TiPd Shape Memory Alloy Research Articles

Effect of Ternary Additions X (Co, Rh, Ir) on Electronic Properties of TiPd Shape Memory Alloy: An ab-initio Study

Effect of Ternary Additions X (Co, Rh, Ir) on Electronic Properties of TiPd Shape Memory Alloy: An ab-initio Study

The compositional stability of the P-phase in Ni–Ti–Pd shape memory alloys

The precipitation of the P-phase in Ni–Ti–Pd and Ni–Ti–Pt shape memory alloys has been shown to dramatically increase the martensitic transformation temperature and strength in Ni-rich ternary alloys, yet little is known about the phase's compositional stability. Therefore, the compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content while maintaining the general P-phase Ti11(Ni + Pd)13 stoichiometry. Each alloy was solutionized at 1050 °C followed by water quenching, and aging at 400 °C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti2Pd3, B2 NiTi, P- and P1-phases. The latter precipitate phases became more stable with increasing Ni at the expense of the Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti–29.2Ni–25Pd (at.%) or Ti11(Ni7Pd6) as compared to the P1-phase 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti5Ni5Pd.

TiPd Shape Memory Alloy Studied by PAC Method

Perturbed angular correlation (PAC) method was applied to study the martensitic phase transition of the TiPd shape memory alloy doped with In, Hf, and Zr. The hyper ne interaction parameters and their concentration and temperature dependences for In/Cd and Hf/Ta probe atoms were determined. The in uence of ternary element additions on the electric eld gradients at Pd site was evidenced. A decrease of the martensite start temperature (MS) and an increase of the width of the hysteresis loop (TH) with an increasing concentration of the impurities in TiPd alloy was observed. These relationships are much stronger for In and Zr, than for Hf admixture.

Morphology and Crystallography of Martensite Plate with Long Period Stacking Structure in Ti-Pd Shape Memory Alloy

The morphology and crystallography of martensite plates with a long period stacking structure in Ti-Pd shape memory alloy were investigated by transmission electron microscopy. In addition to B19 (2H) martensite, an 18R(2\\bar1)6 structure was observed in equiatomic Ti-Pd alloy quenched above 1373 K. Three fundamental plate variant combinations were identified in the plate group in the region consisting exclusively of 18R martensite. These were designated A:B, A:C and A:D types, and their morphologies and crystallographic characteristics are a wedge with type II, a spear with type I and a fork with compound twin relations, respectively. Duplex martensitic phases coexisting in the same area, namely, “two-in-one” structures, were also observed.

Martensitic transformation in TiPd shape memory alloys studied by PAC method with 111Cd probes

Perturbed angular correlation (PAC) method was applied to study the martensitic phase transition of the TiPd shape memory alloy doped with 111In/ 111Cd probe atoms. The hyperfine interaction parameters and their concentration and temperature dependences for probes with cubic and noncubic surroundings of the lattice sites, consistent with the respective crystal structures in martensite and austenite phase, were determined. A strong dependence of the martensite start temperature ( M S) and shape of the hysteresis loop ( T H) on the small admixture of the In impurities in TiPd compound was evidenced. The observed decrease in the M S depends not only on the amount of the third element, but also on the element itself. The data were compared with those obtained with 181Hf/ 181Ta probes in TiPd alloy with hafnium admixture.

Anomalies in physical properties and diffuse scatterings for iron-doped Ti-Pd shape memory alloys

Transformation behaviour in Ti-(50-x)Pd-xFe shape memory alloys was investigated by electrical resistivity and specific heat measurements. The alloys with x = 14, 16 and 18 exhibit an obvious first order martensitic transformation but the alloys with x ≥ 19 do not exhibit a first order transformation down to 4.2 K. However, the alloys with x ≥ 19 show a negative temperature coefficient in electrical resistivity below a specific temperature Tmin. In addition, specific heat measurements at cryogenic temperatures revealed that the Debye temperature of the first order transformation-suppressed state is significantly lower than that of the martensite state. These anomalies are suggested to be caused by an instability of the electronic structure of the B2-phase.

Crystallography and Morphology of Antiphase Boundary-Like Structure Induced by Martensitic Transformation in Ti-Pd Shape Memory Alloy

Crystallography and Morphology of Antiphase Boundary-Like Structure Induced by Martensitic Transformation in Ti-Pd Shape Memory Alloy

Martensitic transformation in TiPd shape memory alloys studied by PAC method with 181Ta probes

Perturbed angular correlation (PAC) method was applied to study the martensitic phase transition of the TiPd shape memory alloy doped with 181Hf/ 181Ta probe atoms. The hyperfine interaction parameters and their concentration and temperature dependences for probes with cubic and noncubic surroundings of the lattice sites, consistent with the respective crystal structures in martensite and austenite phase, were determined. A strong dependence of the martensite start temperature ( M S) and the shape of the hysteresis loop ( T H) on the small admixture of the Hf impurities in TiPd compound were evidenced. The observed decrease of the M S value differs from the behavior of TiNi alloy, where adding hafnium as the third element leads to a rise of M S.

