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Eingeladener Vortrag
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Optical and electron metallography have been used to investigate the development of different microstructures in Armco Fe after rolling reductions between 0 and 90%. Simultaneously, the orientation distribution functions have been calculated from pole figures obtained by X-ray diffraction. Different stages of texture development could be assigned to typical microstructures. Strain inhomogeneities, such as microbands and shear bands, caused some broadening of the texture and a slight deviation of one skeleton line from the predicted fibre texture component. The decomposition of orientations near {111} < 121 > , and the strengthening of {211} < 011 > after high rolling reductions, was not due to mechanical twinning but could rather be explained by assuming {211} < 111 > slip. 30 ref.--AA
The role of grain size and ferrite substructure in respect to mechanical properties of an HSLA steel
(1986)
Several heat treatments were applied to an HSLA steel on type StE460 (German standard) to produce four ferrite substructures of different strength and at least two different grain sizes respectively. Whereas the ferrite substructure has a strong influence on yield strength the effect of grain size was negligible though probably to some extent masked by different pearlite volume fractions. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbonitride particles and their mutual interaction. Increasing both grain size and pearlite volume fraction leads to a remarkable shift of transition temperature T sub 27J which was further enhanced by increasing ferrite strength. 16 ref.--AA
TEM study on the effect of machining on the microstructure of a soft magnetic Ni76Fe17Cu5CrMo2 alloy
(1991)
Low-cycle fatigue experiments under combined axial-torsional loading have been carried out on alloy 800 H tubular specimens at room temperature. In comparison with proportional loading, an extra cyclic hardening effect produced by nonproportional loading was observed. The microstructure study highlights the fact that the dislocation arrangement under proportional loading is significantly different from that under nonproportional loading. Mechanical twinning was found in specimens cycled under axial loading and nonproportional loading. It is suggested that mechanical twinning depends not only on shear stress but also on normal stress on the plane of maximum shearing. The extra hardening can be interpreted in terms of the deformation microstructure. Fatigue cracking was initiated generally at the specimen surfaces along the plane of maximum shearing, but under nonproportional loading cracks were found also in the bulk of the specimens. Transcrystalline crack propagation was observed in the specimens after proportional and nonproportional LCF tests.
Phasenbildung in Metall-Halbleiterkontaktschichten und Präparationstechnik für TEM-Untersuchung
(1995)
Cross-sectional transmission electron microscopy, in combination with energy dispersive X-ray spectroscopy and focused beam microdiffraction, was applied to study the solid-state reactions taking place during contact formation of the system Ge(115 nm)/Pd(50 nm)In0.53Ga0.47As. In order to get information about the sequence of the different processes, rapid thermal, annealing experiments in the range 225400 °C were performed. The following features were observed: at 225 °C Pd reacted with the substrate forming the quaternary phase PdxIn0.53Ga0.47As (x 4), and with the Ge-layer forming mainly PdGe and Pd2Ge. Between PdxIn0.53Ga0.47As and In0.53Ga0.47As, a 5 nm thick amorphous Pd-In-Ga-As layer remained, indicating that the first reaction step was solid-state amorphization. After annealing at 350 °C, PdxIn0.53Ga0.47As disappeared and regrowth of In0.53Ga0.47As occured. Finally, at 400 °C, residual Ge from the amorphous top layer diffused to the interface and grew epitaxially on the regrown In0.53Ga0.47As, thus separating the IIIV compound semiconductor from the Pd-Ge reaction products. The interface remained flat, while only about 10 nm of the active In0.53Ga0.47As layer had been modified during the annealing processes.
Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on IN0.53Ga0.47As
(1996)
An extended model of the tension-compression asymmetry of single crystal nickel-base superalloys
(1996)
Interrupted LCF-tests at 850 deg C for Inconel 738LC have been carried out and the specimens have been intensively examined by REM to quantify the evolution of fatigue damage. Surface crack nucleation at oxidatized grain boundaries and coalescence of neighboring flaws occurred during the whole experiment. An anomalous fast single crack growth is observed just after nucleation, followed by a relative stagnation of the propagation in absence of coalescence. A statistical model is proposed that describes these pheonmena. It leads to an integro-differential equation for the crack density f(c,n) after n cycles, similar to the Bolzmann equation which describes the collision of molecules in a dilute gas.
Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As
(1996)
Phase formation in rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As has been investigated by means of cross-sectional transmission electron microscopy, convergent-beam electron diffraction, and energy-dispersive x-ray analysis. Solid-phase regrowth is observed to occur similarly as in Pd/Ge contacts on GaAs or InP. The reaction starts at low temperatures with the formation of an amorphous Pd–In–Ga–As layer, which crystallizes at elevated temperatures yielding hexagonal Pd4In0.53Ga0.47As being first described in this work. At temperatures .250 °C, this phase decomposes due to epitaxial solid-phase regrowth of In0.53Ga0.47As and formation of Pd–Ge phases. The stable composition is reached at temperatures .350 °C with excess Ge diffused through top Pd–Ge to the contact interface and growing epitaxially on the semiconductor.
Mechanical and thermal response of a nickel-base superalloy upon grinding with high removal rates
(1997)
X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (XTEM) were used to study the formation of AlN films by N+2 ion implantation of aluminium at energies of 3 keV and 100 keV. In both cases, a two-stage mechanism was found, comprising first the oriented precipitation of small particles of the hexagonal AlN-phase, followed by growth and coalescence finally forming a continuous AlN-layer while increasing the implantation dose from 1×1017 cm-2 to 2×1017 cm-2. The results of both methods are in excellent agreement and furthermore provide complementary information concerning chemical composition and binding energies as well as microstructural details.
The formation of AlN films prepared by N+2 ion implantation into aluminium was investigated using X-ray and Auger photoelectron spectroscopy ( XPS, AES) as well as cross-sectional transmission electron microscopy (XTEM). After 100-keV N+2 implantation of low doses (1×1017 cm−2), the formation of hexagonal AlN nanocrystals (crystal size <5 nm, Ncrystal=1017 cm−3) was observed. Their orientation is strongly correlated with the aluminium matrix. With the dose increasing to 3×1017 cm−2, crystal growth follows, finally forming a homogeneous AlN-layer. Furthermore, the diffraction patterns show an increasing amount of misorientation with increasing dose. From the crystal size distribution, we conclude that continuous nucleation takes place. Samples implanted with an energy of 3 keV exhibit analogous behaviour. Nitride growth was further investigated using microstructured AlN formed by 3-keV implantation through movable TEM-masks (structure size: 15–150 mm).
In the case of high N+2 doses (D&5×1017 cm−2), AlN is detected by AES in the shielded area at a distance of up to 10 mm from the exposed region. The Diffusion coefficient was calculated to be 10−10 cm2 s−1. The formation of AlN proceeds in two steps.
After a continuous nucleation, diffusion-assisted Crystal growth takes place until a homogeneous AlN layer results.
Platinum does not form any adherent oxides and can be easily wetted by tin-based solders. Platinum is also an available metallization in semiconductor laboratories. Therefore we investigated the diffusion of platinum thin-film metallizations into eutectic tin–lead solder by using a high-resolution secondary ion mass spectroscopy (SIMS) profiling from the back side. It is shown that an intermetallic phase (PtSn4) is formed during soldering, which controls the consumption of platinum during soldering and in operation. The consumption of platinum follows the well-known parabolic diffusion law. The activation energy of this process is 0.63 eV. Even at extended heating cycles of 2 min at 250°C, 190 nm from the original 300 nm of the platinum film remain undissolved. This high stability makes platinum a very attractive thin-film metallization for flip-chip (FC) bonding of new microsystems.
Residual stress depth profiles of a cast nickel-base superalloy were measured by regarding the deflections occurring in plate-shaped specimens while successively removing layers from the machined or treated surface by electropolishing. The results are in good agreement with previous findings showing (i) the influence of grinding parameters on the width of so-called white layers, which correspond to steep gradients of residual tensile stress, and (ii) a broad zone of compressive residual stress in the case of shot peening.
Different wear-resistant coatings produced by physical vapour deposition (PVD) were characterized with the aid of cross-sectional transmission electron microscopy (XTEM). All coating systems were optimized by the producers and exhibited good properties with respect to their special applications. The microstructure, texture and chemical composition of binary and ternary systems produced by the arc process [TiN, CrN, Cr2N (Ti, Cr)N on steel substrates] and magnetron sputtering process [TiN, CrN on steel substrates, (Ti, Al)N on Si-substrate] were investigated. All coatings had a more or less columnar microstructure, which was interrupted by interlayers in some cases. Whereas arc coatings always did show some kind of substrate modification, the latter was not observed after magnetron sputtering. Electron diffraction normally revealed a mono-phase fcc structure, except at sites very near to the interface. Only for the systems CrN and (Ti, Cr)N were different additional phases observed at low nitrogen partial pressures.
In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations.
In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems.
There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels.
The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In0.53Ga0.47As (p=4×1018 cm-3). Contact resistivities of 23×10-7 and 67×10-7 ?cm2, respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In0.53Ga0.47As heterojunction bipolar transistors.
