Electron diffraction based analysis of phase fractions and texture in nanocrystalline thin films, part III: application examples.

In this series of articles, a method is presented that performs (semi)quantitative phase analysis for nanocrystalline transmission electron microscope samples from selected area electron diffraction (SAED) patterns. Volume fractions and degree of fiber texture are determined for the nanocrystalline components. The effect of the amorphous component is minimized by empirical background interpolation. First, the two-dimensional SAED pattern is converted into a one-dimensional distribution similar to X-ray diffraction. Volume fractions of the nanocrystalline components are determined by fitting the spectral components, calculated for the previously identified phases with a priori known structures. These Markers are calculated not only for kinematic conditions, but the Blackwell correction is also applied to take into account dynamic effects for medium thicknesses. Peak shapes and experimental parameters (camera length, etc.) are refined during the fitting iterations. Parameter space is explored with the help of the Downhill-SIMPLEX. The method is implemented in a computer program that runs under the Windows operating system. Part I presented the principles, while part II elaborated current implementation. The present part III demonstrates the usage and efficiency of the computer program by numerous examples. The suggested experimental protocol should be of benefit in experiments aimed at phase analysis using electron diffraction methods.

Microstructure and biocompatibility of titanium oxides produced on nitrided surface layer under glow discharge conditions.

The disadvantages of titanium implants are their low wear resistance and the release of titanium elements into surrounding tissue. These can be eliminated by modifying the surface by surface engineering methods, among them nitriding under glow discharge conditions which allow to produce diffusive surface layers. Their combining with an oxide layer might be valuable for biological events occurring at the bone implant interface. The aim of this study was to enhance the titanium biomaterial performance via combining nitriding and oxidizing treatments in one process under glow discharge conditions. The oxynitrided surface layers were produced at 680 degrees C. The obtained layer was TiO + TiN + Ti2N + alphaTi(N) type and about 4-microm thick and was of diffusive character. This layer significantly increased wear resistance and slightly corrosion resistance compared to that of the reference titanium alloy. The produced titanium oxide was about 400-nm thick and built from fine crystallites. This oxide exhibits bioactivity in SBF (simulated body fluid). Osteoblasts of Saos-2 line incubated on this surface exhibited good adhesion and proliferation and ALP release comparable with cells cultured on the reference titanium alloy and TiN + Ti2N + alphaTi(N) surface layers. A quantitative analysis of blood platelets adhering to this layer revealed their highest amount in comparison to that on both the nitrided surface layer and titanium alloy. The presented study provided a simple and reproducible method of combining oxidizing and nitriding under glow discharge in one process. Experimental data in vitro suggests that titanium alloy oxynitriding under low temperatures at glow discharge conditions improves titanium alloy properties and biocompatibility and tissue healing. Therefore, the layer of TiO + TiN +Ti2N + alphaTi(N) type could be valuable for long-term bone implants.

Interactions between molten aluminum and Y2O3 studied with TEM techniques.

Complementary structural characterization of the reaction product region formed due to high-temperature interaction (1273 K) between molten aluminum and dense polycrystalline yttria substrate was performed. The reaction product region extending up to 1 mm into the oxide substrate was characterized by a wavy shape morphology and multilayer structure consisted of three-layered zones. The application of transmission electron microscopy coupled with focused ion beam preparation technique allowed the detailed structural examination of reactively formed compounds and interfaces between different zones and phases. Fine crystalline precipitates of Al(5)Y(3)O(12) (YAG) phase surrounded by the Al(3)Y were detected within the first zone. The second layer consisted of much bigger AlYO(3) (YAP) crystals and the third one, which was the widest zone, revealed a typical C4 microstructure where elongated YAP precipitates accompanied the Al(2)Y metallic channels.

TEM investigation of reaction zone products formed between molten Al and CoO monocrystalline substrate.

