Transient creep behavior and dislocation cell structure development during creep-fatigue deformation of fully annealed Cu-Cr-Zr alloy

Creep-fatigue tests of Cu-0.7Cr-0.09Zr (mass%) alloy, which include stress-holding-type creep and strain-controlled fatigue, were conducted at elevated temperatures. A simple creep test was also carried out in order to compare the results with the results of the creep-fatigue test. The creep strains accumulated during creep deformation in creep-fatigue and simple creep tests were 310% and 12%, respectively. Such a large difference was due to the stacking of normal/inverse-transient creep in the creep-fatigue test. A dislocation cell structure smoothly developed in the simple creep test, whereas the cell intermittently developed in the creep-fatigue test because compressive plastic deformation immediately after creep partly broke apart the cell walls and prevented the cell structure from smoothly developing. Compressive stresses necessary for -1.5% strain were changed as cycling progressed in the creep-fatigue test. A much higher compressive stress would introduce a much higher dislocation density immediately before creep deformation. At the start of creep, these dislocations recovered and their number gradually decreased, which resulted in the appearance of inverse-transient creep.