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Martensitic transformation temperatures and the two-way shape memory effect (TWME) of cold-rolled Ti–Ni and Ti–Ni–Fe alloys are investigated with a dilatometer (DL). While the characteristic features of martensitic (M) transformation temperatures are basically consistent with previous findings on Ti–Ni alloys, the TWME directions of Ti–Ni–Fe specimens were found to be opposite those of the Ti–Ni alloys.

The effect of Co addition on the martensitic transition and magnetic properties of the Ni-Fe-Ga β alloys is investigated. The values of both the Curie temperature T c and martenaitic transition starting temperature M s increase, while the saturation magnetization I s decreases with increasing Co content in the series of Ni 5 1 Fe 2 2 - X Co X Ga 2 7 alloys. On the other hand, the values of both T c and I s increase and M s decrease with increasing Co content in the series of Ni 5 4 - X Fe 1 9 Co X Ga 2 7 alloys. T c and I s show a strong dependence on the average magnetic valence number Zm. Consequently, Co is an effective element to control both the martensitic and the magnetic transition temperatures.

The damping property tanof Cu-Al-Mn-based alloys, where tanis nearly equal to internal friction Q � 1 , was investigated using a Dynamic Mechanical Spectrometer (DMS). It was found that the dependences of frequency and strain amplitude on tanare significantly different between the parent + martensite two-phase and the martensite single-phase states, i.e., tanis mainly influenced by frequency in the two-phase state and by strain amplitude in the martensite state. It was also found that the relative grain size d=D is a function of the damping capacity, where d and D are the grain diameter and the diameter of the wire, respectively, and that tanincreases with increasing d=D. The maximum values of tan � ¼ 0:54 and tan � ¼ 0:07 were obtained in the two-phase state and in the martensite state, respectively, in the specimen of d=D � 1.

Making the Grain Most metals contain a large number of ordered crystalline regions that are separated by disordered grain boundaries. If the material is annealed at elevated temperatures, the larger grains will grow uniformly at the expense of the smaller ones. This process slows down over time, making it hard to create very large grains. Abnormal grain growth, in which a few of the crystalline regions grow much faster and larger than the others, can occur if the material is put through a complex annealing process involving straining of the samples. Omori et al. (p. 1500 ; see the Perspective by Taleff and Pedrazas ) find that a much simpler and shorter annealing process can trigger abnormal grain growth in copper-based shape-memory alloys. Thermal cycling between a high-temperature single-phase region and a lower-temperature two-phase region generated dislocations at low temperatures and grain growth on heating. Because this method does not require external straining of the sample, it is not limited to thin sheets or wires.

Variant rearrangements induced by external magnetic field in Fe–Pd FCT martensite transformed from FCC austenite single crystals have been investigated by means of optical microscopy. Fe–Pd single crystals in fully martensite state contain two large correspondence variants, and a kink due to {1 0 1} twinning is observed at the twinning boundary of the variants. The twinning boundary exhibits both large reversible and small irreversible movement by applying magnetic field as a result of variant rearrangement, and 0.49% of reversible strain is obtained. The variant rearrangement is not completed even though magnetic flux density is increased to maximum of an electromagnet used. The boundary also moves reversibly by application of external compression stress, however, the direction of the boundary movement is opposite with respect to the movement induced by magnetic field and the variant rearrangment is not completed. The reversible strain of 2.8% was also observed when the specimen was compressed.

Phase equilibria between the β (B2 or L2 1 ) and γ (A1) phases in the Ni–Ga–Fe system at 900–1200 °C were determined by energy dispersion X-ray spectroscopy (EDX). The martensitic and magnetic transformation temperatures in β single- and β+γ two-phase Ni–Ga–Fe ferromagnetic shape memory alloys (FSMAs) were also determined by differential scanning calorimetry (DSC) and by vibrating sample magnetometer (VSM), respectively. It was found that the martensitic and magnetic transformation temperatures of the β single-phase alloy increase with decreasing annealing temperature in the region above 600 °C. While the martensitic transformation temperatures decrease with decreasing annealing temperature in the region below 600 °C, the Curie temperature increases and becomes saturated at about 400 °C. Moreover, martensite phases with a 10M or 14M structure were observed by transmission electron microscopy (TEM). These characteristic features are discussed in terms of the thermal stability of the β phase and the order–disorder transition from the B2 structure to the L2 1 structure.

