本文系统地研究了Nb单晶循环变形的应力-应变关系及位错组态。和单向变形相比较,单晶在循环变形后都有应力不对称现象,拉伸时的应力小于压缩时的应力。循环硬化曲线可以分成三个阶段:初始阶段、快速硬化阶段和饱和阶段。初始阶段位错组态为密集的位错网络和碎块状的位错圈。快速硬化阶段出现条带状的位错缠结。饱和阶段的位错组态为条带和条带之间的螺位错,塑性变形主要通过条带间的螺位错往复运动来实现。
Nb single crystals of both [321] and [110] orientations have been cy-clicly deformed in tension-compression at constant strain rate 8×10~(-4)s~(-1) over arange of plastic strain amplitudes between 10~(-3) and 10~(-4). The cyclic hardening, thechanges in shape of crystals and the asymmetry of stress have been studied. Thehardening curve can be divided into three stages, i. e. first, rapid-hardening andsaturated stage. In the first stage of cyclic hardening curve dominant features of dislocationconfigurations are high density networks and debris loops. In the rapid-hardeningstage the main feature is the formation of dislocation bundles. In the saturateda well defined bundle structure fully develops and between them it is filled withonly screw disloca tions and the imposed strain is accommodated mainly bythe motion of screw dislocations travelling to and from between the bundles.Three-dimention cell, two-dimention cell or bundle structures are summarized as thesaturated structures of bcc metals.
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