Fatigue Tests of Copper Single Crystals with Martensitically Transformable Small Dispersed Iron Particles

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It is known that proper heat treatment can produce coherent gamma-iron or incoherent alpha-iron fine precipitate particles in a copper matrix. It is also known that plastic deformation induces gamma*alpha martensitic transformation in the coherent gamma-iron particles. The purpose of this research is to examine the effects of these particles on the fatigue behavior and on the development of fatigue dislocation structure using Cu-Fe alloy single crystals.When Cu-Fe alloy specimens were cyclically deformed under plastic strain control. cyclic hardening was observed regardless of the type (coherent or incoherent) of the particles. The lack of cyclic softening is attributed to the fact that initially coherent gamma-iron particles transform martensitically into incoherent alpha-iron in the early stage of the cyclic deformation. In any specimen, the so-called plateau region was found to exist in the cyclic stressstrain curves. However, different from copper single crystals where the characteristic ladder dislocation structure is observed in the plateau region, dislocations were more irregular and tangled in the Cu-Fe alloy single crystals. This is indicative of the strong effect of dispersed particles on preventing the dislocation rearrangement to form characteristic fatigue dislocation structure.It is concluded from this study that unlike usual coherent dispersed particles, the coherent gamma-iron particles are very effective in improving fatigue resistance of copper because of their transformability.