[6A4] Characterisation of macrozones in titanium alloys using ultrasonic testing
W Y Yeoh
Imperial College London, UK
Titanium alloys (Ti64) are widely used in the aerospace industry for their high strength-to-weight ratio and corrosion resistance. However, Ti64 has been shown to be susceptible to cold dwell fatigue, a failure mode that causes significant reductions in fatigue life. Research over the past years revealed that the presence of macrozones (or microtextured regions) is a potential cause of the onset of cold dwell fatigue. Macrozones refer to clusters of grains having similar preferential orientations and are formed from larger recrystallised grains that are not broken down during the manufacturing process. Conventional inspection methods such as electron backscatter diffraction (EBSD), which are capable of evaluating the macrozones, are generally destructive, time-consuming, costly and they only identify characteristics at an exposed surface. Hence, there is a need to characterise these macrozones non-destructively. Past research has demonstrated the potential of using ultrasonic testing for macrozone characterisation, with the variation of ultrasound attenuation, backscatter and velocity in the presence of macrozones. However, due to the complexity of the microstructure, some physical phenomena that were observed are still not well understood.
In this study, we propose the use of finite element (FE) polycrystalline models to provide a means to systematically study the wave-macrozone interaction. Through this investigation, performed using 2D models, we are able to identify important correlations between macrozone characteristics (size, shape and texture) and ultrasound responses (attenuation, backscatter and velocity). The observed behaviours are then validated experimentally and we will also highlight how this understanding can aid with the characterisation of macrozones in a Ti64 sample.
In this study, we propose the use of finite element (FE) polycrystalline models to provide a means to systematically study the wave-macrozone interaction. Through this investigation, performed using 2D models, we are able to identify important correlations between macrozone characteristics (size, shape and texture) and ultrasound responses (attenuation, backscatter and velocity). The observed behaviours are then validated experimentally and we will also highlight how this understanding can aid with the characterisation of macrozones in a Ti64 sample.
