Solid State Phenomena Vol. 186

Abstract: Two types of different oxides multifunctional thin films were deposited by PLD technique on the surface of Si and MgO substrates. First of them was CoO doped with Ca content characterized by fcc (halite) structure and second one was perovskite-type LaCoO3 compound. Their microstructure, chemical/phase composition and morphology were examined by means of diverse techniques (SEM, TEM, EDS). For the surface topography observations of thin films the Atomic Force Microscopy (AFM) was applied. Nanohardness and scratch tests (adhesion measurements) were also performed for estimation of (Co,Ca)O and LaCoO3 films mechanical properties and quality. Obtained results confirm that using PLD technique it is possible to carry stoichiometric composition of different compounds from the target to single crystal substrate however the microstructure and properties of obtained thin films are highly influenced by the substrate’s material and laser ablation parameters (laser wavelength, energy density, time and target-substrate distance).

Abstract: Ferromagnetic semimetals are valuable materials for spintronic applications . Recently, several theoretical papers reported that a good candidate in this respect is zinc-blende (ZB) CrTe. We report the THEED measurements of thin CrTe layers obtained by pulsed laser deposition on (100) KCl substrate by YAG:Nd 3+ laser. Layers were grown from tablets of pressed powder Cr₂Te₃. Films have good mirror-like morphology. High resolution diffraction patterns show a number of sharp Debye rings. Careful analysis points on the complex composition of the layers consisting mainly with hexagonal and cubic CrTe. Hexagonal structure of CrTe shows an unexpected lattice constants a = 4.181Å, c = 7.324 Å), while in the literature (J. Dijkstra et al. J. Phys. Cond. Matter 1, 9141 (1989)) these constants are 3.997Å, c = 6.222 Å. Inclusions of Te as well as hexagonal Cr are not excluded. The phases of Cr₂Te₃ and Cr₃Te₄ are observed as well.

Abstract: In this paper we presented results of investigation of carbonaceous-palladium materials obtained in the CVD (Chemical Vapor Deposition) process. This investigations were carried out with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), equipped with spectrum imaging for cathodoluminescence (CL). The composites will be applied as a active layers in hydrogen and also hydrocarbons detectors. Our measurements showed that some of Pd nanoparticles have a graphite shell and also are optically active. This particle in CL spectrum reveal the peak wavelength around 525 nm (2,36 eV).

Abstract: The CrSi compacts containing 10, 20, 30 and 40 at. % Si sintered from mixed elemental powders were used as targets for reactively deposited magnetron (Cr,Si)N coatings. The silicon substrates were kept either at ambient temperature or heated up to 600 °C. The microstructure observations were performed using TECNAI FEG (200 kV) with EDAX X-ray Energy Dispersive Spectroscopy (EDS) system and JEOL 3010 (300 kV) with Gatan Energy Filtering (GIF) attachment microscopes. The thin foils were cut using QUANTA Focused Ion Beam (FIB) system. The performed investigations proved that increasing silicon content in coatings deposited at 600 °C using CrSi10, CrSi20 and CrSi30 targets caused a refining of their fully crystalline CrN-type columnar microstructure from ~ 40 to ~ 35 and ~ 25 nm. The deposition performed from the same targets, but at ambient temperatures, i.e. without resistive heating of the substrates, produced coatings of mixed crystalline-amorphous type. They were characterized by gradient microstructure, i.e. amorphous material was prevailing close to the substrate and decreasing close to coating surface. The rising of silicon content in the targets resulted in decreasing amount of crystalline phase. The coatings obtained from Cr40Si target were fully amorphous independently of substrate temperature during deposition. The measurements of local chemical compositions obtained using EDS technique indicated that the Cr:Si ratio in the coatings roughly reproduced that present in the targets used for their deposition. Additionally, these measurements indicated that all coatings are contaminated with oxygen. The mapping of chemical composition using GIF technique of mixed crystalline-amorphous coatings proved that they are enriched in Cr and Si, respectively. The present results showed, that relying on single CrSi target magnetron sputtering the crystalline-amorphous nano-composite could be obtain at silicon additions from 10 to 30 at %, i.e. well above were that type of microstructure is formed during deposition using double target magnetron systems. Additionally, for the first time, the measurements helped to prove that the crystallites and amorphous material are enriched in chromium and silicon respectively, i.e. confirmed presence of CrN/Si3N4 composite.

Abstract: The effect of damage on microstructure of multilayer coatings (TiN/Ti/a-C:H) have been analyzed. They were deposited through Pulsed Laser Deposition technique (PLD). The coatings microstructure was characterized using TECNAI F20 (200kV) FEG. The phase and chemical composition were described by EDS (Energy Dispersive X-Ray Spectroscopy) and electron diffraction patterns respectively. Coatings damage resistance was tested by pushing diamond ball with 1N of the applied load (static test). Thin foils were prepared directly from the wear track by focused ion beam method (FIB) using QUANTA 200 3D DualBeam. The multilayer coatings were characterized by strongly dislocated microstructure in TiN layers (like in single layered TiN), while a-C:H were amorphous. After mechanical test the multilayer TiN/Ti/a-C:H coating was strongly deformed. Ceramic TiN and a-C:H layers showed brittle cracking, while very thin metallic Ti layers (presented at each interface) deformed plastically. Deformation lines were propagating in 450 to crystalline growth direction. The wear of crystalline TiN layers caused cracks along {111} planes. The presence of metallic phase lead to the cracking resistance properties increase and the increase an energetic cost of propagating cracks.

