E驅≈3S Journal of the European Ceramic Society 20(2000)537-544 Chemical vapor deposition of zro2 and C/zrO2 on mullite fibers for interfaces in mullite/ aluminosilicate fiber-reinforced composites K. Nubianb B Saruhana,*B Kankaa M. Schmuckera H. Schneidera G. Wahlb a German Aerospace Center, Institute for Materials Research, 51147 Koln, Germany bUniversity of Braunschweig, Institute for Surface Technology, 38108 Braunschweig Germ Accepted 10 August 1999 Abstract For the realization of crack deflection and fiber pull-out in aluminosilicate fiber-reinforced dense mullite-matrix composites suitable fiber /matrix- interfaces are an important requirement in order to obtain sufficiently weak bondings between fibers and matrices. Two types of chemical vapor deposited(CVD)fiber/matrix-interfaces have been studied in the present work porous Zro and C/zrO2-double layers. In the latter case, carbon was burned out to form a gap during the processing of composites(fugitive coating). Porous ZrO2 coatings were produced by an optimized CVD-process with Zr-acetylacetonate as a precursor. The con stancy of the layer thickness depended on the deposition temperature. It was found that at a temperature of approximately 300C and a pressure of 5 hPa, suitably uniform layers with thickness ranging between 100 and 300 nm were achieved. The coatings contained approximately 15 wt% carbon which produced, after annealing in air, a porous structure. The deposition kinetics can be described by a first order reaction. The carbon layer in C/ZrO -double layers was produced by using propane. The thickness of carbon layer was 10 and 100 nm, respectively. Aluminosilicate fiber/mullite matrix composite prepegs were fabricated by infiltration of coated and unidirectionally oriented fiber(0 )with a slurry, containing a pre-mullite powder, calcined at 1.C. Uniaxial hot- pressing of dried prepegs was carried out at 1250C for 15 min, at 20 MPa. Prepegs with ZrO2 fiber/matrix- interfaces were hot pressed in air, while the samples with C/ZrO -interfaces were processed in flowing argon. After hot-pressing, samples with C/zrO2- interfaces were heat-treated in air (1000C) in order to bl arn out the C-layer (fugitive coating). These composites yielded a con- trolled fracture with a high deflection rate and a favorable fracture strength of about 200 MPa, due to crack-defiection and fiber tolerant than those having C/ZrO, double layer systems. C 2000 Elsevier Science Ltd. All rights reserved e, they are less damage pull-out. Composites with ZrO2-interfaces, on the contrary yielded no crack deflection or pull-out. Therefo Keywords: Aluminosilicate fibres; Composites; Interfaces; Mullite matrix; ZRO thus lowering the shear strength and constituting a pre- ferred path for the diversion of matrix-originating Thermal protection systems consisting of oxide-based cracks. An example of this approach is given by Si-O-N fiber-reinforced composites can contribute significantly in the reduction of no and emission in the combustion coating on SiC-fibers. The required porosity was gen erated with latex polystyrene mixed with Si3 N4 and chambers of aircraft engines and stationary gas turbine SiOx-powders. Push-out tests showed that only those m乙mm(③ mics, less cooling, thus, less fuel consum necessary. Nevertheless, stror matrix-interfaces due chanical perature. Another method, describing a successful pseud ss of ceramic composites, porous fiber coating system by means of CVD, used a making them less damage tolerant and, therefore, less The carbon source was methane, and the Sic source reliable for the application was either methyltrichlorosilane or tetrachloride. After For achievement of advantageous failure in the com heat-treatment at a temperature range between 800 and posites, one approach is to apply porous interphases, 1200C under reduced pressure(1-100 Torr), crystalline 4 Corresponding author. Tel. +49-2203-601-3228: fax: +49-2203- SiC with a resulting porosity of 12% was obtained. 