The research was aimed at microstructure characterization of the reaction products formed between molten aluminium and CoO single crystal during a sessile drop wettability test performed in vacuum at 700 and 1000 degrees C for 120 min using contact heating procedure. The solidified Al/CoO couples were sectioned and used for cutting thin foils with focused ion beam. The transmission electron microscopy and energy dispersive X-ray spectroscopy were used for microstructure and local chemical analysis. The interaction of molten aluminium with CoO substrate at 700 degrees C caused the formation of a corrugated 10-40 microm thick reaction zone (RZ). It consisted of aluminium matrix and Al(2)O(3) crystallites varying in size, i.e. of approximately 0.2 microm near the Al drop/RZ interface, growing up to 1-2 microm at the RZ centre and very fine nano-crystallites near the RZ/CoO interface. The reaction of aluminium with CoO at 1000 degrees C produced much thicker RZ of approximately 280 microm characterized by layered microstructure of alternating fine crystalline Al(2)O(3) and coarser Al(13)Co(4) layers. Moreover, at the RZ/CoO interface the presence of a cobalt layer was also identified.

HREM characterization of nano-composite Au/SiO2 layers.

Nano-composite layers of Au nano-crystallites embedded in amorphous silica matrix were obtained by a radio-frequency co-sputtering technique. Glass or single crystal silicon wafers were chosen as substrates. After deposition, the layers were heat treated at 900 degrees C for 60 min. Microstructure of the layers was investigated using a TECNAI G(2) FEG SuperTwin (200 kV) transmission electron microscope. Thin foils were cut using a focused ion beam Quanta 3D. The investigations confirmed that the applied process allowed obtaining nano-composite layers containing spherical Au crystallites of average size of approximately 3 nm embedded in an amorphous silica matrix. Some of the nano-crystallites were twinned. The layers were heat treated in subsequent step and rise of the crystallite average size up to 5.5 nm confirming activation of diffusion processes was seen. Presence of irregularly shaped Au crystallites in the latter layers indicates incomplete sintering due to short annealing time.

Microstructure of electrodeposited NiFe/Cu multilayers.

NiFe/Cu multilayer films have been electrodeposited potentiostatically on (001)-oriented Si and polycrystalline Cu substrates by a single bath technique. Standard error of mean and energy dispersive X-ray studies of single NiFe(Cu) layers allow us to establish the right deposition parameters for NiFe and Cu sublayer. Standard error of mean results reveal the layered structure of deposits for relatively thick bilayer thickness (ca. approximately 200 nm). The modulated structure of NiFe/Cu multilayers with extremely thin bilayer thickness (nominal period Lambda= 8 nm) was investigated by transmission electron microscope techniques. A columnar structure of the deposit with column diameter in the range from 10 to 30 nm was observed. These results are comparable with X-ray diffraction measurements of crystallites size obtained by Scherer equation. The line scans acquired using EDS confirmed the layered structure of the deposit, but pointed towards possibility of intermixing of species from alternating sublayers especially in case of those with finer period.

TEM investigation of ductile iron alloyed with vanadium.

This article presents results of the processing and microstructure evolution of ductile cast iron, modified by an addition of vanadium. The ductile iron was austenitized closed to the solidus (1095 degrees C) for 100 h, cooled down to 640 degrees C and held on at this temperature for 16 h. The heat treatment led to the dissolution of primary vanadium-rich carbides and their subsequent re-precipitation in a more dispersed form. The result of mechanical tests indicated that addition of vanadium and an appropriate heat treatment makes age hardening of ductile iron feasible. The precipitation processes as well as the effect of Si content on the alloy microstructure were examined by scanning and transmission electron microscopy. It was shown that adjacent to uniformly spread out vanadium-rich carbides with an average size of 50 nm, a dispersoid composed of extremely small approximately 1 nm precipitates was also revealed.

Nano-TiC obtained through a reaction of MWCNTs with Zr(Y,Ti)O2.

The zirconia nanopowder stabilized with 2.5 mol% Y(2)O(3) and doped with 18 mol% TiO(2) (Zr(Y,Ti)O(2)) was homogenized with 5.2 wt% multiwall carbon nanotubes (MWCNT) through colloidal processing. The resultant mixture was heat-treated for 2 h at 1200 degrees C in vacuum under a pressure of 5 x 10(-4) mbar. The microstructure characterization was performed using the TECNAI FEG (200 kV) SuperTWIN transmission electron microscope, equipped with the integrated EDAX detector. The TEM observations of the as-received samples showed single strands of the carbon nanotubes uniformly dispersed among zirconia crystallites. Heat treatment of the Zr(Y,Ti)O(2)-MWCNT mixture caused the transformation of carbon nanotubes into polycrystalline TiC nanofibres and nanorods as confirmed by both the energy dispersive X-ray spectroscopy microanalysis and the high-resolution electron microscopy (HREM) observations. Relying on the above, a mechanism of the TiC in situ crystallization controlled by carbon diffusion through the newly formed TiC phase was discussed.

