E≈S Journal of the European Ceramic Society 20(2000)531-535 Mechanical characterisation of mullite-based ceramic matrix composites at test temperatures up to 1200c P.W.M.Peters.*,B. Daniels a, F. Clemens b, W.D. Vogel b DLR Institute of Materials Research, 51170 Koln Daimler Chrysler/ Dornier Fors lung, 88039 Friedrichshafen, Germany Accepted 10 August 1999 Abstract Nextel 610 fibre-reinforced mullite-based matrix fabricated by Dornier Forschung was characterised at DLR Institute of Mate- rials Research. The material was produced by the polymer route after coating the fibres with a 0 I um thick carbon layer. The composite was manufactured by infiltrating the fibres with a slurry containing a diluted polymer and mullite powder, curing in an autoclave and subsequently heat treating and pyrolysis of the polymer. A final heat treatment in air is performed to remove the carbon coating and to reduce the residual stresses A(0/90/0/ 90/0/90)s-laminate was produced with an average fibre volume fraction of 45.6% and a porosity of 15.9%. Dog-bone-type tensile specimens with a width of 10 mm were cut from the plate by water jet and tested at temperatures up to 1200C in air. The tensile strength at room temperature measured 177. 4 MPa and linearly decreased to 145.2 MPa at a temperature of 800C. A stronger decrease occurred at 1000 and 1200 C. In contradiction to ceramic matrix com- posites manufactured by the Cvl-route the stress-strain behaviour is nearly linear up to failure. The modulus of the composite(at room temperature 108.8 GPa)is analysed on the basis of the expected moduli of the fibres and the mullite matrix. It can be con- cluded that the contribution of the matrix to the modulus of the composite is low, caused by porosity and components other than mullite. The intralaminar shear strength at room temperature measured 36 MPa. This value reflecting shear transfer capability of fibre to matrix limits the amount of fibre pull-out. C 2000 Elsevier Science Ltd. All rights reserved. Keywords: Aluminosilicate fibres; Composites; Laminates: Mechanical properties; Mullite matrix 1. Introduction giving rise to a loss of the crack deflective capability, if interfacial reaction products increase fibre/matrix bond Ceramic matrix composites(CMCs) are under devel- ing. Application of protective coatings is a possibility to opment for high temperature applications as e. g in aero reach short and medium term oxidative resistance. 2.3 engines, rocket nozzles and re-entry heat shields. In Long term oxidation resistance for thousands of comparison with monolythic ceramics these fibre rein- hours, however, can only be reached if the material forced ceramics are attractive due to the increased system is composed of components each of which is toughness and decreased flaw sensitivity. First genera- oxidation resistant. For this reason in recent years tion CMCs were usually produced on the basis of che- CMCs with oxide fibres and oxide matrices have drawn mical vapour deposition (impregnation) making use of much attention. In the absence of weak layers sur- fibres surrounded by a carbon coating. These CMCs rounding the fibres a different crack deflection mechan- how on loading multiple matrix cracking which leads to ism must be activated as is for example possible on the a gradual loss of the contribution of the matrix to the basis of a different coefficient of thermal expansion of composite stiffness. This so-called quasi-ductility is fibre and matrix and a special geometrical arrangement reached due to the fact that matrix cracks do not pen of closely packed fibres in a finescale porous matrix. 4 trate the fibres but deflect at or in the C-layer. The main Crack deflection in the usual sense can be realized with draw back of these CMCs is, that in high temperature oxidative environments the carbon layer is consumed crack deflective materials(e. g. monazites 5.6) porous interphases 5,6 fugitive interphases 0955-2219/00/S. see front matter C 2000 Elsevier Science Ltd. All rights reserved PII:S0955-2219(99)00250Mechanical characterisation of mullite-based ceramic matrix composites at test temperatures up to 1200C P.W.M. Peters a,*, B. Daniels a , F. Clemens b, W.D. Vogel b a DLR Institute of Materials Research, 51170 KoÈln, Germany bDaimlerChrysler / Dornier Forschung, 88039 Friedrichshafen, Germany Accepted 10 August 1999 Abstract Nextel 610 ®bre-reinforced mullite-based matrix fabricated by Dornier Forschung was characterised at DLR Institute of Mate￾rials Research. The material was produced by the polymer route after coating the ®bres with a 0.1 mm thick carbon layer. The composite was manufactured by in®ltrating the ®bres with a slurry containing a diluted polymer and mullite powder, curing in an autoclave and subsequently heat treating and pyrolysis of the polymer. A ®nal heat treatment in air is performed to remove the carbon coating and to reduce the residual stresses. A (0/90/0/90/0/90)s-laminate was produced with an average ®bre volume fraction of 45.6% and a porosity of 15.9%. Dog-bone-type tensile specimens with a width of 10 mm were cut from the plate by water jet and tested at temperatures up to 1200C in air. The tensile strength at room temperature measured 177.4 MPa and linearly decreased to 145.2 MPa at a temperature of 800C. A stronger decrease occurred at 1000 and 1200C. In contradiction to ceramic matrix com￾posites manufactured by the CVI-route the stress±strain behaviour is nearly linear up to failure. The modulus of the composite (at room temperature 108.8 GPa) is analysed on the basis of the expected moduli of the ®bres and the mullite matrix. It can be con￾cluded that the contribution of the matrix to the modulus of the composite is low, caused by porosity and components other than mullite. The intralaminar shear strength at room temperature measured 36 MPa. This value re¯ecting shear transfer capability of ®bre to matrix limits the amount of ®bre pull-out. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Aluminosilicate ®bres; Composites; Laminates; Mechanical properties; Mullite matrix 1. Introduction Ceramic matrix composites (CMCs) are under devel￾opment for high temperature applications as e.g. in aero engines, rocket nozzles and re-entry heat shields. In comparison with monolythic ceramics these ®bre rein￾forced ceramics are attractive due to the increased toughness and decreased ¯aw sensitivity. First genera￾tion CMCs were usually produced on the basis of che￾mical vapour deposition (impregnation) making use of ®bres surrounded by a carbon coating. These CMCs show on loading multiple matrix cracking which leads to a gradual loss of the contribution of the matrix to the composite sti€ness.1 This so-called quasi-ductility is reached due to the fact that matrix cracks do not pene￾trate the ®bres but de¯ect at or in the C-layer. The main drawback of these CMCs is, that in high temperature oxidative environments the carbon layer is consumed giving rise to a loss of the crack de¯ective capability, if interfacial reaction products increase ®bre/matrix bond￾ing. Application of protective coatings is a possibility to reach short and medium term oxidative resistance.2,3 Long term oxidation resistance for thousands of hours, however, can only be reached if the material system is composed of components each of which is oxidation resistant. For this reason in recent years CMCs with oxide ®bres and oxide matrices have drawn much attention. In the absence of weak layers sur￾rounding the ®bres a di€erent crack de¯ection mechan￾ism must be activated as is for example possible on the basis of a di€erent coecient of thermal expansion of ®bre and matrix and a special geometrical arrangement of closely packed ®bres in a ®nescale porous matrix.4 Crack de¯ection in the usual sense can be realized with . crack de¯ective materials (e.g. monazites 5,6) . porous interphases 5,6 . fugitive interphases. 0955-2219/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(99)00250-2 Journal of the European Ceramic Society 20 (2000) 531±535 * Corresponding author