Stress and temperature dependence of creep in Alloy 600 in primary water

The stress and temperature dependence of creep of commercial nickel-base Al loy 600 was investigated through constant load, step-load, and step-tempera ture creep tests in deaerated primary water containing 40 to 60 cc/kg hydro gen. To analyze creep rates for Alloy 600 in the mill-annealed (MA) conditi on, effective stresses were estimated using applied stresses and instantane ous strains. The apparent activation area was determined to be V by the mul tiple regression analysis of creep rates. The apparent activation energy fo r creep has a weak stress dependence and was determined to lie between 188 and 281 kJ/mole for the effective stress range of 117 to 232 MPa. Creep rat es were better correlated with effective stress than applied stress and the stress exponent of Alloy 600 MA was determined to be 2.2 at 337 degreesC a nd 5.1 at 360 degreesC. The magnitudes of the stress exponent, activation e nergy, and activation area can be interpreted to support a creep mechanism controlled by dislocation-climb and nonconservative motion of jogs in comme rcial Alloy 600 MA. The activation area agreed with that determined from ca rbon in solution, implying thermally activated dislocation glide as another possible creep mechanism.