An evaluation of mechanical properties of YBaCuO and (Sm,Gd)BaCuO bulk superconductors using Vickers hardness test at cryogenic temperatures

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
_IC
at cryogenic temperatures was calculated. The K
_IC
of YBaCuO and (Sm,Gd)BaCuO decreased with decreasing temperature to 0.6 MPa√m and 0.8 MPa√m, respectively.