Composition Range Of Ti Research Articles

Facilitation of detwinning through controlling crystal structure in Ti–Zr–Ni–Pd high temperature shape memory alloys

Ti–(Zr, Hf)–Ni alloys, in which Zr or Hf is added to Ti–Ni shape memory alloys, are expected to be excellent high temperature shape memory alloys because they have martensitic transformation temperatures above 100°C and high strength at elevated temperatures by utilizing H-phase precipitation. However, during reorientation of martensite variants, deformation stress increases with applied strain without showing a plateau region, making it difficult to obtain a large shape recovery strain. In the martensite phase of Ti–(Zr, Hf)–Ni alloys, thin and dense (001)B19′ compound twins are introduced during the martensitic transformation, and the detwinning of martensite variants becomes difficult to occur, resulting in the increase in deformation stress during the variant reorientation. Therefore, we propose a new alloy-design concept to control the crystal structure by adding a fourth element in order to facilitate detwinning. In this paper, we first considered the cause of (001)B19′ compound twinning in Ti–(Zr, Hf)–Ni alloys, and then selected Pd as the fourth element to change the crystal structure for preventing the formation of (001)B19′ compound twins. Experimental investigations of the effects of alloy composition on the crystal structure, transformation temperatures, and precipitate formation realized this alloy-design concept through presenting a candidate composition range of Ti–(15–20)Zr–49.7Pd and surrounding Ni-containing alloys for new high temperature shape memory alloys which readily undergo detwinning.

Facilitation of Detwinning Through Controlling Crystal Structure in Ti-Zr-Ni-Pd High Temperature Shape Memory Alloys

Ti-(Zr, Hf)-Ni alloys, in which Zr or Hf is added to Ti-Ni shape memory alloys, are expected to be excellent high temperature shape memory alloys because they have martensitic transformation temperatures above 100°C and high strength at elevated temperatures by utilizing H-phase precipitation. However, during reorientation of martensite variants, deformation stress increases with applied strain without showing a plateau region, making it difficult to obtain a large shape recovery strain. In the martensite phase of Ti-(Zr, Hf)-Ni alloys, thin and dense (001)B19′ compound twins are introduced during the martensitic transformation, and the detwinning of martensite variants becomes difficult to occur, resulting in the increase in deformation stress during the variant reorientation. Therefore, we propose a new alloy design concept to control the crystal structure by adding a fourth element in order to facilitate detwinning. In this paper, we first consider the cause of (001)B19′ compound twinning in Ti-(Zr, Hf)-Ni alloys, and then select Pd as the fourth element to change the crystal structure for preventing the formation of (001)B19′ compound twins. Experimental investigations of the effects of alloy composition on the crystal structure, transformation temperatures, and precipitate formation realized the concept with presenting a candidate composition range of Ti-(Zr, Hf)-Pd-based alloy systems for new high temperature shape memory alloys which readily undergo detwinning.

The partial liquidus projection and solidification sequences in Ti-(40–60) Al-(5–30) Nb alloys

The properties of Ti–Al–Nb alloys strongly depend on alloy compositions and microstructures. Proper design of these important aspects requires detailed knowledge of the solidification sequences and liquidus projection. However, there are still some conflicts between previous experimental and calculated results about the liquidus projections in the composition range of Ti-(40–60)Al-(5–30)Nb and this has hindered Ti–Al–Nb alloy development. In this present work, we explicitly investigated the as-cast microstructures and phase constitution of 50 alloys with the composition range of Ti-(40–60)Al-(5–30)Nb and clarified the solidification sequences. We re-constructed the partial liquidus projection and found that the primary β phase region extend to just below 55 at.% Al content and the primary α phase region extend to just below 24 at.% Nb content. Moreover, it was observed that the invariant reaction between Liquid, β, α and γ phases is a peritectic reaction (Liquid+β+γ→α) and all the Liquid+β+γ, Liquid+β+α and Liquid+α+γ three-phase regions are of peritectic type. The present work provides essential information necessary for optimizing the Ti–Al–Nb thermodynamic database to accelerate alloy development.

