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Tubular specimens of Zr-2.5Nb, 23 mm internal diameter, have been creep tested in-reactor at 570 K. Specimens were biaxially stressed by internal pressure, with transverse stresses from 103 to 317 MPa. Two separate experiments are reported (a) U-501/2 which has specimens quenched from 1045 K; cold drawn 2, 12, or 20 percent and aged at 773 K for 24 h, and (b) U-501/3 which has specimens extruded; cold drawn 10, 23, or 33 percent and stress relieved at 673 K for 12 h.
Creep curves for quenched, cold-worked, and aged specimens (U-501/2) are best fitted by linear creep rates beyond 1000 h. Increasing cold-work between quenching and aging decreases creep strength; material with 20 percent cold-work creep at about twice the rate of material with 2 percent cold-work at the same stress.
Creep curves for cold-drawn and stress-relieved specimens (U-501/3) are best fitted by a time exponent of about 0.8, that is, creep strain = A × Bt0.8 where t = time and A and B are parameters which depend on material and stress indicating that creep rate may be decreasing with time. Creep rates increase with amount of cold work: the specimens with 33 percent cold-work creep about 40 percent faster than those with 10 percent cold-work.
Increasing amounts of cold-work is, therefore, detrimental to the in-reactor creep strength of Zr-2.5Nb either after extruding or between (α + β)-quenching and aging.
zirconium, irradiation, zirconium alloys, tubes, internal pressure, creep strength, cold working
Atomic Energy of Canada Limited, Chalk River Nuclear Labs., Chalk River, Ontario