Columnar Cross-section Research Articles

Vein pattern vs. columnar fracture shape in Cu-Zr thin film metallic glasses: Driving force and mechanism

Numerous studies have been published in the past showing the presence of vein-like or columnar fracture shapes in thin film metallic glasses (TFMGs), while the reason behind the different features remains poorly understood. This study uncovers the reason behind this phenomenon in Cu-Zr TFMGs’ by considering experimental evidence and analysis. Oxidation during deposition is the reason for the presence of the columnar feature after the cleavage, as shear banding cannot raise the temperature enough for the regional melting process to end up in the vein pattern. In several studies, unnoticed or unreported oxygen is proposed to be the reason for reporting metallic glasses' columnar cross-sections.

Hindered thermal warping triggers tensile cracking in the cores of compressed columns of a fire-loaded tunnel segment structure: Efficiency and accuracy of beam theory prediction, compared to FEM

The nonlinear Finite Element Method (FEM) is the current gold standard for the thermo-mechanical analysis of reinforced concrete structures. As an alternative, this paper is devoted to a model reduction strategy which reduces the CPU time by a factor of 500. This strategy combines Fourier series-based solutions for the thermal conduction problem, and thermo-elastic Timoshenko beam theory. Temperature histories known to be relevant for fire accidents enter series solutions quantifying the conduction of heat into a closed cell frame consisting of slabs, walls, and columns. Corresponding temperature profiles are translated into thermal eigenstrains. The latter are represented as the sum of three portions: (i) their cross-sectional averages (called thermal eigenstretches); (ii) their cross-sectional moments (called thermal eigencurvatures); and (iii) the remaining eigenstrain distributions (called eigenwarping). The latter portion is hindered at the cross-sectional scale, giving rise to non-linearly distributed self-equilibrated thermal stresses. The eigenstretches and eigencurvatures, in turn, are constrained at the scale of the frame structure. Together with external mechanical loads, they enter the exact solutions of thermo-elastic Timoshenko beam theory with equivalent cross-sections accounting for the different material properties of concrete and steel. Axial normal stresses, quantified from beam-theory-related normal forces and bending moments, are superimposed with the hindered-warping-induced stresses. These stresses agree well with corresponding results obtained by the nonlinear FEM. As regards the load carrying behavior of the columns, excessive thermal tensile strains at the periphery of the columns trigger, in the core of the columns, large tensile stresses which even exceed the strength of concrete. Respective cracking events are considered through reduced effective columnar cross-sections. Right after initiation of cracking, around 12min after the start of the heating process, the cracks propagate for some 30sec quite rapidly, and very much slower thereafter. If the initial cross-sections of the columns are increased, more pronounced hindered thermal warping, together with less quickly evolving compressive forces, results in earlier cracking. Overall, it is concluded that tensile cracking is the key material non-linearity, at least during the first 30min of the fire test, with maximum temperatures up to 300°C.

Toward morphologically induced anisotropy in thermally hysteretic dielectric properties of vanadium dioxide

The Bruggeman homogenization formalism was used to numerically investigate the dielectric properties of a columnar thin film (CTF) made from vanadium dioxide. For visible and near-infrared wavelengths, the CTF is electromagnetically equivalent to a homogeneous orthorhombic material. Over the 58–72 °C temperature range, the eigenvalues of the CTF’s relative permittivity dyadic are highly sensitive to temperature and vary according to whether the CTF is being heated or cooled. The anisotropy revealed through the eigenvalues and the anisotropy of the associated hysteresis were investigated in relation to temperature for CTFs of different porosities and columnar cross sections. When the free-space wavelength is 800 nm, the CTF is a dissipative dielectric material that exhibits temperature-dependent anisotropy and anisotropic hysteresis. In contrast, when the free-space wavelength is 1550 nm, the CTF can be a dissipative dielectric material, a hyperbolic material, or a metal-like material, depending on the temperature and the porosity of the CTF. As the porosity of the CTF decreases from 0.55 to 0.3, the anisotropy of the CTF becomes more pronounced, as does the anisotropy of the hysteresis. Only relatively modest variations in anisotropy and hysteresis arise in response to varying the columnar cross-sectional shape, as compared to the variations induced by varying the porosity.

