Electron-beam Physical Vapor Deposition Technique Research Articles

Development of deposition beam current dependent microstructure and nanomechanical properties in ZrO2-8wt%Y2O3 thermal barrier coatings produced by electron beam-physical vapor deposition technique

8 wt% yttria stabilized zirconia (8YSZ) coatings have been produced by changing the beam currents of electron beam-physical vapor deposition. The phase composition, microstructure, roughness, nanomechanical properties and residual stress were characterized and analyzed. The as-deposited 8YSZ coating was mainly composed of the metastable tetragonal phase. The enhancement of deposition beam current caused larger crystallite sizes and root mean square roughness, which confirmed by microscopic observations and atomic force microscopy technique. The nanomechanical properties were evaluated by an instrumented nanoindentation test. It was found that Young's modulus and hardness increase with the improvement of deposition beam current, which is due to the lower porosity. The thermal residual stresses generated in the deposition process was measured by two-dimension X-ray diffraction using sin2ψ technique. The measurement result indicated that residual stresses were dependent on the coating process.

Spectroscopic and morphological studies of SiO2 graded index thin films fabricated at oblique incidence angles

The present paper reports the fabrication of single layer graded index SiO2 thin films at various oblique incidence angles by using Static glancing angle deposition (GLAD) setup. These SiO2 films have been fabricated by using the electron-beam physical vapor deposition technique via ingeniously designed jig holder by placing the substrates at different angles of incidence of the incoming plasma. The optical properties of these films were studied by using UV–Vis–NIR spectrophotometer. The coating at various incidence angles of deposition from 10 to 80° reveals that there is a variation in refractive index of the material from 1.46 to 1.38. The microstructural studies of these films were further ascertained by field emission scanning electron microscopy, which reveals increase in the porosity of the film with deposition at oblique angle of incidence. The contact angle measurement of the films indicated the decrease in contact angle of these films with increasing angle of deposition indicating the hydrophilic nature of the samples. Owing to this behavior, these films find applications in antireflection (AR) coatings for flat panel displays, protective coatings, solar cells and optoelectronic devices etc.

Effect of substrate temperature on microstructure and nanomechanical properties of Gd2Zr2O7 coatings prepared by EB-PVD technique

In the present work, gadolinium zirconate (Gd2Zr2O7) coatings have been developed on Inconel-718 substrates by electron beam physical vapor deposition (EB-PVD) technique. The structural, morphological and mechanical properties as a function of substrate temperature have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and scratch tests. XRD analysis revealed that the coatings showed cubic defect fluorite phase, and no secondary phase formation was observed in the coatings during deposition. The decrease in the lattice constant of the fluorite phase with increasing deposition temperature was explained on the basis of strain relaxation and vacancy concentration. Increased surface roughness of the coatings has been found with increasing substrate temperature as a result of increased crystallite size. An improved coating adhesion achieved for the coating deposited at higher substrate temperature of 973 K was confirmed by scratch test. Nanoindentation measurements indicated higher hardness (7.7 GPa) and resistance to plastic deformation and better capability to accommodate deformation energy for the coatings prepared at higher deposition temperature.

Investigation of Isothermal Oxidation Behavior of Thermal Barrier Coatings (TBCs) Consisting of YSZ and Multilayered YSZ/Gd2Zr2O7 Ceramic Layers

Rare-earth zirconates have a big potential as top coat material of TBCs due to their superior high-temperature properties. TBCs are usually produced by thermal spray methods or electron beam physical vapor deposition (EB-PVD) techniques. Cold gas dynamic spray (CGDS) is a promising deposition method for production of dense and non-oxide bond coat compared to other thermal spray processes, while EB-PVD process provides good adhesion and strain tolerance for top coating layers of TBCs. In this study, in order to observe the effect of Gd2Zr2O7 on the oxidation behavior of TBCs, CoNiCrAlY was sprayed on substrate material using the CGDS method, afterward, yttria-stabilized zirconia (YSZ) and YSZ/Gd2Zr2O7 were deposited using EB-PVD technique. After deposition, specimens were isothermally oxidized in a high-temperature furnace at 1100 °C for 8, 24, 50, and 100 h. Microstructures of oxidized samples were examined and thermally grown oxide layer of TBCs were comparatively evaluated.

