Determination of Internal Strain and Residual Stress in Wires HTSC-2 Using Neutron Stress Diffractometry

The main task in creating high-current cables based on HTSC-2 wires for thermonuclear installations is to maximize the resistance of the cable to mechanical stresses. Its solution is directly related to the strength of the HTSC-2 wires, which is determined by the supporting steel tape substrate. Therefore, the diagnosis of stresses in the carrier tape is of particular importance. The only direct method for measuring internal strains and residual stresses inside a material is neutron stress diffractometry. However, its application to thin steel tapes is limited by the intensity of the neutron beam. In this study, by the example of a 100-µm-thick AISI 310S stainless steel tape applied as a substrate in manufacturing HTSC-2 wire at the National Research Center Kurchatov Institute, it is shown that this restriction can be circumvented if the measurements are carried out on stacks of tapes similar to HTSC stacks in high-current cables. In this approach, the diagnosis with neutron stress diffractometry is performed on the AISI 310S tape as delivered, after mechanical polishing, and after applying a YSZ buffer layer. The high sensitivity of the method is noted, which makes it possible to determine the crescent-shaped deformation of the tape and the degree of its stretching after mechanical polishing and to measure the residual stresses arising during the deposition of the YSZ layer. The results obtained show that the neutron stress diffractometry has good prospects for diagnosing internal strains and stresses in HTSC stacks of high-current cables.