In-situ neutron diffraction study of phase stability and equilibria in the Ti-rich part of the Ti–Al binary system

Three alloys with composition range of Ti-(25–35)Al (atomic %) were in-situ investigated using neutron diffraction to clarify the phase stability and equilibria in the Ti-rich part of the Ti–Al binary system. The phase transformation sequences of these three alloys were identified based on the neutron diffraction results and differential scanning calorimetry. No superstructure diffraction of β0 has been found in the neutron diffraction patterns. It is concluded that the β0 phase in the examined composition range is thermodynamically unstable. Based on the phase transformation sequences of these three alloys, combining the characters of congruent type relationship and peritectoid type relationship, the phase equilibria among β, α and α2 phases were confirmed as a peritectoid type, with two peritectoid reactions, i.e., β+α→α2 and β +α2→α.

Polarization rotation associated with phonon dynamics in monoclinic C phase near morphotropic phase boundary studied by diffuse and inelastic X-ray scattering from a Ti-composition-gradient Pb[(Mg1/3Nb2/3)1–xTix]O3 single crystal

ABSTRACTWe have investigated polarization rotation associated with phonon dynamics in the relaxor ferroelectrics Pb[(Mg1/3Nb2/3)1–xTix]O3. The intensity distributions of the diffuse scattering patterns show intensity- crossover behavior in the monoclinic-C(MC) phase over a wide Ti composition range (29 < x < 32 mol%). The transverse acoustic (TA) mode of the crossover region along the [001] direction softens and is damped, strongly correlating with the central peak intensity, which originates in the polar regions. These results indicate that the lattice can easily deform in the MC phase, and the polarization can rotate easily by associating with the TA mode.

Hydrothermal synthesis and properties of solid solutions and composite nanoparticles in the TiO 2–SnO 2 system

Solid solutions and composite nanoparticles in the TiO 2–SnO 2 system were directly formed via the hydrothermal treatment of precursor solutions of TiCl 4 and SnCl 4 under weakly basic conditions in the presence of urea. The rutile-type (Ti, Sn)O 2 solid solutions were formed in the composition range of Ti 0–70 mol%. The composite nanoparticles consisting of anatase- and rutile-type phases were formed at the composition of Ti 80 and Ti 90 mol%. The change in the lattice parameters a 0 and c 0 of the rutile-type solid solutions followed the Vegard Law. The crystallite size of the rutile-type solid solutions was in the range of 5–10 nm. The diffuse reflectance spectra varied with changing Ti content in the precipitates. The photocatalytic activity of composite nanoparticles synthesized at 240 °C was higher than that synthesized at 180 °C. The composite nanoparticles consisting of anatase- and rutile-type phases with compositions Ti 0.90Sn 0.10O 2 and Ti 0.80Sn 0.20O 2 showed improved photocatalytic activity.

The bulk metallic glass formation in Zr–Al–Ni–Ti quaternary system

The optimum metallic glass compositions are located close to the intersecting line of the e/ a-constant and atomic size-constant planes in a quaternary composition chart. According to these criteria, a series of Zr–Al–Ni–Ti quaternary alloys have been designed and prepared by suction casting. The electron concentration and average atomic size of two ternary glass forming alloys, Zr 60Al 20Ni 20 and Zr 53Al 23.5Ni 23.5, have been used. Pure glass state is reached only within a small composition range of Ti. Ti addition deteriorates the thermal stabilities, but maintains the same glass forming abilities of bulk metallic glasses.

