INVESTIGATION OF QUALITY OF HIGH-RESISTIVE COATINGS OF SUPERCONDUCTING WIRES WITH ACOUSTIC-EMISSION METHOD

Mechanism and kinetics of fracture of electrolytic chrome coatings on multifilamentary Nb3Sn-based superconductoring wire have been investig ated with the methods of acoustic emission (AE) and electron microscop y when developing superconductors for the ITER magnetic system. Coatin gs 1, 3, and 8 mu m thick of the following three types were obtained b y varying the electrolyte composition and the mode of precipitation pr ocess: milk chrome (Cr), hard CT and black Cr. The detected acoustic s ignal and analysis of AE spectra processed in digital form with a spec ially designed analyzer of AE signals. Milk Cr coatings are shown tb h ave the greatest crack resistance at any coating thickness, the same i s for black Cr but at thickness of 1 to 3 mu m. In these coating the m icrocracks formation is going by the ductile mechanism. Hard Cr coatin g have the least resistance to brittle cracks at any thickness.