Investigation into metallic material grain size measurement from ultrasound backscattering using ultrasonic arrays

Abstract

Material grain size is a crucial factor influencing material properties. Conventional ultrasound transducers can be used to evaluate material grain size by measuring ultrasound backscattering from material microstructures. However, the stochastic nature of microstructural backscattering means that this method requires a large number of accurate immersion measurements in order to obtain an accurate result. This limits its applicability in certain scenarios, for example, on-line measurements in manufacturing or in service. Ultrasonic phased arrays offer a significant advantage in that a single array probe can focus an ultrasound beam on multiple points using different focal laws, potentially replacing the need for multiple measurements using a conventional transducer. This paper presents a novel approach where the classic Margetan's back scattering method is adapted to be used with full matrix capture data from an ultrasonic array. This is achieved either by using the array data to simulate A-scans from focused transducers or by using the total focusing method of imaging. It is shown that only a single full matrix capture dataset is required to measure material grain size, which increases measurement efficiency significantly and makes on-line measurements possible. The experimental validation was conducted on copper (EN1652). A good agreement is shown between the experimentally measured grain sizes from ultrasonic arrays and metallography.