Recent progress on ductile Cu–Al–Mn-based shape memory alloys (SMAs) is presented. The various properties of superelasticity (SE), the shape memory effect (SME), the two-way memory effect (TWME) and internal friction are enhanced by controlling grain size and texture through thermomechanical treatments. It is also shown that the control of stress-induced martensitic transformation due to cold-rolling of Cu–Al–Mn SMAs results in low thermal expansion (LTE). In addition, the medical application of the Cu–Al–Mn-based SMAs to guidewire is introduced.

The martensitic transformation and magnetic properties of Cu-Ga-Mn β alloys were investigated. The alloys in the composition range Cu-21 at%Ga-(13-15)at%Mn were found to exhibit a thermoelastic martensitic transformation from an L2 1 parent to a 2H martensite in the ferromagnetic state. This martensitic transformation disappeared with the precipitation of the ω phase induced by aging at room temperature.

The effect of texture and β grain size on the superelasticity (SE) in Cu-Al-Mn-based alloys was investigated by tensile testing. The SE strain increases with increasing relative grain size d/t (d: grain size and t: specimen thickness), which is explained as being due to a relaxation of the grain constraint in the polycrystalline specimens. On the other hand, Cu-Al-Mn-Ni alloy recrystallized after heavy cold-rolling in the fcc (α) + bcc (β) two-phase region showed a {112} strong recrystallization texture. The SE strain depends on the testing direction on the textured sheet specimens, and the largest value of SE strain was obtained in the specimen tested along the direction of 45° from the rolling direction (RD).

The shape memory effect (SME) and the two-way shape memory effect (TWME) of Cu-Al-Mn alloys induced by single bending deformation at room temperature were investigated in relation to the microstructural features of grain size and texture. It was found that the control of the texture and/or grain size significantly improves not only the SME, but also the TWME. Especially, the specimen with near {112} texture obtained by cold-rolling and further recrystallization showed a high degree of TWME (e TWME = 3.6%) in the surface strain which is of the highest level of the TWME in the Cu-base shape memory alloys. It can be concluded that a high level of TWME in the bending deformation mode can be obtained from specimens with an excellent SME.

Farromagnetic shape memory alloys have been developed in the Co-Ni-Al ternary system with β + γ two-phase structure. The β(B2) phase of the Co-33Ni-27Al and Co-34Ni-28Al alloys exhibits both paramagnetic/ferromagnetic transition and a thermoelastic martensitic transformation from β to β' (L1 0 ). The microstructure of both alloys shows the primary p phase surrounded by the y (Al) phase which brings about the drastic effect in the improvement of the hot workability. By annealing in the two-phase region after solution treatment, the y phase precipitates along grain boundaries in the β phase, besides in the β grain. The alloys annealed at 1273 K showed a good cold workability and a thermal activated shape memory effect. These ferromagnetic and ductile shape memory alloys are very promising for one of the new smart materials.

This paper presents a simple method to examine whether a ferromagnetic shape memory alloy can be used as an actuator by controlling the transformation temperature by magnetic field. Both Fe–Pd and NiAlCo alloys are studied. The analysis results show the recently discovered alloy of NiAlCo cannot be used. Although an Fe–Pd alloy can be used, in principle, for magnetic field actuation, the work extracted by magnetic actuation is small.

The martensitic transformation and shape memory (SM) effect in Co-Al alloys containing 0-16 at%Al were investigated by differential scanning calorimetry (DSC) and bending tests. It was found that the martensitic transformation temperatures decrease and the thermal hystereses increase with increasing Al content. It was also found that an incomplete SM effect occurring in pure Co can be enhanced by the addition of Al over 4at% and that Co-Al alloys containing Al over 10 at% show an excellent SM effect. Co-Al SM alloys possessing high reverse transformation temperatures over 200°C and martensitic transformation in the ferromagnetic state show promise as a new type of SM alloys.

A phase-change random access memory (PCRAM) with multiresistance characteristics was fabricated. In this multiple PCRAM device, Ge2Sb2Te5 (GST) and Ge1Cu2Te3 (GCT) are utilized as phase-change materials to realize high and middle-resistance states, respectively. Since GCT has simultaneously lower melting point and higher crystallization temperature than GST, recording of multiple states was directly achieved without any additional step. It was confirmed that multiple resistances of 103, 104, and 105 Ω were measured by a selection of current pulse during crystallization. From this work, it is expected that a device structure with GST and GCT can be one of the candidates for an effective multilevel cell operation in PCRAM.

