Hideji Suzuki

Segregation of Solute Atoms to Stacking Faults

An experimental evidence was given for the segregation of solute atoms to stacking faults in alpha-brass. The stacking fault energy in an alpha-phase solid solution with face-centered cubic structure usually decreases continuously with the increasing concentration of solute atoms. The solute atoms in that alloy tend to segregate to the stacking faults due to chemical interaction. A simple calculation indicates that the solute atoms segregate to such a high concentration as the stacking fault energy becomes a negative value with considerable magnitude, provided that the concentration of solute atoms is in thermal equilibrium at rather low temperature. The width of an extended dislocation should increase indefinitely if the stacking fault energy becomes lower than a negative value. Alpha-brass with 30% zinc, which was annealed at 120°C and 150°C for a week and two days, respectively, after cold-work reveals extended dislocations with extremely wide stacking faults of the order of several microns. Meanwhile,...

Deformation of Thin Copper Crystals

Stress/strain curves of many number of copper crystals having various radii from 0.06 to 1 mm were measured. The range of easy glide increases considerably when the radius of crystal decreases. In the case of suitably oriented crystal the range of easy glide reaches to 50 per cent in shear, when the radius of crystal decreases less than 0.1 mm. The extrapolation of the range of easy glide to the infinitesimal radius gives a value between 40 to 80 per cent in shear irrespectively to the initial crystal orientation. The hardening rate in the easy glide region considerably decreases with the decreasing crystal radius. Meanwhile, the critical shear stress, the stress required for the transition from the easy glide to the rapid hardening region, the hardening rate in rapid hardening region reveal only slight dependence on the crystal radii, i.e. the former two slightly increase and the last slightly decreases with the decreasing crystal radii. These results are discussed qualitatively by introducing a concept ...

On the Energy of the Interstitial Atom in Graphite

Self-and migration energies associated with interstitial carbon and xenon atoms in graphite are calculated, taking account of the relaxation around the interstitials. Assuming that the graphite lattice consists of thin elastic plates held together by the weak interaction forces and subjected to the transverse force by the interstitial atom, the strain form is obtained by solving the equations for the bending plates. Then, employing a suitably chosen interaction potential between the interstitial and all other atoms, the relaxation and the energies associated with the interstitials are calculated. In case of the carbon atom, the self-energy is 2.5 ev, the migration energy 0.016 ev and the ratio of strain energy to the total self-energy 0.49, and in case of xenon, they are 15.1 ev, 0.03 ev and 0.79 respectively.

Effect of Dislocations on the Thermal Conductivity of LiF

Phonon scattering by dislocations was studied by measuring the thermal conductivity of deformed LiF crystals from 1.5 to 300 K. The conductivity is not proportional to T 2 , as observed by Sproull et al. , but is approximately proportional to T 3.5 or to T 3 depending on the deformation mode. After annealing at 300°C for 10 min, the temperature dependence of the conductivity decreased. These results cannot be described in terms of the phonon scattering due to the static strain field around dislocations. The theory of phonon scattering by vibrating dislocations, advanced by Nabarro and Ninomiya, gives a consistent interpretation both to the temperature dependence and to the magnitude of the observed thermal conductivity.

Plastic Flow in Solid Helium

The plastic deformation of solid helium 4 is investigated by measuring the force required to move steel ball in solid helium at a nearly constant speed. Any force-displacement curve reveals marked yield drop and gradually reaches to a constant force, which is of the order of 2×10 5 dyn. It is concluded that the plastic flow in solid helium takes place primarily by the motion of dislocations. The force required for steady motion is proportional to the cubic root of the velocity of the steel ball at 2.1 K, but the force increases by about 10 5 dyn irrespectively of the speed of the steel ball below 1.6 K. Shear stress-shear strain curves of helium crystals are estimated from the force-displacement curves of the steel ball, and are discussed in terms of multiplication and motion of dislocations.

Recovery of Irradiation Hardening of Copper Single Crystals around 0°C

The hardening of copper single crystals irradiated with about 10 16 fast neutrons/cm 2 in a pile at about 90°K was investigated and the recovery of the hardening by annealing at up to room temperature was studied. A bump was always observed in the region of easy glide if the crystal had not been annealed by more than 30 minutes at 0°C, as Makin already observed. Small serrations were also observed in the region of easy glide before the bump, and they disappeared at the same annealing condition as the bump. A divacancy mechanism is proposed to explain these observations.

Plastic Flow in bcc 3He

The plastic flow in bcc 3 He was investigated by the same method as that used for hcp 4 He in a previous paper. The flow stress in bcc 3 He is smaller than that of hcp 4 He roughly by an order of magnitude. In contrast to hcp 4 He it is difficult to observe the yield drop at the initial stage of the plastic deformation in bcc 3 He. The observed results are analysed as shear flow of polycrystalline aggregates. At high strain rates the shear flow takes place by the operation of three pencil glide systems, and below a certain strain rate it proceeds by the pencil glide on two systems and climb of the dislocations of the systems. The strain rate dependence of the flow stress suggests that dislocations move at a constant velocity independent of the flow rate.

Plastic Flow in hcp 4He. II

The plastic flow in hcp 4 He was investigated by using a new equipment which was designed to improve the accuracy of measurements. The pronounced yield drop is always observed at moderately low temperatures or in high speed tests, but the yield drop becomes almost undetectable in low speed tests at high temperatures, where the steady flow stress is proportional to one fourth power of the flow rate. At low temperatures and at high pressures flattened upper yield points are observed frequently, and the steady flow stress becomes independent of the flow rate in low speed tests.

Lattice Thermal Conductivity of Deformed Copper-Aluminum Alloy Crystals at Low Temperatures

Phonon scattering by dislocations at liquid helium temperature has been studied by measuring the thermal conductivity of Cu–15 at % Al alloy crystals deformed by various amounts. Curves of lattice thermal conductivity vs. temperature plotted in log -log scale are concave upwards in the temperature range between 1.6∼4.2°K. These experimental data cannot be described by the scattering of phonons by the static strain field around dislocations through anharmonicity. The result is interpreted by assuming resonance scattering due to vibrating edge dislocations in their Cottrell atmospheres in addition to the scattering due to electron-phonon interaction.

Plastic Deformation on the Fracture Surfaces of Germanium Crystals Cloven at Room Temperature

The fracture surfaces of germanium crystals cloven at room temperature have been examined by optical and electron microscopes and also by X-ray diffraction. These observations give evidences that plastic deformation takes place in thin surface zones of fracture surfaces. It is proposed that the surface zones were deformed by imperfect deformation twinning which would take place along {123} Plane in the ideal case. The deviation of the twin boundary from the ideal one is attributed to the high Peierls force in germanium. These deformation twins may be formed through the large stress concentration at the tip of crack. The most significant group of twins is formed along the fracture surface so as to cover it, and the twinning dislocations are created at the tip of crack. Another significant group of twins is formed at the step of crack where large shear stress exists.