Formation of New Ti-based Metallic Glassy Alloys

New Ti-based bulk glassy alloys were synthesized in a multi-component alloy system of Ti-Cu-Ni-AI-Zr-Si-B. In a wide composition range of Ti > 50 at %, single-phase glass rods with diameters up to 2.5 mm were prepared using a conventional copper-mold casting method. The new Ti-hascd glassy alloys show compressive strength above 1900 MPa. The plastic (serrated) strain under compression is lager than 0.01. The new Ti-hased glass phase exhihits relatively high thermal stability with a large supercooled liquid region (ΔT x ) above 50 K. These glassy alloys. however, exhibit complex crystallization behavior characterized by multiple exothermic-reaction peaks on their differential scanning calorimeter (DSC) curves. The glass-forming ability of this complex system is discussed on the basis of knowledge available for bulk glass formation.

Super-high strength shape memory thin films

Using a sputter-deposition technique, super-high strength shape memory films have been developed with Ti-Ni-Cu alloys having the composition range of Ti: 51-55, Ni: 40-46, Cu: 4-6 (at. %). The maximum stress applicable without any permanent strain is about 1.5 GPa, being accompanied with a perfectly recoverable strain of about 5% on heating above A t . The maximum shape recovery stress measured by thermal cycling test under various constant stresses is 900 MPa with a shape recovery strain of 4.6%. A superelasticity with 850 MPa shape recovery stress and small hysteresis is attained for 53.5Ti-37.0Ni-9.5Cu thin films. These excellent properties are due to two factors; one is the existence of very thin plate bct precipitates with large coherency strains in the B2 parent phase, which are produced by heating the as-sputtered amorphous films with Ti-rich contents (more than 50%), and the other is ternary alloying.

Probing for mechanical and tribological anomalies in the TiC/amorphous hydrocarbon nanocomposite coating system

We have performed a detailed examination of the mechanical properties and the friction and wear characteristics of titanium-containing amorphous hydrocarbon (Ti–C:H) coatings as a function of the Ti composition from 0 to 45 at.%. Elastic modulus and hardness were measured with instrumented nanoindentation. Friction coefficient and coating wear rate during unlubricated sliding against WC–Co in a ball-on-disk configuration were also measured. Deposited by inductively coupled plasma (ICP)-assisted hybrid chemical vapor deposition/physical vapor deposition (CVD/PVD), these Ti–C:H coatings consist of nanocrystalline TiC clusters embedded in an a-C:H matrix, and are thin film TiC/amorphous hydrocarbon (a-C:H) nanocomposite materials. As the Ti composition increases, the elastic modulus and hardness of the coatings exhibit smooth variations. In contrast, relatively abrupt transitions occur in the friction coefficient and the wear rate of the coatings over a relatively narrow (20–30 at.%) Ti composition range. Our results indicate bimodal friction and wear behaviors for the TiC/a-C:H nanocomposites, a-C:H-like at Ti compositions below 20%, and TiC-like at Ti compositions above 30%. Our results indicate that two different coating wear mechanisms operate as the volume fraction of nanocrystalline TiC clusters changes. Over the entire range of Ti compositions examined, no anomalous changes in elastic modulus or hardness of the Ti–C:H coatings were observed.

Development of composition-insensitive SMA thin films with high recovery strength and large recovery strain

After reviewing the microstructures formed in Ti-rich Ti-Ni based thin films and the associated shape memory properties, it is shown that thin films of composition-i nsensitive shape memory alloys (SMA) can be developed by utilizing the formation of coherent bet thin plate precipitates. Ti-rich sputter-deposited thin films of Ti- Ni-Cu alloys are presented as such an example, which exhibit excellent shape memory properties of 500 MPa recovery stress with about 5 % recovery strain for the Ti-composition range of 51-54 at. %. Necessary conditions for producing such thin films are (1) Ti-rich content, i.e., over 50 at. %, (2) the amorphous initial state, (3) heat treatment at low temperatures near the crystallization temperature and (4) ternary alloy system. It is suggested that the same approach will be possible for the other ternary alloys such as Ti-Ni-Pd, Ti-Ni-Hf, etc..

