Kazuyuki Enami

Magnetic-Field-Induced Martensitic Transformation in Ni2MnGa-Based Alloys.

The magnetic controllability of the thermoelastic martensitic transformation, which is the origin of the shape-memory effect, has been investigated. We have carried out neutron diffraction measurem...

Alloys Design of PdTi-Based Shape Memory Alloys Based on Defect Structures and Site Preference of Ternary Elements

Defect structures and site preference of ternary elements in B2-type PdTi alloys are evaluated in order to design PdTi-based smart materials using the pseudo-ground state analysis (or analysis performed at near zero Kelvin). It has been found that this analysis can predict types of defect structures in these alloys which are of antistructure (substitution) type regardless of alloy compositions. Substitution behavior predicted is as follows: (1) most elements belonging to groups 1A through 5A occupy Ti sites only; (2) most elements belonging to groups 6A through 8A occupy Pd sites only; and (3) the others studied occupy either sites when these sites are unfilled with the corresponding constituent elements (Pd or Ti). Moreover, effects of both offstoichiometry and 3dtransition elemental additions on martensitic transformation start temperature (MS) in PdTi alloys are evaluated as a function of electron-atom ratio (e/a). It has been found that M, is strongly related to the e/a value when 3d electrons of ternary additions are taken into account, although the effect of e/a on M, differs if their substitution behavior is different. Changes in M, per e/a are estimated to be 900 K when Pd-site substitution elements, such as Cr, Mn, Fe, Co, and Ni are added, while changes in M, per e/a are 790 K when Ti-site substitution elements such as V are added. This suggests that M, is influenced not only by the e/a value but also by atomic configurations.

Thermomechanical behavior of Ti-25Pd-24Ni-1W shape memory alloy reinforced Ti matrix smart composites

Abstract A Ti-matrix composite reinforced by a TiPd-based shape memory alloy (SMA) with the composition of Ti–25at.%Pd–24at.%Ni–1at.%W was fabricated by sheath rolling of the SMA plates (whose austenite start temperature was 465 K) and Ti matrix plates, which were alternatively laminated and inserted in a SUS304 stainless steel pipe before rolling. Heat-treated sheath-rolled composite was found to have a multi-layered interface structure between the SMA plate and Ti plates. The thermomechanical behavior of the composite was investigated experimentally and analytically. The 0.5% yield stresses of the composite increased with increasing temperature at temperatures higher than A s (0). This stress behavior could be explained based on a one-dimensional analytical model. Hence, it can be concluded that the stress increase is caused by the accumulation of residual compressive stress formed in the matrix by a martensite-to-austenite transformation of the SMA during heating and the yield stress increase of the SMA at high temperature.

Processing of TiPd shape memory alloy reinforced Ti-matrix composites and their mechanical properties

Abstract Ti and Ti-2Cu matrix composites reinforced by TiPd-based shape memory alloys (SMAs) were fabricated by sheath rolling of Ti or Ti-2Cu plates with TiPd fiber. Fibers of three TiPd SMAs were used as reinforcements. The Youngs modulus of TiPd fiber increased with increasing temperature above austenite start temperature, A s . Good bonding between the fiber and matrix was obtained by heat treatment at 1123 K for 3.6 ks following sheath rolling at the same temperature. A multi-layered reaction region was formed in the vicinity of the interface between Ti or Ti-2Cu matrix and TiPd-based SMA fiber. Tensile tests were performed at various temperatures for Ti-2Cu matrix composites containing Ti–22Pd–27Ni–1W and Ti/Ti–25Pd–24Ni–1W fiber. It was found that the 0.5% offset stress of these composites increased with increasing temperature. This stress increase is mainly caused by residual compressive stresses generated in association with shape memory effects of the TiPd-based SMAs. Surface observations of fractured specimens showed that interfacial layers were fractured in a ductile fracture mode.

Electron Microscopy Study of ScMnO3

We observed high-resolution transmission electron microscopy (HRTEM) images of ScMnO3 under the conditions E=400 kV and Cs=1.0 mm, and attempted computer simulations of the images using the multislice method, the results of which strongly support the X-ray Rietveld analysis in our previous study.