Microstructures and properties of (TiCrZrVAl)N high entropy ceramics films by multi-arc ion plating

High entropy ceramics (HECs) films (TiCrZrVAl)N were deposited on Inconel 718 alloys by multi-arc ion plating (MAIP) equipment at different nitrogen flow ratios RnN2/(N2+ Ar). The effects of Rn (0%, 20%, 50%, 80%, 90%) on the evolution of microstructure, mechanical properties, and tribological properties of films were systematically studied. The films deposited at low Rn exhibited an amorphous structure and smooth cross-section, whereas the films at Rn of 50% and higher showed a face-centered-cubic (FCC) NaCl-type structure with loose columnar cross-section. With the increase of Rn, the content of the N element increased, the Cr element decreased, and other elements (Ti, Zr, V, Al) nearly remained stable. The films' hardness and elastic modulus increased gradually and reached the maximum value of 31.08 ± 1.81 GPa and 387.66 ± 12.49 GPa, respectively, when Rn was 80%. The films deposited at Rn of 20% invalided easily in tribology tests, whereas the films prepared under Rn exceeded 20% presented outstanding wear resistance and obtained the minimum wear rate of 7.4×10-16 m3/(N·m) when Rn is 80%.

Influence of the nitrogen content on the corrosion resistances of multicomponent AlCrNbYZrN coatings

In this study, the relationship between the nitrogen content and the corrosion resistances of non-equimolar multicomponent AlCrNbYZrN films (N = 13–49 at.%) is probed. While there was no linear relationship between nitrogen content and corrosion resistance, the results clearly show that the corrosion resistances of the films were instead determined by their nitrogen-induced porosities i.e. the less porous the sample, the higher the corrosion resistance. The 23, 30 and 37 at.% N samples were denser while the 13 at.% N sample was porous and the 49 at.% N film had an underdense nanocrystalline columnar cross section permitting the ingress of electrolyte.

Microstructural analysis and electrical behaviours of co-sputtered W–Ag thin films with a tilted columnar architecture

W–Ag thin films are produced by magnetron co-sputtering technique using glancing angle co-deposition configuration. Different samples are prepared with similar conditions (same pressure, thickness and tungsten target current) but with a variable Ag target current changing from 0 to 80 mA. The effect of the Ag target current on the film structure and electrical properties is investigated using scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction and van der Pauw technique. Thin films with inclined columns are obtained and the columns section becomes more anisotropic for the films prepared with the lowest Ag target currents. The elemental composition of the films also changes as a function of the Ag target current, varying from tungsten-rich (at low current) to homogeneous (at high current). W–Ag thin films exhibit different crystallographic structures. If the fcc Ag phase is always present, the metastable A15 β-W is pointed out only at low Ag target current while at high current, only the bcc α-W phase is present. The microstructural analysis shows that the core of the columns is formed by W while Ag covers the columns as grains. Room temperature electrical resistivity decreases with Ag target current, whereas its anisotropy decreases. This behaviour correlates with the change in the columnar cross-section morphology.

Revisitation of the structure zone model based on the investigation of the structure and properties of Ti, Zr, and Hf thin films deposited at 70–600 °C using DC magnetron sputtering

The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantitative data on the lattice strain, crystallite size, surface roughness, and electrical resistivity reduced to that of the bulk material were plotted both against the unnormalized and normalized substrate temperatures. The latter data plots show a smaller dispersion than the former ones. The lattice strain and reduced resistivity of all Ti, Zr, and Hf thin films display a sharp bend at a normalized temperature of ∼0.30–0.35. The film surface, cross-sectional morphologies, and film property changes display a clear transition from zones 1 to 2 through zone T. The data obtained in this paper are utilized to systematically explain the effectiveness and appropriateness of the use of the normalized substrate temperature to categorize the film structure, morphologies, and properties of thin films.The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantit...

