In situ observations of crack formation in multi-filament Bi-2223 HTS tapes
摘要
High temperature superconducting tapes (BSCCO filaments embedded in Ag) were subjected to uniaxial tension in an environmental scanning electron microscope, allowing in situ observation of cracking of the ceramic filaments. The first cracks were found to appear in the ceramic filaments at a strain around 0.15%. More cracks formed with increasing strain. The cracks covered the entire thickness of the filament, but did not continue into the surrounding (ductile) Ag matrix. These `tunnel cracks' appeared somewhat zigzag, indicating intergranular cracking mode. At low strains, crack blunting occurred at the ceramic/Ag interfaces of the tunnel cracks. At higher strain `split cracks' formed at the tunnel cracks. The split cracks ran parallel with the ceramic/Ag interface just inside the ceramic layer.