Gas turbines in power generation systems use both nickel and cobalt-based superalloys for
vanes, blades, discs and combustion chamber components. Cobalt-based superalloys have
the advantage over nickel based superalloys in that they have a higher thermal conductivity
and hence a greater thermal shock resistance, a greater resistance to thermal fatigue and
also a better corrosion resistance. However, in some applications coatings have to be applied
to such alloys because of their poor oxidation resistance. The creep strength of cobalt-based
superalloys depends primarily on solid solution strengthening and the interaction between the
hard carbides and alloy defects, such as dislocations and stacking faults.
There is a need to develop an understanding of the microstructural changes that occur in
cobalt-based superalloys, with both time and temperature, for life prediction, refurbishment
and failure investigations... cont'd.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.