| The cyclic creep behaviour of Zircaloy-4 was investigated over the temperature range of 390∼430℃ (0.32 Tm-0.34 Tm) and the stress range of 15-18 ㎏/㎟ (147.1∼176.5 ㎫). Constant stress creep tests were carried out in the experiment. Square wave cyclic stress was chosen with the minimum stress equals to 10% of the maximum stress and frequency was 3 cpm. The stress exponents for the cyclic creep, n_c, were 7.59, 7.14, 6.79 and 6.48 at the temperature of 663, 678, 693 and 703K, respectively, The apparent activation energies for the cyclic Creep, Qc, were 68.59, 65.82, 63.01 and 59.74 ㎉/㏖ at the stresses of 15. 16. 17 and 18 ㎏/㎟, respectively. Cyclic creep rate was higher than static creep rate because of a cyclic creep acceleration. Larson-Miller parameter of zircaloy-4 under the cyclic creep conditions was obtained as P=(T+460) (log t_r+21). Transgranular fracture was dominated over the experimental range. |
|
