Objectives

The initiation and growth of cracks under service conditions may limit the lifetime of high-temperature components. Two of the most severe mechanisms of crack growth occur when:

• cracks, initiated through failure of a protective coating or oxide scale, propagate into the substrate alloy and continue to grow undetected, significant for internal cooling passages in gas turbine blades, for example
• disruption of the protective oxide scale results in internal oxidation of grain boundaries (stress assisted grain boundary oxidation), observed in turbine blades, discs and even bolts.

This project addressed both of these problems and in each case:

• surveyed and developed existing measurement techniques for application to these problems
• developed models to identify service conditions where there is a high probability of these mechanisms operating.