting point above 1600 °C. In order to obtain said ceramic composite material the invention suggests that the interface material consists of one or more ceramic oxides not exhibiting solid solubility, eutecticum below the temperature of manufacture or use or reactivity with any of the matrix or possibly reinforcing materials and in combination with said materials providing a stress field liable to micro-cracking, said matrix and possibly reinforcing materials essentially being substantially pure.

Description

A ceramic composite, particularly for use at temperatures above 1400°C

The present invention refers to a ceramic composite material comprising matrix and possibly reinforcing mate¬ rials and an intermediate weak interface material and parti¬ cularly adapted for use at temperatures above 1400°C and in oxidizing environment, said matrix and possibly reinforcing materials consisting of the same or different ceramic oxides having a melting point above 1600°c.

Ceramic composite materials might be divided into materials reinforced by particles, whiskers or elongated fibres. Said materials are prepared by powder processes and sintering or by gas-phase infiltration. The materials hitherto mentioned in the literature often are based on the provision of desired composite characteristics by means of a weak interface material between the matrix and the reinfor¬ cing material, preferably fibres, said interface material consisting of carbon or boron nitride, see e.g. Frety, N. , Boussuge, M. , "Relationship between high-temperature development of fibre-matrix interfaces and the mechanical behaviour of SiC-SiC composites", Composites Sci. Techn. 37 177-189 (1990) and Singh, R.N. , "Influence of high tempera- ture exposure on mechanical properties of zircon-silicon carbide composites", J. Mater. Sci. 26 117-126 (1991), respectively. Both carbon and boron nitride have a layered structure which makes them weak in one direction and this can be utilized for deflecting cracks along the interface between fibre and matrix. Both carbon and boron nitride, however, are very sensitive to oxidation which starts al¬ ready at relatively low temperatures of about 500-800°C. In order to enable the use of ceramic composites at high tempe¬ ratures in oxidizing atmosphere, such as in combustion chambers of gas turbines, rocket nozzles etc. other oxida- tion-resistent weak interface materials are required. An attempt to provide such materials has been mentioned in Carpenter, H.W. , Bohlen, J. . , "Fiber coatings for ceramic matrix composites", Ceram. Eng. Sci. Proc. vol 13 9-10 (1992) . In said attempt composites have been manufactured with SiC fibres and a layered Sic interface in an Sic mat¬ rix. Experiments also have been made with interfaces of a porous oxide in a SiC/SiC composite. However, SiC is stable in an oxidizing environment only up to 1000°C, at higher temperatures a SiO- layer always is formed on the surface in oxidizing atmosphere. Often Si0₂ is not stable-together with other oxides but reacts therewith and forms strong bonds to adjacent materials. Therefore, Si0₂ does not constitute a useful interface material in the present connection. Thus there is still a need for improved composite materials which might be used in oxidizing environments at temperatures above 1400°C.

The object of the present invention now is to suggest such a ceramic composite material and the feature essen¬ tially distinguishing the invention is that the interface material consists of one or more ceramic oxides not exhi¬ biting solid solubility, eutecticum below the temperature of manufacture or use or reaction with any of the matrix or pøssibly reinforcing materials and in combination with said materials providing a stress field liable to micro- cracking, said matrix and reinforcing materials being sub¬ stantially pure.

One of the most obvious interface materials is ZrO- which fills the requirements as to oxidation resistance and good high temperature characteristics. In US A 4 732 877 recently has been suggested an interface of Zr0₂ in a compo¬ site of 1₂0₃/A1₂0₃. According to said patent, however, the only object of Zr0₂ is to act as a diffusion barrier and prevent a reaction between reinforcing fibres and matrix. The interface obtained is strong by its binding to said materials and not weak as is necessary in ceramic composi¬ tes for the present use. Thus the present invention refers to an interface material for a ceramic composite material in which the matrix and/or the reinforcing material consist of a ceramic oxide comprising one or more metals and having a melting point above 1600°C, said oxide not exhibiting solid solubi¬ lity, eutecticum below the temperature of manufacture or use or reactivity with any of the other oxides in the interface or the matrix or reinforcing materials. As examples of such oxides there can be mentioned A1₂0₃, Zr0₂, Hf0₂, Al₂Ti0₅, Sn0₂, Y₂°₃' ^BeA-'-2⁰4' y^ttri^u:ra aluminium garnet (YAG) , LaCrO.-, mullite, BeO and Cr₂0₃. Preferably the reinforcing material is present as fibres but also particulate and layer form are possible.

