Ti Nanocrystals Research Articles

Transmission Electron Microscopic and X-ray Diffraction Based Study of Crystallographic Bibliography Demonstrated on Silver, Copper and Titanium Nanocrystals: State of the Art Statical Review

This statistical review compares the crystallographic structures of functional nanocrystals composed of silver (Ag), copper (Cu) and titanium (Ti) using transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses. TEM provides high-resolution imaging to directly visualize individual nanoparticles' size, internal shape and crystallinity. Statistical analysis quantifies variations in lattice parameters, crystal structure, size distributions, phase compositions, lattice strains, preferred orientation and lattice volume of these three crystalline nanomaterials. The review highlights the complementary roles of TEM and XRD in comprehensive Ag, Cu and Ti nanocrystalline materials characterization. The crystallographic functional parameters of Ag were 2θ= 38.1° (111), 44.3° (200) and 64.4° (220); for Cu crystal 43.3° (111), 50.4° (200), 74.1° (220), 89.9° (311) and 95.1° (222) and 35.1° (100), 38.4° (002), 40.2° (101), 53.0° (102), 63.0° (103), 70.7° (110), 76.2° (112), 82.3° (201) demonstrated for Ti nanocrystals. The crystallographic predominant plane or Miller indices were also revealed by selected area electron diffraction (SAED) on TEM. The FCC structure of Ag and Cu is shown in larger lattice volumes compared to the HCP structure of Ti and prefer oriented. The degree of crystallinity of Ti, Cu and Ag nanocrystalline materials was observed at 90.0%, 98.0% and 100.0% respectively. This quantitative comparison provides valuable insights into the structural property relationships in these nanocrystals, enabling rational design strategies for optimizing their performance in various functional applications.

Nonthermal Plasma Synthesis of Metallic Ti Nanocrystals

Nanoscale metallic titanium (Ti) offers unique energetic and biocompatible characteristics for the aerospace and biomedical industries. A rapid and sustainable method to form purified Ti nanocrystals is still in demand due to their high oxygen affinity. Herein, we report the production of highly purified Ti nanoparticles with a nonequilibrium face center cubic (FCC) structure from titanium tetrachloride (TiCl4) via a capacitively coupled plasma (CCP) route. Furthermore, we demonstrate a secondary H2 treatment plasma as an effective strategy to improve the air stability of a thin layer of nanoparticles by further removal of chlorine from the particle surface. Hexagonal and cubic-shaped Ti nanocrystals of high purity were maintained in the air after the secondary H2 plasma treatment. The FCC phase potentially originates from small-sized grains in the initial stage of nucleation inside the plasma environment, which is revealed by a size evolution study with variations of plasma power input.

Atomic scale formation mechanism of the Amorphous-Nanocrystalline biphase structure in TiSiN Coating: Phase field crystal simulation and experimental characterization

TiSiN nanocomposite coatings have exceptional strength, toughness, and corrosion resistance due to their unique biphase amorphous/nanocrystalline structure with tiny TiN grains embedded in an amorphous Si3N4 phase. However, the unclear formation process makes microstructural control challenging. In this study the phase field crystal method has been employed to analyze the microstructure evolution in TiSiN coatings, uncovering a four-step formation mechanism for the amorphous-nanocrystalline structure. The initial stage results in appearance of concentration heterogeneities and the development of the triangular-like short-range order (Stage I). This stage is followed by the nucleation of nanocrystals in Ti-rich zones and the transformation of triangular short-range to the long-range order with a square symmetry (Stage II). Then, during coarsening stage, Ti-rich polycrystalline nanocrystals are formed (Stage Ⅲ) followed by the vacancy migration from the polycrystalline nanocrystals to amorphous phase and formation of monocrystalline Ti nanocrystals embedded in amorphous phase (Stage Ⅳ). The simulation results are compared qualitatively with aberration-corrected High-Resolution Scanning Transmission Electron Microscopy and High-Resolution Transmission Electron Microscopy images from our study.