A significant improvement in the degree of superelasticity in Cu-Al-Mn ductile polycrystalline alloys has been achieved through the addition of Ni and control of the recrystallization texture by thermomechanical processing, which contain the annealing in the fcc (α) + bcc (β) two-phase region, followed by heavy cold reductions of over 60 pct. The addition of Ni to the Cu-Al-Mn alloys shows a drastic effect on the formation of the strong {112} 〈110〉 recrystallization texture. Superelastic strains on the order of 7 pct, 3 times larger than those in other Cu-based shape-memory alloys (SMAs), have been realized in the textured Cu-Al-Mn-Ni alloys. The superelastic strains obtainable in the textured Cu-based SMAs are on a par with those attainable in Ni-Ti-based alloys.

Martensitic transformation temperatures and the two-way shape memory effect (TWME) in ductile Cu-Al-Mn alloys deformed at room temperature were investigated using differential scanning calorimetry (DSC) and the bending test. The M s and A f temperatures were found to increase slightly with increasing degree of pre-deformation, while the M f and A s temperatures decreased. The TWME is strongly influenced by the M s temperature and the grain size of the specimens, i.e., the highest degree of TWME is always obtained in the specimens with M s -100°C and the TWME increases with increasing ratio of grain size to specimen width, where the maximum value of TWME = 3.2% was obtained in the present study. In situ observation of the surface relief at several temperatures on the deformed specimens was also performed and it was found that some restricted martensite variants grow and shrink with temperature change without the typical self-accommodation microstructure in the specimens with large TWME.

The functionality of a pulse timing discriminator, which is commonly required in optical communication systems and artificial neuromorphic engineering, was implemented into chalcogenide phase-change materials. GeSbTe (GST) and GeCuTe (GCT), which exhibit opposite refractive index behavior in their respective crystalline and amorphous phases, were employed. A GST/GCT double layer enabled the order of arrival of two counter-propagating femtosecond pulses to be encoded as a difference in the degree of amorphization of the GCT layer, i.e., either a brighter or darker contrast of the amorphized area with respect to the crystalline background. Nonthermal ultrafast amorphization contributed to a picosecond time resolution in the discrimination of the pulse arrival order.

We investigated the temperature dependence of electrical resistance of a reactively sputtered Mo-oxide film with a composition near MoO3 and found that the sputtered Mo-oxide film shows a large electrical resistance drop of much more than 104-fold at over 350 °C. Such a large drop in electrical resistance was found to be caused by a phase transition from an amorphous state to a crystalline state. It was confirmed that a W/Mo-oxide/W device shows a typical resistive switching effect of a phase change random access memory material and exhibits reversible resistive switching by the application of unidirectional set and reset voltage. The resistance contrast of the device had a large value of about 105–106. Furthermore, the Mo-oxide film showed much better thermal stability in the amorphous state than conventional phase change materials. These results indicate that the Mo-oxide film is a promising oxide-base phase change material for phase change random access memory.

The resistive switching behavior of a low resistive p-type α-Fe2O3 thin film sandwiched between Fe bottom electrode and top electrodes of various materials (Fe, Ni and TiN) was studied by current-voltage measurements. When TiN was used for top electrode of memory cell, the reversible resistive switching behavior was observed for over 100 cycles. From impedance measurement, it was suggested that the resistive switching behavior in the TiN/p-type α-Fe2O3/Fe device is attributed to the change of the contact resistance in the interface between TiN and α-Fe2O3 layers.

The effect of Co addition on the order-disorder transition temperature, Ms temperature, ductility, hardness and the shape memory properties of ductile Cu-Al-Mn shape memory (SM) alloys was investigated by differential scanning calorimetry (DSC), cold-rolling, and tensile test techniques. It was found that the addition of Co to the Cu-Al-Mn alloys stabilized the B2 phase and decreased the Ms temperature. In the Cu 71 Al 17 Mn 10 Co 2 alloy, the B2 to L2 1 ordering transformation was suppressed by quenching from 900°C and the retained B2 parent phase transformed to the 6M martensite. In several other alloys of this system, the presence of the CoAl (B2 type) precipitate phase was observed. Even though the CoAl precipitate caused a decrease in the cold-workability and the degree of elongation, it nonetheless improved the SM and pseudoelastic (PE) properties of the alloy by solid solution or/and precipitation hardening.