In combination with the matrix and possibly reinfor- cing materials the interface material has to form a stress field which either results into micro cracks in the inter¬ face material or into cracks between the latter and the matrix/reinforcing material. Alternatively, the stress field might cause crack deflection as such also without micro cracks occuring. The desired stress field occurs either by the difference in thermal expansion coefficient between the interface material and the matrix/reinforcing materials or by differences in thermal expansion coefficient between various inherent phases of the interface material. Stresses also might be generated by the fact that the interface material as such has an anisotropic structure with diffe¬ rent thermal expansion coefficients in various crystal directions. A further possibility to form stresses is that phases of the interface material undergo a phase conversion which results in a change of volume. The interface material also might be a composite in which the two inherent phases have different elastic characteristics or different thermal expansion coefficients which creates the desired stress situation. As examples of some well-serving interface mate- rials it might be mentioned Al₂Ti0₅, cordierite, unstabili- zed Zr0₂, Sn0₂, Bf0₂, mullite, YAG, YAG+Zr0₂, Al₂0₃+Zr0₂ and l₂ i0₅+ l₂0₃. Of said substances, l₂ iO_s and cordierite act as interface materials due to their anisotropy, while Zr0₂ and Sn0₂ act by micro-cracks. YAG, Hfθ₂, Zr0₂, Al₂Tiθ₅, cordierite, mullite and Sn0₂ act as interface materials due to differences in thermal expansion while Zr0₂ and possibly Hf0₂ might be subjected to phase conversion. Preferably, the interface material has a thickness of at least 2 μm. When the interface material is r0₂ it is used in the form of powder or sol during coating of a fibre reinforcing material in order to avoid chemical binding of Zr0₂ to the fibres.

Based on the above mentioned the following examples of well-serving composite, systems of reinforcing material/in¬ terface/matrix might be mentioned.

Al₂0₃/Al₂Ti0₅/Al₂0₃ YAG/Al₂Ti0₅/YAG 1₂0₃/Al₂Ti0₅/ AG YAG/Al₂Ti0₅/Al₂0₃ Al₂0₃/Zr0₂/Al₂0₃ YAG/Zr0₂/YAG YAG/Zr0₂/Al₂0₃ Al₂0₃/Zrθ₂/YAG Al₂0₃/Hf0₂/Al₂0₃ YAG/Hf0₂/YAG Al₂0₃/Hf0₂/YAG YAG/Hf0₂/Al₂0₃ Hf0₂/Al₂Ti0₅/Hf0₂ A1₂0₃/YAG/A1₂0₃ Al₂0₃/Sn0₂/Al₂0₃ YAG/Sn0₂/YAG .YAG/Sn0₂/Al₂0₃ Al₂0₃/Sn0₂/YAG Al₂0₃/mullite/Al₂0₃ mullite/Zr0₂/mullite YAG/Al₂0₃+Zr0₂/YAG Al₂0₃/YAG+Zr0₂/Al₂0₃ YAG/Al₂0₃+Al₂Ti0₅/YAG Hf0₂/Al₂0₃+Al₂Ti0₅/Hf0₂

Example 1

Plates of A1₂0₃ of 0,25 mm thickness were coated with a thin layer of Al₂Ti0₅. This was made by submerging the plates in a slurry of Al₂Ti0₅ powder in water. After drying the covered plates were stacked and sintered by hot-pressing at 1700°C for 4 hours. After sintering the Al₂Ti0₅ layer was about 5 μm. thick. The Al₂Ti0₅ layer comprised micro cracks deflecting cracks, which was proved by diamond indentation or bending tests. Example 2

Fibres of 1₂0₃ (ALMAX, Mitsui, Japan) were covered with a thin layer of Al₂Ti0₅. This was made by immersing the fibres into a Al-Ti-alkoxide. After gelling and drying the coated fibres were stacked in a plaster mould and a Al₂0₃ powder slurry was poured thereon.

After drying the slip-cast bodies were sintered by hot-pressing at 1500°C for 4 hours. After sintering the Al₂Ti0₅ layer was about 3 μm thick. The Al₂Ti0₅ layer com- prised micro-cracks deflecting cracks which was proved by diamond indentation or bending tests. Example 3

Plates of A1₂0₃ of 0,25 mm thickness were coated with a thin layer of Zr0₂. This was made by immersing the plates in a slurry of Zrθ₂-powder in water. After drying the coated plates were stacked and sintered by hot-pressing at 1700°C or 4 hours. The Zr0₂ layer had a thickness of about 5 μm after sintering. Stress-induced micro cracks occurred bet¬ ween the layer and the A1₂0₃-material. These deflected cracks which was proved by diamond indentation or bending tests. Example 4

.Plates of 1₂0₃ of 0,25 mm thickness were coated with a thin layer of Hf0₂. This was made by immersing the plates in a slurry of Hf0₂-powder in water. After drying the coated plates were stacked and sintered by hot-pressing at 1700°C for 4 hours. The layer of Hf0₂ was about 5 μm thick after sintering. Stress-induced micro-cracks occurred between the layer and the A1₂0₃-material. These deflected cracks, which was proved by diamond indentation or bending tests. Example 5

