Understanding the "blue spot": sodium chloride hot salt stress-corrosion cracking in titanium-6246 during fatigue testing at low pressure

E. A. Saunders, T. P. Chapman, A. R.M. Walker, T. C. Lindley, R. J. Chater, V. A. Vorontsov, D. Rugg, D. Dye

Research output: Contribution to journalArticle

3 Citations (Scopus)

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.

LanguageEnglish
Pages2-20
Number of pages19
JournalEngineering Failure Analysis
Volume61
DOIs
Publication statusPublished - 1 Mar 2016

Fingerprint

Fatigue testing
Sodium chloride
Stress corrosion cracking
Titanium
Sodium Chloride
Salts
Fatigue of materials
Fractography
Titanium alloys
Crack initiation
Fracture mechanics
Atmospheric pressure
Gas turbines
Energy dispersive spectroscopy
Contamination
Engines
Air

Keywords

  • fractography
  • hot salt stress-corrosion cracking
  • novel technology application in failure analysis
  • pressure implication
  • titanium-6246
  • fatigue tests
  • stress-corrosion cracking (SCC)

Cite this

Saunders, E. A. ; Chapman, T. P. ; Walker, A. R.M. ; Lindley, T. C. ; Chater, R. J. ; Vorontsov, V. A. ; Rugg, D. ; Dye, D. / Understanding the "blue spot" : sodium chloride hot salt stress-corrosion cracking in titanium-6246 during fatigue testing at low pressure. In: Engineering Failure Analysis. 2016 ; Vol. 61. pp. 2-20.
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Understanding the "blue spot" : sodium chloride hot salt stress-corrosion cracking in titanium-6246 during fatigue testing at low pressure. / Saunders, E. A.; Chapman, T. P.; Walker, A. R.M.; Lindley, T. C.; Chater, R. J.; Vorontsov, V. A.; Rugg, D.; Dye, D.

In: Engineering Failure Analysis, Vol. 61, 01.03.2016, p. 2-20.

Research output: Contribution to journalArticle

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T2 - Engineering Failure Analysis

AU - Saunders, E. A.

AU - Chapman, T. P.

AU - Walker, A. R.M.

AU - Lindley, T. C.

AU - Chater, R. J.

AU - Vorontsov, V. A.

AU - Rugg, D.

AU - Dye, D.

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