Nondestructive Observation of Dislocation Structure using ECCI Method and Embryology of Fatigue Cracks.

使用 ECCI 方法无损观察位错结构和疲劳裂纹的萌芽。

• 批准号: 12450284
• 负责人: HASHIMOTO Satoshi
• 金额: $ 9.28万
• 依托单位: Osaka City University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450284/
• 关键词: Fatigue; ECCI Method; Dislocation Structure; PSB; Single Crystal; Nondestructive Observation; ECCI

Intragranular fatigue cracks are initiated frequently along the persistent slip bands (PSBs) at which cyclic plastic strains are localized. Dislocation structure of the PSB is characterized by a ladder-like structure which consists of dislocation wall and channel. Hence, by detecting this ladder-like dislocation structure, we can predict the fatigue crack initiation. However, a material must be shaped to a thin foil in order to observe the dislocation structure using a conventional TEM. In the present research project, we make attempt to perform nondestructive dislocation observation using Electron Channelling Contrast Imaging (ECCI) method, with a view to predicting the fatigue cracking.Copper single crystals having defined stress axes were prepared by the Bridgman method. The copper single crystals were cyclically deformed at a constant plastic strain amplitude γ_<p1>=2x10^<-3> until various numbers of cycles. Surfaces of the fatigued single crystals were observed by the ECCI method. … More During the cyclic deformation tests, we recorded shapes of hysteresis loops and calculated the Bauschinger energy parameter β_E from the hysteresis loop shape. It has been proposed that the β_E value became a local maximum when the PSBs begin to develop. In the single crystal having [123] tensile axis, the β_E value became a local maximum at 1200 cycle. The ECCI observations after 1500 cycles revealed band-like contrasts along a primary slip plane. On the other hand, no characteristic contrast could be detected at the ECCI observation at 500 cycles. When we observed the band-like contrast at a high magnification, the ladder-like dislocation structure where the wall spacing was about 1.4 μm. Being very similar to the PSB observed using the TEM, the observed band-like contrast must be the PSB structure in the vicinity of specimen surface. At the single crystal having [001] tensile axis, grid-like contrast was detected in the ECCI observation. It is likely that this contrast is attributed to the labyrinth dislocation structure which has been reported in TEM observation at the [001] tensile axis.From the abovementioned observations, we can suggest that the prediction of fatigue cracking is possible by detecting the PSB structure using the nondestructive ECCI observation. Less

晶内疲劳裂纹常沿着循环塑性应变集中的持久滑移带萌生。PSB的位错结构是由位错壁和位错沟道组成的阶梯状结构。因此，通过检测这种阶梯状位错结构，我们可以预测疲劳裂纹的萌生。然而，为了使用常规TEM观察位错结构，必须将材料成形为薄箔。在本研究项目中，我们尝试使用电子衍射对比成像（ECCI）方法进行非破坏性位错观察，以期预测疲劳裂纹。铜单晶在恒定的塑性应变幅γ_<p1>= 2 × 10 ~ 4下循环变形，<-3>直到不同的循环次数。用ECCI方法观察了疲劳单晶的表面。 ...更多信息 在循环变形试验中，记录了滞回曲线的形状，并由滞回曲线的形状计算了Bauschinger能量参数β E。当PSB开始发育时，β_E值出现极大值。拉伸轴为[123]的单晶在1200次循环时β_E值出现极大值。1500次循环后的ECCI观测结果显示，沿主滑移面沿着存在带状对比。另一方面，在500次循环的ECCI观察中未检测到特征对比度。在高倍率下观察带状衬度时，发现了壁间距约为1.4 μm的阶梯状位错结构。与透射电镜观察到的PSB非常相似，观察到的带状衬度必须是样品表面附近的PSB结构。在具有[001]拉伸轴的单晶中，在ECCI观察中检测到网格状对比度。这可能是由于在[001]拉伸轴上TEM观察到的迷宫状位错结构引起的，从上述观察结果可以看出，通过使用无损ECCI观察来检测PSB结构来预测疲劳裂纹是可能的。少