Study on Fatigue Slip Bands and Nucleation of Microcracks by Using Scanning Tunneling Microscope

建立了扫描隧道显微镜(STM)，其最大扫描面积为7.1um×7.4um，最大高度分辨率为0.1 nm，并观察到了循环应变形变的高纯金、银、铜的疲劳滑移带。利用特制的4点循环弯曲机，在1500或2000微米的恒应变范围内，对观察到的薄板试件在空气中进行3000或5000次循环变形，从疲劳金的STH图像中将滑移带分为两种类型。也就是说，观察到高度为50-200 nm、间距为500-2000 nm的粗滑移带和高度为50-80 nm、间距为50-300 nm的细滑移带。此外，随着循环次数的增加，粗滑移带的间距和高度有减小的趋势，而细滑移带的影响不明显。粗滑移带可以看作是。细滑移带的聚集。另一个令人感兴趣的是，沿着淤泥线观察到了类似半圆形挤压的图案。静态弯曲变形的滑移带的STM图像显示，它们的高度和间距分别为20~30 nm和150~500 nm，与疲劳Au样品的滑移带相比，它们的分布更加均匀。在疲劳银的情况下，与银相比，高度的变化略小，它们的高度和间距分别为15-30 nm和200-400 nm。不幸的是，我们无法观察到铜的扫描隧道显微镜图像。这被认为是由于氧化层的形成而找不到进行STM观察的适当条件。在上述结果的基础上，对进一步取得的成果进行了讨论。

A Scanning Tunneling Microscope (STM) with a maximum scanning area of 7.1mum X 7.4mum and a maximum height resolution of 0.1 nm was built in our laboratory, and fatigue slip bands of cyclically strain deformed high purity Au, Ag or Cu were observed with this STM. The observed thin plate specimens were cyclically deformed in air at a constant strain range of 1500 or 2000 muepsilon for 3000 or 5000 cycles by using the specially built 4 points cyclic bending machine.From the STH images of fatigued Au, slip bands were divided into two types. That is, the coarse slip bands with the height of 50-200 nm and the spacing of 500-2000 nm and the fine ones with the height of 50-80 nm and the spacing of 50-300 nm were observed. Furthermore, there existed a tendency that the spacing as well as the height of the coarse slip bands decreased as the number of cycles increased, while no effect was observed in the fine slip bands. The coarse slip bands could be regarded as. the aggregation of the fine slip bands. Another point of interest was that semicircular extrusion like patterns were observed along the silp lines. The STM images of the slip bands deformed by static bending revealed that their heights and spacings were 20-30 nm and 150-500 nm, respectively, and which were distributed more uniformly compared to the fatigued Au specimens' slip bands. In the case of fatigued Ag, variation in the heights was a little less compared to the Ag and their heights and spacings were 15-30 nm and 200-400 nm. Unfortunately we could not observe the STM images of Cu. This is regarded that we could not find the adequate condition for STM observations because of the formation of oxide layer. Based on the above mentioned results, discussions were made to get further achievement.