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），最大扫描面积为7.1 μ m X 7.4 μ m，最大高度分辨率为0.1 nm，观察了循环应变变形的高纯Au、Ag或Cu的疲劳滑移带。利用特制的四点式循环弯曲机，对观察到的薄板试样在空气中以1500或2000 μ epsilon恒定应变范围内进行3000或5000次循环变形。根据疲劳Au的STH图像，将滑动带分为两种类型。即观察到高度为50 ~ 200 nm、间距为500 ~ 2000 nm的粗滑带和高度为50 ~ 80 nm、间距为50 ~ 300 nm的细滑带。随着循环次数的增加，粗滑动带的间距和高度有减小的趋势，而细滑动带则没有变化。粗滑移带可视为。细滑动带的聚集。另一个有趣的点是，沿着滑丝线观察到半圆形挤压样图案。静态弯曲滑移带的STM图像显示，滑移带的高度和间距分别为20 ~ 30 nm和150 ~ 500 nm，与疲劳试样的滑移带相比，滑移带的分布更加均匀。在疲劳银的情况下，高度的变化略小于银，其高度和间距分别为15-30 nm和200-400 nm。不幸的是，我们无法观察到Cu的STM图像。这被认为是由于氧化层的形成，我们无法找到合适的条件进行STM观测。在此基础上进行了探讨，以期取得进一步的成果。

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.