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

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.