Multi-layer ohmic contact systems such as Au/Pt/Ti/Pt on III-V double layers such as n-InGaP/p+-GaAs are of considerable technological relevance, e.g. for heterojunction bipolar transistors. The paper shows that such contacts can be effectively reacted through the InGaP layer and exhibit very good contact resistances (0.1 O mm) to the base layer if the thickness of the first Pt layer is properly matched to the thickness of the contacted InGaP layer. Interdiffusion and phase formation associated with the annealing processes are studied by cross-sectional analytical transmission electron microscopy, thin-film x-ray diffraction and Auger electron spectroscopy depth profiling. Thermal ageing experiments up to 400 °C show good electrical stability. Device related reliability tests do not show any degradation effect related to this novel base contact.
Recent progress in the development of A1GaN/GaN heterostructure field effect transistors (HFETs) Shows the great potential towards high temperature / high power electronics. Nevertheless investigations on reliability properties of GaN-based devices are still at the beginning. The frequently used Ti/A1 based ohmic and Pt based Schottky contacts suffer from strong Degradation after aging at elevated temperatures. Therefore new contact systems have to be employed. Concerning the source and drain metallization we used an amorphous WSiN barrier layer as applied for GaAs on top of the Ti/Al-based ohmic contact. This technique significantly reduces the in-diffusion of the Au-containing overlayer, furthermore the barrier layer guaranties smooth contact morphology after RTA and aging, respectively. For the Schottky metallization the Ir/Au system was used. Reliability studies performed on HFET devices containing refractory Ti/A1/Ti/Au/WSiN ohmic and Ir/Au Schottky contacts demonstrate stable conditions during 120h aging at 500°C.
Die volle Leistung einer auf Reibung basierenden Bremse wird erst nach einem Einlaufvorgang erreicht. Dieser ist notwendig, um auf Belag und Scheibe eine sogenannte Reibschicht aufzubauen. Da diese Zwischenschicht das Reibungsverhalten des Systems maßgeblich bestimmt, ist es wichtig, sich Klarheit über ihre chemische Zusammensetzung, Mikrostruktur und die daraus resultierenden Eigenschaften zu verschaffen.
Als Basismaterial diente ein phenolharzgebundener Belag Jurid 57-62, der mit verschiedenen Parametern (Flächenpressung und Umdrehungsgeschwindigkeit) gegen eine Stahlscheibe getestet wurde. Es wurden Dauerbremsungen von jeweils einer Stunde bzw. bis zu einem maximalen Belagverschleiß von 1 mm simuliert, wobei die Entwicklung der Reibzahl und die Oberflächentemperatur der Scheibe registriert wurde.
Zur Analyse der Reibschichten auf dem Bremsbelag wurden mehrere Methoden parallel angewandt. So wurden Verschleißpartikel, die aus der Reibschicht stammen, gesammelt bzw. abgekratzt und nach Dispergieren auf Kohlefolien direkt im Transmissionselektronenmikros-kop (TEM) untersucht. Ferner wurden von einigen ausgesuchten Belagproben Mikrotom-schnitte sowie dünne Querschnittsfolien für die TEM-Untersuchung präpariert, um den Verbund Reibschicht-Grundmaterial darstellen zu können. Als Ergänzung wurden ferner oberflächenmorphologische und –analytische Verfahren wie REM/EDX und ESCA eingesetzt.
Die Ergebnisse deuten darauf hin, dass die Reibschicht nanokristallin ist, und dass fast alle anorganischen Bestandteile des Bremsbelags sowie Eisenoxid von der Bremsscheibe in sehr fein verteilter Form vorliegen. Bei Belägen ohne Metallanteil bildet eine Barium-Eisen-Sulfatphase offenbar die Grundstruktur der Reibschicht, während auf eisenhaltigen Belägen Eisenoxid dominierend ist. Die nanokristalline Mikrostruktur entsteht, ähnlich wie beim mechanischen Legieren, durch einen Mahlvorgang von Verschleißpartikeln zwischen den Reibpartnern. Bei Überlastung des Belags tritt Zersetzung der Polymer-Bindephase ein, was zu einem raschen Anstieg der Verschleißrate führt.
Ti/TiN multilayer coatings with multilayer periods in the range 550 nm and a final thickness of 2 µm were deposited on steel substrates by cyclic modulation of nitrogen gas flow into the chamber of a PVD sputtering device. Coating characterization was performed by cross-sectional transmission electron microscopy, glancing-angle X-ray diffraction and instrumental indentation testing. Individual a-titanium and titanium nitride layers were always observed, although for the finer microstructures, the TiN layers were thicker than the Ti layers by a factor three. The plastic hardness of the films increased steadily with decreasing layer spacing, following a HallPetch relationship. Finally, a hardness value of 42 GPa was reached, which is similar to that of a thick TiN monolayer, prepared under the same coating conditions.