Irradiation induced stress relaxation and high temperature deformation behavior of neutron irradiated Ti based shape memory alloys

Abstract Several tools using Ti based shape memory alloys (SMA) such as SMA coupler, connector, jack system and in-vacuum gate valve, have been developed to promote the remote maintenance and the quick replacement technology for fusion core parts. Recently, irradiation induced stress relaxation (IISR) has become a concern for components of the fusion core. IISR may be a severe problem for SMAs as well as the structural materials in the fusion reactor. The IISR of TiNi SMA and TiPd high temperature shape memory alloys (HTSMA), which have both transformation temperatures and working temperatures 400 K higher than those of TiNi alloys, may be controlled by the migration of vacancies rather than interstitials. This mechanism facilitates restoration of the damaged state to normal state under irradiation. TiPd HTSMAs may be used to fabricate irradiation-resistant shape memory devices for temperatures up to 800 K if proper heat treatments can be developed.

Theoretical Analysis and Basic Experiments for the 3D Displacement Measurement Using Ring-Shaped Laser Beam

For flexible 3D positioning of a complex 3D mechanism, it is needed to measure 3D displacement of the end-effecter of the mechanism in high precision and by non-contact method. It was common to use plural sensors or scales together to measure the 3D displacement. However, it is difficult to calibrate the sensitivities of the plural sensors or scales. A novel 3D displacement measurement is proposed using an optical system in which lens focuses are collected at the center of the sphere, which has been used for the radius measurement of the sphere. Instead of facing in the XY direction that has high sensitivity, new ideas are necessary for the measurement in the Z direction of the optics where focuses are collected at the center of the sphere. The displacement in the XY direction and the one in the Z direction can be measured at the same time by using a ring-shaped laser beam instead of a simple ray.

Effects of residual strain on deformation processes of neutron-irradiated TiNi and TiPd shape memory alloys

Abstract TiNi and TiPd shape memory alloys (SMA) reveals good workability and shape memory properties and these SMAs seem to be one of hopeful functional materials in a severe irradiation field. The effects of irradiation induced residual strain on the deformation processes of TiNi and TiPd SMAs after neutron irradiation with fluences ( E > 1 MeV) up to 3.9 × 10 24 m −2 at Japan Materials Testing Reactor (JMTR) were investigated by the remote controlled X-ray diffraction measurement. Residual strains of TiNi SMAs took place over damage of 0.1 dpa and the strains were not completely removed by post-irradiation annealing at 473, 523 and 573 K. On the other hand, residual strains of TiPd SMAs scarcely occurred after irradiation, and furthermore, the TiPd SMA seems to be an irradiation-resistant material. This may be explained by a difference between the irradiation response of a parent phase and that of a martensitic phase to neutron irradiation. Deformation processes of SMAs are associated with stress fields generated by irradiation in a parent phase with B2 type ordered structure or in a martensitic phase with 2H and 9R type close-packed structures.

Deformation behavior of TiPd-Cr high temperature shape memory alloys

High temperature tensile tests were carried out for TiPd-Cr alloys with the composition of Ti50Pd50-XCrX (X = 0, 1, 2, 3, 4at.%Cr). When the alloys with 0, 1 and 2at.%Cr were deformed around Ms, neither shape memory effect nor pseudoelasticity was observed. Dominant factors governing the deformation process at high temperatures around Ms are the slip deformation rather than that accompanied by the martensitic transformation in these alloys. On the other hand, the higher Cr content above 3at.%Cr alloys exhibit shape memory effects even at higher temperatures above 600K. The residual strain around 0.6% was found to exist in these alloys. This is due to a sort of stabilization of martensitic phase by recrystallized grain boundary of parent phase. These results suggest that there is enough possibility in developing the high temperature TiPd based shape memory devices working at any temperature up to 800K if we choose a proper alloy composition and an optimum technique for improving the mechanical properties.

Effect of neutron irradiation on deformation behavior in TiPd-Cr high temperature shape memory alloys

Deformation behavior of TiPd-Cr high temperature shape memory alloys, which were neutron irradiated at 490K with a maximum fast neutron fluence of 3.9×1024m−2, was measured by high temperature tensile tests. Abrupt changes in stress-strain curves were observed at an irradiation temperature of 490K. Neutron irradiated Ti50Pd50-XCrX (X=0, 1, 2, 3, 4) alloys exhibited Radiation Induced Pseudoelasticity (RIPE) and it is characterized by recoverable strain (including elastic strain) of 2% because of presence of back stress taken place in aggregates of irradiation induced defects. Youngs moduli of irradiated alloys showed minima around As of each alloy. It is confirmed that martensitic transformation in TiPd based alloy is a little affected by neutron irradiation. The degradation of high temperature shape memory capability, however, is so little on deformation behavior that we can apply TiPd based devices to nuclear fission and fusion field.