Annealing of cold worked two-phase Zr-2.5 Nb—Associated microstructural developments

Coarsening of second phase in a two-phase Zr–2.5Nb: On the role of phase boundaries

“…The selected starting structure came from the first pilgered stage of the Indian processing route of Zr-2.5Nb pressure tube [1,2,[6][7][8]. The alloy, chemical composition listed in Table 1, is typically cast, forged and then hotextruded in a two-phase field.…”

“…The alloy, chemical composition listed in Table 1, is typically cast, forged and then hotextruded in a two-phase field. This was then subjected to a two-stage pilgering, with intermediate annealing, so that the desired microstructure and crystallographic texture were obtained [1,[6][7][8]. A first pilgered sample, with 58% reduction in wall thickness, provided the starting material for the present study.…”

“…For example, pressure tubes in pressurized heavy water reactors (PHWRs) are usually made of this alloy [1][2][3][4]. The fabrication of the actual components [1,2,[6][7][8][9][10] involves different stages of thermo-mechanical processing. The microstructure of a finished pressure tube consists of deformed, but stress-relieved, hexagonal a grains with 10-15% lamellar body-centered cubic (bcc) b [6,8].…”

“…The fabrication of the actual components [1,2,[6][7][8][9][10] involves different stages of thermo-mechanical processing. The microstructure of a finished pressure tube consists of deformed, but stress-relieved, hexagonal a grains with 10-15% lamellar body-centered cubic (bcc) b [6,8]. This microstructure and its stability during service are of critical importance [11,12].…”

“…The second-phase b is typically located at the a-a grain boundaries-as nearly continuous filaments in the coldworked state or in a more globularized form at the end of primary recrystallization [1,8]. The latter provides an interesting starting structure for a grain and particle coarsening study, where both primary and second phases may grow.…”