Tetsuro Suzuki

Nonlinear anelasticity of magnesium

An approximate solution of the equation of motion of a nonlinear anelastic reed at or near resonance is presented. The steady state solution reproduces the well‐known nonlinear resonances. The solution also predicts the existence of automodulations, i.e., self‐excited modulations of the amplitude and phase at constant power of excitation of the reed. Numerical examples of such automodulations are presented for an antisymmetric deformation potential. Experimental studies of finite amplitude oscillations of a magnesium reed vibrating at 72 and 431 Hz at room temperature confirm the existence of automodulations. The experimental results can be semiquantitatively described in terms of the solution given. The assumption that finite deformation by twinning represents the essential nonlinearity leads to a self‐consistent interpretation. The relaxation time of twinning is obtained from the analysis of the automodulation and is 22 msec in the sample investigated. It is proposed that point defects control the relax...

Autooscillations and nonlinear anelasticity

Abstract In conclusion it can be stated that a novel phenomenon, a mechanical autooscillation, has been described theoretically and shown to exist experimentally. These autooscillations occur when a nonlinear anelastic solid is forced into large amplitude oscillations in the vicinity of a martensitic transformation. They manifest themselves as a low frequency automodulation of the a martensitic transformation. They manifest themselves as low frequency automodulation of the forced vibration of such a solid.

Non-Linear Mechanical Model for Martensitic Transformation

A non-linear mechanical model for the martensitic transformation is proposed. The formation process of the nucleus of the martensitic phase is described as the results of the evolution of the transverse lattice waves in a non-linear dispersive lattice of the parent phase. A significant role of the dispersion relationship in the martensitic transformation is found; it is the dispersion relationship of the transverse lattice waves in the parent phase that governs the structure of the martensitic nucleus. However, the presence of such strong anomaly in the dispersion relationship as accompanied by a soft phonon is not required for the nucleation of the martensitic phase.

On the mechanism for martensitic transformation from fcc to bcc

Abstract The mechanisms for martensitic transformation from fcc to bcc, those by Bain, Kurdjumow and Sachs (K–S), Frank or Bogers and Burgers, are reexamined on the basis of the comparison of the cohesive energy. The cohesive energy of the transient lattices formed by those mechanisms is estimated by use of the embedded atom method potential for Fe. In the process of the calculation, it has been realized that the shear deformation involved in all of the latter three mechanisms must be carried out in a reinterpreted sense slightly different from the strict sense of the word. In an ideal situation, where the formation of the martensite without any constraint from the surrounding austenite is allowed, the saddle point energy for the latter three mechanisms is equal to the maximum energy for the Bain deformation process between fcc and bcc. However, if the constraint that the distance between the close-packed planes is kept constant during the martensitic transformation is imposed, only the mechanism by K–S can bring fcc lattice to bcc lattice among the latter three.

Numerical study of transverse lattice waves connected with martensitic transformation

The behavior of the transverse lattice wave connected with the nucleation process of martensite is studied, taking into account the anharmonicity, by use of one-dimensional model for the crystal. The key factor which determines the behavior of the transverse lattice waves according to the model is its amplitudeA with respect to the critical amplitudeAc. As far asA < Ac, the presence of the transverse lattice wave does not lead to the initiation of the martensite. Depending on the variation ofA andAc with temperature, the model suggests two alternative processes for the initiation of the martensitic transformation. 1) In case the variation ofAc with temperature is larger than the variation ofA with temperature, the transverse lattice wave develops into the stable nuclei of the martensite, as soon asAc becomes smaller thanA with decrease of temperature. 2) In case the variation ofA with temperature is larger than the variation ofAc with temperature, the transverse lattice wave represents the heterophase fluctuation whenA « Ac. The stable martensite is formed with the reduction ofA as temperature is reduced. The presently available experimental data suggest the process 1) as the nucleation mechanism of the martensite. The prominent role of the interface energy between the martensite and the austenite in determining both the structure of the martensite and the dispersion relationship of the transverse lattice wave in the austenite is pointed out.

Precipitation Process of Carbon in Alpha-Iron

The precipitation process of carbon in alpha-iron was studied by measuring the internal friction, and by observing the precipitates by electron microscope. The experimental results are expressed fairly well by the formula which expresses the sum of the two processes, one being the absorption of carbon atoms by the precipitates by way of dislocations and the other being the absorption of carbon atoms through the surfaces of the precipitates by the diffusion-limited process. The observation of the precipitates supports this explanation of the precipitation process.

On the formation of martensite

Abstract This paper provides arguments towards the resolution of the “nucleation dilemma” in the formation of martensite. The dilemma arises because there seens to be no direct connection between the inherent tendency towards instability of the body-centered parent phase as evidenced by partially soft phonons and the formation of a classical nucleus of the product phase in an elastically hard parent phase. It will be argued that the combined action of a static elastic bias field and a diffusion-like thermally activated process can resolved the dilemma. This combination will provide the mechanism by which the microscopic interactions controlling the phonon dispersion and the macroscopic elastic fields together control the process of nucleation.

Composition effects on properties of the perovskite superconductor Ba(Pb, Bi)O3

Compositional change of the superconducting transition temperature T c has been examined for the hot-pressed ceramics of (Ba, Sr)(Pb, Bi)O 3 and Ba(Sn, Pb, Bi)O 3 . Results for both systems are summarized as the T c contour maps of respective composition diagrams, which proved to be highly anisotropic with respect to composition coordinates. Temperature dependence of the normal resistivity, the Hall coefficient, and the lattice constant were also measured as function of composition. These results are discussed in connection with the T c characteristics, and also with the previously reported pressure effect shown by these materials.

Barrier energy for the b. c. c.-f. c. c. martensitic transition in sodium

Abstract Using an Ashcroft empty-core model pseudopotential, we have calculated the binding energy of the intermediate structures between b. c. c. and f. c. c. sodium at zero temperature for two homogeneous-deformation reaction-path models, namely those of Bain (1924) and Zener (1948). Bains model gives a lower barrier energy than that of Zener : 9·2 K per atom, much lower than a previous estimate based on the second-order elastic constants.

Measurement of Static and Dynamic Elastic Moduli of Shape Memory Alloys.

The mechanism of the so-called rubberlike elasticity in shape memory alloys such as Au–Cd and Cu–Au–Zn alloys is investigated using the measurement of static and dynamic elastic moduli. A large difference between the static and dynamic elastic moduli is found. While the dynamic modulus remains almost unchanged during room-temperature annealing for 3 days, the static modulus increases appreciably during the same annealing, corresponding to the appearance of the rubberlike elasticity. These experimental results are discussed in terms of the pseudoelasticity due to twin boundary motion.