Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 02, 2019 - November 04, 2019
It is well known that dislocation structures are formed during cyclic deformation in metals. However, the formation mechanism of the dislocation structures in bcc metal is not yet elucidated. In this study, the dislocation structures in a polycrystalline Fe－3 mass%Si alloy are investigated using high voltage electron microscopy (HVEM), and the formation mechanisms of the dislocation walls in bcc metals are discussed. Push-pull fatigue tests were conducted with a constant total strain amplitude of 1 × 10-2 at a strain rate of 4 × 10-3 /s. Plastic strain amplitude during the fatigue test slightly decreased from 8.4 × 10-3 to 7.9 × 10-3. The fatigue test was stopped at 30 cycles, and thin foils parallel to the (001) plane and the (111) plane were extracted. The dislocation structures in the foils were observed using the HVEM equipped scanning transmission electron microscopy (STEM) detector in Nagoya University. The dislocation walls parallel to (110) were found to be formed during the first few tens cycles of fatigue in both of the (001) foil and the (111) foil. In order to determine the Burgers vectors of the dislocations, the (111) foil was observed. The Burgers vectors were identified by the invisibility criterion as a/2 [111] and a/2 [111]. Slip planes were also investigated by trace analysis and stereo observation. From these analysis, the two types of dislocations were characterized as (211)[111] and (112)[111]. It seems to be reasonable that the (110) walls were lie in the direction bisecting the angles between the Burgers vectors of a/2 [111] and a/2[111].
