Structure and phase transformations during hot deformation of Bi(Pb)2223 high-Tc superconductor: II. Texture and microstructure

M.F. Imayev1, N.Y. Parkhimovich1
1Institute for Metals Superplasticity Problems RAS, 39, Khalturin Str., Ufa, Russia, 450001
Abstract
The effect of hot deformation by torsion under quasi-hydrostatic pressure at temperature T=865C with the twist rates of ω1 = 5.14·10-5 and ω2 = 1.85·10-4 rpm on the basal plane texture strength (factor F), the mean colony length of the matrix phase (L), the mean area (S) and the volume fraction (V) of particles of (Sr,Ca)14Cu24O41 and (Sr,Ca)2CuO3 secondary phases in a high-temperature superconducting ceramics based on the (Bi,Pb)2Sr2Ca2Cu3O10+d {Bi(Pb)2223} phase has been studied. The correlation between all of the mentioned parameters was observed: with increasing the twist angle the F, S and L values grew reaching the maximum and then decreased. During deformation incompatible intercolony sliding led to dislocation accumulation near the colony boundaries that resulted in their local migration and growth of the colony size. The growth of particles of secondary phases was caused by their coagulation/coalescence. The decrease in the F, S and L values after reaching the maxima was caused by dynamic recrystallization. Refinement of the secondary phase particles occurred due to intergrowth of the Bi(Pb)2223 phase colonies into the particles. It was found that with increasing the twist rate from ω1 to ω2 the L value increased. In the case of the torsion with the twist rate of ω2 the softening occurred only via the local migration of the colony boundaries, whereas in the case of the torsion with the twist rate of ω1 other relaxation mechanisms, such as diffusion creep and/or dislocation sliding, presumably operated as well. This is why the colony size was
Received: 29 October 2016   Revised: 09 November 2016   Accepted: 13 November 2016
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