Investigation of quality of high-resistive coatings of superconducting wires with acoustic emission method

The mechanism and kinetics of fracture of electrolytic chrome coatings on multifilamentary Nb/sub 3/Sn-based superconducting wire have been investigated with the methods of acoustic emission (AE) and electron microscopy when developing superconductors for the ITER magnetic system. Coatings 1, 3, and 8 /spl mu/m thick of the following three types were obtained by varying the electrolyte composition and the mode of precipitation process: milk chrome (Cr); hard Cr; and black Cr. The detected acoustic signal and AE spectra were processed in digital form with a specially designed analyzer of AE signals. Milk Cr coatings are shown to have the greatest crack resistance at any coating thickness, the same is for black Cr, but at thickness of 1 to 3 /spl mu/m. In these coating the microcracks formation is going by the ductile mechanism. Hard Cr coating have the least resistance to brittle cracks at any thickness.<
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