Growth of co-sputtered titanium-strontium films: influence of strontium concentration and ion bombardment

Strontium-containing titanium films were synthesized by non-reactive magnetron sputtering from elemental targets. Three series of depositions were carried out at (1) different relative Sr-to-Ti target powers, (2) different sputter-gas pressures, and (3) different bias voltages. Large amounts of oxygen were detected in films with high Sr concentrations as well as in films exhibiting a porous morphology. By the addition of Sr, amorphous regions appeared in the coatings with a corresponding reduction of the crystalline volume fraction. The amorphous phase fraction increased with increasing Sr content. Upon increasing the Sr contents to 7.2at.% and higher, completely X-ray amorphous coatings were obtained. However, from high-resolution transmission electron microscopy imaging of the film containing 7.2at.% Sr, Ti nanocrystals of the order ~6nm embedded in an amorphous matrix were observed. Furthermore, the absolute value of the floating potential increased with decreasing sputter-gas pressure, resulting in a more energetic ion bombardment of the growing films. Strong resputtering of strontium resulted in very low Sr concentrations in films deposited at floating potential and low gas pressures or with an applied bias voltage. Films deposited at floating potential and high gas pressures exhibited a porous columnar morphology and had low degrees of crystallinity with correspondingly small grain sizes (~9nm), whereas denser and more crystalline films with larger grains (~18nm) were obtained from depositions at floating potential and low gas pressures and from depositions with an applied bias voltage. Film hardness scaled linearly with film electron density, as evidenced from nanoindentation and X-ray reflectivity measurements.

Sputtering growth of Ni–Ti shape memory alloy nano fibers on porous alumina membrane

Abstract A novel method of preparing a large number of fiber-shaped Ni–Ti nano crystals with medium aspect ratio in the order of 10 was examined. A target of nickel–titanium shape memory alloy was sputter-deposited on a porous alumina membrane having holes with 200 nm diameter in average. The porous geometry of the substrate caused the growth of columnar structure under the sputtering conditions, the argon gas pressure of 0.2 Pa and the substrate temperature of 250 °C, which would provide homogeneous alloy films, if the surface of substrate was flat. The columnar structure thus obtained was the assemble of isolated columns which were weakly adhered with each others, and could be separated into individual ones by applying ultrasonic vibration. Each column had a fibrous shape of diameter about 200 nm and 2.5 μm long (the aspect ratio was 12.5). The crystals can exhibit both martensitic transformation and the R-phase change with the total amount of latent heat 18 J g −1 , indicating that 75% of the nano crystals was active to these transformations.

Effect of Nanocrystal Distribution on Mechanical Properties of Ti-Based Metallic Glasses

Ti45Zr5Cu45Ni5 metallic glasses in which Ta and Al were substituted for Cu were evaluated in terms of mechanical properties, thermal properties and microstructures in order to determine the factors contributing to an improvement in plasticity. Samples are examined by compression testing, differential scanning calorimetry, X-ray diffractometry and electron microscopy. Mold-cast Ti45Zr5Cu44Ni5Ta1 bulk specimens were confirmed to consist of a metallic glass matrix and nanocrystals homogeneously dispersed at high density within the matrix. The yield stresses of both Ti45Zr5Cu45� xNi5Tax and Ti45Zr5Cu45� xNi5Alx are approximately 1800 MPa, and the maximum plastic strain of 3.1% was obtained for the Ti45Zr5Cu44Ni5Ta1 specimen. The Ti45Zr5Cu45� xNi5Alx bulk specimens exhibited poorer plasticity due to the formation of larger crystalline grains. (doi:10.2320/matertrans.MF200616) Various kinds of Ti-based amorphous aloys and metallic glasses have been developed, 1-12) due mainly to the light weight and high corrosion resistance properties of Ti. Ti- based metallic glasses are therefore attractive candidates for light-weight, high-strength and biocompatible structural materials. However, fully metallic glasses exhibit only elastic deformation, and activation of many shear bands in metallic glasses is necessary for plastic deformation. The homogeneous dispersion of nanocrystals in metallic glasses is one method for preparing metallic glasses that undergo plastic deformation by the activation of shear bands. Recently, Ti-based bulk metallic glasses exhibiting plastic deformation have been reported, 6,11) although the micro- structures of the materials have yet to be clarified. If the plastic deformation in Ti-based bulk metallic glasses is caused by the dispersion of nanocrystals, it may be possible to increase the plastic strain by optimizing the density, distribution, and morphology of the nanocrystals. Many Ti alloys exhibit solid-state phase transformation from austenite � -Ti to martensite � 00 -Ti. Whenstabilizers are added to the Ti alloys, the martensite transformation temperature (� transus) decreases with increasingstabilizer content due to stabilization of the � -Ti phase. When such alloys are quenched, it is expected that � -Ti nanocrystals will precipitate. In the present study, Ta and Al asand � stabilizers were substituted for Cu in Ti45Zr5Cu45Ni5 and the resultant alloys were rapidly quenched to form bulk metallic glasses. The mechanical and thermal properties and micro- structures of the glasses were investigated with respect to the dispersion of nanocrystals. 2. Experimental Procedures Ingots with nominal compositions of Ti45Zr5Cu45Ni5, Ti45Zr5Cu45� xNi5Tax and Ti45Zr5Cu45� xNi5Alx (x ¼ 1; 2; 3; 4; 5) were prepared by Ar-arc melting, and cylindrical bulk specimens of 1 mm in diameter and 30 mm in length were prepared by Cu mold casting of the ingots. Differential scanning calorimetry (DSC) measurements were performed to determine the glass transition temperature (Tg), crystal- lization temperature (Tx), and supercooled liquid region (� Tx ¼ TxTg) at a heating rate of 0.67 K/s. The micro- structures of the specimens were characterized by X-ray diffractometry (XRD) using a rotating Cu anode, scanning electron microscopy (SEM), and transmission electron mi- croscopy (TEM). The mechanical properties of the speci- mens were examined at room temperature through compres- sion tests at a strain rate of 1 � 10 � 4 /s using an Instron-type machine.

