Electron-beam Physical Vapor Deposition Method Research Articles

Effect of annealing temperature on the structural, optical, morphological, and photocatalytic properties of TiO2 thin films prepared by sol-gel spin-coating and electron beam physical vapor deposition

TiO2 thin films were prepared by sol-gel spin-coating (SGSC) and electron beam-physical vapor deposition (EB-PVD) methods and annealed at different temperatures (Ta ). X-ray diffraction spectroscopy (XRD) results show that the TiO2 films prepared by the SGSC method transformed from the anatase single phase to the coexistence of anatase and rutile with the increase of Ta . However, TiO2 films prepared by the EB-PVD method existed only in the anatase phase, and the crystalline strength was enhanced with the increase of Ta . Meanwhile, particles of TiO2 targets annealed at different Ta showed a rutile phase for TiO2 target particles in the EB-PVD method. The results indicate that the EB-PVD method hinders the nucleation growth and phase transformation of TiO2 films. Scanning electron microscopy and atomic force microscopy also show that the grain size and R ms of TiO2 thin films prepared by the SGSC method increased with the increase of Ta , and the grain size becomes inhomogeneous when the rutile phase is formed. Ultraviolet–visible results show that the forbidden bandwidth and light absorption capacity increase with increasing Ta . For the EB-PVD method, the grain size and surface roughness gradually increased when the Ta of the films was less than 800 °C, while annealing at 800 °C changed the direction of growth and nucleation, and also produced surface cracks; XRD verified the hypothesis that the EB-PVD method hinders the nucleation growth as well as the phase transition of the films. Weak differences in the optical absorption properties and bandgap values of the films also indicate that the EB-PVD method hinders the phase transformation of TiO2 films. Finally, the results of degradation of methylene blue (MB) under simulated visible light showed that the films prepared by the SGSC method gradually improved the photocatalytic performance with the enhancement of the crystalline strength of the anatase phase. The TiO2 films prepared by the EB-PVD method improved the photocatalytic performance with the increase of the active area.

Photocatalytic degradation of methylene blue by TiO2/Nd2O3 composite thin films

To improve the photocatalytic property of TiO2 thin films, the composite thin films of TiO2/Nd2O3 structure were fabricated by electron-beam physical vapor deposition method, and the photocatalytic property of the fabricated films was experimentally studied in the present work. The XRD and Raman analyses show that the TiO2/Nd2O3 films are mainly hexagonal crystalline phase of Nd2O3. The XPS analysis for the chemical state changes of Ti, O and Nd of the basic elements in the films is confirming the electron flow in the internal electric field which generated in the TiO2/Nd2O3 films. The surface morphology shows the lattice distortion which affects the changes in the energy band structure. Moreover, the formation of n-n homojunctions improved the separation efficiency of electrons and holes, and enhanced the catalytic activity. The photocatalytic performance for the methylene blue target dye shows that the sample with TiO2 thickness of 20–25 nm has better performance, high degradation efficiency and high reaction rate.

Investigation of vermiculite infiltration effect on microstructural properties of thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition method (EB-PVD)

Thermal barrier coatings (TBCs) are protective coating systems that are mostly utilized to improve the thermal insulation and functional performance of gas turbine engines and other aircraft components that are both stable and movable. These coatings protect materials operating in harsh conditions from structural damage caused by corrosion, oxidation, the CaO-MgO-Al2O3-SiO2 effect (CMAS), thermal shock, volcanic ash, and vermiculite deposits at high temperatures. In this study, CoNiCrAIY metallic bond coatings were coated on Inconel 718 super alloy using a high velocity oxygen-fuel (HVOF) deposition technique. Then, single YSZ, Gd2Zr2O7 (GZ), and double YSZ/GZ based ceramic topcoats were applied to the bond coats by using the electron beam physical vapor deposition (EB-PVD) method. The produced TBC samples and the uncoated Inconel 718 superalloy substrate were subjected to vermiculite (VM) deposition at 1250 °C for 4 h, and then the coatings were characterized. To determine the phase structures, microstructural and mechanical properties of the TBCs, X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer elemental mapping analysis (EDS), stereo microscopy analyses, porosity, and hardness measurements were used. The obtained results were comparatively evaluated with the recent related studies in the literature.

