The rolls of precipitation particle on static creep behavior have been studied by many researchers, but that of cyclic creep has not been studied. The purpose of this work is to examine the effects of precipitate on static and cyclic creep behavior, using simple Cu-Co alloy system.
Cu-2.39% Co alloy specimens were solution treated and aged 3.6 ksec., 172.8 ksec. at 973K which produced fine and coarse precipitates respectively. To examine the roll of alloy matrix only, solution treated Cu-0.63% Co alloy specimens were also prepared.
These specimens were creep tested under static and cyclic stress with stress range of 60-150 Mpa at 550K Cu-0.63% Co Solid Solution specimens show cyclic acceleration, and dislocation cell structures were produced both static and cyclic creep tested specimen.
But Cu-2.39%Co specimens with fine precipitates show very small creep strain and cyclic retardation. Microscopies of these static and cyclic creep tested specimen reveal that cell was not formed and very small amounts of dislocation were produced.
Cu-2.39%Co specimens with coures precipitates show intermediate creep behavior, i.e. while cyclic acceleration and cell forming tendency are observed at high stress range, when stress is lowered, cyclic retardation is occurred.
From the above experimental results, it is concluded that when the dislocations form cell structure, climb controlled recovery of cell structure is the rate controlling process and cyclic stress enhances that process by cliclic acceleration mechanism discussed by many other researchers. But when the dislocation density is low and cell structure is not formed, rate controlling process is stress assisted climb which occurs at the particle interface, and cyclic stress decreases the average climb velocity and dislocation density, so cyclic retardation occurs.