Order-disorder, martensitic and magnetic transformations in the Ni 2 AlMn alloys have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The critical temperatures corresponding to the above transformations have been determined. It is shown that, on aging at low temperature, the parent phase structure changes from that of B2 to L2 1 by an ordering reaction causing the Ms temperature to decrease. The Curie temperature which has the highest value of about T c = 92°C at the Ni 2 AlMn composition decreases steeply on deviating from the stoichiometric composition. Two kinds of new martensite phases have also been detected in the as-aged Ni-21Al-25Mn and Ni-22Al-25Mn alloys.

The effect of alloying elements on the Ms temperature, ductility and the shape memory properties of Cu–Al–Mn ductile shape memory (SM) alloys was investigated by differential scanning calorimetry, cold-rolling and tensile test techniques. It was found that the addition of Au, Si and Zn to the Cu73–Al17–Mn10 alloy stabilized the martensite (6M) phase increasing the Ms temperature, while the addition of Ag, Co, Cr, Fe, Ni, Sn and Ti decreased the stability of the martensite phase, decreasing the Ms temperature. The SM properties were improved by the addition of Co, Ni, Cr and Ti.

The effectiveness of thermal chemical-vapor-deposited (CVD) manganese oxide (MnOx) for their application in the copper (Cu)-through-silicon-via (TSV) structure as a barrier layer was investigated by X-ray photo-electron spectroscopy (XPS), transmission electron spectroscopy (TEM), and capacitance-voltage (C-V) measurements. TEM data revealed the conformal growth of 20 nm-thick MnOx on the surface of plasma-TEOS SiO2 in the sidewall of TSV by thermal CVD. An excellent barrier property for MnOx over the thermal SiO2 was confirmed up to the maximum annealing temperature of 500°C. In the case of plasma-TEOS SiO2, the barrier property was good up to 400°C, but beyond that temperature, the barrier property was found deteriorated. On the contrary, the barrier performance of MnOx grown on the surface of ozone-TEOS SiO2 was found to be negligibly small. Even at room-temperature, we did observe the Cu2p signal emanating from MnOx/SiO2 region. Therefore, care must be taken while using either MnOx as a barrier layer upon ozone-TEOS SiO2 or ozone-TEOS SiO2 itself as a dielectric liner in along the side wall of TSVs, before integrating them into 3D-LSIs.

Martensitic and magnetic transformations of the Heusler Ni50Mn50−yXy (X=In, Sn and Sb) alloys were investigated by differential scanning calorimetry measurement and the vibrating sample magnetometry technique. In all these alloy systems, the austenite phase with the ferromagnetic state was transformed into the martensite phase, which means that these Heusler alloys have potential as Ga-free ferromagnetic shape memory alloys (FSMAs). Furthermore, multiple martensitic transformations, such as two- or three-step martensitic transformations, occur in all these alloy systems. It was confirmed by transmission electron microscopy observation that the crystal structure of the martensite phase is an orthorhombic four-layered structure which has not been reported in other FSMAs. Therefore, the present Ga-free FSMAs have the great possibility of the appearance of a large magnetic-field-induced strain.

Tensile and compressive stress–strain characteristics for Ni–Ga–Fe ferromagnetic shape memory alloys at several temperatures were investigated by mechanical test and a critical stress versus temperature diagram was obtained. The crystal structure of the martensite phase obtained by tensile-stress-induced martensitic transformation was estimated from the degree of the transformation strain. Stress-induced martensite transformed from the parent phase with an L21 structure showed a 14M structure by tensile stress and by further applying stress, the 14M structure martensitically was transformed into an L10 structure. Moreover, it was found in the compressive test that variant rearrangement occurred by very low compressive stress less than 3 MPa, which is similar to the phenomenon seen in Ni–Mn–Ga alloys.

