Ti50Ni25Cu25 Alloy Research Articles

Investigation of crystal structure formation by electropulse treatment of amorphous Ti50Ni25Cu25 alloy ribbons

The study of the effect of electropulse treatment with a variable duration on the crystallization processes and the structure of a amorphous TiNiCu alloy with 25 at.% Cu in comparison with isothermal annealing and heating at a constant speed was carried out. The alloy was fabricated by rapid-quenching from the liquid state (melt spinning technique) at the cooling rate of the melt of about 106 °C/s in the form of a ribbon with a thickness of 28 μm with a surface crystal layer with a thickness of about 2-3 μm. To remove the crystal layer, the method of double-sided electrochemical polishing was used. The studies were carried out by methods of differential scanning calorimetry, metallography and scanning electron microscopy. It was established that the formation of the crystalline phase in the electropulse treatment of the amorphous ribbon occurs from the surface to the inner part due to the predominant formation and growth of columnar crystals with subsequent nucleation and growth of crystals in the rest of the ribbon.

Comparative analysis of the crystallization mechanisms and kinetics in the Ti50Ni25Cu25 alloy amorphized by melt quenching or severe plastic deformation

The crystallization mechanisms and kinetics in amorphous Ti50Ni25Cu25 alloy produced by different methods of amorphization have been studied by X-ray diffraction at room temperature and in situ synchrotron diffraction upon heating up to 823 K. One of the amorphous states was obtained by melt quenching (MQ) at a cooling rate of ≈106 K/s. The other amorphous state was realized in a polycrystalline alloy of the same composition by high pressure torsion by four revolutions of the movable anvil (HPT4). Differential scanning calorimetry was used to determine the temperatures of crystallization and glass transition, as well as a change of the thermal effect as a function temperature. It is shown that the amorphous states under consideration substantially differ in the mechanisms and temperature parameters of crystallization. The amorphous phase produced by HPT4 was found to be less stable with respect to heating than the amorphous phase obtained by MQ. The origins of the difference in the crystallization kinetics of the amorphous phases obtained by MQ and HPT4 are discussed.

EXAFS and EELFS Spectroscopy in Analyzing the Atomic Structure of the Bulk and Surface Ti50Ni25Cu25 Alloy Domains upon Extreme Impacts by Megaplastic Deformations and Quenching from a Melt

EXAFS and EELFS Spectroscopy in Analyzing the Atomic Structure of the Bulk and Surface Ti50Ni25Cu25 Alloy Domains upon Extreme Impacts by Megaplastic Deformations and Quenching from a Melt

Crystallization of Ti-Ni-Cu-(Cr, Fe, Mn) metallic glasses

In the present work we study crystallization of the Ti50Ni22Cu22TM6 (TM stands for other transition metals: Cr, Mn and Fe) glassy alloys produced by rapid solidification of the melt. The effect of the additional transition metals Cr, Mn and Fe in stabilization of a cP2/B2 type phase is clarified in comparison with the base ternary Ti50Ni25Cu25 alloy. The transformation temperature and heat effects were studied by differential scanning calorimetry. The structure of the samples in the as-prepared and annealed states was examined by X-ray diffraction and transmission electron microscopy. Polymorphic transformation mechanism leading to the formation of the cP2/B2 type phase is studied in detail. Crystal nucleation and growth initiate on the free surface of the Fe-bearing alloy leading to the strong< 100 >texture formation and weak exothermic reaction which changes the shape of the DSC curves. On the contrary, the crystallization occurs within the entire volume of the Mn- and Cr-containing samples, indicating the effect of nucleation and growth of pre-existed nuclei in the glassy state on the heat release of crystallization and the resulted microstructure.

Investigation of thermal-structural characteristics at two-way shape memory effect of rapid quenched laminated amorphous-crystalline ribbons of Ti50Ni25Cu25 alloy

The work is devoted to the study of processes of structural changes leading to the realization of the two-way shape memory effect (TWSME) in the rapid quenched amorphous-crystalline alloy Ti50Ni25Cu25. The object of the study was a rapid quenched laminated amorphous-crystalline Ti50Ni25Cu25 alloy ribbon with a thickness of about 39 um and with a thickness of surface crystal layer about 10 μm was present on the non-contact side relative to the quenching wheel. In the ribbon under study, without any additional heat treatments the TWSME with bending deformation from a rectilinear shape during heating and cooling in the range of martensitic transformation is manifested. The samples were characterized by means: scanning and transmission electron microscopy; X-ray diffraction analysis; differential scanning calorimetry; measuring the characteristics of the crystalline layer during the implementation of TWSME and the temperature dependence of the form change. It was shown that the formation of a laminated amorphous-crystalline composite occurs due to the martensitic transformation of B2∼B19 in the crystal layer and the accompanying TWSME as a result of which the crystal layer is reduced.