Investigation of failure mechanism of thermal barrier coatings (TBCs) deposited by EB-PVD technique

Failure mechanism of thermal barrier coatings (TBCs) prepared by electron beam physical vapor deposition (EB-PVD) technique owing to formation of micro cracks was investigated. The TBCs were deposited on the Ni-based super alloy IN-100 and the micro cracks were observed within the top ceramic coat of thermally cycled TBCs at 1050°C. It was observed that these cracks propagate in the ceramic coat in the direction normal to interface while no cracks were observed in the bond coat. SEM/EDS studies revealed that some non-uniform oxides were formed on the interface between ceramic top and metallic bond coat just below the cracks. Study proposed that the cracks were initiated due to stress owing to big difference in Pilling-Bed worth ratio of non-uniform oxides as well as thermal stress, which caused the formation of cracks in top ceramic coat leading to failure of TBCs

Ozone gas sensor based on nanocrystalline SrTi1−xFexO3 thin films

We report on the use of nanocrystalline SrTi1−xFexO3 (STF) for sensing ozone gas. Amorphous thin films were evaporated by the electron-beam physical vapor deposition technique and then converted to a polycrystalline form, as shown by X-ray diffraction patterns, after ex situ annealing at a relatively low temperature (550°C). The influence of the iron content on the microstructure was investigated by both scanning electron microscopy (SEM) and atomic force microscopy (AFM), which revealed that the surface roughness of the films increased slightly as the amount of iron increased. Electrical resistance measurements were carried out to determine the response of the films upon exposure to ozone and when compared to other oxide metal sensors, STF films can also be considered as good candidates for application as ozone gas sensors.

Structural features and gas tightness of EB-PVD 1Ce10ScSZ electrolyte films

The structure of Ceria doped Scandia Stabilized Zirconia (1Ce10ScSZ) electrolyte film deposited by EB-PVD (Electron Beam-Physical Vapour Deposition) technique on NiO-ZrO2 substrate was characterized by electron microscopy. The highly porous substrate was densely covered by deposited film without any spallation. The produced electrolyte layer was of a columnar structure with bushes, bundles of a diameter up to 30 μm and diverse height. Between the columns, delamination cracks of few microns length were visible. The annealing of zirconia film at 1000 °C resulted in its densification. The columnar grains and delaminating cracks changed their shape into a bit rounded. High magnification studies revealed nanopores 5–60 nm formed along the boundaries of the columnar grains during annealing. High-quality contacts between the electrolyte film and anode substrate ensured good conductivity of the electrolyte film and high efficiency of SOFC.

Potential Sensor Based on Electrochemical ${\rm NiFe}_{2}{\rm O}_{4}$ Film Prepared by EB-PVD

The potential sensor is the key element and the major obstacle to realizing corrosion monitoring and control of the infrastructures in civil engineering. A novel solid-state potential sensor is prepared by the electron-beam physical vapor deposition technique. The phase composition of the oxidation film is investigated by X-ray diffraction. Also, the montmorillonite material with three-dimensional layered structure is used as the carrier material to prepare the conductive layer of the potential sensor. Furthermore, the potential stability of the sensor is verified in the simulated concrete pore solution. The results indicate that the potential sensor based on NiFe2O4 film is suitable to assembling the corrosion monitoring and control systems in civil engineering.

