| Abstract Scope |
Jet engine titanium is a robust product with exceptional specific fatigue crack initiation resistance in most circumstances. It can be difficult to study because we are concerned with crack initiation at the 1-in-1,000 component level, or 1 in 2,000 tonnes melted, at lifetimes of 20,000 flights – an integrity level similar to that of nuclear primary circuits. Rather than statistical approaches to scatter this has lead us to a hypothesis-based approach where we examine, by modelling (CPFEM / DDP) and experiment (TEM, SAXS, APT and HEDM), the micromechanics of specific microstructural features. Another issue in titanium can be vacuum or subsurface fatigue crack initiation and growth, which is significantly slower than in air – implying a role for environment in cracking, Taking this further, we have recently started to be able to find H in titanium microstructures using cryo atom probe tomography, allowing the investigation of NaCl and AgCl-associated hot salt stress corrosion cracking (HSSCC) in service. |