Methodology to evaluate the quality of diffusion bonded joints by ultrasonic method

Abstract

The quality and the soundness of diffusion bonded joints are generally evaluated by metallographic techniques, shear strength/tensile strength etc. Since these conventional methods are of destructive in nature, inspection on actual products is difficult. Therefore, non-destructive testing of diffusion bonded joints is required to evaluate the quality and to study the interphase properties. The ultrasonic A-scan method is suitable for diffusion bonded joints, since the sensitivity is 0.01-0.0001% as compared to the X-ray and Gamma ray methods having sensitivity of 0.5-2% only. In the present work, Ti-6Al-4V was bonded with Ti-6Al-4V at 1073 K at varying pressures of 1.6-4 MPa for a bonding time of 4 h so as to obtain bonds with interfaces of varying bonded area fraction. The shear strength of the bond is correlated with bonded area fraction which is measured using metallographic technique. The bonded samples are tested using ultrasonic flaw detector for the soundness of the joints. The ratio between the amplitude of interface wall echo to amplitude of surface echo is calculated and correlated with the bonded area fraction.