Preparation of the NiFe2O4 electrochemical film for the solid-state reference electrode based on EB-PVD

As the key material of the solid-state reference electrode, NiFe2O4 electrochemical film, was prepared by the electron beam-physical vapor deposition technique for the corrosion monitoring sensors of the reinforced concrete structures. The Ni–Fe binary alloy film was obtained by two-source evaporation based on the evaporation currents control. After the heat treatment and the post-oxidation processes, NiFe2O4 spinel film was achieved successfully. Furthermore, the microstructure, phase composition, component and texture of the prepared state, heat treatment state and oxidized state films were investigated in detail, respectively. The results indicate that the NiFe2O4 electrochemical film was very suitable for mass production by using the optimized preparation processes.

IMPROVED CORROSION RESISTANCE OF NANOSTRUCTURED COPPER DEPOSITED BY EB-PVD IN ACIDIC MEDIA

Electron Beam-Physical Vapor Deposition (EB-PVD) is being used in coating component for many applications such as electronic industry for producing nanostructures and ICs coatings. In this work, nanostructured copper was deposited on glass using EB-PVD technique. Surface and elemental characteristics of EB-PVD coatings investigated and evidenced corrosion resistance of nanostructured coatings produced by this technique are higher than Cu sheet in chloride media.

Corrosion behaviour of nanostructured copper thin films in comparison with copper sheet in drinking water

Copper thin films were deposited on glass at 70 and 150°C substrate temperature using electron beam-physical vapour deposition technique. The morphology of the deposited film was investigated by scanning electron microscopy. Corrosion behaviour of these films was studied by potentiodynamic polarisation and electrochemical impedance spectroscopy methods. Results showed the corrosion resistance of copper deposits was higher than the copper sheet in water. The higher corrosion resistance of copper deposits is described by the formation of protective CuO, while the main corrosion product of copper sheet in water is malachite, which is not a protective morphology.

Corrosion behavior of copper thin films deposited by EB-PVD technique on thermally grown silicon dioxide and glass in hydrochloric acid media

Copper thin films were deposited on oxidized single crystal silicon and glass surfaces, at 70 °C and 150 °C substrate temperature using Electron Beam-Physical Vapor Deposition technique. The morphology and crystal orientation of the deposited film were investigated by SEM and XRD, respectively. Corrosion behavior of these films in hydrochloric acid was studied by potentiodynamic polarization method. Results showed that the corrosion resistance of CG 70 (deposit on glass at 70 °C substrate temperature) was higher than all deposits and than copper sheet because of its higher ability to form passive layer.

An evaporation system for film deposition using electron beam sources

EBPVD (electron beam physical vapor deposition) technique offers independence and freedom in control of microstructure and composition of the coating via manipulation of controlling process parameters such as pressure level, substrate temperature, gas content (in case of reactive evaporation), power (voltage, current) and evaporant composition. The process based on the above technique allows the production of films from a wide range of materials such as, metallic, dielectrics and semiconductors with relatively low deposition time. Though commercial coaters are available with transverse electron guns, their parameters are not negotiable. The design issues are not addressed in any literature. Some of the design issues and construction of an evaporation system will be presented in this paper. The evaporation system will be described in three parts, which consist of gun chamber, substrate chamber and specific accessories. The specific accessories correspond to substrate heater, substrate rotation, substrate holder maneuverability (heightwise), ion cleaning, film thickness monitor, crucible indexing and upstream/downstream pressure controller. Also the design issues related to the power source, which will energize the guns, will be presented in this paper.

Effect of overall composition on thermally induced solid-state transformations in thick EB PVD Al/Ni multilayers

Multilayered Ni/Al samples 20–70 μm thick of different average stoichiometries were prepared by electron-beam physical vapour deposition technique. The periodicity in the multilayers varied between 0.2 μm and 0.8 μm. The course of the solid-state transformations initiated by heating the samples at a constant rate has been studied. Intermetallic Al 3Ni was found to be the first phase to form upon heating of all samples studied. Further reactions were dependent on the average composition of the sample so that Al–Ni compounds increasingly richer in Ni formed as the nickel content increased. In general, the phases Al 3Ni, Al 3Ni 2, AlNi, and AlNi 3 have been observed upon heating the samples to 600 °C. The phases were more likely to form in succession rather than to grow simultaneously.

