Objectives. Development of oxide ceramic matrix composite (OCMC)

Transcription

1 10 th CMCee ; ; Dresden Aqueous slurries for oxide ceramic composites: Correlation between mechanical properties of the composite and composition of the Al 2 O 3 / ZrO 2 powder. Arne Rüdinger, Dr. F. Raether; Fraunhofer ISC / Center for High Temperature Materials and Design Walter E.C. Pritzkow; W.E.C. Pritzkow Spezialkeramik Objectives Development of oxide ceramic matrix composite (OCMC) Simple processing one step process No vacuum, no re-infiltration High strength Superior fracture toughness High thermal shock resistance Project/funding: AiF; Thermoschockbeständiges Keramik-Kompositmaterial für die Wärmetechnik ; Project partner Walter E.C. Pritzkow Spezialkeramik

2 Processing of the OCMC Slurry with ceramic particles Preform made from alumina fibre rovings or woven fabric Impregnating of preform with slurry Heat treatment, sintering of ceramic particles Porous ceramic matrix, reinforced by alumina fibres Requirements for slurry and matrix Water based slurry for fabrication of oxide ceramic-matrix-composites Long-term stable slurry; fabrication of large OCMC components Al 2 O 3 or Al 2 O 3 -ZrO 2 matrix HT-stability; hydrothermal stability; chemical stability Defect-free matrix Matrix without drying and sintering cracks High matrix-strength and interlaminar shear strength (ILSS) Porous matrix; weak fiber-matrix bondage; damage-tolerant behavior Max. sinter temperature 1200 C Degradation of fiber-strength

3 Requirements for slurry and matrix sintered OCMC with drying and sintering cracks sintered OCMC without drying and sintering cracks fiber matrix Slurry has to penetrate small voids between fibers Drying and sintering shrinkage have to be small Al 2 O 3 and ZrO 2 powder particles tested in slurry 1400 mean grain size d50 [nm] Z A1 A2 A3 B1 C B2 D E F ceramic powders

4 Matrix / slurry preparation 70 wt % mixture of fine and coarse powder e coarse powder fine powder 1 wt % PVA binder stabilisation with hydrochloric acid Characterization methods Grain size distribution Zetasizer Density and porosity Archimedes standard method Shrinkage Thermo-Optical- Measurement Device Thermal diffusivity Netzsch 3-Point-Bending Zwick; Standard method for CMC

5 Characterization of dried and sintered matrices pure Al 2 O 3 -matrix Variation of ratio between fine and coarse alumina- powder type C and F Lowest porosity with 10 20% fine powder Shrinkage increases with amount of fine powder Characterization of dried and sintered matrices pure Al 2 O 3 -matrix Variation of ratio between fine and coarse alumina- powder type C and F 20 % of fine powder leads to lowest sintering temperature

6 Characterization of dried and sintered matrices pure Al 2 O 3 -matrix Variation of ph-value of slurry; fine and coarse alumina-powder type C and E ph-value of 2-3 of slurry leads to high density, low porosity and high densification of matrix Characterization of dried and sintered matrices pure Al 2 O 3 -matrix Variation of fine alumina powder A1-A3 and B1; coarse powder type C Increasing particle size of fine powder leads to higher density of matrix

7 Characterization of dried and OCMC pure Al 2 O 3 -matrix Variation of fine aluminapowder A1-A3 and B1 B2; coarse powder type C Increasing size of fine powder leads to lower 3-point bending strength of OCMC Characterization of dried matrices Al 2 O 3 -ZrO 2 matrix Variation of amount of fine ZrO 2 powder type Z in mixture with Al 2 O 3 -powder type F (and E) Increasing amount of Al 2 O 3 -powder leads to decreasing shrinkage during sintering

8 Characterization of sintered matrices Al 2 O 3 -ZrO 2 matrix Variation of amount of fine ZrO 2 powder type Z in mixture with Al 2 O 3 -powder type F (and E) Thermal diffusivity of sintered matrix depends on amount of ZrO 2 (indicates sintering neck formation) Type of coarse alumina powder affects sintering behaviour Properties of OCMC Al 2 O 3 -ZrO 2 matrix Variation of amount of fine ZrO 2 powder type Z in mixture with Al 2 O 3 -powder type F (and E) amount of ZrO 2 powder affects bending-strength of OCMC Type of coarse alumina powder affects bending-strength of OCMC 70 m-% of alumina type F or E leads to best mech. properties

9 Conclusions SEM-investigation of OCMC with pure Al 2 O 3 - matrix Bad penetration of slurry Delamination Cracks have minor effect Cavities have minor effect When the woven fabric is fully infiltrated with slurry bendingstrength of OCMC is > 200 MPa Matrix without cracks AND fully infiltrated woven fabric bendingstrength > 300 MPa coarse powder fine powder bending strength cracks cavities fibre bunde filled MPa - / + - / + - / + A1 F A1 D A1 B A2 F delamination A2 D A2 B A3 D delamination A3 D A3 B C F C F delamination C D delamination B1 F delamination B1 D B1 C B2 F B2 F B2 F B2 D delamination B2 D B2 D B2 B1 delamination B2 B B2 B Properties of OCMC Al 2 O 3 -ZrO 2 matrix Variation of amount of fine ZrO 2 powder type Z in mixture with Al 2 O 3 -powder type F (and E) Variation of sintering temperature For a certain mixture, there is no shrinkage during sintering up to 1200 C 1200 C is maximum for sintering OCMC because of fibre damage

10 Properties of OCMC Al 2 O 3 -ZrO 2 matrix Variation of amount of fine ZrO 2 powder type Z in mixture with Al 2 O 3 -powder type F and E Strength of matrix after sintering (ball-on-ring test) With increasing amount of alumina, the matrix strength is decreasing Strong influence of type of alumina on matrix strength Summary: mech. properties of OCMC ILS (L/D = 5) and 3-point bending strength (L/D = 20) bending-strength Young-modulus ILS MPa GPa MPa Al 2 O 3 -ZrO 2 type I Al 2 O 3 -ZrO 2 type II Al 2 O Fiber volumen content: 37 vol-% Porosity OCMC: 29 vol-% Tensile strength: MPa ILS measured by short bending test L/D=5 DIN EN and -5

11 Conclusions Powder particle size, mixture and ph-value affect matrix and OCMC properties coarse powder fine powder Powders with high sintering activity lead to denser matrix and better OCMC properties Bending strength and ILS of OCMC with Al 2 O 3 -ZrO 2 matrix is higher than pure Al 2 O 3 -matrix Damage-tolerant fracture behaviour one step process without vacuum and re-infiltration Application tests of OCMC parts showed comparable performance to OCMC parts from competitors (according to our project-partner ) Acknowledgment Funded by the AiF : Thermoschockbeständiges Keramik- Kompositmaterial für die Wärmetechnik ; Application-tests by MTU, EADS Astrium and NLR arne.ruedinger@isc.fraunhofer.de