Ludovic Edmond Camille Molliex

Alumina/alumina composite with a porous zirconia interphase —Processing, properties and component testing

Abstract Novel oxide ceramic composites (NOCC) was a four year European programme aimed to develop an all-oxide ceramic matrix composite (CMC) and processing route, carry out a characterisation programme on the material and demonstrate it in a combustor rig at conditions representative of a gas turbine engine. The fibre used was a single crystal monofilament (Saphikon Inc.), which was chosen for its temperature and creep resistance. Alumina (aluminium oxide) was chosen for the fibre and matrix, and zirconia as a weak interphase coating on the fibre. Tape casting followed by hot pressing was chosen as the manufacturing route for the composite, with hot isostatic pressing (HIPping) as an alternative densification process. Cross-ply material with fibre volume fractions of around 30% was found to have moderate strength (100–130 MPa), but retained composite properties at elevated temperatures and after extended periods at elevated temperatures (1000 h at 1400°C). In addition, the material was found to withstand thermal cycling (>1300 cycles to 1200°C), retaining its as-fabricated properties. Computational fluid dynamics (CFD) calculations were carried out for a combustor rig, and a CMC tile was designed. The temperatures, stresses and strains in the tile were predicted using finite element (FE) analysis and combustor tiles were manufactured. A tile was successfully tested in a rig at temperatures >1260°C and up to 46 cycles. Some of the issues that remain to be addressed with the material and manufacturing method are cost, delamination during manufacture, and consistency. It is likely that, due to the high cost of the fibre and relatively modest usable strength, the material will remain as a model material. The promising results on long term static and cyclic ageing proves that the concept of an all-oxide CMC is valid and points the way to future development of this class of material.

Development of Ultra High Temperature Ceramic Composites for Gas Turbine Combustors

All-oxide ceramic composites as a material with potential for long life-time applications at temperatures in the 1400–1600°C range in combustion environments were studied. The properties of available polycrystalline and single crystal oxide fibres were summarised. The literature on stable weak interfaces in all-oxide composites was reviewed. Composites with single crystal fibres, a polycrystalline matrix of the same material as the fibres, and a compatible high temperature stable weak oxide interphase was suggested to be the most promising approach. Recent progress in an ongoing European project aiming at development, scale-up and property evaluation of all-oxide composites is reported. The composite will be applied to a simple prototype combustor tile and tested in a combustor rig.© 1997 ASME

OXIDE/OXIDE CERAMIC MATRIX COMPOSITES IN GAS TURBINE COMBUSTORS

Gas turbine combustor concepts designed to give improved control of NOx emissions require the usage of hot uncooled walls. The main material properties needed in this application include mechanical and chemical stability at temperatures in excess of 1400°C for long times (>10 000 hours). Composites made from single crystal oxide fibre reinforced oxide with a compatible high temperature stable weak oxide interphase are potential candidate materials to meet these requirements. Alumina was chosen as a model material, unidirectional and 2D composites were processed and a suitable weak zirconia interphase was designed. The process was scaled-up to make production of larger panels and components possible. Mechanical testing was carried out at room temperature to characterise the performance of the material in the as produced and thermally aged condition. Room temperature mechanical properties compared well with other current ceramic composites and excellent high temperature stability was demonstrated. The applicability of the composite as a material for uncooled combustor walls is to be further assessed by evaluation in a combustor test rig. Results from computational fluid dynamics and finite element calculations as well as results from combustor rig tests of monolithic and composite ceramic tiles will be presented.Copyright

Processing and properties of oxide matrix/oxide fibre composite

Abstract An all-oxide composite was fabricated. Single crystal alumina fibres were coated with a carbon/zirconia slurry, dried, and uniaxially aligned by winding. Matrix material, alumina with 5 vol.-% unstabilised zirconia added, was tape cast on top of the fibres. Pre-pregs were cut, stacked, and laminated to cross-ply material. Final sintering was done by hot isostatic pressing. A heat treatment was added to remove the carbon and create a porous zirconia interphase. Flexure strengths around 200 MPa were obtained for composites at room temperature while a strength of 124 MPa was recorded at 1200°C. The mechanical properties and non-brittle behaviour was sustained after aging at 1400°C for 1000 h in air.