Macit Ozenbas

Microstructural characteristics of gas tungsten arc synthesised Fe-Cr-Si-C coating

Abstract The gas tungsten arc (GTA) method was used to synthesise Fe-Cr-Si-C alloy coatings, and processing effects on the coating were investigated experimentally. Coatings were developed on an AISI type 1040 steel substrate. Four different regions were obtained in the surface coating; and in these regions either a hypoeutectic or a hypereutectic microstructure was found. The hypoeutectic microstructure consisted of primary dendrites of austenite (γ) phase and eutectic M7C3 (M=Cr,Fe) carbides. On the other hand, the hypereutectic microstructure consisted of M7C3 primary carbides and eutectic. A hypoeutectic or hypereutectic microstructure was determined by the combination of particularly carbon concentration, solidification rate, and extent of substrate melting. The higher hardness of the hypereutectic microstructure is attributed especially to the formation of M7C3 primary carbides. The lower hardness of the hypoeutectic microstructure is related to three effective parameters: first, the presence of γ phase in the primary dendrites; second, excessive dilution from the base material; and third, relatively low concentrations of chromium and carbon.

Micropatterned lead zirconium titanate thin films

Micropatterning of Pb(Zr0.52Ti0.48)O-3 (PZT) thin films with line features as small as 350 nm was demonstrated through capillary molding of organometallic solutions within the continuous channels of an elastomeric mold. Despite the large stresses that develop during the evaporation of the solvent, pyrolysis of the organics, and the densification and crystallization of the inorganic gel, the patterned crystalline PZT films were crack-free and mechanically robust. Flawless regions as large as I cm(2) were obtained. The cross-sectional shape of the patterned PZT lines was trapezoidlike. Single perovskite PZT grains that formed during annealing at 600-700 degreesC completely filled the cross-sectional area of the patterned lines. Lead acetate, zirconium propoxide, and titanium isopropoxide were used as the starting materials. Substrates used included silver tape, stainless steel plate, silicon wafer, and platinum-coated silicon wafer.

Growth of selenium thin films

Quantitative measurements of the formation and growth of selenium films on sapphire, glass, aluminium and nickel substrates have been made for various substrate temperatures (T) and evaporation times (t) using a scanning electron microscope (SEM). The film formation and growth process was thought to be a mechanism of the adsorption of impinging selenium atoms on the stable clusters, and the growth of these clusters as evaporation continues. The difference in the values of the activation energies for the growth of selenium on different substrates was explained by considering them as apparent energies which contain the adsorption, desorption, surface diffusion and binding energy terms. The experimental results also indicated an increase in there-evaporation of adatoms from the substrates at higher temperatures.

FeCrC, FeW, and NiAl Modified Iron-Based Alloy Coating Deposited by Plasma Transferred Arc Process

The technique of alloying X120Mn12 steel substrate by plasma transferred arc process was used for development of a surface having high wear resistance. High carbon ferrochromium, ferrotungsten, and nickel-aluminum intermetallic powders were combined to form M7C3 carbides inside Fe-based composite surface coating. The phase transformations on these coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM) with energy dispersive spectrometry microanalysis, differential thermal analysis and X-ray diffraction (XRD). The microstructure studies of the superficial layers of the coating revealed a phase mixture of interdendritic austenite (γ) phase structure and fine eutectic M7C3 carbides. The new formed coated surfaces were investigated by change of alloying elements (Cr, W, Ni), size of dendrites, change of eutectic reaction temperatures, hardness, carbide volume ratio of hard phases, and coating thickness as the processing parameters (powder feed rate and heat input). The dry sliding wear tests were performed on a pin on disc machine. The wear rates of the tests were affected by the powder feed rate, powder type, and applied load. Results revealed that processing powder combination used in this study (FeCrC–FeW–NiAl) provided the best option with superior combination of properties on surface of X120Mn12 steel substrate.

Crystallization of amorphous selenium thin films

The crystallization of amorphous Se (a-Se) films prepared by vacuum deposition at <10-5 Torr onto glass substrates at 20°C was examined. The amorphous-to-crystalline transition was obtained by annealing of the films between 40–90°C. The crystalline structures resulting from annealing at different temperatures have been identified by SEM (Scanning Electron Microscope). X-ray and TEM (Transmission Electron Microscopy) studies showed that these structures were hexagonal. The thicknesses of the films used were 2250, 6600 and 11800 A. By heating the film, crystallization started at the substrate-film interface and proceeded towards the surface. The radius, r, of the crystallites increased linearly with heating time. Assuming an Arrhenius type of relationship, the activation energies for crystallization were calculated. They showed that the thicker the film, the higher is the activation energy.