Effect of deposition parameters and heat-treatment on the microstructure, mechanical and electrochemical properties of hydroxyapatite/titanium coating deposited on Ti6Al4V by RF-magnetron sputtering

Functionally graded HA/Ti coatings were deposited on silicon and Ti6Al4V substrate by radio-frequency (RF) magnetron sputtering. The effect of RF-power, negative bias and heat-treatment on the microstructure, mechanical and electrochemical properties of the coatings were characterized by SEM, XRD, FTIR, AFM Nanoindentation and electrochemical workstation. The obtained results showed that the as-deposited HA/Ti coatings were characteristic of amorphous structure, which transformed into a crystal structure after heat-treatment, and reformed O–H peak. The content of crystallization was increasing with the increase of negative bias. A dense, homogenous, smooth and featured surface, and columnar cross-section structure was observed in SEM observation. AFM results showed that the surface roughness became higher after heat-treatment, and increased with increasing RF-power. The mechanical test indicated that the coating had a higher nanohardness (9.1 GPa) in the case of −100 V and 250 W than that of Ti6Al4V substrate, and a critical load as high as 17 ± 3.5 N. The electrochemical test confirmed the HA/Ti coating served as a stable protecting barrier in improving the corrosion resistance, which the corrosion current density was 1.3% of Ti6Al4V, but it was significantly influenced by RF-power and negative bias. The contact angle test demonstrated that all the coatings exhibited favorable hydrophilic properties, and it decreased by 20–25% compared to that untreated samples. Thus all results indicated that magnetron sputtering is a promising way for fabricating a better biocompatible ceramic coating by adjusting deposition parameters and post-deposition heat treatments.

High-speed Epitaxial Growth of (110) SrTiO3 Films on (110) MgAl2O4 Substrates using Laser Chemical Vapour Deposition

Epitaxial (110) SrTiO3 films were prepared on (110) MgAl2O4 substrates using laser chemical vapour deposition (LCVD). The effect of the deposition temperature on the orientation and microstructures was investigated. The (111)/(110) co-oriented SrTiO3 films were prepared in the temperature range 980–1030 K, while epitaxial (110) SrTiO3 films were obtained in the range 1063–1073 K. The films showed columnar cross-sections with truncated prismatic surface grains. The deposition rate of the epitaxial films ranged from 20 to 25 μm h−1, which was 35–250 times higher than the rates reported for conventional CVD.

Effect of Li addition on the formation of Na-β/βʹʹ-alumina film by laser chemical vapor deposition

Films composed of a mixture of Na-β- and βʹʹ aluminas (β/βʹʹ-alumina) were prepared via laser chemical vapor deposition (CVD) upon the addition of Li. The effect of the Li source gas on the phase formation, microstructure and deposition rates of the β/βʹʹ-alumina films was investigated. The Na-β/βʹʹ-alumina films were formed at a Li/Al precursor supply ratio (RLi/Al) of 0.1–1.0 within a deposition temperature (Tdep) range of 1100–1220K. The Na-β/βʹʹ-alumina phase was exclusively formed at Tdep=1165–1185K and RLi/Al=0.1–0.5, whereas α-Al2O3 (with minor amounts of LiAlO2 and LiAl5O8) was predominantly observed at Tdep>1223K and RLi/Al >1.0. The Na-β/βʹʹ-alumina films were composed of polygonal facets in sizes of several hundred nanometers with a columnar cross section. The deposition rate of the Na-β/βʹʹ-alumina film was 60µmh−1.

High-speed deposition of oriented orthorhombic NaTaO3 films using laser chemical vapor deposition

We demonstrated the high-speed laser chemical vapor deposition of orthorhombic NaTaO3 (o-NaTaO3) films. The orientation of the o-NaTaO3 films was changed from (101) to (112) to (001) plane as the increase of deposition temperature from 823 to 913K. o-NaTaO3 films had faceted surfaces and columnar cross sections. The deposition rates of o-NaTaO3 films were 48–120µmh−1, which are 192–6000 times higher than those offered by wet-chemical routes.

Effect of the vacuum degree on the orientation and the microstructure of β-SiC films prepared by laser chemical vapour deposition

β-SiC films were prepared on AlN substrates by laser chemical vapour deposition (LCVD) using a diode laser and hydrido-polycarbosilane as a precursor at different vacuum degrees. The effect of the vacuum degree on the orientation and the microstructure of the β-SiC films was investigated. The preferred orientation of β-SiC films shifted from (111) to (311), the surface morphologies changed from faceted to rectangular and the columnar cross-section became thicker while increasing the vacuum degree from 0.4 to 7KPa. The high deposition rate ranged from 180 to 240µm/h.

