On the Differentiation of Diffusion Bond Strength Using the Total Acoustic Energy Reflected from the Bond

Abstract

Diffusion bonding is a well known metallurgical joining technique which allows similar and dissimilar materials to be bonded together in near net shape. Due to this feature, wider use of this technique is now being made, especially in aerospace industries. Therefore, the differentiation of diffusion bonds with little variation in their acoustic response is of critical importance since relatively significant changes in bond strength may be a consequence. The challenge at the present time is to find ultrasonic techniques that are sensitive enough to detect small changes at the original interface. A number of diffusion bonds has been made that shows only a slight variation in a single frequency reflection measurement with significant changes in the bond strength. Present work indicates that an energy measurement can differentiate the strength achieved in these diffusion bonds. This evaluation procedure is based on Parseval’s theorem [1] which states that the energy in the time domain is proportional to the energy in the frequency domain. The results of earlier measurements on Cu against Cu [2,3] are reanalyzed and compared with those obtained recently on Cu against Ni [4,5] as well as Ti-6A1-4V against Ti-6A1-4V. It is found that the sensitivity of the normalized energy measurements to changes in the bond strength is enhanced over single frequency reflection coefficient measurement and that the energy reflected is mainly originating at the voids still present in the original interface.