Synthesis of pure (ligandless) titanium nanoparticles by EB-PVD method

Pure (ligandless) nanoparticles of titanium (4–20 nm) in a porous NaCl matrix (29–43 nm) were synthesized by the method of electron beam physical vapor deposition (EB-PVD). Independent electron beams were used to preheat the compacted cylinder from NaCl salt and Ti ingot up to formation of liquid melts. Evaporation of the initial materials from the melt surface, vapor flow mixing, and deposition of the mixed vapor on the surface of the water-cooled copper substrate took place in vacuum. Deposited condensate composition was regulated by the intensity of the vapor flows of evaporated materials. Results of studying the structure (SEM) and element composition of the condensate (EDS), phase composition (XPA), and the size of the nanoparticles (TEM) and crystallites (XPA + Scherrer equation), as well as their thermal stability in NaCl–Ti–O system (TGA), are given. It is shown that the dimensions and phase composition of titanium nanoparticles can be further controlled by heat treatment of the initial NaCl–Ti condensate, produced at low condensation temperatures. Investigations of the kinetics of oxidation of NaCl–Ti condensates in air (TGA) show that breaking of the vacuum in the chamber titanium nanoparticles in the porous NaCl matrix demonstrates high adsorption ability to moisture and oxygen from the air. With temperature increase up to 250–400 °C, practically all the moisture is removed, and further heating activates the process of titanium nanoparticle oxidation. Obtained results are considered from the viewpoint of physical and chemical adsorption.

Theoretical estimation of fatigue life under regular cyclic loading

A model is proposed for the fatigue life estimation of the material with consideration of microstructure, stress concentration and cyclic load ratio. In the fatigue life estimation, the factors, such as grain size, stress concentration and cyclic load ratio are taken into account in the parameter representing the fatigue limit. In order to fill the model, it is sufficient to have results from monotonic tensile testing and characteristics of microstructure of the initial material. The model is tested using the fatigue testing results for specimens of Ti–6Al–4V titanium alloy condensate prepared by electron-beam physical vapor deposition method (EB PVD-method). The specimens had manufacturing defects, such as column defects of different diameters reaching the specimen surface. The model is also tested using the experimental fatigue data for the Ti–6Al–4V titanium alloy taken from the literature for various cyclic load ratios. Comparison between results of calculation and experiment showed a good agreement. The approach proposed can be used for the rapid assessment of fatigue resistance characteristics in new materials development, and also for the remaining life evaluation of structures with no costly and long-term fatigue and fatigue crack growth resistance tests

A study on the radiation resistance of CdWO4 thin-film scintillators deposited by using an electron-beam physical vapor deposition method

In this paper, we report the first successful fabrication of CdWO4 thin film scintillators deposited on quartz glass substrates by using an electron-beam physical vapor deposition method. The films were dense, uniform, and crack-free. CdWO4 thin-film samples of varying thicknesses were investigated by using structural and optical characterization techniques. An optimized thickness for the CdWO4 thin-film scintillators was discovered. The scintillation and the optical properties were found to depend strongly on the annealing process. The annealing process resulted in thin films with a distinct crystal structure and with improved transparency and scintillation properties. For potential applications in gamma-ray energy storage systems, photoluminescence measurements were performed using gamma rays at a dose rate of 10 kGy h−1.

Nondestructive characterization of thermal barrier coating by noncontact laser ultrasonic technique

We present the application of a laser ultrasonic technique in nondestructive characterization of the bonding layer (BL) in a thermal barrier coating (TBC). A physical mode of a multilayered medium is established to describe the propagation of a longitudinal wave generated by a laser in a TBC system. Furthermore, the theoretical analysis on the ultrasonic transmission in TBC is carried out in order to derive the expression of the BL transmission coefficient spectrum (TCS) which is used to determine the velocity of the longitudinal wave in the BL. We employ the inversion method combined with TCS to ascertain the attenuation coefficient of the BL. The experimental validations are performed with TBC specimens produced by an electron-beam physical vapor deposition method. In those experiments, a pulsed laser with a width of 10 ns is used to generate an ultrasonic signal while a two-wave mixing interferometer is created to receive the ultrasonic signals. By introducing the wavelet soft-threshold method that improves the signal-to-noise ratio, the laser ultrasonic testing results of TBC with an oxidation of 1 cycle, 10 cycles, and 100 cycles show that the attenuation coefficients of the BL become larger with an increase in the oxidation time, which is evident for the scanning electron microscopy observations, in which the thickness of the thermally grown oxide increases with oxidation time.

