Papers by Author: Kazuhiro Otsuka

Abstract: “Glass”, a frozen disordered-state, has been found in areas as diverse as amorphous solids, magnetic alloys, ferroelectrics, superconductors, and even in models of biological evolutions. In the present review we introduce a new class of glass–the “strain-glass”, which was discovered very recently. Strain glass is derived from a martensitic system, where the local-strain is frozen in disordered configuration. The first example of strain glass was found in the well-studied Ni-rich Ti50-xNi50+x martensitic system in its “non-transforming” composition regime (x>1.5). Contrasting to the familiar martensitic transition, the strain glass transition is not accompanied by a change in the average structure, or a thermal peak in the DSC measurement. It involves a dynamic freezing process with broken ergodicity, during which nano-sized martensite domains are frozen. More interestingly, the seemingly “non-martensitic” strain glass exhibits unexpected properties: shape memory effect and superelasticity, like a normal martensitic alloy. Strain glass bears a striking similarity with other two classes of glasses: cluster-spin glass and ferroelectric relaxor. These ferroic-transition-derived glasses can be considered as a more general class of glass: ferroic glass. The finding of strain glass may provide new opportunities for martensite research from both fundamental side and application side.

Abstract: Low frequency internal friction of Ti49Ni51 binary and Ti50Ni40Cu10 ternary shape memory alloys has been measured. The effect of solution and aging heat treatments on the damping property was examined. The temperature spectrum of internal friction for TiNi binary alloy consists, in general, of two peaks; one is a transition peak which is associated with the parent-martensite transformation and is rather unstable in a sense that it strongly depends on the frequency and decreases considerably when held at a constant temperature. The other one is a very high peak of the order of 10-2, which appears at around 200K. It appears both on cooling and on heating with no temperature hysteresis, and is very stable. The behavior of the peak is strongly influenced by the heat treatments. The trial of two-stage aging with a purpose of improving the damping capacity has been proved unsatisfactory. TiNiCu has a very high damping, the highest internal friction reaching 0.2, but by quenching from very high temperature, say 1373K, the damping is remarkably lowered. For the realization of high damping the quenching from a certain temperature range around 1173K seems the most preferable condition.

Abstract: High purity BaTiO3 single crystal was aged below its Curie temperature for different times. The reverse transformation (from tetragonal to cubic) temperature was measured precisely by differential scanning calorimetry (DSC). It was observed that the reverse transformation temperature increased with increasing aging time, indicating ferroelectric phase became stable with aging. This behavior is the same as found in ferroelastic alloys. The origin of the stabilization effect in ferroelectric single crystals was discussed with respect to the distribution of point defects.