To overcome the scaling limits of flash memory, new phase change materials has been intensively studied for phase change random access memory (PCRAM). Currently, Ge-Sb-Te (GST) film has been widely studied for commercial PCRAM. However, GST shows a poor thermal stability of amorphous phase because of its low crystallization temperature (~160 °C). Consequently, GST PCRAM shows a poor data retention property in high temperature and is suppressed to show a low thermal disturbance resistance in high density array. Recently, Sutou et al. have found that GeCu2Te3 (GCT) shows higher crystallization temperature (~230 °C) than GST. Moreover, they demonstrated that the reset process in GCT memory cell exhibits lower power consumption than that in GST memory cell, which is due to a low melting point of GCT (~500 °C). Since GCT shows phase change speed as fast as GST, it is promising PCM for future PCRAM.The memory cell resistance in PCRAM is very essential factor for accuracy in data reading. As the memory cell size is scaled down, the resistance of the memory cell becomes dominated by the contact resistance between the phase change material (PCM) and electrode. Nevertheless, studies of contact resistance in PCRAM are still limited. To understand the contact resistivity and its contrast between amorphous and crystalline states is more essential for future PCRAM. Therefore, in this study, the contact resistivity of GCT to electrodes was investigated using the circular transfer length method (CTLM). A CTLM pattern was fabricated by photolithography in order to measure the contact resistivity. GCT amorphous film was deposited on SiO2/Si substrates by co-sputtering of GeTe and CuTe targets. For comparison, GST amorphous film was also prepared. GCT crystalline film was obtained by heating the as-deposited amorphous film up to 300 °C in an Ar atmosphere. After reverse sputtering of the surface of the GCT layer, a metal electrode was deposited on the GCT films in the same chamber to prevent the surface oxidation effects. Electrical resistance of the CTLM patterned samples were measured by four-point probe method. Based on the obtained results, the contact resistivity of GCT to electrode was calculated. Current (I) - Voltage (V) characteristics of GCT CTLM samples showed an Ohmic behavior in both amorphous and crystalline states. The contact resistivity could be successfully obtained from GCT CTLM samples in both states since the relationship between the total resistance of CTLM samples and the gap spacing showed a liner relation. The contact resistivity of W/amorphous GCT (as-deposited) contact was calculated to be 3.9×10-2 Ω cm2, while that of W/crystalline GCT (annealed at 300 °C) contact was found to be 4.8 ×10-6 Ω cm2. The ρ c of W/amorphous GST (as-deposited) was 3.2 ×10-2 Ω cm2, whereas that of W/crystalline GST (annealed at 300 °C) was 1.4×10-5 Ω cm2. The resistivity contrast in GCT between amorphous and crystalline state was about one order of magnitude smaller than that in GST. Meanwhile, the contact resistivity contrast in GCT between amorphous and crystalline state was slightly larger than that in GST. Based on the obtained results, we calculated the total resistance of simple memory cell model. When the PCM layer thickness, t is over 10-2 m, the resistance contrast of the GCT memory cell was 17 times smaller than that of the GST cell. This is because the cell resistance is dominated by the ρ of PCM. Meanwhile, the resistance contrast of the GCT cell becomes 4 times larger than that of the GST cell at t < 10 nm because the cell resistance is dominated by the ρ c of PCM to electrode. Therefore, GCT is expected to show not only better thermal stability but also better accuracy in data readout than GST. In the presentation, we will also discuss the electrode dependence of the contact resistivity in GCT film.

Phase Change Random Access Memory (PCRAM) is a promising candidate as next generation non-volatile memory. The principle of PCRAM relies on the resistance contrast between crystalline and amorphous states of phase change material (PCM). Generally, the crystalline phase shows a low electrical resistance (set state), while the amorphous phase shows a high electrical resistance (reset state). The phase transition of PCM is achieved by way of Joule heating induced by an electrical pulse. Currently, Ge-Sb-Te films, namely Ge2Sb2Te5 (GST) compound film, are widely studied for PCRAM application because they show fast phase change speed and excellent reversibility of phase transition. However, GST has a low crystallization temperature (~160°C), which limits high temperature data retention capability. In addition, GST possesses a relatively high melting point (~630°C), which leads to a high power consumption for reset operation. Moreover, with further scaling down of PCRAM memory cell, the thermal disturbance between cells becomes serious problem. To overcome those weakness and problem, it is desired to develop new PCMs with high crystallization temperature and low melting point. From the above background, we have studied the effect of doping element, X on the crystallization temperature in Ge-Te-based PCMs and found that Al, Si and Cu are very effective to improve the thermal stability of Ge-Te amorphous film, based on the total bonding enthalpy of amorphous Ge-Te-X. Among them, Ge-Cu-Te ternary film has been found to have various advantages for PCRAM application. According to Ge-Cu-Te ternary phase diagram, there is a GeCu2Te3 (GCT) ternary compound which shows a melting point of around 500°C. Moreover, Cu2Te-Ge33.3Te66.7 pseudobinary phase diagram indicates that the liquidus line deeply decreases toward the compound composition like eutectic-type phase diagram, which suggests that the amorphous phase can be easily obtained around the compound composition. In this study, the phase transition characteristics of GeTe-CuTe pseudobinary films were investigated. GeTe-CuTe pseudobinary films, including GeCu2Te3 compound film, with a thickness of 200 nm were fabricated by co-sputtering of GeTe and CuTe targets on SiO2/Si substrate. Moreover, to evaluate the memory operation characteristics, simple memory devices with GCT layer were fabricated using a conventional photolithography technique. It was found that in GeTe-CuTe pseudobinary film, the crystallization temperature increases with increasing Cu content in the range of Cu < 15 at.% and the maximum value of about 250°C is obtained, and then the crystallization temperature decreases with further increasing Cu content. The GCT amorphous was found to show the crystallization temperature of about 230°C. It was confirmed that the GCT memory cell exhibits a reversible phase transition between amorphous and crystalline states and shows a lower power consumption for reset operation than GST memory cell. In addition, it was also found by static laser testing that the phase change speed of the GCT film is as fast as that of GST film. Furthermore, it was found that the GCT shows unique phase transition characteristics, namely, a small volume expansion and reflectance decrease by crystallization. Such changes upon phase transition for the GCT are opposite to those for conventional PCMs. It was suggested from AIMD simulation that such unique phase transition characteristics may be caused by unusual structural features of GCT amorphous, such as short Cu bond lengths, threefold rings, and dense Cu-rich regions. In this presentation, the phase transition characteristics of Ge-Cu-Te ternary films and the memory device characteristics will be discussed.