Fatigue life calculation for titanium alloys considering the influence of microstructure and manufacturing defects

A model is presented for calculation of the fatigue life to crack initiation in specimens with surface stress concentrators. The model is tested for the results of fatigue testing specimens of Ti–6Al–4V titanium alloy condensate prepared by electron-beam physical vapor deposition method (EB PVD-method). The specimens had manufacturing defects, such as column defects of different diameters reaching the specimen surface. Comparison between results of calculation and experiment showed a good agreement. In order to fill the model, it is sufficient to have the results from monotonic tensile testing and characteristics of microstructure and texture of the starting material.

Electrochemical Characteristics of Cell Cultured Ti–Nb–Zr Alloys After Nano-Crystallized Si-HA Coating

The aim of this study was to investigate the electrochemical characteristics of nano crystallized Si-HA coating on Ti-Nb-Zr alloy after human osteoblast like (HOB) cell attachment. The Ti-Nb-Zr alloy was manufactured with 35 wt.% of Nb and 10 wt.% of Zr by arc melting furnace to appropriate physical properties as biomaterials. The HA and Si-substituted coatings were prepared by electron-beam physical vapor deposition method with 0.5, 0.8 and 1.2 wt.% of Si contents, and nano aging treatment was performed 500 degrees C for 1 h. The characteristics of coating surface were analyzed by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. To evaluate of cell attachment on cell cultured surface, the potentiodynamic test was performed on the surface using HOB cells. The results showed that the Si-HA coating surface showed higher tendency of cell attachment than that of single HA coating, corrosion resistance value was increased by dense of cell attachment.

Surface characteristics of hydroxyapatite-coated layer prepared on nanotubular Ti–35Ta–xHf alloys by EB-PVD

In this study, we investigated the surface characteristics of hydroxyapatite (HA)-coated layers prepared by electron-beam physical vapor deposition (EB-PVD) on nanotubular Ti–35Ta–xHf alloys (x=3, 7, and 15wt.%). Ti–35Ta–xHf alloys were first prepared by arc melting. Formation of a nanotube structure on these alloys was achieved by an electrochemical method in 1M H3PO4+0.8wt.% NaF electrolytes. The HA coatings were then deposited on the nanotubular surface by an EB-PVD method. The surface characteristics were analyzed by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction (XRD). The electrochemical behavior was examined using a potentiodynamic polarization test in 0.9% NaCl solution. The Ti–35Ta–xHf alloys had an equiaxed grain structure with α″+β phases, and the α″ phase disappeared with increases in Hf content. The Ti–35Ta–15Hf alloy showed higher β-phase peak intensity in the XRD patterns than that for the lower Hf-content alloys. A highly ordered nanotubular oxide layer was formed on the Ti–35Ta–15Hf alloy, and the tube length depended on Hf content. The HA coating surface formed at traces of the nanotubular titanium oxide layer and completely covered the tips of the nanotubes with a cluster shape. From the potentiodynamic polarization tests, the incorporation of Hf element and formation of the nanotubular structure were the main factors for achieving lower current density. In particular, the surface of the HA coating on the nanotubular structure exhibited higher corrosion resistance than that of the nanotubular titanium oxide structure without an HA coating.

The mechanical properties and microstructure of the bionic alloy–ceramic laminated composite

In the present work, the bionic alloy–ceramic laminated composite was fabricated by electron beam–physical vapor deposition method. The ingots of Ni–20Co–12Cr–4Al (wt.%) and ZrO 2–8 mol%Y 2O 3 were used as the sources of the alloy layer and ceramic layer, respectively. The laminated composite was generally destroyed within the ceramic layer when the interlaminar strength was determined, which revealed that the excellent interface bonding between the ceramic layer and the alloy layer. The obvious diffusion interfaces between the ceramic and alloy layers were readily detected, which was favorable to the mechanical properties of the laminated composite. In the heat treatment process, the diffusion of the flaws within the ceramic layer and/or alloy layer to the interface between the ceramic layer and alloy layer was easier compared with the occurrence of interlaminar diffusion. It was confirmed by the X-ray diffractometer that the reaction of the ceramic layer with alloy layer was simple physical diffusion. The tensile strength of the laminated composite increased first and then decreased as the heat treatment time increased, which was attributed to the mutual reaction of the increase in the relative density with the formation of the flaws located at the interface.

Effect of surface stress concentrators and microstructure on the fatigue limit of the material

A calculation model is developed that makes it possible to predict the fatigue limit σ−1 of specimens with technological surface defects based on the data on the material microstructure and stress concentrator geometry. The fatigue test results are presented for specimens with technological defects under symmetric lateral bending that are made of Ti–6Al–4V titanium alloy condensate produced by the electron-beam physical vapor deposition method. The results obtained are used to calculate σ−1 based on the developed model and are in very good agreement with the experimental data.

