INFLUENCE OF THERMAL CYCLING ON THE MECHANICAL-PROPERTIES OF VGF MELT-TEXTURED YBCO

Hardness and fracture toughness of VGF melt-textured Y1Ba2Cu3O7-x are investigated as well as the influence of thermal cycling on these prop erties. The hardness is found to be load dependent. Introducing a true hardness, Ho, concept, leads to a load independent isotropic hardness , H-0 = 5.5-6.5 GPa. The fracture toughness, K-1C, is isotropic and am ounts to 1.5-2.0 MPa root m. The absence of any anisotropy in K-1C can be ascribed to the homogeneous distribution of fine Y2Ba1Cu1O5 inclus ions. Thermal cycling changes the measured hardness but does not affec t the true hardness. After thermal cycling the fracture toughness drop s substantially and the threshold for fracture decreases. (C) 1997 Els evier Science B.V.