抄録
X-ray diffraction is a useful means for the study of change in structure of materials. There have been a number of publications related to X-ray observations in creep of metallic materials. However, it is noted that these observations are not sufficiently adequate to account for the change in microstructures that occurs in the material during creep process, because of inadequacy of ordinary technique of X-ray diffraction in its resolving power.
Recently the instrumentation in the field of X-ray diffraction has achieved great progress in this country, and even exquisite techniques of X-ray diffraction have been made available, providing high resolving power, such as the X-ray micro-beam technique and the double crystal monochrometer technique. These new techniques have high resolving power to account for the change in microstructure of materials.
The authors applied the X-ray micro-beam technique to the study of the creep, and investigated the micro-structural changes in 0.06%C steel during creep at 450°C under constatnt stress of 8kg/mm2 and 12kg/mm2. The results obtained from the micro-beam technique are as follows:
(1) In the case of 8kg/mm2, the diffraction spots were diffused slightly with increasing creep strain, and split in to small sharp spots. These results show that while with the increasing strain the cell size remains constant, the misorientation between the cells increases and the lattice distorsion within the cells decreases. The dislocation density on the cell walls increases with strain.
(2) In the case of 12kg/mm the diffraction spots are diffused in arc, with increasing strain, and in the arc many split spots are found. These split spots are diffused to parallel the radius of the Deby-Sherrer ring. These results show that while the cell size remains constant with strain, it is smaller than in the case of 8kg/mm. The misorientation between the cells increases and the lattice distorsion with in the cells also increases with strain. The dislocation density on the cell walls increases with strain more rapidly than in the case of 8kg/mm.
In addition to this, we measured the changes in half-value breadth obtained from ordinary X-ray diffraction patterns and observed the micro-structural changes of the surface of the specimens by means of an electron microscope. The findings by the X-ray micro-beam technique agree with that by the above mentioned techniques.
