Quantitative polarised light microscopy of metals

Abstract

For most engineering metals a material’s crystal structure can play a significant role in its performance in service. This is particularly relevant for materials that display pronounced differences in their physical properties depending on the arrangement and orientation of these crystals. Examples of such alloys are titanium and aluminium which are employed in a wide range of applications from medical to structural. Conventionally, the crystal structure of these materials is measured using various X-ray and electron diffraction techniques. Unfortunately, these are generally costly, time-consuming and therefore impractical in an industrial quality assurance setting. On-going research at Swansea University has demonstrated that a simpler alternative offers a solution to this problem. The project aimed to build on this research to develop a semi-automated method to conduct this analysis. The work involves extensive characterisation of various materials using optical and electron microscopes; this will focus on the direct correlation of electron diffraction data to polarised light microscopy. The project will concentrate on developing this apparatus to provide high quality, reliable information on material crystal structures. Electron Backscatter Diffraction (EBSD) is the most well-known approach to investigate the crystal orientation of polycrystalline material. However, when compared to optical microscopy EBSD is an expensive approach, very time consuming and complex laboratory technique needed to plot a crystal orientation map. The research offers a novel approach for optically anisotropic (titanium) and isotropic (aluminium) material to plot the crystal orientation map. The aim of the research is to offer a simpler, cheaper, and less time-consuming method which can be affordable by a middle-class company to have access to the crystal orientation map.