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Fatigue of Superplastic-Nanocrystals

超塑性纳米晶体的疲劳

基本信息

批准号：
09650715
负责人：
VINOGRADOV Alexei
金额：
$ 2.18万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650715/
关键词：
Ultrafine Grained Material UFG Superplasticity Fatigue Cyclic Deformation 繰返し変形ナノ結晶材料銅

项目摘要

In order to investigate fatigue mechanisms of ultrafine grained materials showing superplasticity at room temperature, we have examined cyclic stress-strain response of (1) single crystal specimens, (2) ultrafine grained copper produced by "Equal Channel Angular Extrusion (ECAE)" method, and (3) Pb-62%Sn and Zn-22%AI alloy fine-grained by the ECAE method.Fundamental aspects of the cyclic response in crystalline materials were investigated in single- and tr-crystal specimens of copper, Fe-Cr alloy and Fe-Ni-Cr alloy. The single crystal experiments revealed that fatigue deformation gives rise to formations of "persistent slip bands" (PSBs) at a certain range of plastic strain amplitude. The formation of the PSBs induced a drastic changes in Bauschinger energy parameter. In the fatigue tests on the tricrystal specimens, it was experimentally shown that residual stresses between adjoining grains is one-of sources for the Bauschinger effect in the crystalline materials.in the cyclic deforma … More tion tests on ultrafine grained copper to characterize basic feature of fatigued nano-crystals, following results were obtained. The stress amplitude of the copper fined-grained by the ECAE method became up to 250 MPa. The Bauschinger effect was also significantly high. However, this kind of excellent property of the ultrafine grained copper was very sensitive to heat treatment : both the Stress amplitude and the Bauschinger effect were apparently reduced by an annealing at 200ﾟC.In the monotonic tensile tests, both the Pb-Sn and Zn-Al specimens showed large elongations even at room temperature. These two materials also showed significant strain-rate dependence of flow stress. In the cyclic deformation tests, the stress amplitudes in the Pb-Sn and Zn-Al alloys were almost saturated from the beginning of the experiments, although a cyclic hardening curve of the annealed copper was divided clearly into the hardening and saturation stages. The stress amplitude and the Bauschinger effect in the Zn-Al alloy apparently increased with increasing strain rate. On the other hand, the Pb-Sn alloy revealed no strain rate dependence of the stress amplitude and the Bauschinger effect. This tendency obtained in the cyclically deformed Pb-Sn alloy is completely different from the result in the monotonic- test. (The cyclic response of the annealed copper was -. independent of the strain rate as well as the yield stress under monotonic deformation.) The absence of the strain-rate dependence in the cyclically deformed Pb-Sn alloy can be attributed to the missing of thermally activated processes which are dominant in the monotonic deformation : the applied plastic strain was probably accommodated substantially by dislocation motion because the plastic strain amplitude is very low with compared to the monotonic deformation. On the other hand, the cyclic deformation in the Zn-Al alloy may involve the thermally activated processes such as dislocation climb and grain boundary diffusion. It is feasible that the plastic strain can not be accommodated only by the dislocation motion because the grain size of the Zn-Al was very small. Less

为了研究超细晶材料在室温下的超塑性疲劳机理，我们研究了（1）单晶试样，（2）等通道转角挤压（ECAE）法制备的超细晶铜，（3）用ECAE方法对Pb-62%Sn和Zn-22%Al合金进行了细晶化，研究了单晶和三晶材料循环响应的基本问题。铜、铁铬合金和铁镍铬合金的晶体试样。单晶实验表明，在一定的塑性应变幅范围内，疲劳变形会引起“持久滑移带”（PSB）的形成。PSB的形成引起了Bauschinger能量参数的剧烈变化。在三晶试样的疲劳试验中，实验表明，相邻晶粒间的残余应力是晶体循环变形中包申格效应的来源之一。materials.in ...更多信息对超细晶铜进行疲劳试验，以表征疲劳纳米晶的基本特征，得到以下结果。通过ECAE方法细晶化的铜的应力幅高达250 MPa。包辛格效应也非常高。然而，超细晶铜的这种优异性能对热处理非常敏感：200 ℃退火明显降低了应力幅和Bauschinger效应。在单调拉伸试验中，Pb-Sn和Zn-Al试样即使在室温下也表现出很大的伸长率。这两种材料也表现出显着的应变率依赖性的流动应力。在循环变形试验中，Pb-Sn和Zn-Al合金的应力幅从试验开始就几乎饱和，而退火铜的循环硬化曲线明显分为硬化和饱和两个阶段。Zn-Al合金中的应力幅和Bauschinger效应随应变速率的增加而明显增大。另一方面，Pb-Sn合金的应力幅和Bauschinger效应没有应变率依赖性。在Pb-Sn合金循环变形中得到的这种趋势与单调试验的结果完全不同。(The退火铜的循环响应为-。与应变速率以及单调变形下的屈服应力无关。在循环变形的Pb-Sn合金的应变率依赖性的情况下，可以归因于在单调变形中占主导地位的热激活过程的缺失：所施加的塑性应变可能基本上由位错运动来调节，因为塑性应变幅度与单调变形相比非常低。另一方面，Zn-Al合金的循环变形可能涉及位错攀移和晶界扩散等热激活过程。由于Zn-Al合金的晶粒尺寸很小，仅依靠位错的运动是不能容纳塑性应变的。少