A range of combustor lining components have been made from silicon carbide with graphic interlayers. To enable suitable designs to be made measurements of properties such as the tensile stiffness have been carried out.
The thermal shock and cycling behaviour has been investigated by repeatedly heating the sample to 1400 C in a blast of hot turbine gas and then cooling in a blast of cold gas. No degradation in properties was observed after 750 cycles. Monolithic silicon carbide shattered on the first heating cycle.
A major concern was the behaviour of samples subject to vibration, effectively high cycle fatigue in bending, as this might lead to the delamination of the silicon carbide layers after each growth along the crack deflecting interlayers. However, both laboratory fatigue tests in bending and vibration tests where the sample is loaded at its fundamental frequency have shown that the fatigue behaviour of the laminate is as good as that of the monolith.
Full scale rig-testing of the lining shown in the figure has also been carried out. The increased thermal shock resistance of the laminate was again borne again. In initial tests it was found that the monolithic material had cracked, whilst the laminates remained uncracked. In the final test, the metal parts of the rig melted, again before there was any damage to the laminates.
The work so far has shown that despite the lack of toughening when stressed in tension and their relatively low shear strength, these materials possess useful properties when tested under realistic conditions.
A new way of making toughened ceramics has recently been demonstrated by two the proposers. Ceramic powders are formed into thin sheets and then coated,before compacting together and wintering without any pressure. The principal objective of this programme is to see whether this novel approach can be developed into a cheap and simple method for making a wide range of ceramics components and overcome the appalling economic problems that are associated with existing techniques for making high toughness ceramic composites such as the chemical vapour infiltration of fibre preforms(CVI).
To do this methods will be developed for making layered ceramic parts. Demonstrator parts will be designed, fabricated and then rig tested enabling the performance of components made by this technique to be compared with that of existing materials. Work will also be carried out to develop interfacial layers capable of withstanding high temperatures and to develop a quantitative understanding of the macroscopic properties in terms of the microstructural variables to enable the properties to be optimised for the particular application.
Funding SchemeCSC - Cost-sharing contracts
TS23 1PS Billingham
461 81 Trollhattan