Increased endothelial cell adhesion and elongation on micron-patterned nano-roughpoly(dimethylsiloxane) films

The success of synthetic vascular grafts is largely determined by their ability to promotevital endothelial cell functions such as adhesion, alignment, proliferation, and extracellularmatrix (ECM) deposition. Developing such biomaterials requires the design and fabricationof materials that mimic select properties of native extracellular matrices. Furthermore, cellsof the native endothelium have elongated and aligned morphology in the directionof blood flow, yet few materials promote this type of morphology initially, butrather rely on blood flow to orient endothelial cells. Therefore, the objective ofthis in vitro study was to design a biomaterial that mimics the conditions of themicro- and nano-environment of vascular intima tissue suitable for endothelial celladhesion and elongation to improve the efficacy of small synthetic vascular grafts.Towards this end, patterned poly(dimethylsiloxane) (PDMS) films consisting ofperiodic arrays of nano-grooves (500 nm), with spacings ranging from 22 to 80 µm, and alternating nano- and micron roughness were fabricated using a novel electron beamphysical vapor deposition method followed by polymer casting. By varying pattern spacing,the area of micron- and nano-rough surface was controlled. In vitro rat aortic endothelialcell adhesion and elongation studies indicated that endothelial cell function was enhancedon patterned PDMS surfaces with the widest spacing and greatest surface area ofnano-roughness, as compared to more narrow pattern spacings and non-patternedPDMS surfaces. Specifically, endothelial cells adherent on PDMS patterned films ofthe widest spacing (greatest nano-rough area) displayed almost twice as muchelongation as cells on non-patterned surfaces. For these reasons, the present studyhighlighted design criteria (the use of micron patterns of nano-features on PDMS)that may contribute to the intelligent design of new-generation vascular grafts.

Macro-microscopic morphology and phase analysis of TiAl-based alloys sheet fabricated by EB-PVD method

TiAl-based alloys sheet with thickness of 0.3–0.4 mm as well as dimension of 150 mm × 100 mm was fabricated successfully by using electron beam-physical vapor deposition(EB-PVD) method. The microscopic morphology and phase composition of specimens in various states were analyzed by atomic force microscope(AFM), scanning electron microscope(SEM) and X-ray diffractometer(XRD), respectively. The results indicate that the as-deposited TiAl-based alloys sheet has good surface quality and is composed of γ, α 2 and τ phase. There is natural delamination inside the sheet, of which the microstructure is columnar crystal, and the component shows a gradient change along the normal direction of substrate. After the vacuum hot pressing treatment and subsequent homogenization treatment, the columnar crystal transforms into the coarse fully lamellar microstructure, the delamination phenomenon and τ phase disappear, α 2 phase decreases obviously, and the composition tends to uniformization.

Experimental study on the in-plane thermal conductivity of Au nanofilms

Abstract The in-plane thermal conductivity of Au nanofilms with thickness of 23 nm, which are fabricated by the electron beam-physical vapor deposition method and a suspension technology, is experimentally measured at 80–300 K by a one-dimensional steady-state electrical heating method. Strong size effects are found on the measured nanofilm thermal conductivity is much less than that of the bulk material. With the increasing temperature, the nanofilm thermal conductivity increases. This is opposite to the temperature dependence of the bulk property. The Lorenz number of Au nanofilms is about three times larger than the bulk value and decrease with the increasing temperature, which indicates the invalidity of the Wiedmann-Franz law for metallic nanaofilms. *Supported by National Natural Science Foundation of China (Grant No. 50606018)

Residual Stress in Zirconia Coating by EB-PVD Method

The Ni-based superalloy IN738LC was used as the substrate material, and CoNiCrAlY powder was pressureless plasma-sprayed on the substrate as the bond coating. Zirconia was coated as the top coating by the electron beam-physical vapor deposition (EB-PVD) method. In the EB-PVD process, the specimens were kept at 1223K and rotated with 5rpm, 10rpm and 20rpm. According to the microscopic observation and the result of the pole figures, the top coatings had a columnar structure, which was made by the piling up of (111) planes. The cross section of the column had a diamond shape, and its diagonal was parallel to the rotation axis. The residual stress on the surface of the top coatings was evaluated by the X-ray diffraction method. Each diffraction profile was separated into the 133 and the 331peak, and the residual stress was measured by the sin2ψ method. The measured residual stresses were –76.7MPa for 5rpm, –63.0MPa for 10rpm and –25.1MPa for 20rpm.

