Ultrasonic evaluation of TiAl and ⁴⁰Cr diffusion bonding quality based on time-scale characteristics extraction

To solve the problem of ultrasonic pulse-echo method in the evaluation of kissing bond and unbond in TiAl and ⁴⁰Cr diffusion bonding, a characteristics extraction algorithm was proposed. The algorithm was based on continuous wavelet transform to convert ultrasonic TiAl and ⁴⁰Cr diffusion bonding interface signals into time-scale domain. The ultrasonic tests were performed by an ultrasonic C-scan imaging system using a 10 MHz focused transducer. The time-scale amplitude and phase of the interface signals were calculated and analyzed to distinguish the kissing bond and the unbond from the perfectly bonded interface. The kissing bond can be detected by the scale-dependent amplitude combined with phase variation and the unbond can be measured by the opposite phase. The amplitude and phase characteristics were extracted to reconstruct the amplitude and phase characteristics images for TiAl and ⁴⁰Cr diffusion bonding specimens evaluation. The amplitude and phase characteristics images are effective in the evaluation of bonding quality.