CREEP-BEHAVIOR OF A NI-15CR SOLID-SOLUTION ALLOY AT LOW STRESSES AND INTERMEDIATE TEMPERATURES

Creep in a Ni-15Cr solid solution alloy at low stresses and intermedia te temperatures was investigated using the helicoidal spring specimen technique. The applied stress ranged from 0.2 to 5.0 MPa, the testing temperatures from 973 to 1123 K (homologous temperatures T/T-m from 0. 59 to 0.65, where T-m is the solidus temperature). The intercept grain size of creep specimens ranged from 47 mu m to 254 mu m. It was found that under the above conditions, viscous creep of the Bingham type oc curs, characterized by a low threshold stress which decreases with inc reasing temperature. The temperature, applied stress and grain-size de pendence of the steady-state creep strain rate can be interpreted in t erms of the transition from Coble diffusional creep to Harper-Dorn dis location creep controlled by dislocation core diffusion.