Experimental works are done to assess the seismic behavior of concrete beams reinforced with superelastic alloy (SEA) bars. Applicability of newly developed Cu-Al-Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, have been proposed as partial replacements for conventional steel bars in order to reduce residual deformations in structures during and after intense earthquakes. Four-point reverse-cyclic bending tests were done on 1/3 scale concrete beams comprising three different types of specimens - conventional steel reinforced concrete (ST-RC), SEA reinforced concrete (SEA-RC), and SEA reinforced concrete with pre-tensioning (SEA-PC). The results showed that SEA reinforced concrete beams demonstrated significant enhancement in crack recovery capacity in comparison to steel reinforced beam. Average recovery of cracks for each of the specimens was 21% for ST-RC, 84% for SEA-RC, and 86% for SEA-PC. In addition, SEA-RC and SEA-PC beams demonstrated strong capability of recentering with comparable normalized strength and ductility relative to conventional ST-RC beam specimen. ST-RC beam, on the other hand, showed large residual cracks due to progressive reduction in its re-centering capability with each cycle. Both the SEA-RC and SEA-PC specimens demonstrated superiority of Cu-Al-Mn SEA bars to conventional steel reinforcing bars as reinforcement elements.

Pedunculated hepatocellular carcinoma (HC) is an uncommon tumor of the liver. We present the case of a 56-year-old man with pedunculated HC arising from the lower surface of the liver. We recommend sagittal magnetic resonance imaging, which offers a superior choice of scanning planes, in the diagnosis of pedunculated HC.

Since the discovery of Fe–Ni alloys showing low thermal expansion (LTE) in 1896, many Invar alloys have been developed based on magnetovolume effect where negative thermal expansion is induced by magnetic transformation. Herein, we show that the control of stress-induced martensitic transformation due to cold working of the Cu–Zn–Al polycrystalline alloy results in the LTE. This type of LTE material is easily fabricated by conventional cold rolling, and the coefficient of thermal expansion in the range from about 0 to 32×10−6 K−1 can be obtained by controlling the reduction ratio. The LTE effect due to the present method can also be obtained for other shape memory (SM) alloys such as Ni–Ti, Cu–Mn–Al and Ni–Al base alloys, which have high potential for various practical applications.

The martensitic and magnetic transitions of Ni 54 Ga 27 Fe 19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer. The alloy is martensitically transformed from a L2 1 to a martensite phase with a 14M (7R) structure. The ferromagnetic transition is also accompanied by the martensitic transformation from a paramagnetic parent phase to a ferromagnetic martensite phase in the temperature interval between M s (= 293 K) and M f (= 274 K). The Ni-Ga-Fe system is promising as a ferromagnetic shape memory alloy.

