| Research Abstract |
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.
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