Structure and properties of an alumina/amorphous-alumina/platinum catalytic system deposited on FeCrAl steel.

We have investigated the properties and structure of alumina films obtained as a result of thermal oxidation of 0H18J5 steel under a mixture of SO(2) and O(2) atmosphere and then covered with layers of magnetron-sputtered alumina and platinum. The catalytic tests and transmission electron microscopy investigations reveal that theta-Al(2)O(3) films containing acidic and basic sites are distinguished by high catalytic activity, whereas amorphous and alpha-Al(2)O(3) films show neutral activity. The platinum films deposited on them contribute to the enrichment of the laminar system with basic sites, and consequently raise the catalytic activity of the system. The investigations performed indicate that the catalytic activity of the system may be tailored to the desired level by the control of the thickness of the individual layers of coating.

Advances and problems with TEM characterization of Cr/CrN multilayer coatings.

Multilayer Cr/CrN/Cr/Cr(N,C) and Cr/CrN with 8 and 32 layer coatings were deposited on austenite substrates using pulsed laser deposition (PLD) technique. The microstructure observations were performed using Philips CM20trade mark, TECNAI G(2) F20 - TWINtrade mark and JEOL EX4000trade mark transmission microscopes. The performed experiments indicated that lowering the argon flow from 60 to 30 cm(3)/s during chromium ablation changes buffer layers microstructure from nearly amorphous to nano-crystalline. The nitride or carbo-nitride layers turned out to be less sensitive to changes in nitrogen flow during deposition. The columnar microstructure of Cr layers is coarser than those in CrN ones under the same deposition condition. This observation proved also that relying on PLD technique as thin as 30 nm layers might be formed within multilayer Cr/CrN coatings.

Scanning electron microscopy and transmission electron microscopy in situ studies of grain boundary migration in cold-deformed aluminium bicrystals.

The crystallography of recrystallization has been investigated in channel-die deformed pure aluminium bicrystals with {100}<011>/{110}<001> orientations. The microstructural and microtextural changes during the early stages of recrystallization were followed by systematic local orientation measurements using scanning and transmission electron microscopes. In particular, orientation mapping combined with in situ sample heating was used to investigate the formation and growth of new grains at very early stages of recrystallization. Grain boundary migration and 'consumption' of the as-deformed areas was always favoured along directions parallel to the traces of the {111} slip planes that had been most active during deformation.

Structure studies of ball-milled ZrCuAl, NiTiZrCu and melt-spun ZrNiTiCuAl alloys.

ZrNiTiCu and ZrNiTiCuAl alloys were amorphized using either a melt-spinning or ball-milling process in a high-energy planetary mill. The elemental powders were initially blended to the desired composition (in at.%) of Zr, 65; Cu, 27.5; Al, 7.5 and of Ti, 25; Zr, 17; Cu, 29; Ni, 29, respectively. The composition of alloys was chosen to be the same as for the bulk amorphous ZrCuAl and easy glass-forming ZrNiTiCu alloys. An almost fully amorphous structure was obtained after 80 h of milling in the case of both compositions. Transmission electron microscopy studies of ball-milled powders revealed the presence of nano-crystallites [2-5 nm for ZrCuAl and smaller (1-3 nm) for the ZrTiNiCu alloy]. High-resolution transmission electron microscopy of melt-spun ZrNiTiCuAl ribbons provided evidence of the amorphous structure.

Defects formed within hardness indenter interaction zone in Al2O3-ZrO2 composite.

The Al(2)O(3)-10 wt% ZrO(2) composites were subjected to hardness tests using a Vickers diamond indenter up to 98.1 N. The microstructure observation using a transmission electron microscopy technique helped to identify up to four zones differing in defect level and character. The densest dislocation tangles, twins accumulation and frequent presence of three slip systems were found in regions that were in contact with the sides of the diamond pyramid. The second zone, characterized by two, or at least one, active slip systems, started at the bottom of the indentation mark and extended up to a distance comparable with the depth of indentation. In the third zone, with a thickness comparable to that above, only some alpha-Al(2)O(3) crystallites showed the presence of dislocations, whereas other crystallites were defect free. In the last zone the alumina crystals were left unaffected but the ZrO(2) crystallites showed twinning characteristic of strain-induced transformation.