Creep in a Cu-14at.%Al solid solution alloy at intermediate temperatures and low stresses

The helicoid spring specimen technique was applied to investigate creep of a Cu-14at.%Al solid solution alloy at homologous temperatures from 0.54 to 0.65 and stresses ranging from 0.2 to 5.0 MPa. At stresses lower than about 1 MPa, Coble-type creep was found to dominate, associated with a threshold stress apparently independent either of grain size or of temperature. At stresses above about 1 MPa, another creep mechanism obviously contributes to the measured creep rate. This mechanism operating in parallel with Coble creep is characterized by the fact that the steady state creep rate is proportional to the second power of stress and inversely proportional to the third power of grain size and is most probably grain boundary diffusion controlled. This mechanism, called the non-viscous mechanism in the present work, is similar to that considered by Gifkins and Kaibyshev et al. to result from the motion of grain boundary dislocations (grain boundary sliding) accomodated by slip of lattice dislocations in thin layers along grain boundaries, although these workers assumed the creep rate to be inversely proportional not to the cube but to the square of the grain size.