Addressing the challenge of characterisation across the length scales

One of the biggest issues facing the microscopy of materials is the length scale issue. Components that are used in every day life are typically on the length scale of millimetres to several meters. For example, the aluminium alloy wing skin on a modern passenger aircraft is tens of meters long. The high strength steel bars used for impact resistance to protect passengers in cars are typically around a meter in size. There are, of course, many examples of finer scale artefacts of huge technological importance, including among many, computer chips and catalysts. Irrespective of which artefact is considered, the over-riding conclusion is that the properties are determined by the microstructure; the microstructure that is important is at the atomic or near atomic dimensions. Taking the example of the aluminium wing skin, the strength is derived from strengthening precipitates typically 10-100nm in size. The exact strength obtained is a direct function of the interface between the precipitates and the matrix- i.e. the local atomic structure. So, there is clearly a problem: to understand the properties of the component (say 10 meters long) we need to understand the atomic scale microstructure (10-10 m), i.e. 100 billion times difference in length scale! Is what we examine at 10-10 m in any way representative of all areas of the component? In the absence of a technique that will really allow an answer to this problem, microscopists have had to ?do the best you can?. We remain some way off a complete solution (although techniques such as synchrotron radiation and neutron diffraction help).