Genjiro Mima

Recovery of Irradiated Fe-Al-N Alloys

Two kinds of Fe-Al-N alloy were irradiated in the JRR-2 reactor with neutron doses of 1–2×1019 n/cm2 at about 60°C. Using internal friction and torsion test techniques, the atomistic behavior of the structure was studied through observation of the changes brought to the mechanical properties by neutron irradiation and subsequent annealing. The internal friction measurements revealed that irradiation brought about release of nitrogen from Fe8N and AlN. Moreover, the damping curves indicated, upon analysis, the existence of two new peaks, at −120° and −145°C. With annealing, recovery of radiation hardening started from a temperature between 150° and 200°C, and terminated by −350°C.

Studies of voids produced by creep in Magnox

Tensile stress was applied at a constant temperature to an alloy called Magnox (composed of Al 0.79, Be 0.006, Fe 0.0079wt%, and Mg balance). Number of voids and length of grain boundary migration produced by creep were measured.The principal results obtained by experiments were as follows:(1) Except for high velocities of creeping such as about 10% elongation/hr., number of voids was the maximum at 300°C for creeping velocity of lower than about 4% elongation/hr.(2) Though with a few exceptions, the length of grain boundary migration was generally large at the temperature and creeping velocity for a large number of voids. (In most cases, the maximum length corresponded with the maximum number of voids).

Some Torque-Twist Relations on the Low Temperature Dynamic Torsion Test of Low Carbon Steel

The present investigation was carried out for the size effects of test piece and various testing conditions on the torsional fracture behaviour, using a newly developed dynamic torsion machine. Dynamic torque-twist curves were obtained photographically at various temperatures. The maximum rate of straining was 60per second and the range of temperatures from +200°C to -196°C.Yield and fracture strength and plastic strain to fracture were not affected by the variation of gauge length of the test piece, but yield and fracture strength increased with decreasing of the diameter. The size effects on torsional strength were also appeared for hollowed specimens as well as for solid ones. In the static torsion test, farcture type at comparatively low temperature had a ductile manner and the cleavage fracture appeared only at -196°C under the tested conditions. On the other hand, in the dynamic test, the specimens used for the investigation took a ductile fracture, excepting a specimen having a larger grain than the A.S.T.M. No 4.The torque-twist curves in static test or room temperature dynamic test dropped at maximum torque after drop in load. To the contrary, in the low temperature dynamic test, after reaching the maximum stress, torque suddenly decreased with increasing twist angle and then kept a constant value until the beginning of fracture. Ruptured specimen with cleavage type due to the dynamic torsion test had been broken at maximum torque. These strange phenomena in the fracture manners and the torque-twist curves were discussed and assumed to be due to the temperature rise in the tested part connected with the rapid large plastic deformation.

Effects of cold-working on low-temperature electrical resistivity of aluminium

The purpose of this research was to make clear the effects of cold-drawing, particularly of medium and heavy cold working, upon the electrical resistivity of metal. Two kinds of commercially pure aluminium, the nominal grades of 99.9% and 99.99% purity were used. The measurements of the electrical resistivity were made at -196°C using the specimen of 1m in length and 1mm in dia.In the diagram of the relation between the electrical resistivity and the reduction of the section area, the electrical resistivity was, in its maximum at the point of about 40% reduction and in its minimum at 70%. And yet the discrepancy between the maximum and minimum value was small. When the reduction was over 80%, the resistivity increased abruptly. The curves obtained for both grades of aluminium were quite similar.This research was not a completely quantitative one, because we could not clarify the structural changes of the crystal lattices according to the varied stages of the reduction. Therefor, the explanation for the experimental results was confined to the tentative and qualitative suggestion.

Change of macrostructure and dimention of bent aluminium by successive isothermal annealing

There are many investigations on recrystallization of cold rolled aluminium sheets, but few on recrystallization phenomena of cold bent one. But forming occupies the greater parts in cold forming works and when such a bent material is heated in working or using, the metallurgical defects have frequently appeared. Nevertheless, probably nothing has been reported on the investigations which studies systimatically how to prevent from these accidents. This is a study on the changes of macrostructure and dimension of cold bent aluminium which take place through successive isothermal annealing. The findings are summarized as follows:The appearances of recrystallized grain in the longitudinal section almost correspond with the stress distribution diagram induced from stress-strain curve.Under low temperature annealing, there is a slight change in curvature of bending and the magnitude of shrinking in dimention increases remarkably caused by recrystallization on strain field below the value near 0.10. But when these samples are heated at temperature higher than 480°C, large shrinking in dimension and coarse grain in the longitudinal section take place, to which attention must be paid in practice.

Recovery of cold twisted zirconium by low temperature annealing

An inhomogenious deformed state is produced in the cold worked metal. This inhomogenious state must be larger in the high symmetric crystal than the low symmetric one. For example, in the alpha-zirconium of hexagonal closed packed crystal, the homogenity or internal stress which is produced by the cold work, must be larger than in cubic iron crystal and in copper.Thus, if cold worked zirconium were annealed at low temperature or aged at room temperature after cold working, comparatively great size change could be expected, which would be worth while considering the accurate size of zirconium parts of atomic reactors.Twisted zirconium wire specimens of various working degrees were anneald with whole torsion apparatus which was dipped freely hanging in the oil bath. The temperatures of oil bath were 100, 170, and 300°C, After annealing for proper time, the apparatus was picked up and the returning angle was read at the pointer.The regults are as follows:-(1) The strain recovery by low temperature annealing occurres in two stages, the first one is rapid and the second one is slow.(2) The relationship between the logarithmus of annealing time and the strain recovery is linear.(3) The strain recovery of zirconium is greater than that of copper.The process of the recovery at low annealing temperature is expressed by kuhlmann, cottrells formula. We consider that the inhomogenity owes to the interference of boundaries and the relaxation within grains as considered by Zener.In the heat treatment for the purpose of releasing those internal stress, the proper annealing temperature range is 300-350°C. For this purpose, as high temperature as possible and the first recovery stage are economical.