Evaluation of Amorphous Diffusion Bonding by Nonlinear Ultrasonic Method

The characteristic of bond interface in amorphous diffusion bonding, of which evaluation is impossible by conventional method, was quantitatively evaluated by the second harmonic amplitude. Steel bars were bonded with Ni‐based amorphous film. Conventional ultrasonic method, e.g. the echo height reflected from bond interface, could not identify samples manufactured at different bonding temperatures 1050, 1150 and 1250°C. Therefore, nonlinear ultrasonic method was applied for distinguishing the difference of bond strength. The nonlinear ultrasonic method is to measure the higher harmonics generated by nonlinear stress‐strain relationship at weak bonds. Measurements were conducted in contact using piezoelectric transducers in through‐transmission. The fundamental and second harmonic wave frequencies are 5 and 10 MHz. To measure second harmonic wave amplitude, a commercial superheterodyne receiver and pulse inversion method were used. The pulse inversion method is the digital signal processing to extract only...