Aims and objectives: 

The project aims to characterise critical microstructures within engineering metals using ultrasound. This encompasses both the grain texture and volumetric sizes of these microstructures. Finally, it is hoped that an understanding of the physics of the wave behaviours will facilitate the development of a method for industrial application. 

NDT problem to be solved: 

Most metals are polycrystalline, and their critical performances are determined by the grain microstructures. The NDE group at Imperial College has developed a breakthrough methodology to extract volumetric texture from the speeds of compressional ultrasound. It has been validated on a conventional water-bath system, which, in addition, has produced experimental evidence that the shear waves propagating through a metal sample are strongly affected by the microstructures. The amplitudes of the shear waves correlate with the grain sizes in the propagation direction, and they vary significantly when the waves propagate in different directions in 3D, which indicates the exciting possibility to simultaneously evaluate the texture and the volumetric morphologies of the microstructures non-destructively from the same ultrasound setup. 

Progress so far: 

Up until now, a double-through transmission setup was used to experimentally determine ultrasonic transmission data for several Ti-6Al-4V samples in all possible orientations in space. Using an already implemented algorithm and from a single set of experimental measurements, it is possible to calculate the polycrystal velocity profile, as well as the attenuation profile of both longitudinal and shear waves. The longitudinal velocity profile can also be used to predict the texture of that sample and, in the future, it is hoped that the attenuation profile of shear waves can be used to calculate the volumetric morphology of the sample microstructures.