Fatigue strength of an (α + β)-type titanium alloy Ti-6Al-4V produced by the electron-beam physical vapor deposition method

The fatigue test results are presented for an (α + β )-type titanium alloy Ti-6Al-4V in the form of two-layered smooth specimens (the first layer is a condensate prepared by the electron-beam physical vapor deposition method, the second one is a substrate from a standard sheet material of the same type) and condensate specimens. It has been found that the presence in the condensate of deposition defects such as droplets lowers the fatigue limit of the material by approximately 1.5 times as compared to that of the condensate which is free of defects. It is shown that in the absence of droplets, the fatigue limit of the condensate is no lower than that of the substrate material. The microstructure, texture and fracture surfaces of the materials under study are analyzed, on the basis of which the fatigue limits of the defectless condensate and substrate material are calculated using approaches of linear fracture mechanics. Good agreement has been obtained between calculated and experimental data.

Analysis on Residual Stress in Electron Beam-Physical Vapor Deposited Thermal Barrier Coating using Hard Synchrotron X-Rays

The distribution of the residual stress in the thermal barrier coating, which was made by an electron beam-physical vapor deposition (EB-PVD) method, was determined using X-ray stress measurements. As the bond coating, NiCoCrAlY was low-pressure plasma sprayed on the substrate of austenitic stainless steel. The 8 mass% Y2O3-ZrO2 was coated on the bond coating using the EB-PVD method as the top coating. The top coating had the preferred orientation with the <111> axis direction perpendicular to the coating plane. The distribution of the in-plane residual stress in the top coating was measured using laboratory X-rays. The value of the in plane stresses was deter-mined by the sin2 φ method after the separation of the 133 and 331 diffractions. The distribution of the out-of-plane strain in the top coating was measured using the strain scanning method with hard synchrotron X-rays. The out-of-plane strain was obtained from the 333 diffraction which had strong intensity due to the preferred orientation. The measured value of the in-plane stress in the top coating was a large compression, and steeply decreased near the interface between the top and the bond coating. The distribution of the out-of-plane stress showed a compression, and its magnitude was smaller than that of the in-plane stress.

Concentration dependence of microstructure and soft magnetic properties in the FeSi–ZrO2 granular films

Magnetic films composed of FeSi and ZrO2 with the oxide concentration in the range of 21–35wt% were prepared by using electron beam-physical vapor deposition method. From X-ray diffraction patterns, it was found that the magnetic film consisted of α-Fe and ZrO2. Energy dispersion X-ray spectroscopy analysis showed that Si composition was around 1.5wt%. The transmission electron microscopy images showed that a granular structure was obtained for the films containing high ZrO2 content, with the Fe(Si) grain size of around 10nm. While for the film containing low ZrO2 content, the structure is more like a random aggregate of the Fe(Si) and ZrO2 phases. High saturation magnetization of 11.02–16.8kG and comparatively large electrical resistivity of 392.5–75.1μΩcm were obtained for the films. The coercivity of the film containing 21wt% ZrO2 was much smaller than that of the film with 35wt% ZrO2 concentration. It is assumed that the existence of ZrO2 could reduce the grain size of the magnetic granules while weakening the magnetic interaction among the magnetic granules.

Concentration dependence of microstructure and soft magnetic properties in the FeSi?ZrO2 granular films

Magnetic films composed of FeSi and ZrO 2 with the oxide concentration in the range of 21–35 wt% were prepared by using electron beam-physical vapor deposition method. From X-ray diffraction patterns, it was found that the magnetic film consisted of α-Fe and ZrO 2 . Energy dispersion X-ray spectroscopy analysis showed that Si composition was around 1.5 wt%. The transmission electron microscopy images showed that a granular structure was obtained for the films containing high ZrO 2 content, with the Fe(Si) grain size of around 10 nm. While for the film containing low ZrO 2 content, the structure is more like a random aggregate of the Fe(Si) and ZrO 2 phases. High saturation magnetization of 11.02–16.8 kG and comparatively large electrical resistivity of 392.5–75.1 μΩ cm were obtained for the films. The coercivity of the film containing 21 wt% ZrO 2 was much smaller than that of the film with 35 wt% ZrO 2 concentration. It is assumed that the existence of ZrO 2 could reduce the grain size of the magnetic granules while weakening the magnetic interaction among the magnetic granules.