Ferrous Shape Memory Alloy So-called shape memory alloys “remember” the shape they are processed into, and can return to that shape after being deformed by heat. A limitation for most metal-based shape memory alloys is the extent to which they can be deformed elastically. Tanaka et al. (p. 1488 ; see the Perspective by Ma and Karaman ) demonstrate an iron-based alloy that shows much higher levels of superelastic strain, surpassing the performance of nickel-titanium alloys. In addition to high superelastic strain, this ferrous shape memory alloy has much higher strength than NiTi and copper-based shape memory alloys and, consequently, a high-energy absorption capability. These properties may allow shape memory alloys to be exploited as strain sensors or energy dampers.

The electrical resistance on the crystallization process of sputtered-deposited Ge1Cu2Te3 film was investigated by two-point probe method. It was found that the amorphous Ge1Cu2Te3 film crystallizes into a single Ge1Cu2Te3 phase with a chalcopyrite structure, which leads to a large resistance drop. The crystallization temperature of the Ge1Cu2Te3 amorphous film was about 250 °C, which is about 70 °C higher than the conventional Ge2Sb2Te5 amorphous film. The activation energy for the crystallization of the Ge1Cu2Te3 amorphous film was higher than that of the Ge2Sb2Te5 amorphous film. The Ge1Cu2Te3 compound with a low melting point can be expected to be suitable as the phase change material for PCRAM.

An ingrowing toenail has no definitive treatment. Previously, effective methods were complicated but easy ones had less effect. We show both an easy and an effective way with Cu-Al-Mn-based shape-memory alloys (SMAs). They have a characteristic shape which patients themselves can detach easily without any pain. But they also have enough corrective force. Cu-based SMAs cost much less than Ni-Ti-based alloys. Despite not being appropriate for all cases of ingrowing toenails, it is an easy, effective and less costly alternative.

GeTe-Sb2Te3 pseudobinary compounds are attracting considerable attention as phase change materials for optical disk and phase change random access memory (PRAM). In these compounds, Ge2Sb2Te5 (GST) has been used for an optical disk memory such as DVD-RAM because the crystallization by laser beam heating is very fast (∼20ns). Recently, the GST has been much considered as material for PRAM and, therefore, the electrical resistance change due to crystallization and the phase change by applying an electrical current have been widely investigated. On the other hand, although GeTe compound has been suggested as the phase change material for the optical disk by Chen et al in 1986, the study focusing on the phase change material for PRAM is limited. Since GeTe is known to show the phenomenon of electrical switching, this compound has a potential of PRAM. In this study, the electrical resistance and crystalline structural changes on crystallization process in Ge-Te thin films were investigated.Films of amorphous Ge100–xTex (x : 46-94) with 200 nm thickness were deposited by sputtering of GeTe alloy target or co-sputtering of GeTe and Te targets on SiO2/Si substrates. In-situ electrical resistance measurements during heating process of these films were performed by two point probe method in a heating rate of 2∼50°C/min. X-ray diffraction (XRD) analysis was employed for the structural identification of thin films for 10-60° in 2′ using X-ray diffractometer with Cu-K. Transmission electron microscope (TEM) analysis was carried out to investigate the microstructure and to identify crystalline structure. The compositions of these films were confirmed by energy dispersive X-ray spectroscopy (EDS) attached TEM.All as-deposited Ge-Te films were confirmed amorphous by XRD and TEM. From the in-situ electrical resistance measurements, it is found that resistance change with crystallization process depends on the composition and the stoichiometric GeTe compound shows abrupt electrical resistance change at around 190 °C. The crystallization temperature of GeTe was higher than that of GST and resistance difference between the amorphous and the crystal was also larger. While the electrical resistance of GST film gradually decreased with increasing temperature after the crystallization at around 160 °C, that of GeTe film showed small temperature dependence after crystallization. It was found by X-ray measurement observation that the amorphous GeTe compound film crystallized first into a cubic state, and then into a stable rhombohedral state by further heating. The crystallization kinetics of Ge-Te thin films will be also presented.

It has recently been reported that the movement of twin (or variant) boundaries, induced by a magnetic field during the martensitic transformation, affects the magnetic properties and shape change in the ferromagnetic NiGaMn shape memory (SM) alloys. These observations suggest that the NiGaMn SM alloys with an L2{sub 1} (Ni{sub 2}GaMn: Heusler) structure have the potential for use as a new type of smart materials whose SM properties can be controlled not only by temperature and stress, but also by a magnetic field. Very recently, the present authors have detected that in the alloys with compositions near the stoichiometric Ni{sub 2}AlMn, the ferromagnetic L2{sub 1} phase appears on low-temperature aging and it transforms martensitically from B2 to 2M. This suggests that the NiAlMn Heusler alloys could also exhibit unique magnetic and SM properties similar to those of the NiGaMn alloys. It is the purpose of this article to report the results of investigations on the magnetic properties of the NiAlMn Heusler alloys.

