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承受轴向载荷的小型卧式电液疲劳试验机，并对原位观察系统进行了改进。改进后的系统特性如下所示。(1)轴向载荷达到(]SY.+-。[)施加98kN时，可在环境空气中用高倍镜观察试件表面。(2)可进行频率为0.001- 10hz的载荷控制或位置控制疲劳试验。(3)由于试验机放置在计算机控制的X-Y自动台上，观测点的移动精度可达2ma。此外，在疲劳试验过程中，视野的移动可以通过计算机控制的自动工作台来消除。(4)由于设置了特殊的旋转夹具，可以观察试件的整个圆周。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。为了研究基本的S-N特性，在应力比R=-1的正弦波下，使用Ti-33.8wt进行了表面观察的疲劳试验。虽然TiAl几乎没有塑性变形，但在某些γ -TiAl晶粒中观察到几种类型的滑移（单滑移、双滑移、双滑移），这些滑移是塑性变形的证据。随着应力循环次数的增加，滑移线的数量也随之增加。结果表明，累积滑移变形是TiAl材料疲劳断裂的原因，也是传统金属材料疲劳断裂的原因。结果表明，新研制的疲劳试验机和改进后的扫描激光显微镜式原位观察系统运行良好。通过设置额外的仪器，可以在水中或高温下进行现场观测。

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.