Taku Okamoto

Precise Calibration of Displacement Vector Map during Superplastic Deformation in Tetragonal Zirconia Polycrystal

In previous papers, the present authors observed grain motion in tetragonal zirconia polycrystal during superplastic deformation, and showed the displacement vector map of 748 grains. The map had an interesting feature such as transient domain structure. However, the authors did not pay much attention to the measurement error at that time. In this paper, the influence of measurement error on the map was quantitatively investigated. After precise calibration, it was revealed that measurement error did not have much influence on the feature, and statistics of grain motion was discussed on the calibrated map.

Estimation theory for random force exerted on grains during superplastic deformation of ceramics

This paper focuses on grain motion during superplastic deformation in TZP (Tetragonal Zirconia Polycrystal) ceramics. After estimation theory for random force was developed, the kinetic data of grains were stochastically analyzed, and random force acting on grains was estimated: At an earlier stage of superplastic deformation, distribution of random force differs between the loading direction and its normal direction. As superplastic deformation advances, however, it becomes identical in two directions. Such the change in the random force is discussed in terms of constraint by surrounding grains.

Random walk analysis of grain motion during superplastic deformation of TZP

This study focuses on grain motion in TZP (Tetragonal Zirconia Polycrystal) ceramics during superplastic deformation. The specimen was 16 times elongated repeatedly at 1400°C in air. The increment of true plastic strain was set to be 2%, and the specimen was deformed up to 30.3% true plastic strain finally. After each deformation, displacement vectors of specified 748 grains were measured from their position vectors determined by FE-SEM micrographs. As a result, the grains move to the tensile loading direction in zigzag way. And also, the zigzag motion changes with plastic strain: The grains move randomly (random walk motion) by the first 15% true plastic strain, and then grain motion becomes spatially uniform gradually. It is related to changes of constraint of surrounding matrix.