Atomic force microscopes (AFMs) are capable of high-resolution mapping of structures and the measurement of mechanical properties on nanometre scales within gaseous, liquid and vacuum environments. The contact mode high-speed AFM (HS-AFM) developed at Bristol Nano Dynamics Ltd. operates at speeds that are orders of magnitude faster than conventional AFMs, and is capable of capturing multiple frames per second. This allows for direct observation of dynamic events in real-time, with nanometre lateral resolution and subatomic height resolution. HS-AFM is a valuable tool for the imaging of nanoscale corrosion initiation events, such as metastable pitting, grain boundary (GB) dissolution and short crack formation during stress corrosion cracking (SCC). Within this study HS-AFM was combined with SEM and FIB milling to produce a multifaceted picture of localised corrosion events occurring on thermally sensitised AISI 304 stainless steel in an aqueous solution of 1% sodium chloride (NaCl).HS-AFM measurements were performed in situ by imaging within a custom built liquid cell with parallel electrochemical control. The high resolution of the HS-AFM allowed for measurements to be performed at individual reaction sites, i.e. at specific GB carbide surfaces. Topographic maps of the sample surface allowed for accurate measurements of the dimensions of pits formed. Using these measurements it was possible to calculate, and subsequently model, the volumes of metal reacting with respect to time, and so the current densities and ionic fluxes at work. In this manner, the local electrochemistry at nanoscale reaction sites may be reconstructed.

The microstructure of the oxide scale and metal bulk in ferritic 9Cr-1Mo steel was observed in order to explore the oxidation and carburisation mechanisms upon exposure to a CO2 gas environment at high temperature and high pressure. An experimental 9Cr-1Mo steel sample that had been oxidised at 580ºC for more than 165000 hrs in the coolant gas consisting primarily of CO2 gas was analysed. In order to elucidate the oxidation characterisation, scanning Raman spectrometry was used to analyse the oxide close to the metal/oxide interface. Carbon was found to be deposited in the spinel layer. The microstructure and the distribution of elemental chemical composition were examined and analysed using optical and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis. Raman signals from the oxide scale were analysed in order to explore the possibility of deriving strain information close to the oxide-metal interface. The results are discussed with relation to understanding the mechanisms of oxidation and carburisation which aim to underpin extension of the service life of components fabricated from this steel.