Orientation imaging using spatially resolved acoustic spectroscopy

The term 'orientation imaging microscopy' describes generic techniques for imaging the orientation of crystalline structures of heterogeneous media. Typically, scanning electron microscope techniques are used, such as electron backscatter diffraction or transmission electron microscopy. We have developed an acoustic technique that can perform equivalent measurements. The key to enabling a practical acoustic method is spatially resolved acoustic microscopy (SRAS), a robust laser ultrasonic technique for quantitatively determining the surface acoustic wave velocity at a high spatial resolution. Here we present quantitative determination of crystallographic orientation of large nickel grains by comparing the measured SAW velocity in multiple propagation directions, with a data base of calculated velocity surfaces for all orientations. As well as discussing the method of determining the crystallographic orientation details are also presented of the recent advances in the capabilities of the latest generation of instrumentation, including significant increase in the data acquisitions rate and the reduction in size and complexity of the SRAS instrument itself.