Characterization and properties of Ti-containing amorphous carbon nanocomposite coatings prepared by middle frequency magnetron sputtering

Ti-containing amorphous carbon (Ti-aC) nanocomposite coatings were deposited by using a modified closed field twin unbalanced magnetron sputtering system which is arc assisted and consists of two circles of targets, at a substrate temperature of 100 °C. The coatings exhibit good mechanical properties that are greatly influenced by the substrate bias voltage and Ti concentration. For coatings prepared at a bias of 100 V, the hardness increases from 12 GPa at a Ti concentration of 1 at.% to 27 GPa at 31 at.%. High-resolution transmission electron microscopy showed that the coatings contain Ti nanocrystals embedded in the amorphous carbon matrix. The average grain size decreases from 10 nm at 4 at.% Ti to 6 nm at 31 at.% Ti. The coating with 4 at.% Ti exhibits excellent tribological performance with a low friction coefficient of 0.07 and a wear rate of 1.4 × 10 − 16 m 3/Nm.

Impulse plasma deposition of magnetic nanocomposite layers

The most characteristic feature of the IPD method is that the synthesis proceeds in the impulse plasma itself, with the participation of ions. The IPD growth mechanism, originating from clusters of constituent materials, makes this method particularly suitable for the fabrication of nanocomposite layers. The material synthesised in the present experiment was an Fe–Ti alloy. The sources of Fe and Ti were the internal electrodes of two independent impulse plasma accelerators operated in an alternate mode. It appeared that the Fe–Ti alloy forms at the interface between the Fe and Ti nanocrystals as a result of the surface diffusion due to the coalescence of the nanocrystals.

Phase stabilities of fcc Ti nanocrystals

A model for the equilibrium transition size and temperature between hcp and fcc structure of nanocrystals Ti has been established in terms of the effect of surface stress on the internal pressure of nanocrystals. It was found that as size and temperature decreased, the relative stability of fcc structure in comparison with hcp structure increased. The obtained result is consistent with other theoretical and experimental data.

Synthesis of large-area germanium cone-arrays for application in electron field emission

High-vacuum electron-beam evaporation was used to synthesize germanium (Ge) cone-arrays on N+-type (100) Si. The surface morphology of Ti nanocrystals’ catalyst and Ge cone-arrays was investigated by scanning electron microscopy and atomic force microscopy. The lattice constant of the Ge cones determined from x-ray diffraction was nearly identical to that of bulk Ge. The mechanism of Ge cone-arrays’ formation was investigated. The electron field emission properties of the as-prepared Ge cone-arrays were studied based on current–voltage measurements and the Fowler–Nordheim equation.