Creep mechanism in Fe-1.8 At. Pct Mo alloy at high temperatures

Abstract

High temperature creep of Fe-1.8Mo alloy, the stress exponent,n, of which is about 4, has been studied to check whether then value can be a good indication of the creep mechanism or not. Creep tests were carried out at 1124 K under 5.9 to 39.2 MPa. After sudden stress increments during the steady-state creep, inverse-type transient creep curves were obtained with no instantaneous permanent strain. Mean internal stresses were determined by stress-transient dip-tests using a back extrapolation technique. The mean internal stress was obviously smaller than the applied stress. These results indicate that creep deformation of Fe-1.8Mo alloy under the present conditions is controlled by the viscous glide motion of dislocations, thoughn is not close to 3. Steady-state creep rates as well as the value ofn calculated from the Orowan-type equation using experimentally obtained values for every parameter, are in reasonable agreement with the observed ones. These findings suggest that classification of creep behavior according to then value is not appropriate in some cases for discussing mechanisms of high temperature creep.