Abstract
Vickers hardness properties of bulk superconductors have been investigated to estimate the mechanical properties of bulk materials. However, the test at cryogenic temperatures had not been conducted at all. Then we conducted Vickers hardness test on (001) plane of YBaCuO and (Sm,Gd)BaCuO bulk superconductors from 40 to 293 K. The hardness of YBaCuO and (Sm,Gd)BaCuO increased with decreasing temperature up to 19 000 MPa and 10 000 MPa, respectively. Furthermore, the cracks caused by the indentation were observed with SEM, and the fracture toughness K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IC</sub> at cryogenic temperatures was calculated. The K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IC</sub> of YBaCuO and (Sm,Gd)BaCuO decreased with decreasing temperature to 0.6 MPa√m and 0.8 MPa√m, respectively.
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