Investigating Corrosion Using a High Speed AFM

There are significant safety and economic incentives to prevent the failure of structural
components in the nuclear industry[1]. Stainless steels are widely utilised in the nuclear
industry due to their amicable mechanical properties, however, they remain susceptible to
corrosion. Corrosion can be affected by a number of different factors and as such is
considered a highly complex process that is under much ongoing research[1]. Conjoint
corrosion and stressing of a metal or alloy, such as stainless steel, can result in stress
corrosion cracking (SCC)[2]. SCC results in significant degradation of component structural
strength whilst being difficult to identify in early stages, thus, SCC is often undetected prior
to failure[1]. The unpredictable nature of SCC calls for considerable research in the
mechanisms under which SCC and other forms of destructive corrosion occur, in steels and
other engineering alloys[2].
To investigate the processes by which corrosion occurs it is required that the sample is
imaged in controlled environments[3]. The field of atomic force microscopy (AFM) has
allowed for high-resolution imaging of structures and the measuring mechanical properties
at nanometre scales in varying gaseous, liquid and vacuum environments[4]. AFM has a
multitude of applications in materials, surface and biological sciences, and is considered one
of the most versatile and significant tools in nanoscience.
Significant effort to increase the imaging rate in recent years has allowed for dynamic
nanoscale events to be observed directly in real time[3]. The applications for high-speed
AFM (HS-AFM) are still relatively new and unexplored, and advances in HS-AFM
technology are ongoing. HS-AFM is a valuable tool for studying solid-liquid interfaces and
so has the potential for use in corrosion studies as it offers the opportunity to observe
dynamic nanoscale structures within in vivo conditions[3].
Laferrere et al. have previously demonstrated the use of the Bristol contact mode HS-AFM
to image nanoscale corrosion events, with parallel electrochemical control[3]. This work
demonstrated the ability of HS-AFM to image steels clearly in liquid environments and the
potential for new insights into corrosion at nanoscales[3]. The main aims of this PhD are to:
- Investigate the conditions that may lead to corrosion and SCC initiation, and to observe
and measure changes to the sample as corrosion takes place in real time using HS-AFM.
- Demonstrate the capability and potential of HS-AFM for applications in material and
corrosion science.

References:
[1] R. Cottis et al., Shreir's Corrosion. Elsevier Science, 2009.
[2] R. Cottis, National Physical Laboratory, Teddington, 2000. 1
[3] O. Payton et al., Nanotechnology, vol. 23, no. 20, p. 205704, 2012.
[4] H.-S. Liao et al., Rev. of Scientific Instruments, vol. 84, no. 10, p. 103709, 2013.