Dielectric properties of BaTi2O5 thick films prepared on Pt-coated MgO(110) single-crystal substrate by laser chemical vapor deposition

BaTi2O5 (BT2) films were deposited on Pt-coated MgO(110) single-crystal substrates by laser chemical vapor deposition. The single-phase BT2 thick films were deposited at high deposition rates. The BT2 thick films consisted of elongated grains with columnar cross-section. With increasing the deposition temperature (Tdep), the orientation of BT2 thick films changed from (112) to (511), and the grain size increased. The (112)-oriented BT2 thick film deposited at Tdep=956K had dielectric constant (ε′) of 67 and dielectric loss (tanδ) of 0.015, while the (511)-oriented BT2 thick film deposited at Tdep=964K had ε′ of 74 and tanδ of 0.019 at 300K and 1MHz.

Supramolecular Columnar Liquid Crystals with Tapered-Shape Simple Pyrazoles Obtained by Efficient Henry/Michael Reactions.

A straightforward synthesis of mesogenic pyrazoles starting from benzaldehydes by a combination of efficient Henry and Michael reactions led to novel supramolecular liquid crystals. The mesogens are fluorescent 3,5-dimethyl-4-(di or trialkoxyphenyl)pyrazoles and, in spite of the tapered shape of these molecules and their structural simplicity (only one phenyl ring), columnar liquid-crystal phases were formed that are stable at room temperature. The self-assembled structure was studied by XRD and the columnar cross section contains two molecules on average with an antiparallel arrangement of pyrazoles interacting through hydrogen bonds. In contrast, the single-crystal structure of a trimethoxy analog did not show hydrogen-bonded pyrazoles but chains of head-to-tail arranged molecules.

Fabrication and physico-mechanical properties of thin magnetron sputter deposited silver-containing hydroxyapatite films

As a measure of the prevention of implant associated infections, a number of strategies have been recently applied. Silver-containing materials possessing antibacterial activity as expected might have wide applications in orthopedics and dentistry. The present work focuses on the physico-chemical characterization of silver-containing hydroxyapatite (Ag-HA) coating obtained by radio frequency (RF) magnetron sputtering. Mechanochemically synthesized Ag-HA powder (Ca10⿿xAgx(PO4)6(OH)2⿿x, x=1.5) was used as a precursor for sputtering target preparation. Morphology, composition, crystallinity, physico-mechanical features (Young's modulus and nanohardness) of the deposited Ag-HA coatings were investigated. The sputtering of the nanostructured multicomponent target at the applied process conditions allowed to deposit crystalline Ag-HA coating which was confirmed by XRD and FTIR data. The SEM results revealed the formation of the coating with the grain morphology and columnar cross-section structure. The EDX analysis confirmed that Ag-HA coating contained Ca, P, O and Ag with the Ca/P ratio of 1.6±0.1. The evolution of the mechanical properties allowed to conclude that addition of silver to HA film caused increase of the coating nanohardness and elastic modulus compared with those of pure HA thin films deposited under the same deposition conditions.

Pulsed laser deposition of Pb(Zr0.52Ti0.48)O3 thin film on cobalt ferrite nano-seed layered Pt(111)/Si substrate: effect of oxygen pressure

The effect of oxygen pressure during pulsed laser deposition of Pb(Zr0.52Ti0.48)O3 (PZT) thin films on CoFe2O4 nano-seed layered Pt(111)/Si substrate was investigated. The PZT film deposited at oxygen pressure lower than 25 mTorr is identified as both perovskite and pyrochlore phases and the films deposited at high oxygen pressure (50-100 mTorr) show the single-phase perovskite PZT that has a perfect (111)-orientation. In addition, the film deposited at PO2 of 50 mTorr has a uniform surface morphology, whereas the film deposited at PO2 of 100 mTorr has a non-uniform surface morphology and more incompacted columnar cross-section microstructure. The polarization of film deposited at 100 mTorr is higher than that deposited at 50 mTorr, but shift of the hysteresis loop along the electrical field axis in the film deposited at PO2 of 100 mTorr is larger than that of the film deposited at PO2 of 50 mTorr.