Investigation of the effect of electric pulse heat treatment of rapid-quenched Ti50Ni25Cu25 alloy ribbons with a thin surface crystal layer on the structure formation from an amorphous state

This work is devoted to the study of the influence of electric pulse heat treatment of rapid-quenched Ti50Ni25Cu25 alloy ribbons (at. %) with a surface crystal layer. The object of the study was a rapid-quenched layered amorphous-crystal ribbon with a thickness of about 30 µm and a width of about 1.5 mm, in which a thin surface crystal layer (2.5 µm) was present on the non-contact side relative to the quenching wheel. The alloy samples were subjected to electric pulse treatment by passing a single pulse of electric current through the sample with a variable duration. For comparison, samples of the alloy were obtained, crystallized by standard isothermal heat treatment. The samples were characterized by means of scanning electron microscopy techniques, energy dispersive X-ray analysis and differential scanning calorimetry. It was shown that electric pulse treatment with an exposure time of less than 1 second leads to a significant change in the formed crystalline structure in comparison with the structure obtained by isothermal treatment. The microstructure of such samples in cross section is characterized by an uneven distribution of crystals over the thickness of the ribbon: columnar crystals are observed from the contact and non-contact sides of the ribbon, and large crystals are present in the inner part of the ribbon.

Specific Features of the Atomic Structure of Ti50Ni25Cu25 Alloy Rapidly Quenched from Melt

A complex study of the structure of Ti50Ni25Cu25 alloy obtained in the initial amorphous state by rapid quenching (melt spinning) have been performed for the first time. The investigations are carried out by methods of neutron diffraction, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electron microdiffraction. It is found that the topological and composition short-range atomic order, corresponding to three superstructure types (B2, L21, and L12), is formed within localized nanodomains (up to 1 nm) in amorphous Ti50Ni25Cu25 alloy upon solidification. It is also demonstrated for the first time that the alloy has an amorphous–crystal structure, which contains (along with individual microspherulites that underwent thermoelastic martensitic transformation B2 ↔ B19) nanocrystalline ensembles with the B2, L21, or L12 structure up to 10 nm in size, which are localized in the amorphous matrix.

Specific Features of the Atomic Structure of the Ti50Ni25Cu25 Alloy Amorphized during Rapid Quenching from a Melt

This paper presents results of the structural study of the Ti50Ni25Cu25 alloy formed under rapid quenching from a melt. The studies were performed using neutron and X-ray diffraction and transmission and scanning electron microscopy. It has been revealed that this alloy has an amorphous nanocrystalline structure, which contains В2, L21, and L12 ensembles of nanocrystals with sizes to several nanometers in an amorphous matrix alongside with microspherolites, which have sustained the thermoelastic В2–В19 martensitic transition. It has also been shown for the first time that topological and compositional short-range atomic order is formed in the amorphous matrix of the Ti50N25Cu25 alloy in the form of localized nanodomains by the same three types of superstructures (В2, L21, L12).

High pressure torsion induced structural transformations in Ti- and Zr-based amorphous alloys

The melt-spun (MS) Ti50Ni25Cu25 alloy and the Zr62Cu22Al10Fe5Dy1 bulk metallic glass (BMG) were subjected to high pressure torsion (HPT). X-ray diffraction (XRD) measurements show a shift of the first diffraction halo to a low angle after HPT processing, which corresponds to an increase in the values of the radius of the first coordination sphere and the free volume. Direct density measurements confirmed an increase in free volume values. A special TEM procedure was used for a detailed study of the microstructure of both amorphous alloys after HPT processing. The study revealed the formation of a large density of shear bands (SBs) in both alloys. Nanocrystals are formed directly in shear bands as a result of strain-induced nanocrystallization. Amorphous nanoclusters with a size of 20 nm are formed in an amorphous matrix surrounding the SBs in the HPT-processed MS alloy Ti50Ni25Cu25. The formation of nanoclusters was not observed in BMG Zr62Cu22Al10Fe5Dy1 after HPT processing.

