[3B4] Characterising microtexture regions using model-based ultrasonic array analysis
D Harra, K Tant, E Mohseni, A Gachagan and M Tabatabaeipour
University of Strathclyde, UK
Titanium alloys are extensively used across diverse industries such as aerospace, automotive, medical and consumer goods, owing to their exceptional strength-to-weight ratio, corrosion resistance and biocompatibility. The achievement of optimal mechanical properties heavily relies on the presence of a fine-grained microstructure devoid of localised textures. However, the manufacturing process of the near α-phase titanium alloy Ti-6Al-4V is susceptible to the influence of mechanical and thermal processes, which can induce the formation of microtexture regions (MTRs). Within these regions, large contiguous crystals exhibit a singular preferential orientation, thereby serving as potential sites for crack initiation. This phenomenon renders the material more susceptible to fatigue and consequently reduces the lifespan of the component. As a result, there is a continuous demand within the industrial sector for non-destructive evaluation techniques that enable the characterisation of the microstructure in terms of grain size, orientation and distribution, as well as the detection of macrotextures.
This study presents a framework for the generation of synthetic polycrystalline microstructures incorporating a singular elliptical region of constant orientation, which represents an MTR. The paper leverages the power of modelling tools to generate synthetic polycrystalline microstructures and study ultrasonic wave propagation within these domains to discover a relationship between ultrasonic wave characteristics and MTRs to localise and characterise them. To this end, synthetic polycrystalline microstructures incorporating a singular elliptical region of constant orientation, which represents an MTR, were generated. These microstructures were subsequently imported into the OnScale finite element (FE) software to enable two-dimensional modelling of ultrasonic wave propagation through the microstructure. The study used both through-transmission (TT) and pulse-echo (PE) ultrasonic array configurations. Circular waves traversed the domain, capturing data on both the opposite side and at the transmission point. Two cases were simulated: (a) where the microstructure displayed statistical isotropy; and (b) where the microstructure included an elliptical MTR measuring 4.5 mm × 0.5 mm.
For the assessment, an ultrasonic inspection on a 10 mm2 block of titanium was simulated. The grain structure of the material was modelled using two eight-element arrays with an element pitch of 1 mm and a test frequency of 10 MHz on each side of the sample and exhibited an average grain size of 50 microns. Full matrix capture (FMC) was used to acquire data from the simulated configuration. Time-of-flight (TOF), signal attenuation and backscattered noise amplitude were computed across all transmit/receive combinations and analysed for MTR attributes. Through statistical analysis, matrices for each of the three ultrasonic characteristics were obtained that allowed for the determination of which characteristic was most sensitive to the MTR in terms of MTR localisation.
This study presents a framework for the generation of synthetic polycrystalline microstructures incorporating a singular elliptical region of constant orientation, which represents an MTR. The paper leverages the power of modelling tools to generate synthetic polycrystalline microstructures and study ultrasonic wave propagation within these domains to discover a relationship between ultrasonic wave characteristics and MTRs to localise and characterise them. To this end, synthetic polycrystalline microstructures incorporating a singular elliptical region of constant orientation, which represents an MTR, were generated. These microstructures were subsequently imported into the OnScale finite element (FE) software to enable two-dimensional modelling of ultrasonic wave propagation through the microstructure. The study used both through-transmission (TT) and pulse-echo (PE) ultrasonic array configurations. Circular waves traversed the domain, capturing data on both the opposite side and at the transmission point. Two cases were simulated: (a) where the microstructure displayed statistical isotropy; and (b) where the microstructure included an elliptical MTR measuring 4.5 mm × 0.5 mm.
For the assessment, an ultrasonic inspection on a 10 mm2 block of titanium was simulated. The grain structure of the material was modelled using two eight-element arrays with an element pitch of 1 mm and a test frequency of 10 MHz on each side of the sample and exhibited an average grain size of 50 microns. Full matrix capture (FMC) was used to acquire data from the simulated configuration. Time-of-flight (TOF), signal attenuation and backscattered noise amplitude were computed across all transmit/receive combinations and analysed for MTR attributes. Through statistical analysis, matrices for each of the three ultrasonic characteristics were obtained that allowed for the determination of which characteristic was most sensitive to the MTR in terms of MTR localisation.