High temperature properties of the Cr[sbnd]Nb[sbnd]Al[sbnd]N coatings with increasing Al contents

CrNbAlN coatings with Al content from 0 to 12at.% were deposited by d.c. reactive magnetron sputtering. The coatings were annealed in protective atmosphere at 800 and 900°C for 1h and exposed to air at 800, 900 and 1200°C for different times. The chemical composition, structure, microstructure, hardness and adhesive/cohesive strength of the coatings, in as-deposited and annealed conditions, were investigated and the oxidation resistance was evaluated. As expected, the Al content increased gradually in the coating with increasing power density in the Al target; nitrogen was kept approximately constant. All coatings exhibited columnar cross section morphology and fcc NaCl-type B1 phase structure. After thermal annealing, an increase in the grain size and a decrease in the lattice parameter were observed, which led to either a decrease in the hardness or lower adhesion/cohesion strength than the as-deposited coatings. The onset oxidation temperature was approx. 900°C for all coatings. High Al content coatings showed minimum oxidation when exposed to 800°C for 2h and to 900°C for 0.5h in air. The Al-free and low Al coatings exhibited lower oxidation resistance; Cr2O3 and CrNbO4 coexisting together although signs of the cubic nitride phase were still detected. The increase of Al was beneficial to the improvement of the thermal stability and oxidation resistance of the CrNbAlN coatings.

High-speed deposition of titanium carbide coatings by laser-assisted metal–organic CVD

A semiconductor laser-assisted chemical vapor deposition (LCVD) of titanium carbide (TiCx) coatings on Al2O3 substrate using tetrakis (diethylamido) titanium (TDEAT) and C2H2 as source materials were investigated. The influences of laser power (PL) and pre-heating temperature (Tpre) on the microstructure and deposition rate of TiCx coatings were examined. Single phase of TiCx coatings were obtained at PL=100–200W. TiCx coatings had a cauliflower-like surface and columnar cross section. TiCx coatings in the present study had the highest Rdep (54μm/h) at a relative low Tdep than those of conventional CVD-TiCx coatings. The highest volume deposition rate (Vdep) of TiCx coatings was about 4.7×10−12m3s−1, which had 3–105 times larger deposition area and 1–4 order lower laser density than those of previous LCVD using CO2, Nd:YAG and argon ion laser.

Effect of laser power on orientation and microstructure of TiO2 films prepared by laser chemical vapor deposition method

The TiO2 films were prepared on Pt/Ti/SiO2/Si substrate by a laser chemical vapor deposition method. With increasing laser power (PL) from 48 to 98W, the deposition temperature (Tdep) monotonously increased from 849 to 929K. At Tdep=849K (PL=48W), the rutile TiO2 film was prepared with strong (110) and (200) peaks. With increasing Tdep from 849 to 883K (PL=71W), the intensity of (110) peak increased. The (110)-oriented TiO2 films were obtained for Tdep beyond 903K (PL=81W). All TiO2 films showed faceted grains with the columnar cross-section. With increasing Tdep, the grain size increased and the column became wider. The high deposition rate (Rdep) ranged from 13.04 to 24.84μmh−1.

Preparation of TiO2 thick film by laser chemical vapor deposition method

A TiO2 film was prepared on Pt/Ti/SiO2/Si substrate by a laser chemical vapor deposition method. The rutile TiO2 film with pyramidal grains and columnar cross-section was obtained at a high deposition rate (R dep = 11.4 μm h−1). At 300 K and 1 MHz, the dielectric constant (e r) and loss (tanδ) of the TiO2 film were about 73.0 and 0.0069, respectively. The electrical properties of TiO2 film were investigated by ac impedance spectroscopy over ranges of temperature (300–873 K) and frequency (102–107 Hz). The Cole–Cole plots between real and imaginary parts of the impedance (Z′ and Z′′) in the above frequency and temperature range suggested the presence of two relaxation regimes that were attributed to grain and grain boundary responses. The ionic conduction in the rutile TiO2 film was dominated by the oxygen vacancies.