Single-crystal-fibres of A1₂0₃ (from Saphicon, USA) were coated with a thin layer of Zr0₂. This was made by immersing the fibres in an aqueous Zr0₂~sol. After gelling and drying the coated fibres were stacked in a plaster mould and an Al₂0₃-powder slurry was poured thereon. After drying the slip-cast bodies were sintered by hot-pressing at 1500°C for 4 hours. After sintering the Zr0₂ layer was about 3 μm thick . Stress-induced micro-cracks occurred between the layer and the 1₂0₃-material. These deflected cracks which was proved by diamond indentation or bending tests. Example 6

Plates of A1₂0₃ of 0,25 mm thickness were coated with a thin layer of Sn0₂. The plates were immersed in Sn0₂-sol and stacked on each other and then dried after which they were sintered in air at 1450°C under a certain uniaxial pressure for 4 hours. After sintering the Sn0₂-layer was about 2,5 μm thick. The Sn0₂~layer formed micro-cracks deflecting cracks which was proved by diamond indentation or bending tests.

Claims

C l a i m s

1. A ceramic composite material comprising matrix and possibly reinforcing materials and an intermediate weak interface material and particularly intended for use at temperatures above 1400°C and in oxidizing environment, the matrix and reinforcing materials consisting of the same or different ceramic oxides having a melting point above 1600°C, c h a r a c t e r i z e d i n that said interface material consists of one or more ceramic oxides not exhibi¬ ting solid solubility, eutecticum below the temperature of manufacture or use or reactivity with any of the matrix or reinforcing materials and in combination with said materials providing a stress field liable to micro-cracking, said matrix and reinforcing materials being substantially pure.

2. A composite material according to claim 1, c h a ¬ r a c t e r i z e d i n that the stress field is formed either by differences in thermal expansion coefficient between the interface material and the matrix and possibly reinforcing materials or between various inherent phases in the very interface material; or by the latter as such having aniso-tropic structure with different thermal expansion coef¬ ficient in different crystal directions; or by providing a phase conversion between the phases of the interface mate¬ rial and hence a volume change or by the interface material being a composite having at least two phases which have different elastic characteristics or different thermal expansion coefficient.

3. A composite material according to claim 1 or 2, c a¬ r a c t e r i z e d i n that the interface material is selected from the group consisting of Al₂Ti0₅, cordierite, unstabilized Zr0₂, Sn0₂, Hf0₂, mullite, yttrium-aluminium- garnet (YAG), YAG+Zr0₂, Al₂0₃+Zr0₂ and Al₂Ti0₅+Al₂0₃.

4. A composite material according to claim 3 in which the interface material is Zr0₂, c h a r a c t e r i z e d i n that, in order to avoid chemical binding of Zr0₂ to fibres during fibre coating, a Zr0₂ in the orm of powder or sol is used.

5. A composite material according to any of the claims 1 to 4, c h a r a c t e r i z e d i n that the reinforcing material consists of fibres.

6. A composite material according to any of the claims l to 5, c h a r a c t r i z e d i n that the interface material has a thickness of at least 2 μm.

AMENDED CLAIMS

[received by the International Bureau on 31 August 1993 (31.08.93); original claims 1-3 amended; remaining claims unchanged (2 pages)]

1. A ceramic composite material comprising matrix and possibly reinforcing materials and an intermediate weak interface material and particularly intended for use at temperatures above 1400°C and in oxidizing environment, the matrix and reinforcing materials consisting of the same or different ceramic oxides having a melting point above 1600°C, c h a r a c t e r i z e d i n that said interface material consists of one or more ceramic oxides not exhibi¬ ting solid solubility, eutecticum below the temperature of manufacture or use or reactivity with any of the matrix or reinforcing materials and in combination with said materials providing a stress field liable to interfacial cracking, said matrix and reinforcing materials being substantially pure.

2. A composite material according to claim 1, c h a ¬ r a c t e r i z e d i n that the stress field is formed either by differences in thermal expansion coefficient between the interface material and the matrix and possibly reinforcing materials or between various inherent phases in the very interface material; or by the latter as such having anisotropic structure with different thermal expansion coef- ficient in different crystal directions; or by the interface material being a composite having at least two phases which have different elastic characteristics or different thermal expansion coefficient.

3. A composite material according to claim 1 or 2, c h a- r a c t e r i z e d i n that the interface material is selected from the group consisting of Al₂Ti0₅, unstabilized ^• Zr0₂, Sn0₂, Hf0₂, mullite, yttrium-aluminium-garnet (YAG), YAG+Zr0₂, Al₂0₃+Zr0₂ and Al₂Ti0₅+Al₂0₃. 4. A composite material according to claim 3 in which the interface material is Zr0₂, c h a r a c t e r i z e d i n that, in order to avoid chemical binding of Zr0₂ to fibres during fibre coating, a Zr0₂ in the form of powder or sol is used.

5. A composite material according to any of the claims 1 to 4, c h a r a c t e r i z e d i n that the reinforcing material consists of fibres. 6. A composite material according to any of the claims 1 to 5, c h a r a c t e r i z e d i n that the interface material has a thickness of at least 2 μm.