696480 The only effective way in coating of fiber surfaces in E-mail address: bilge saruhan(@ drde(B Saruhan) fiber tows or fabrics with thin ceramic layers is to 0955-221999/S- see front matter o 2000 Elsevier Science Ltd. All rights reserved PII:S0955-2219(99)00251-4Chemical vapor deposition of ZrO2 and C/ZrO2 on mullite ®bers for interfaces in mullite/aluminosilicate ®ber-reinforced composites K. Nubianb, B. Saruhana,*, B. Kankaa , M. SchmuÈckera , H. Schneidera , G. Wahlb a German Aerospace Center, Institute for Materials Research, 51147 KoÈln, Germany bUniversity of Braunschweig, Institute for Surface Technology, 38108 Braunschweig, Germany Accepted 10 August 1999 Abstract For the realization of crack de¯ection and ®ber pull-out in aluminosilicate ®ber-reinforced dense mullite-matrix composites, suitable ®ber/matrix-interfaces are an important requirement in order to obtain suciently weak bondings between ®bers and matrices. Two types of chemical vapor deposited (CVD) ®ber/matrix-interfaces have been studied in the present work porous ZrO2 and C/ZrO2-double layers. In the latter case, carbon was burned out to form a gap during the processing of composites (fugitive coating). Porous ZrO2 coatings were produced by an optimized CVD-process with Zr-acetylacetonate as a precursor. The con￾stancy of the layer thickness depended on the deposition temperature. It was found that at a temperature of approximately 300C and a pressure of 5 hPa, suitably uniform layers with thickness ranging between 100 and 300 nm were achieved. The coatings contained approximately 15 wt% carbon which produced, after annealing in air, a porous structure. The deposition kinetics can be described by a ®rst order reaction. The carbon layer in C/ZrO2-double layers was produced by using propane. The thickness of carbon layer was 10 and 100 nm, respectively. Aluminosilicate ®ber/mullite matrix composite prepegs were fabricated by in®ltration of coated and unidirectionally oriented ®ber (0) with a slurry, containing a pre-mullite powder, calcined at 1100C. Uniaxial hot￾pressing of dried prepegs was carried out at <1250C for 15 min, at 20 MPa. Prepegs with ZrO2 ®ber/matrix-interfaces were hot￾pressed in air, while the samples with C/ZrO2-interfaces were processed in ¯owing argon. After hot-pressing, samples with C/ZrO2- interfaces were heat-treated in air (1000C) in order to burn out the C-layer (fugitive coating). These composites yielded a con￾trolled fracture with a high de¯ection rate and a favorable fracture strength of about 200 MPa, due to crack-de¯ection and ®ber pull-out. Composites with ZrO2-interfaces, on the contrary yielded no crack de¯ection or pull-out. Therefore, they are less damage tolerant than those having C/ZrO2 double layer systems. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Aluminosilicate ®bres; Composites; Interfaces; Mullite matrix; ZRO2 1. Introduction Thermal protection systems consisting of oxide-based ®ber-reinforced composites can contribute signi®cantly in the reduction of NOx and emission in the combustion chambers of aircraft engines and stationary gas turbine engines. Relying on good thermal properties of the cera￾mics, less cooling, thus, less fuel consumption will be necessary. Nevertheless, strong bonding at the ®ber/ matrix-interfaces due to the chemical and mechanical interactions causes brittleness of ceramic composites, making them less damage tolerant and, therefore, less reliable for the application. For achievement of advantageous failure in the com￾posites, one approach is to apply porous interphases, thus lowering the shear strength and constituting a pre￾ferred path for the diversion of matrix-originating cracks. An example of this approach is given by Si±O±N coating on SiC-®bers.1 The required porosity was gen￾erated with latex polystyrene mixed with Si3N4 and SiO2-powders. Push-out tests showed that only those coatings which were retreated with a silica layer displayed a reasonably low (25 MPa) friction-stress at room tem￾perature. Another method, describing a successful pseudo porous ®ber coating system by means of CVD, used a 0.5±50 mm thick layer of carbon-enriched SiC-coating.2 The carbon source was methane, and the SiC source was either methyltrichlorosilane or tetrachloride. After heat-treatment at a temperature range between 800 and 1200C under reduced pressure (1±100 Torr), crystalline SiC with a resulting porosity of 12% was obtained. The only e€ective way in coating of ®ber surfaces in ®ber tows or fabrics with thin ceramic layers is to 0955-2219/99/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(99)00251-4 Journal of the European Ceramic Society 20 (2000) 537±544 * Corresponding author. Tel.: +49-2203-601-3228; fax: +49-2203- 696480. E-mail address: bilge.saruhan@dlr.de (B. Saruhan)