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

众所周知，适当的热处理可以在铜基体中产生共格的伽马铁或非共格的α-铁的细小沉淀颗粒。我们还知道，塑性变形会在共格的伽马-铁颗粒中诱发伽马*α马氏体相变。本研究的目的是考察这些颗粒对铜铁合金单晶在塑性应变控制下循环变形时疲劳行为和疲劳位错结构发展的影响。无论粒子的类型(相干或非相干)如何，都可以观察到循环硬化。没有循环软化的原因是，在循环变形的早期阶段，最初的共格伽马铁粒子以马氏体形式转变为非共格的α-铁。在任何试件中，循环应力-应变曲线中都存在所谓的平台区。然而，与在平台区观察到特征的梯形位错结构的铜单晶不同，铜-铁合金单晶中的位错更加不规则和缠绕。这表明弥散粒子对防止位错重排形成特征的疲劳位错结构有很强的作用。研究表明，与通常的共格弥散粒子不同，共格的伽马-铁粒子由于其可变性，在提高铜的抗疲劳性能方面非常有效。

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.