Kohji Yamakawa

Hydrogen migration in cold worked Pd around 50K

In previous papers, the diffusivities of hydrogen isotopes in Pd and Pd dilute alloys were obtained from the rate of an electrical resistivity increase for the hydrogen (deuterium) ordering around 50 K. The interstitially dissolved hydrogen interacts with the lattice defects containing the impurity atoms because the volume dilatation and change of electronic configuration are caused by the introduced hydrogen. The migration energies of hydrogen isotopes in the Pd alloys increase from those in pure Pd with the increasing concentration of alloying atoms at a low temperature range. The energy of hydrogen in cold worked Pd would also be affected by the trapping of hydrogen around the dislocations. In the present work, the diffusivity and migration energy of hydrogen in cold worked Pd have been determined by the measurement of an electrical resistivity increase due to the ordering of hydrogen around 50 K.

Point Defect Clusters at a Twin Boundary in Pure Aluminum

Point defect clusters at a twin boundary in pure aluminum are observed by transmission electron microscopy. At the coherent twin boundary, characteristic triangular loops of the vacancy type are formed in quenched specimens, while loops of the interstitial type are formed in electron-irradiated specimens. The direction of the triangles of the vacancy loops is opposite to those of the interstitial loops. These facts can be explained as arising from the difference in the atomic arrangement of the second nearest-neighbor layers around the dislocation loops. It can be concluded that whenever a faulted loop is formed on a stacking fault, the loop is triangular. During electron irradiation of a boundary which contains a vacancy loop, the vacancy loop grows or shrinks depending on the environment around it, while an interstitial loop always grows.

Hydrogen migration in Lu at low temperatures

Abstract The migration of hydrogen in Lu is determined by electrical resistance measurements in temperature range of 140–170 K. Disordered hydrogen atoms, which are formed by quenching, migrate to order during annealing in the above temperature range. The rate of the resistance decrease depends on the ordering rate of hydrogen. From the resistance decrease during isothermal annealings, the activation energy of hydrogen migration is determined as 0.43 eV (41.5 kJ mol −1 ).

X-ray diffuse scattering of quenched copper single crystals

Abstract X-ray diffuse scattering was measured for quenched copper. The diffuse scattering near the (111) and (222) reflections was observed at room temperature for as quenched and successively annealed samples from 200 to 800°C. A sharp and strong subpeak accompanied by a thermal diffuse scattering was appeared on a smaller angle side of the (111) Bragg angle. The subpeak was disappeared after annealing at 400°C. A characteristic feature of this scattering is from vacancy type dislocation loops, of which the mean radius is estimated to be about 1 nm, associated with a caustic scattering.