Abstract
During hot component fatigue tests there have been two cases of low life crack initiation of gas turbine rotating parts manufactured from the Titanium alloy Ti-6246. Both exhibited a small (~0.1 mm) elliptical 'blue spot' at the origin. Through validated striation count work and fracture mechanics it was established that fatigue had propagated with a near-nil initiation life. Early investigation suggested that the 'blue spot' was possibly a region of stage 1 fatigue growth, and was therefore a material behaviour concern with potential implications for service. During an investigation of a later cracking incident in this alloy, subsequently shown to have resulted from stress-corrosion cracking (SCC), near-identical fractographic characteristics to that seen in the "blue spot" were found that subtly differentiated it from stage 1 fatigue. Also, similar 'blue spots' have since been identified on Ti6246 Laboratory hot LCF test specimens and found to have been due to contamination by NaCl, through the application of focussed long-term EDX examination and other novel chemical analyses techniques. By the application of those techniques, fractography, and comparison against these specimens, Rolls-Royce and Imperial College London have collaborated to show that the original two component 'blue spots' were subtle examples of NaCl-related Hot Salt Stress-Corrosion Cracking (HSSCC). Such cracking has not been found to occur in service components, due to air pressure within the engine, and the effect is therefore confined to Laboratory and component tests at near-atmospheric pressure or below.
| Original language | English |
|---|---|
| Pages (from-to) | 2-20 |
| Number of pages | 19 |
| Journal | Engineering Failure Analysis |
| Volume | 61 |
| Early online date | 23 Jun 2015 |
| DOIs | |
| Publication status | Published - 1 Mar 2016 |
Funding
The authors would like to thank members of the Rolls-Royce Deutschland Failure Analysis team (Dahlewitz, Germany) for their work on the ST1 and ST2 investigations, provision of test specimens, and support — Karin Frank, Heike Floege, Matthias Goebel, Sarah Mouti, and Gunter Friedel. We would also like to thank John Chamberlain, Jane Woolrich, Mark Dixon and Alex Davidson of Rolls-Royce plc; the former for his work on the reaction chemistry understanding, and the latter three for their support and test specimen provision. The images and graphs shown in Figs. 9–11 ,–15, and 17–20 were provided by Tamara Chapman.
Keywords
- fractography
- hot salt stress-corrosion cracking
- novel technology application in failure analysis
- pressure implication
- titanium-6246
- fatigue tests
- stress-corrosion cracking (SCC)
Fingerprint
Dive into the research topics of 'Understanding the "blue spot": sodium chloride hot salt stress-corrosion cracking in titanium-6246 during fatigue testing at low pressure'. Together they form a unique fingerprint.Cite this
- APA
- Author
- BIBTEX
- Harvard
- Standard
- RIS
- Vancouver