HIGH-TEMPERATURE DEFORMATION OF BRIDGMAN MELT-TEXTURED YBCO

Large bars were melt-textured using a modified Bridgman method. Neutro n diffraction analysis revealed the absence of any large angle grain b oundary and a FWHM of < 6 degrees. Smaller specimens cut from the bars were deformed under flowing oxygen in the temperature range 850-950 d egrees C applying strain rates from 1x10(-5) to 5 x 10(-4) s(-1). Thes e high temperature deformation experiments reveal that the predominant deformation mechanism is dislocation glide and climb controlled by cl imb at Y-211 particles and that no significant grain boundary sliding occurs. TEM investigations support a deformation mechanism based on di slocation movement, i.e. the dislocation density of the deformed sampl es is 2-3 orders of magnitude larger (n(D) > 10(9) cm(-2)) than that o f undeformed samples. Critical current density measurements clearly fo llow the induced microstructural changes. An improvement of the mechan ical properties is expected by introducing a bimodal Y-211 distributio n. (C) 1998 Elsevier Science S.A. All rights reserved.