Improvement of scanning laser microscope type in situ observation system and microscopic observation of fracture process in intermetallic compounds

研制了可在扫描激光显微镜下施加轴向载荷的紧凑型卧式电液疲劳试验机，并改进了现场观察系统。改进后的系统的特点如下：(1)在高达(]sy.+-的轴向载荷下。[)98kN，可在高倍率的环境空气中观察试件表面。(2)可进行频率为0.001-几十赫兹的载荷控制或位置控制疲劳试验。(3)试验机放置在计算机控制的X-Y自动工作台上，观察点可移动到2最大精度。由于设置了特殊的旋转夹具，可以观察到试件的整个周长，利用该系统对TiAl金属间化合物的疲劳过程进行了详细的观察。为了研究S-N合金的基本特性，用Ti-33.8wt.%Al合金在应力比R=-1的正弦波作用下进行了疲劳试验和表面观察。虽然TiAl几乎不发生塑性变形，但在一些γ-TiAl晶粒中观察到了几种类型的滑移(单滑移、双滑移、孪晶)，它们是塑性变形的证据。此外，随着应力循环次数的增加，滑移线的数量也增加。结果表明，TiAl的疲劳断裂以及传统金属材料的疲劳都是由累积滑移变形引起的，验证了新研制的疲劳试验机和改进的扫描激光显微镜原位观察系统的良好性能。通过设置额外的设备，现场观察将能够在水中或在高温下进行。

The compact horizontal type elctric-hydrauric fatigue testing machine which could apply axial load under the scanning laser microscope was newly developed, and in situ observation system was improved. Characteristic of the improved system are shown in the following.(1) During axial load of up to (]SY.+-。[) 98kN is applied, the specimen surface can be observed in the ambient air with high magnification.(2) Load controlled or position controlled fatigue test with frequency of 0.001-tens Hz can carreid out.(3) As the testing machine is placed on a computer-controlled X-Y automatic stage, the observation point can be moved of 2mum accuracy. Also, movement of visual field during fatigue test can be cancelled by the computer-controlled automatic stage.(4) Because a special rotation jig is set, the whole circumference of the specimen can be observed.By using this system, fatigue process of the TiAl intermetallic compounds are observed in detail. To study a basic S-N characteristics, fatigue tests attended with surface observation were carried out under sine wave of stress ratio R=-1, by using a Ti-33.8wt.% Al.Although TiAl hardly deformed plastically, several types of slip (single slip, double slip, twin) which were the evidence of the plastic deformation were oberved in some of gamma-TiAl grain. Also, number of slip lines were increased as number of stress cycles increased. It is concluded that the accumulated slip deformation causes the fatigue fracture of TiAl, as well as the fatigue in traditional metallic materials.It is confirmed that the newly developed fatigue testing machine and the improved scanning laser microscope type in situ observation system function well. By setting up additional apparatus, in situ observation will be able to carry out in water or at elevated temperature.