Morphology and crystallography of Ti2Pd phase precipitated in B2 parent and B19 martensite matrices in Ti-rich Ti–Pd alloys

Morphology and crystallography of Ti2Pd phase of C11b structure precipitated in B2 parent and B19 martensite matrices in Ti-rich Ti–Pd shape memory alloy have been investigated by transmission electron microscopy observations. Three Ti2Pd variants were recognized in the specimen aged above Af temperature, i.e., in the B2 matrix. On the other hand, four Ti2Pd variants were confirmed in the specimen aged below As temperature, i.e., in the B19 matrix. The orientation relationship between the Ti2Pd precipitate and each matrix is consistent with the number of Ti2Pd variants. The Ti2Pd precipitates in the B2 and the B19 matrices have a disk and a polygonal plate shapes, respectively. The c-axis of Ti2Pd precipitate in the B2 matrix is perpendicular to the disk surface. On the other hand, that in the B19 matrix is parallel to the plate surface. These differences are well explained by the magnitude of coherent strain.

Morphological and crystallographic aspects of Cl1b-type precipitates nucleated in martensitic and parent phase matrices in Ti-rich Ti-Pd shape memory alloys

Ti 2 Pd phase with C11 b -type structure which precipitates in Ti-rich Ti-Pd shape memory alloys may nucleate either in martensitic phase or parent phase depending upon thermal treatment conditions, since the transformation temperatures are around 800 K. In the alloy aged above A f , three C11 b -type precipitate variants are always observed by TEM. The orientation relationship between those three variants and the B19 structure, which was transformed from B2 structure after the precipitation, is as follows: Variant I (001) Ti2Pd //(101) B19 ; Variant II (001) Ti2Pd //(101) B19 ; Variant III (001) Ti2Pd //(010) B19 . The shape of the precipitates was deduced to be disk-like and/or elliptic. On the other hand, only the variants I and II are observed when the precipitates are nucleated in martensitic phase. Since the difference between the lattice spacing of (010) B19 and (001)/3 Ti2Pd is about 20%, the formation of a third variant in the martensitic matrix is energetically unfavorable.

Effect of Aging on Martensitic Transformation in Ti-Rich Ti-Pd Shape Memory Alloy

Effect of aging on successive martensitic transformation in a Ti–47 at%Pd shape memory alloy has been studied by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). After short time aging successive transformation takes place in Ti–47 at%Pd alloy irrespective of aging temperature. On the other hand, after relatively prolonged period only the specimen aged above 1073 K shows successive transformation. The change of transformation behavior with aging condition is discussed on the basis of equilibrium between TiPd matrix and Ti2Pd precipitate. The homogeneity range of TiPd compound is also estimated from the transformation behavior and TEM observations.

Martensitic Transformation in Ti-Rich Ti-Pd Shape Memory Alloys

A systematic study on martensitic transformation in Ti-rich Ti–Pd alloys has been carried out using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The alloys quenched from the single region of B2 parent phase show a successive transformation during DSC measurement. On the other hand, the furnace-cooled alloys show a single transformation. The successive transformation behavior is closely related to the formation of fine Ti2Pd precipitates with C11b-type structure during transformation cycle. The first peak on DSC heating curve is attributable to the reverse martensitic transformation of the TiPd matrix, while the second one is due to the reverse martensitic transformation in local regions around the Ti2Pd precipitates where Pd concentration is higher than that in matrix. Morphological characteristics of the precipitate are also discussed.

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

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 Young's 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.

Crystallography and Boundary Structure of Twins in Ti-Ni and Ti-Pd Martensites

Morphology and crystallography of twins in the martensite in Ti-Ni and Ti-Pd shape memory alloys are reviewed on the basis of recent electron microscopy observations. It has been confirmed that there are five and three twinning modes in Ti-Ni and Ti-Pd martensites, respectively. The morphology and crystallography of newly found deformation twin in Ti-Ni martensite are briefly reported. The irrational nature of Type II twin boundary has been clarified by high resolution electron microscopy observations in edge-on state. There are neither ledge nor step structures at the irrational boundary.

Ti-NiおよびTi-Pd形状記憶合金のマルテンサイトにおける第II種双晶の界面構造

Ti-NiおよびTi-Pd形状記憶合金のマルテンサイトにおける第II種双晶の界面構造

Transmission electron microscopy of twins in martensite in TiPd shape memory alloy

Twins in the B19 martensite in the TiPd shape memory alloy have been investigated by conventional transmission electron microscopy (CTEM) and electron diffraction. There were three twinning modes, i.e. 111 Type I, 〈121〉 Type II and 101 compound twins, in the martensite. The 111 Type I and 〈121〉 Type II twinnings which were conjugate to each other coexisted in a same martensite variant. The 111 Type I twins were dominantly observed and the 〈121〉 Type II twins were less frequently observed. The former twinning was considered to be a lattice invariant shear. The Type II twin plate appeared in two types of forms. The first one was directly connected to the Type I plate. In other words, the twin plate was inclined at crystallographically defined angle. The second one branched off from the Type I plate. Since there was no martensite variant consisting wholly of the 〈121〉 Type II twins throughout the present observations, the 〈121〉 Type II twins were considered to be a deformation twin due to the elastic interaction during the transformation. The 101 compound twinning was also considered to be a deformation twin which was introduced as result of elastic interactions during the transformation since the twin had an isolated fashion in the martensite variant consisting of 111 Type I twins.

Effects of residual strain on deformation processes of neutron-irradiated TiNi and TiPd shape memory alloys

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.