Session: 19-02: Material Characterization by Ultrasonic waves

Paper Number: 98265

98265 - Characterisation of Macrozones in Titanium Alloys Using Ultrasonic Testing 

Titanium alloys (Ti-64) are widely used in the aerospace industry for their high strength-to-weight ratio and corrosion resistance. However, Ti-64 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 uncovered that the presence of macrozones (or microtextured regions) is a potential cause to 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 us with 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, 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 Ti-64 sample.

Presenting Author: Wei Yi Yeoh Imperial College London