Adhesion of thin films

The periodic cracking technique for determining the work of adhesion of thin metallic films was applied to two different substrate systems which were metallic substrates (Al, Cu and steel sheet) and a polymeric substrate (ABS, acrylonitrile butadiene styrene). The original model assumes elastic behaviour of the composite and is insufficient for such an application since the substrates exhibit plastic deformation before failure takes place. The model, however, is quite sufficient for obtaining relative magnitudes of the work of adhesion values. The films were vacuum deposited at <10-5 Torr onto the substrates. The adhesion increased with increasing substrate temperature and cleanliness of the substrate surfaces. The adhesion values were higher on the electropolished surfaces in comparison to the rough ones. To support the results obtained from the periodic cracking technique, microhardness measurements and tape tests were also performed on the same specimens.

Formation of Al-Si intermetallic phases

In this article, a study on the formation of intermetallic compounds at the interface between aluminum thin film and silicon substrate is presented. We studied four systems: Al/Si, Al-(5at%)Fe/Si, Al-(5at%)Cr/Si, and Al-(5at%)Ni/Si. After vacuum deposition of the films, the samples were annealed at different temperatures and time intervals. X-ray, SEM, and EDS analysis showed the sequential formation of several intermetallic phases at the interfaces. Using this data, a model will be given about the formation of the observed intermetallic phases.

Plasma assisted low temperature electron beam deposited NiO thin films for electro-optic applications

This study aims to create high quality nickel oxide (NiO) thin films at low temperatures, which is a prerequisite for coatings on temperature sensitive substrates. NiO chunks were evaporated by electron beam source, and NiO thin films were deposited at a thickness value around 250 nm. Depositions were performed at different experimental conditions: oxygen flow rate, deposition temperature, deposition rate, and plasma assistance. Deposited films were analyzed with regard to the structural, optical, and electrical aspects. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy results reveal that films are grown in cubic nickel oxide phase with preferred orientation of (111) plane. Nonstoichiometry of NiO films increases with increasing oxygen flow rate and plasma assistance leads to stoichiometric NiO films. Needle, spherical, and cuboidal particle formation were seen in scanning electron microscopy (SEM) images. Grain size, lattice parameter, and grain morphology were used to explain the variations ...

Comparative study on deposition of fluorine-doped tin dioxide thin films by conventional and ultrasonic spray pyrolysis methods for dye-sensitized solar modules

Abstract. Fluorine-doped tin dioxide (FTO) thin films were produced via conventional spray pyrolysis and ultrasonic spray pyrolysis (USP) methods using alcohol-based solutions. The prepared films were compared in terms of crystal structure, morphology, surface roughness, visible light transmittance, and electronic properties. Upon investigation of the grain structures and morphologies, the films prepared using ultrasonic spray method provided relatively larger grains and due to this condition, carrier mobilities of these films exhibited slightly higher values. Dye-sensitized solar cells and 10×10  cm modules were prepared using commercially available and USP-deposited FTO/glass substrates, and solar performances were compared. It is observed that there exists no remarkable efficiency difference for both cells and modules, where module efficiency of the USP-deposited FTO glass substrates is 3.06% compared to commercial substrate giving 2.85% under identical conditions. We demonstrated that USP deposition is a low cost and versatile method of depositing commercial quality FTO thin films on large substrates employed in large area dye-sensitized solar modules or other thin film technologies.

Pb(Zr0.52Ti0.48)O3 Films on Stainless Steel by Chemical Solution Deposition

The present work describes the preparation of Pb(Zr0.52Ti0.48)O3 thin films by chemical solution deposition. Lead acetate, zirconium propoxide and titanium isopropoxide were used as starting materials. Substrates used were stainless steel foils of 0.025 mm thick (AISI 304). The preparation of stock solution and heat treatment procedure was described. Crack-free films were obtained by multilayer coating in which the viscosity of the solution was adjusted such that each layer was approximately 0.2 μm thick. X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations of the PZT thin films relative to the growth conditions were presented. Optimum heat treatment conditions were determined as 600°C and 3 hours to obtain high crystallinity and chemical homogeneity.