Brittle Materials Design, High Temperature Gas Turbine

McLean, A. F.; Fisher, E.A.

doi:10.21236/adb023566

Cited by 10 publications

(8 citation statements)

References 9 publications

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“…While this rework was in process vacuum capability was also added to the die cavity as shown in Figure 3.7. Previous experience with the stator die indicated the advantages associated with die evacuation just prior to material injection 1 ) . Vacuum was supplied through the stationary die half and entered the cavity through the blade tips.…”

Section: Injection Molded Blade Ring Fabricationmentioning

confidence: 99%

Brittle Materials Design, High Temperature Gas Turbine

McLean¹,

Baker²,

Bratton³

et al. 1976

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Section: Injection Molded Blade Ring Fabricationmentioning

confidence: 99%

Brittle Materials Design, High Temperature Gas Turbine

McLean¹,

Baker²,

Bratton³

et al. 1976

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“…The work further concluded that the stochastic nature of ceramics requires a rigorous statistical analysis of properties. The strength of ceramics often conforms to a weibull distribution and as such, a weibull analysis of the results provides a more complete profile of the strength that can be expected [7]. Recent work by General Electric (GE) has developed a SiC/SiC fibre based composite which uses a liquid silicon melt infiltration process to produce the matrix.…”

Section: Figure 2: Improvements To Firing Temperature Of Gas Turbinesmentioning

confidence: 99%

“…The shape and type of flaw will also play a role due to varying stress concentrating effects of different crack tip geometries. Stress intensity, K, given by equation (7) has been introduced to scale the stress amplification of different crack geometries.…”

Section: Toughnessmentioning

confidence: 99%

“…Where P f is the probability of failure, σ is the applied stress, σ 0 is the stress at which probability of failure is 100%, m is the weibull modulus and V is the volume. The weibull modulus is the measure of how closely the material adheres to a weibull distribution, a higher modulus will mean that there is little variation in the strengths measured [7].…”

Section: Statistical Analysis Of Propertiesmentioning

confidence: 99%

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Mullite Whisker Enhanced Zirconia Toughened Alumina Ceramic Matrix Composite for High Temperature Applications

Robertson¹

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Ceramic Matrix Composites (CMC) are an attractive material for high temperature applications because they possess many of the high temperature capabilities of monolithic ceramics but also have enhanced mechanical properties due to their multi-phase structure. Recent successes with incorporating SiC fibre reinforced high temperature CMCs into advanced gas turbines have caused a renewed interest in applying CMCs to other high temperature applications. In this work, an oxide based CMC is proposed as a more oxidation resistant and cost effective CMC. Zirconia Toughened Alumina (ZTA), as the matrix, has enhanced toughness, strength, and creep resistance over single phase alumina or zirconia. ZTA can further be enhanced by the incorporation of single crystal mullite whiskers due to their stability in oxidizing atmospheres at high temperatures. Mullite whiskers are grown through the molten salt method and incorporated into the ZTA matrix using a colloidal processing route. The composition of the ZTA matrix is 15 wt% yttria stabilized zirconia (YSZ), 85 wt% α-alumina. The mullite whiskers make up 20 vol% of the composite, yielding a final composition of 71.6 wt% α-alumina, 12.7 wt% YSZ, and 15.6 wt% mullite. The green compacts are fired in a two stage sintering process incorporating atmospheric pressure sintering to 92% density (to seal the pore channels) and then hot isostatic pressure sintering to full density. The mechanical test results show that baseline ZTA (ZTA n ) with final porosity of 13.2% has a flexural strength of 61.71 ± 0.99 MPa at room temperature and 52.34 ± 15.72 MPa at 1200°C, a fracture toughness of 5.02 ± 0.21 MPa•m 1/2 and a hardness of 10.73 GPa. ZTA with whisker content (ZTA w ) with final porosity of 3.31% reached a flexural strength of 135.76 ± 1.30 MPa at room temperature, 80.52 ± 13.18 MPa at 1200 °C, a fracture toughness of 8.74 ± 0.24 MPa•m 1/2 and a hardness of 11.99 GPa. The addition of whiskers to ZTA has improved room temperature flexural strength by 120.0%, flexural strength at 1200°C by 53.8%, fracture toughness by 74.1%; but the whiskers have little effect on the hardness. Although high temperature flexural strength was improved by the addition of whiskers, the iv improvement to strength at high temperature was not as significant in ZTA w . Degradation of large whiskers was found during cyclic oxidation of ZTA w 1200 °C. v

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“…It is therefore advantageous to develop alternative materials which can operate at temperatures beyond superalloy's capability as seen in Figure 1. In the past, advanced ceramics have been examined as a potential high temperature structural material because they possess high strength, high stiffness, good creep resistance, good environmental and chemical stability, and low density [7]. Unfortunately, their low damage tolerance, especially under tensile loads, has prevented their adoption in applications where reliability is crucial.…”

Section: Ceramic Matrix Composites As High Temperature Materialsmentioning

confidence: 99%

Design, Manufacturing, and Characterization of a Novel Ceramic Matrix Composite

Robertson¹

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A novel ceramic matrix composite (CMC) system consisting of a commercially available SiC fibre, variations of electrophoretically deposited (EPD) fibre-matrix interphases, and a liquid metal melt infiltrated matrix was designed and characterised. A factorial design of experiments approach was undertaken to evaluate the deposition variables which would result in a functioning fibre-matrix interphase.A 2 5-2 partial factorial design matrix was selected with factors: electric potential, deposition time, surfactant, binder, and solids loading. The design matrix was replicated for four different EPD fibre-matrix interphase coating combinations: Al2O3/SiC, BN/PSZ, ZrC/ZTA, and SiC/Si3N4/SiC. Microcomposites were evaluated for tensile properties using a standard displacement controlled tensile test program.Microcomposites were tested at room temperature immediately following fabrication and following exposure to a standard atmosphere at 1000 °C for 1 h. Samples with ZrC/ZTA and SiC/Si3N4/SiC coatings demonstrated the best tensile properties in room temperature tests while samples with BN/PSZ and SiC/Si3N4/SiC coatings demonstrated the best retention of tensile properties following high temperature exposure. Subsequent SEM analysis revealed that coatings with smaller particle diameters as the inner layer of the fibre-matrix interphase coating produced more uniform coatings and the less fibre degradation due to oxidation following high temperature exposure. Additional microcomposites were fabricated for high temperature tensile testing; however, these samples were unable to bear recordable loads, an SEM examination revealed significant degradation of the matrix phase beneath the high temperature adhesive.Optical microscopy was used to evaluate coating thicknesses of coated fibre bundles prior to heat treatments. Measured coating thickness indicated that generally higher deposition times resulted in thicker coatings; however, coatings produced using 25 V electric potential were thicker than coatings produced using 12.5 V and 50 V electric potentials. This is likely due to a greater deposition efficiency factor at 25 V. FEA analysis was used to evaluate the electrical properties of an idealized version of the stationary EPD cell. This analysis showed a significant variation in the electric field along the fibre axis as well as a significant variation in electrical field between fibres in the centre of the fibre bundle and on the outer edge of the fibre bundle.

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Brittle Materials Design, High Temperature Gas Turbine

Cited by 10 publications

References 9 publications

Brittle Materials Design, High Temperature Gas Turbine

Brittle Materials Design, High Temperature Gas Turbine

Mullite Whisker Enhanced Zirconia Toughened Alumina Ceramic Matrix Composite for High Temperature Applications

Design, Manufacturing, and Characterization of a Novel Ceramic Matrix Composite

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