Atomic Force Microscopy Studies of Severely Deformed Amorphous TiNiCu Alloy

The amorphous Ti50Ni25Cu25 alloy was subjected to high pressure torsion (HPT) processing. TEM studies revealed in the structure of the HPT-processed samples the presence of nanocrystals with a size of about 5 nm and amorphous clusters with a size of about 10-30 nm. Atomic force microscopy (AFM) was used to study the surface morphology of foils prepared by ion polishing from the initial amorphous ribbons and HPT-processed samples. AFM images of the foil prepared from the initial ribbon revealed a smooth surface with an average roughness of 0.3 nm. A totally different surface morphology was observed for the foil prepared from the HPT-processed state by the same regime of ion polishing: the presence of holes with a depth of 2-4 nm and a width of 10-30 nm. The changes in the surface morphology, namely the holes-like surface morphology of the HPT-processed state, could be explained by a complex transformation of the amorphous structure, and probably by the variation and redistribution of free volume, which leads to the emergence of a cluster contrast in TEM images.

Cluster structure in amorphous Ti-Ni-Cu alloys subjected to high-pressure torsion deformation

The features of the internal structure's evolution of melt-spun (MS) amorphous Ti50Ni25Cu25 alloy samples subjected to high-pressure torsion (HPT) at 20 and 150 °C were revealed by TEM and STEM – in the planar direction and the cross-sectional direction of the HPT-processed disc-shaped samples.In STEM HAADF observations in the planar direction, areas with brightness contrast with a size of 20 nm are revealed. We assume them to be “amorphous nanoclusters”. In dark-field TEM images, in many areas nanocrystals (with sizes about 5 nm) are revealed, resulting from strain-induced nanocrystallization. In STEM HAADF images, there can be seen nanoclusters (with sizes about 20 nm) separated by bright boundaries. Groups of shear bands (SBs) are revealed on the cross-sectional directions on lamellae cut from the HPT-processed samples. Nanocrystals form directly in the shear bands as a result of strain-induced nanocrystallization. Amorphous nanoclusters are also observed in the amorphous phase surrounding the SBs. Formation of the amorphous nanocluster in the areas surrounding the shear bands has been discovered for the first time. Atomic force microscopy (AFM) was used to study the surface morphology of foils prepared by ion polishing from the initial amorphous ribbons and HPT-processed samples. A hollows-like surface morphology in the HPT-processed state is revealed by AFM, which is reflected as nanocluster contrast in TEM images. The hollows-like surface morphology could be explained by the specifics of etching processes in the HPT-processed state. Brittle fracture of melt-spun Ti50Ni25Cu25 in the as-cast state and after HPT processing is determined during tensile tests. However, observable changes in the fracture surfaces correspond to an increased local ductility in samples subjected to HPT, in comparison with the initial state.

Shape memory effect in a rapidly quenched Ti50Ni25Cu25 alloy

The structural and thermomechanical properties of rapidly quenched layered amorphous–crystalline Ti50Ni25Cu25 composite materials with various ratios of amorphous and crystalline phases are studied. These layered composite materials are shown to exhibit the two-way shape memory effect accompanied by bending deformation without additional thermomechanical treatment. The ratio of amorphous and crystalline phases is found to affect the reversible change in the shape of the composite material.

HPT-induced shear banding and nanoclustering in a TiNiCu amorphous alloy

Special TEM procedure is used to study in detail the microstructure of the melt-spun (MS) amorphous alloy Ti50Ni25Cu25 subjected to high-pressure torsion (HPT). The cross section of an HPT-processed disc-shaped sample is studied. Groups of shear bands (SBs) are revealed on the lamellae cut from the HPT-processed samples. Nanocrystals form directly in the shear bands as a result of strain-induced nanocrystallization. Amorphous nanoclusters with a size of 20nm form in the amorphous phase surrounding the SBs. Formation of the amorphous cluster-type structure in the areas surrounding the shear bands has been discovered for the first time. The obtained results reveal a close connection between the nanocluster structure formation in the HPT-processed MS Ti50Ni25Cu25 alloy and SBs propagation in the amorphous phase.

On the nature of the “double” yield point in Ti50Ni25Cu25 alloy upon high-pressure torsion

The anomalous phenomenon of the “double” yield point attributed with the “crystal ⇒ amorphous state” phase transition during high-pressure torsion of Ti50Ni25Cu25 alloy has been analyzed experimentally and theoretically. Satisfactory correlation between experimental data and theoretical hypothesis has been found.

