Two coating routes have been developed :
- thin adherent laser ablated coatings
- strain tolerant plasma sprayed coatings
A number of different coating materials have been deposited on both C/SiC and SiC/SiC composites and exposed to temperatures in excess of 1000 C.
Best thermal shock resistance and protectiveness to oxidation and gas corrosion was achieved with Mullite and Zirconium silicate coatings which have only a low thermal expansion mismatch with the composite.
For protection against cast iron a capping layer of Alumina or Zirconia is needed. The protectiveness of the coating is related to its thickness, adhesion, porosity and susceptibility to cracking.
Trial components have been manufactured for testing in a radiant tube furnace and a cast iron pouring chute. Two Ring Segments in the Radiant Tube Furnace have survived 1200 at > 1200 C without serious degradation. The performance of coated CMCs in the cast iron pouring tests is superior to that of uncoated materials, a real Trapezoidal Plate has been tested during 15 days on a Production line, surviving 4160 cycles.
B91 2JW Solihull
OX11 0RA Didcot