Reliability of electrodeposited components for fusion application: A process evaluation of the first kind

In a recently conducted test for assessing compatibility of accelerator grid of Neutral beam 1 for their performance at 150 C, failure has been evidenced across an electrodeposited (ED) bond layer, which forms a vacuum boundary with cooling medium. This happens to be the first instance where an electrodeposited bond has been subjected to Hot Helium Leak test under operational conditions of temperature (150 C) and pressure (>2MPa), according to the ITER specifications. Presently there exists no recommended procedure for carrying out an assessment of the bond integrity for electrodeposited surfaces and also no codes are presently available to qualify the process compatibility for the operational requirements including application at around 150 C. Therefore, to arrive at the root cause, it was necessary to undertake a systematic evaluation study to identify the root cause and establish the adhesion characteristics at room as well as operational temperatures. This also serves the objective to assess and to arrive at an understanding of the possibility of recommending a metric for the strength parameters for such bonds. To carry out this assessment, multiple electrodeposited samples ~20, were drawn under different bath conditions. These samples have been subjected to a specially designed test procedure in order to arrive at an assessment of the strength parameters for the bond, the failure of which is considered to be the root cause. Hence, the present study is purported to present itself as a procedure for evaluation of this important manufacturing process. This is possibly first such initiative of its kind. Samples were prepared under three different bath conditions with the parameter variation for electrolyte composition, additives, electrical parameters, time, temperature and pH. Adhesion, being one of the major area of consideration for the pressure application, a specific test, called 'Push' test has been configured (Fig. 1) in such a way that, it simulates the operational scenario and thus evaluate the stress on the bond area in the operational condition. The most important element of this test, is in the identification of procedure that, would test the performance of the bond for the thinnest cross section of surface contact of the deposit with the base material.