Friction and wear characteristics of ceramic nanocomposite coatings: Titanium carbide/amorphous hydrocarbon

Friction and wear characteristics of titanium-containing amorphous hydrocarbon (Ti–C:H) coatings were measured during unlubricated sliding against WC–Co. These Ti–C:H coatings consist of nanocrystalline TiC clusters embedded in an amorphous hydrocarbon (a-C:H) matrix, i.e., they are TiC/a-C:H nanocomposites. The elastic modulus and hardness of the coatings exhibit smooth variations with increasing Ti composition. In contrast, a relatively abrupt transition occurs in the friction coefficient and wear rate of the coatings over a relatively narrow (20–30 at. %) Ti composition range. Our results reveal bimodal friction and wear behaviors for the TiC/a-C:H nanocomposites, a-C:H like at Ti compositions below 20%, and TiC like at Ti compositions above 30%. The two different wear mechanisms that operate as the volume fraction of nanocrystalline TiC clusters changes are discussed.

Voltammetric characterisation of Pt–TiO 2 composite nanomaterials prepared by metal organic chemical vapour deposition (MOCVD)

The voltammetric behaviour of the Ru(NH 3) 6 3+/2+ redox couple was studied on Pt–TiO 2-coated stainless steel and gold electrodes. The Pt–TiO 2 coatings were prepared by metal organic chemical vapour deposition in the Pt:Ti composition range 1:10 to 1:80 atomic ratio. These electrodes behaved as ensembles of nanoelectrodes in which the Pt particles acted as active sites, whereas the TiO 2 matrix was inactive. The voltammetric patterns recorded with all the electrodes in Ru(NH 3) 6Cl 3 solutions displayed quasi-reversible character. Peak current and peak-to-peak separation Δ E p were examined as a function of scan rate. From the Δ E p values the apparent heterogeneous kinetic rate constant of the Ru(NH 3) 6 3+/2+ redox couple was evaluated with the various electrodes. From these values the fractional surface covered by active Pt or inactive TiO 2 was calculated. The active surface area was in all cases less than 0.06%. From X-ray diffraction measurements the Pt crystallite dimension was calculated to be 6 nm for Pt:Ti 1:10 ratio, and less than 3 nm for lower Pt:Ti ratios.

Phase equilibria and transformations in Ti–(25–52) at.% Al alloys studied by electrical resistivity measurements

Phase equilibria and transformations in Ti–(25–52) at.% Al alloys were studied by electrical resistivity measurements over a range of temperatures using a special device that was constructed for this purpose. The α 2, α, β and γ phases are observed to have distinctly different resistivities and temperature dependencies, owing to which phase transitions could be monitored. The results show that the currently accepted Ti–Al phase diagram is, by and large, accurate, except for minor modifications being required to the phase boundaries in the composition range of Ti–(25–43)Al. Also, the α single-phase field is found to extend to the 25Al composition, which points to the absence of a β+ α 2↔ α peritectoid reaction. The room temperature electrical resistivity of stoichiometric α 2Ti 3Al and γ-TiAl are 118 and 31 μΩ cm, respectively, i.e. show a difference of 87 μΩ cm. The changes in resistivity with temperature are also significantly different in that in α 2 the resistivity saturates to a near-constant value near 750°C, whereas that of the γ phase shows a linear and near-constant slope with temperature like most metallic materials. In order to explain these differences, the electrical resistivity of the α 2 and γ phases has been modeled by fitting the data using the Bloch–Gruneisen formulation with certain simplifying assumptions. Good agreement between the calculated and experimental resistivity–temperature curves, and between calculated and experimental values of the residual resistivity and Debye temperature, were obtained. From the model, parameters such as the Fermi velocity, effective mass of a conduction electron, the number of electrons participating in conduction and electron mean free path have been calculated for the two phases. The calculations reveal that the mean free path is of the order of the lattice parameter in the case of α 2, which leads to high resistivity and resistivity saturation. The resistivity of the α 2 phase is also higher than that of the γ phase due to the fact that the Fermi velocity of the electrons is lower, effective electron mass higher and fewer electrons participate in conduction. These factors, coupled with hybridization and localization effects, cause the different electrical resistivity behavior of the two phases.