Structure, phase transformations and properties of the TiNi-TiCu alloys subjected to high pressure torsion

It was performed a complex study of stability, crystallization kinetics and martensitic transformations of the melt-spun (MS) Ti50Ni25Cu25 alloy subjected to high pressure torsion (HPT). The amorphous MS Ti50Ni25Cu25 alloy was subjected to high-pressure torsion (HPT) at temperature of 20°C 10 turnes. HPT processing of the melt-spun amorphous Ti-Ni-Cu alloy does not effect on intensive nanocrystallization. HPT processing leads to a decrease of the energy of structural relaxation during heating up to 400°C, in comparison with the initial MS ribbons. The temperature of crystallization of the MS Ti50Ni25Cu25 alloy decreases after HPT processing. In the MS Ti50Ni25Cu25 alloy HPT processing and subsequent annealing produces noticeably finer grains than annealing at 450°C of the initial MS alloy. Consequently, HPT processing alters the crystallization kinetics of the MS Ti50Ni25Cu25 alloy. The size effect on the stabilization of martensitic transformation in nanocrystalline TiNiCu alloy has been established.

The formation of the two-way shape memory effect in rapidly quenched TiNiCu alloy under laser radiation

The effect of pulsed laser radiation (λ = 248 nm, τ = 20 ns) on structural properties and shape memory behavior of the rapidly quenched Ti50Ni25Cu25 alloy ribbon was studied. The radiation energy density was varied from 2 to 20 mJ mm−2. The samples were characterized by means of scanning electron microscopy, x-ray diffraction, microhardness measurements and shape memory bending tests. It was ascertained that the action of the laser radiation leads to the formation of a structural composite material due to amorphization or martensite modification in the surface layer of the ribbon. Two methods are proposed which allow one to generate the pronounced two-way shape memory effect (TWSME) in a local area of the ribbon by using only a single pulse of the laser radiation. With increasing energy density of laser treatment, the magnitude of the reversible angular displacement with realization of the TWSME increases. The developed techniques can be used for the creation of various micromechanical devices.

Stability of an Amorphous TiCuNi Alloy Subjected to High‐Pressure Torsion at Different Temperatures

The amorphous melt‐spun (MS) Ti50Ni25Cu25 alloy is subjected to high‐pressure torsion (HPT) at temperatures of 20‐150 °C. The bright‐field (BF) TEM images of the alloy change as a result of HPT processing, the view of the bright‐field image depends on the temperature of HPT processing. HPT processing leads to a decrease in the energy of structural relaxation during heating up to 400 °C, in comparison with the initial MS ribbons. The temperature of crystallization of the MS Ti50Ni25Cu25 alloy decreases after HPT processing by 40–20 °C (depends on the temperature of HPT processing). In the MS Ti50Ni25Cu25 alloy, HPT processing and subsequent annealing produces noticeably finer grains than annealing at 450 °C of the initial MS alloy. Consequently, HPT processing alters the crystallization kinetics of the MS Ti50Ni25Cu25 alloy.

Forming the two-way shape memory effect in TiNiCu alloy via melt spinning

Thin ribbons of Ti50Ni25Cu25 (at %) alloy are produced by melt spinning in the amorphous, amorphous–crystalline, and crystalline states, depending on the melt cooling rate. It is shown that laminated amorphous–crystalline composite displays two-way shape memory behavior in bending with no additional thermomechanical treatment. It is established that a slower cooling rate results in a thicker crystalline layer and greater reversible bending deformation in this structural composite.

Evolution of the amorphous structure in melt-spun Ti50Ni25Cu25 alloy subjected to high pressure torsion deformation

Peculiarities of structure and mechanical behaviour of amorphous Ti50Ni25Cu25 alloy were the focus of this research. The melt-spun ribbons of amorphous Ti50Ni25Cu25 were subjected to high pressure torsion (HPT) at temperatures of 20–150 °C in order to modify their structure and mechanical behaviour. Some features of obtained HPT-processed samples were compared with initial state with the help of x-ray diffraction (XRD), transmission electron microscopy (TEM) and nanohardness testing. Analysis of structural data and mechanical behaviour allowed us to assume that severe plastic deformation (SPD) processing of melt-spun Ti50Ni25Cu25 alloy might lead to the formation of the structure similar to the new kind of noncrystalline state – “nanoglass” state.

Effect of Laser Treatment on Shape Memory Properties of TiNiCu Alloy

The work deals with the research of the effect of pulsed laser radiation (λ=248nm) on the structure and the manifestation of the shape memory effects (SMEs) in the Ti50Ni25Cu25 alloy, produced by melt spinning technique. It has been revealed that the proposed method of laser treatment leads to the formation of structural amorphous-crystalline composite demonstrating the pronounced two-way SME. A dependence of the two-way SME on the number of laser radiation pulses was determined.