The purpose of this short chapter is to discuss the ability of the micro-pulling-down system to grow metallic alloy fibers. Preliminary examinations of the material properties of fibers grown in this way and their applicability to industrialization are particularly useful. Some examples of the solidification of such alloys are given here.

The phase change processes of as-deposited Sb-Zn films were investigated. The as-deposited amorphous SbZn film showed an unusual increase in resistance during heating, which was attributed to crystallization of the metastable SbZn phase. Further heating up to more than 300oC resulted in a structural transformation into the stable SbZn phase accompanied by a drop in resistance as in conventional phase change materials. Even though off-stoichiometric Sb-rich films exhibited crystallization into the metastable phase as well, the precipitation of Sb crystalline grains caused an undesirable drop in resistance at temperatures lower than that of the SbZn film. A memory device using an SbZn film showed typical switching behavior and successfully switched from the amorphous to crystal state and vice versa by the application of an electric pulse. These results revealed that stoichiometric SbZn film is a promising novel phase change material for phase change memory with high thermal stability.

We present a novel device architecture for low set and reset currents in phase change random access memory (PCRAM). In this structure, the sidewall of phase-change film is contacted with the vertical heating layer. In particular, to realize a small contact area of under 50 nm2 for low reset current, this structure includes stacked layers consisting of extremely thin phase change material (PCM) and conduction films, the fabrication method of which is proposed. We estimated set and reset currents for the proposed structure by the device simulation method. Here, we confirmed that a contact area of 30 nm2 in this structure, where Ge2Sb2Te5 is used as PCM, provides a reset current of 13.5 µA and a set current of 4 µA, which are promising for the scaling down of PCM. Furthermore, it is confirmed that the thinner PCM in this structure provides less thermal disturbance to the neighboring cell. From the results, we expect this structure to be a promising candidate for a high-density nonvolatile memory architecture with PCM.

The effect of applied strain on martensitic transformation in a superelastic Ti(46.4)Ni(47.6)Nb(6.0) alloy at room temperature was investigated by tensile tests, differential scanning calorimetry measurements, and X-ray diffraction. Reverse transformation starting (A(s)) and finishing (A(f)) temperatures increased with the application of tensile-strain over 13%, the undeformed specimen showing A(s) = -29.2 degrees C and A(f) = 17.9 degrees C, while the 13% predeformed alloy exhibited A(s) = 37.1 degrees C and A(f) = 40.2 degrees C. Furthermore, the values of the A(s) and A(f) for the predeformed alloy almost recovered to those of the undeformed alloy when heated to about 42 degrees C and then showed superelasticity again at room temperature. This characteristic is significant for application in sensors, actuators, and medical devices. Especially, medical stents with such qualities show promise as a new class of self-expandable stents with both excellent mountability and deliverability.

Large magnetic-field-induced strains1 have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field1,2,3. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy4. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.

Ferromagnetic Shape Memory Alloy (FSMA) particulate composites are processed using Spark Plasma Sintering (SPS) with various weight fractions of NiTi (51 at% Ni) and Fe powders. The magnetic properties of these composite specimens were experimentally evaluated using Vibration Sample Magnetometry (VSM). A model for calculating the effective magnetic properties has been presented in this work where Eshelby's inhomogeneous inclusion method considering Mori-Tanaka's mean field theory for larger concentrations of Fe has been used to predict the effective magnetic properties. The analytical results thus obtained are compared with experimental data resulting in a reasonably good agreement.

A new type of medical guide wire with functionally graded hardness from the tip to the end was developed with the use of Cu-Al-Mn–based alloys. The superelasticity (SE) of the Cu-Al-Mn–based alloys in the tip is drastically improved by controlling the grain size, whereas the end of the wire is hardened using bainitic transformation by aging at around 200–400 °C. Therefore, the tip of the guide wire shows a superelasticity and its end has high stiffness. This guide wire with functionally graded characteristics shows excellent pushability and torquability, superior to that of the Ni-Ti guide wire. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 69B: 64–69, 2004