Quality evaluation of CuCrZr to SS diffusion joints using ultrasonic C-scan imaging technique

Plasma facing targets of the ITER divertor are structurally supported by 316L Stainless Steel (SS) to copper alloy (CuCrZr) joint. Dissimilar material joining such as SS to CuCrZr has been prepared using Gleeble 3800 machine with and without Nickel interlayer at various temperature regimes from 850 °C to 1000 °C with uniaxial pressure of 5MPa to 15MPa of holding time of 15 min to 30 mins. The quality of diffusion bonding was tested by an ultrasonic nondestructive method and evaluated in terms of interface bonding ratio. In the present work, Bond interface was examined by ultrasound of frequency 20MHz and the C-scan image of interface was obtained from both sides. The bonding ratio was calculated after the C-scan image was segmented into bonded region and non-bonded region based on an appropriate threshold. To obtain desired threshold, response of 2 mm dia. Flat Bottom Hole (FBH) up to CuCrZr to SS interface were taken in consideration. Different parameters such temperature, pressure and hold time have been evaluated in the diffusion process based on bonding ratio. The paper details the evaluation of SS to CuCrZr joints prepared in different diffusion conditions using ultrasonic C-scan imaging. (author)