Abstract: The purpose of this work is electron microscope investigation of the Ti/TiCN/TiAlN and Cr/CrN/CrN coatings deposited by PVD process. The investigations were performed using scanning and transmission electron microscopy for the microstructure determination. By mind of the transmission electron microscopy the high resolution and phase determination was possible to obtain. The morphology was studied as well the lattice parameters for the layer matrix and substrate phase identification using diffraction methods was applied. After the coating of the aluminium alloys AlSi9Cu and AlSi9Cu4 with the selected coatings there are crystallites detected with the size of several tenth of diameter. The investigated samples were examined metallographically using electron microscope with different image techniques, also EDS microanalysis and electron diffraction was made. As an implication for the practice a new layer sequence can be possible to develop, based on PVD technique. Some other investigation should be performed in the future, but the knowledge found in this research shows an interesting investigation direction. The originality and value of this combination of TEM investigation for PVD deposited surface lasers on aluminium alloys makes the investigation very attractive for automotive and other industry branches. Some practical implications and employment of the surface treatment technology for elements, made from tool materials, with the PVD and CVD methods, to obtain the high wear resistant coatings, makes it possible to improve the properties of these materials by – among others – decreasing for example their friction coefficient, microhardness increase, improvement of the tribological contact conditions in practical use. One original value is it also to applied the PVD method on a common material like aluminium alloy. The double layer coatings worked out In the PVD process on the Al0Si-Cu alloys substrate hale the following configuration of the layers: bottom layer/gradient layer/wear resistant hard surface layer.

Abstract: The nanocrystalline silver powder and the amorphous powders of composition Ni49,5Ti20,5Nb15Zr15 (numbers indicate at%) were prepared by ball milling in the planetary Fritsch mill for 40 hours. TEM studies confirmed almost complete amorphization of milled alloys powders allowed to detect a small fraction of a small intermetallic inclusions within the amorphous matrix. The erosion of composites during contact cycling was similar as in Ag-W composites known as a good contact materials. SEM and TEM studies have shown a low solubility of tungsten in silver after ball milling and no solubility of silver in tungsten. The grain size of silver crystals within powders drastically decreased after milling down to about 30 nm and only a small increase in the grain size up to 200 nm was observed after hot pressing. These results were confirmed using TEM studies of composites after hot pressing. TEM microstructures have shown very narrow transition layer at the amorphous/silver interface (between 10-30 nm thick) containing all elements from the amorphous powders plus silver due to short time of hot pressing. The amorphous part has shown growth of intermetallic phases there, however diffused ring from the amorphous part was still visible. The composites prepared from silver and tungsten have shown presence of coherent tungsten rich precipitates showing typical strain field contrast within fine grains near 100 nm formed most probably during hot pressing of silver solid solution formed during mechanical alloying. The structure of tungsten has shown less defects and consequently less grain refinement than silver particles. SEM studies of the compression tested samples of silver-amorphous composites have shown crack formation at the interfaces of both components most probably due to presence of a brittle transition phase containing all elements.

Abstract: Microstructure of two types of 7475 aluminum alloy matrix composites with additions of 10 wt.% and 20 wt.% of Al₂O₃ or AlN were investigated. Pre-alloyed 7475 aluminum powders were mixed with ceramic particles and milled in a high energy planetary Fritsch ball mill for up to 40h. Subsequently, it was compacted at 380°C/600 MPa. The microstructure of the obtained composites was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The performed investigations proved that both types of composites show a good dispersion of ceramic phases. The composite matrix was characterized by fine grain size, i.e. less than 100 nm and contained a high density of even smaller, Zn, Cu or Fe rich precipitates. The EDS chemical analysis indicated local presence of MgO at the metal/ceramic interfaces in both types of composites. The presented approach allowed to produce a composite with AlN or Al₂O₃ particles in nano-crystalline aluminium alloy matrix.

Abstract: This study investigated alloys with the composition Nd9Fe77B14 and Nd9Fe73Ti4B14 (at.%). Materials were melt spun in the form of a partially amorphous ribbon, which was subsequently annealed at 953K in order to obtain the optimum magnetic properties. The highest properties were obtained for annealing lasting 20 minutes (JHC = 913kA/m, Jr = 0,84T, BHmax = 107kJ/m3). Annealing at 953K results in simultaneous crystallisation in the whole mass of the alloy. The growth of grains is controlled by the duration of the annealing process. The objective of this work was to study the mechanisms of crystallisation and the reasons for a finer structure resulting from the presence of titanium. The phase composition was evaluated by X-ray diffraction. The microstructure was studied using a high-resolution transmission electron microscope. Detailed analysis of titanium distribution in the grains and in the grain boundaries was examined by x-ray spectrometry.

Abstract: Microstructure of terminal area of Al₆₅Cu_32.9Co_2.1 ingots (numbers indicate at.%), obtained via directional solidification was studied. Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray powder diffraction were applied. Point microanalysis by Scanning Electron Microscope was used for examination of chemical compositions of alloy phases. It was found that tetragonal θ phase of Al₂Cu stoichiometric formula was the dominate phase (matrix). Additionally the alloy contained orthogonal set of nanofibres of Al₇Cu₂Co T phase with the average diameter of 50-500 nm and oval areas of hexagonal Al₃(Cu,Co)₂ H-phase, surrounded by monoclinic AlCu η₁ phase rim. Inside some areas of H-phase cores of decagonal quasicrystalline D phase were observed.