Ikushi Yoshida

Damping properties of Ti50Ni50-xCux alloys utilizing martensitic transformation

Abstract The internal friction (IF) and elastic modulus of rigidity were investigated for Ti50Ni50−xCux shape memory alloys for the composition range of 8≦x≦20 by utilizing a low frequency inverted torsion pendulum method. The observed extraordinarily large internal friction and large softening in rigidity are discussed, paying attention to low twinning shears of B19 (orthorhombic) martensite. The attained large internal friction Q−1=0.2 for Ti50Ni30Cu20 at peak temperature, and the shoulder temperature of IF indicate that the alloy system is a good damping material which can be used at temperatures higher than room temperature.

Internal friction of Ti-Ni alloys

The low-frequency internal friction and the modulus have been measured on Ti–Ni alloys of varying compositions, from Ni 49.89 to 51.0 at. %, in a wide range of temperatures covering the martensitic and the reverse transformations. The effect of heat treatment on the internal friction has also been investigated. The internal friction shows a sharp peak around the martensitic transformation and/or the formation of pre-martensitic state ‘R-phase’. The height and temperature of the peak depend strongly on the composition and on the heat treatment. Corresponding to the internal friction peak a remarkable depression of the modulus has been observed. At temperatures lower than 250 K two types of temperature dependences were observed; one is a step-type that changes slowly with temperature, and the other is a peak-type around 200 K. An annealing at 873 K has enhanced the low-temperature internal friction, while the solution heat treatment at 1273 K has appreciably decreased it. In all cases the damping of the parent phase is very low; the internal friction is lower than 10·10−4. The electrical resistivity and the thermoelectric power have been measured.

The Electrical Resistivities of NaNO_2 and KNO_3 Crystals

The d c electrical resistivities of NaNO 2 and KNO 3 crystals were measured by the potentiometer method in the temperature range covering their transition points. The obtained results were found to obey the conventional exponential law and the activation energies in both phases were calculated. It was observed that at the transition point the electrical resistivity shows a steep jump, which is about two∼six times in NaNO 2 and about one hundred times in KNO 3 . A little discussion was made about this phenomenon in connection with the appearance of some disordering in the crystal structure.

Thermal Conductivity of Sodium Nitrite

The thermal conductivity of sodium nitrite single crystals has been measured in the temperature range of 70∼190°C along the direction of three crystal axes. Thermal conductivities in the b - and a -directions show a gradual decrease on heating, over a rather wide temperature range of some fifty degrees below the transition temperature. This decrease has been analyzed as an additive thermal resistivity with the help of a measurement at lower temperatures. Any anomalous behavior has not been found in the temperature dependence of thermal conductivity in the c -direction. A tentative model of the order-disorder arrangement of NO 2 - radicals is proposed for the explanation of the origin of the additive thermal resistivity, in which uneven interatomic forces due to the disordered arrangement are considered as scattering centers of phonons. The predicted temperature dependence is in a qualitative accord with the experimental one.

Thermal Conduction in Ferroelectric Ceramics

Apparatuses were constructed and measurements were made on the thermal conductivity of insulating crystals over the temperature ranges from -200°C to 600°C. For the lower temperature range, the absolute measurement was used, while for the higher one, the comparative method was adopted. The thermal conductivities of ferroelectric PbTiO 3 and antiferroelectric PbZrO 3 showed a rather large step-wise increase, in contrast to the case of BaTiO 3 , as they passed into the paraelectric state. Discussions are given of the relation between the magnitude of thermal conductivity and the crystal structure. It is pointed out that the anharmonic potential for the smaller ions should be responsible for the scattering of phonons in these substances.

Damping properties of metal-piezoelectric composites

Abstract For the purpose of searching for a new damping mechanism, the possibility of utilizing piezoelectric effects was investigated. Experiments of internal friction and electrical property measurements were made on some piezoelectric ceramics and metal–piezoelectric composites. Trials of manufacturing metal–piezoelectric composites are described. The method adopted is the pressing of a mixture of metal and piezoelectric powders into a metal tube, followed by rolling and annealing. Cu–PbTiO 3 composite showed three to five times higher damping compared to the pure Cu rod.

Internal friction of FeMnSiCr shape-memory alloy

Abstract Low-frequency internal friction and elastic moduli of FeMnSiCr shape-memory alloy were measured as a function of temperature from 120 K to 500 K. Two peaks appear in the internal friction curve on cooling and two other peaks on heating. Two of them occur around the phase transformation, and the other two are supposed to be related to the antiferromagnetic transformation. The elastic moduli (square of frequency) show a stepwise change, rather than the steep minimum observed in shape-memory alloys that undergo thermoelastic martensitic transformation. The effect of cooling/heating rate and of frequency was investigated and a conformity with Delormes model was confirmed except for the modulus defect behaviour.

Effect of Heat Treatments on the Damping Characteristics of TiNi-Based Shape Memory Alloys

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.

Anomalous thermoelectric power of Bi/Sb multilayer films and related transport phenomena

Abstract The thermoelectric power of Bi/Sb multilayer films grown on single-crystal Si(111) substrates or on BaF2(111) cleaved surfaces by molecular beam epitaxy method has been measured. An anomalously large negative thermoelectric power was observed on films deposited on Si around room temperature and above, but not on those deposited on BaF2. A possibility of ZT > 1 was suggested.

Magnetic properties of Eu/Se superlattices

Abstract The magnetization of rare-earth superlattices of Eu/Se grown on BaF2(1 1 1) by means of Molecular Beam Epitaxy (MBE) method has been measured in order to clarify the mechanism for the anomalous magnetic properties. Selenium layers in the Eu/Se superlattice act as a separator between Eu layers and the thickness of Se layers was varied from 0.5 to 3 nm, while that of Eu layers was fixed at 1 nm. The crystal structure of samples was characterized by X-ray diffraction and the in situ RHEED observations. A considerably good epitaxial structure was attained for [Eu 1 nm/Se 1 nm] sample, but [Eu 1 nm/Se 0.5 nm] and [Eu 1 nm/Se 3 nm] samples were only polycrystalline. The magnetization process measured at 1.9 K shows that a magnetic phase transition takes place from an antiferromagnetic to a spin-flop state. The critical magnetic field HC is obtained at 3750, 2150 and 1000 G, respectively, for [Eu 1 nm/Se 0.5 nm], [Eu 1 nm/Se 1 nm] and [Eu 1 nm/Se 3 nm] samples. The exchange integral J is dependent on the distance between EuEu layers, i.e., J ∝ d−1.1. The magnetic phase diagram of Eu/Se superlattice has been obtained.