1. According to existing literature [21,22], when the applied stress exceeds a certain stress level, creep deformation in a fine-grained material is governed by dislocation slip instead of grain-boundary sliding. Thus, creep due to dislocation slip plays a dominant role in the deformation at 80 MPa, as shown in Fig;Creep tests above 80 MPa could not be performed because rupture occurred immediately after stress loading