REM-Untersuchung des Oxidschichtwachstums auf der einkristallinen Nickelbasis-Superlegierung SRR 99
(2001)
8 wt% Y2O3-ZrO2 spray powder and thermally sprayed as thermal barrier coatings on outer air seals were characterized by Raman microprobe spectroscopy (RMS) and transmission electron microscopy to investigate the lateral distribution, composition, structure and grain size of ZrO2 phases and to separate ZrO2 and Y2O3. RMS of transfer layers on ZrO2-coated shrouds after rub tests against SiC laser-tipped metallic blades showed the formation of metallic oxides MeIMeII2O4 of spinel type. Wear tracks were partly covered by graphite and spinel-type oxides. In some cases, the latter were better detectable after laser enhanced cleaning by burning off the covering carbon layer.
The formation of a third body layer on a conventional friction material during braking tests was studied in some detail using TEM, SEM, and X-ray photoelectron spectroscopy (XPS) techniques. Plate shaped micro-contact areas representing a compositional mix of all components of the tribocouple and exhibiting a nanocry stalline microstructure were identified after a run-in period.
Patches of white etching layers on rail surfaces were investigated using sophisticated techniques like cross-sectional transmission electron microscopy (XTEM) and synchroton X-ray diffraction. Optical microscopy failed to resolve the microstructure, but in the TEM submicron grains with high dislocation densities and occasional twins, which are characteristic features of high carbon martensite, were observed. The martensitic structure was confirmed by evaluation of synchroton X-ray diffraction line profiles. The latter technique also allowed to determine dislocation densities of the order of 1012 cm-2 and residual compressive stresses of about 200 MPa.
The chemical and microstructural changes occurring during braking simulation tests at the surface of a conventional brake pad material were investigated mainly by scanning and transmission electron microscopy and surface analytical techniques. It can be shown that patches of a third body material develop, comprising a compositional mix of all constituents of the pad and iron oxides from the disk. Milled debris particles still have the crystal structure of barite, the major phase of the pad material, but the grain size is reduced drastically to the nanometer scale. The major wear mechanism is delamination of filler particles from the organic binder, supported by local degradation of the phenolic resin during asperity heating. Quartz crystals are preserved thereby adopting the function of primary contact areas.
The focused ion beam technique - eine interessante Alternative, auch für konventionelle Werkstoffe
(2002)
An attempt was undertaken to obtain a better understanding of the tribological properties of two wear-resistant coatings on tool steel by structural and microchemical analysis of wear particles using a transmission electron microscope. Coatings were deposited by physical vapor deposition and plasma-assisted chemical vapor deposition techniques and tribological properties were derived from reciprocating sliding tests of the coatings against alumina balls. Three types of wear particles were identified by electron diffraction and energy dispersive X-ray spectroscopy: nanocrystalline rutile (TiO2), nanocrystalline graphite and microcrystalline graphite. Low coefficients of friction, of the order of 0.2, were attributed to the formation of solid lubricant films of sub-stoichiometric TiO2-x Magnéli phases and/or graphite.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction. For two typical rapid thermal annealing steps at 750 °C (non-ohmic behaviour) and 850 °C (ohmic behaviour) the intermetallic phases at the metal-semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
Untersuchung der Mikrostruktur asbesthaltiger Bremsbeläge und Möglichkeiten der Asbestsubstitution
(2002)
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
A new type of test sample for the determination of lateral resolution in surface analysis is presented. The certified reference material BAM-L002 Nanoscale strip pattern for length calibration and testing of lateral resolution is an embedded cross-section of epitaxially grown layers of AlxGa1-xAs and InxGa1-xAs on GaAs substrate. The surface of the sample provides a flat pattern with strip widths of 0.4-500 nm. The combination of gratings, isolated narrow strips and sharp edges of wide strips offers improved possibilities for the calibration of a length scale, the determination of lateral resolution and the optimization of instrument settings. The feasibility of the reference material for an analysis of lateral resolution is demonstrated for SIMS.
Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in, the amount of thermal SiO2 oxide on (100) and (111) orientation Si wafer substrates in the thickness range 1.5 - 8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing-incidence x-ray reflectrometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterised by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.
The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The remaining data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonadeous contamination equivalent to ~1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-Ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and, critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2) deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, then these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.