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　　Topic: Characterising the early stages of crack development in environmentally assisted cracking 

　　Speaker: Dr. Alan Turnbull OBE FRS FREng 
　　　　　　　　National Physical Laboratory, UK 

　　Abstract: 

　　A very brief introduction to NPL and the research of the Electrochemistry Group will be presented initially. The main thrust of the presentation will be an overview of corrosion research to characterise the early stages of crack development in environment assisted cracking, focusing particularly on pitting, the pit-to-crack transition, and the measurement of crack growth rate in the small and long crack growth regime. The impact on corrosion and cracking of surface grinding induced changes in near–surface material and mechanical properties is highlighted, noting that awareness of this aspect in the corrosion community still remains limited. A major feature of the presentation is the remarkable insight into the evolution of small cracks from corrosion pits provided by advanced 3D imaging (XRT and FIB-SEM) and supportive finite element analysis. Finally, measurement of corrosion fatigue and stress corrosion small crack growth rate in 12 Cr steam turbine blade steel is presented and discussed in the context of the electrochemical crack size effect.