High temperature deformation of vertical gradient freeze method melt-textured Y1Ba2Cu3O7-x

The deformation behavior of melt-textured Y1Ba2Cu3O7-x (YBCO) prepared by t he vertical gradient freeze (VGF) method was investigated by high temperatu re deformation experiments at temperatures ranging from 850 to 950 degrees C. The experiments were performed in an atmosphere of pure oxygen under uni axial pressure with constant strain rates in the range from 1 x 10(-5) to 5 x 10(-4) s(-1). An analysis of the dependence of the steady state flow str ess on the strain rate and the deformation temperature reveals that the pre dominant deformation mechanism is dislocation glide and climb controlled by climb at Y-211 particles and that no significant grain boundary sliding oc curs. Furthermore, transmission electron microscopy observations of deforme d and undeformed samples support a deformation mechanism based on dislocati on movement. The total fracture strain, however, does not depend on the tem perature or strain rate. Scanning electron microscopy investigations of the fracture faces of samples deformed until fracture reveal that fracture doe s not occur within the Y-123 matrix but along platelet boundaries. An impro vement of the fracture behavior is expected by introducing large Y-211 part icles interconnecting neighboring platelets.