Microstructure of Fe-Based ODS High-Temperature Alloy Sheet Prepared by EBPVD

Large-sized Fe-based ODS (Oxide Dispersive Strengthen) high-temperature alloy sheets were successfully synthesized by EBPVD (Electron Beam Physical Vapor Deposition) technique. The sheets were about 120μm thick, and having a diameter of 1000mm, whose surface roughness was less than 1μm (Ra<1μm). The microstructures were examined by SEM (Scanning Electron Microscope). The grain size was 1-4μm. When the substrate temperature was 600°C, the sheet had sharp irregular polyhedral grain, and when the substrate temperature was 700°C the sheet had quite regular grains. The morphological orientation angle increased with the distance from the center of the sheet. During the first period of deposition, the sheet was growing in a G-L-S mode, which corresponded with the corn-like microstructure in the cross-section. While during the final period, the sheet changed into a G-S growing mode, which corresponded to the smooth columnar microstructure.

Characterization of Thin-Film YSZ Deposited via EB-PVD Technique in Anode-supported SOFCs

An anode-supported solid oxide fuel cell (SOFC) based on yttria-stabilized zirconia (8YSZ) electrolyte that was deposited via an electron-beam physical vapor deposition (EB-PVD) technique, was investigated. A NiO-8YSZ plate was used as both an anode substrate and as a substrate for the deposition of 8YSZ. An additional buffering layer was coated on the anode substrate via a screen printing before the deposition of YSZ film in order to enhance the surface smoothness for the film deposition. In this study, we controlled various experimental variables for the film deposition and subsequent heat treatment process to obtain highly dense and impervious electrolyte film. Consequently, we were able to obtain a large area and dense YSZ film with a uniform thickness of . The surface and cross-sectional microstructure and the corresponding phase of deposited film were thoroughly analyzed by scanning electron microscopy and X-ray diffraction. The electrochemical performance of the EB-PVD unit cell was investigated using dc current-voltage load testing, a dc current interruption technique, and an ac-impedance spectroscopy. Peculiar microstructural features of the deposited film, such as the columnar structure of grains along the growing axis, and the film’s microstructural effect on unit cell performance, were addressed.

Ceramic thermal barrier coatings deposited with the electron beam-physical vapour deposition technique

The deposition of ceramic thermal barrier coatings for high-temperature applications is of great interest. Particularly when the thermal stresses are superimposed by mechanical stresses, the metallic base material will expand much more than the ceramic top layer, so that the coating is not able to withstand the interfacial stresses and will spall off. Therefore such ceramic coatings should have a special type of microstructure to ensure that the complete system can fulfil the desired properties, e.g. thermal shock resistance. By physical vapour deposition (PVD) techniques the microstructure of coatings can be adapted with respect to the several applications. The electron beam (EB)-PVD technique is particularly suitable for the deposition of thermal barrier coatings (TBC), owing to the relatively high deposition rate and the possibility of influencing the microstructure of the coating. The energy of the condensing film varies depending on the temperature of the substrate. It is known that the mobility of the adatom increases within increasing temperature, so long as there is no adatom reflection at a too hot surface. In this paper the connection between the method of heating the substrates during deposition and the resulting microstructure of the coatings is investigated. The aim is to achieve coatings of a columnar microstructure with a thickness of about 200 μm, using the EB-PVD technique to deposit partially stabilized zirconia. Two different types of heat source are investigated, an indirect one using a resistance heater and a direct one using an electron beam. The other deposition parameters such as apparatus geometric, deposition rate, substrate temperature, gas pressure, etc., were kept constant. For both substrate heating methodes the temperature is measured by thermocouples. The type of heating source appears to play an important role, because different coating microstructures and thus various surface temperatures are obtained while measuring the same temperature at the back of the samples. Determination of different surface excitation, which obviously depends on the type of heating source, is also discussed. Some additional investigations are in progress to confirm the observations.