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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.

Micrometric size rods have been fabricated via pulsed laser deposition in vacuum from boron carbidetargets using nanosecond pulses of 1064 and 266 nm and room temperature Si (1 0 0) substrates. Mor-phological, structural and chemical characterization of the microrods was made by applying scanningelectron microscopy, focussed ion beam microscopy coupled to secondary ion mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. Ablation at 1064 nmfavours the formation of microrods with high aspect ratio, sharp edges and pyramidal tips, typically 10 mlong with a cross section of around 2 m × 2 m. Differently, at 266 nm the microrods are of smaller sizeand present a more globular aspect. The analyses of the microrods provide information about their crys-talline nature and composition, based on a mixture which includes boron, boron oxide and boron carbide,and allows discussion of the wavelength dependent growth mechanisms involved.