Talaat Al-Kassab

Investigation of the early stages of decomposition of Cu–0.7at.% Fe with the tomographic atom probe

Abstract The early stages of precipitation of the Fe-rich phase in supersaturated Cu–Fe alloy were studied with the field ion microscope and the tomographic atom probe. The specimens of nominal composition Cu–0.7at.% Fe were homogenized at 1173 K and immediately aged in a salt bath for different times at 803 K to follow the decomposition path at this reaction temperature. In this work, preliminary results on the temporal evolution of the decomposition are presented. In particular, the particle radii and particle number density were determined as a function of the ageing time. At the initial stages of the decomposition concentration, fluctuations were observed, which could be quantitatively characterized. The decomposition sequence is discussed in terms of the nucleation and growth theory.

Thermal stability of nanocrystalline nickel–18 at.% tungsten alloy investigated with the tomographic atom probe

The microstructure of commercially available electrodeposited and thermally aged Ni-W layers with a composition of 18 at.% W was studied by means of field ion microscopy and the tomographic atom probe. In comparison with standard Ni-P or hard chrome coatings, Ni-W layers have a promising application field owing to their specific tribological and electro-erosion properties and in particular because they are manufactured at low cost without harm to the environment. The as-plated state is characterized by the presence of nanocrystalline grains of the Ni-rich fcc phase, with the nanocrystalline structure being preserved up to 700 °C. At this temperature the formation of the ordered Ni 4 W-phase (D1a structure) is observed and finally, after aging at 800 °C, the specimens are completely ordered. Whereas in Ni-P the continuous segregation of P and the grain boundaries is responsible for the thermal stability, in Ni-W grain growth is inhibited by the low mobility of the W atoms.

Investigation of the site occupation of atoms in pure and doped TiAl/Ti3Al intermetallic

Dual-phase TiAl/Ti3Al alloys consisting of a lamellar structure, comprising gamma-phase plus a small amount of alpha2 -phase, with addition of 1, 5 and 10 at.%Nb or 2 at.%Ag were prepared. The samples were investigated by means of the field ion microscopy (FIM), the tomographic atom probe (TAP) and supporting TEM, HRTEM analysis. The influence of doping elements on the variation of the field evaporation and microstructural parameters in the gamma-phase as studied by FIM and TAP will be reported in this contribution. A new algorithmic approach based on TAP results was developed to evaluate the site occupancies in such ordered structures. In addition, computer modelling and simulation of the field evaporation behaviour of the different species including the next neighbour interaction in a FIM specimen are performed for the first time

Application of cold drawn lamellar microstructure for developing ultra-high strength wires

Abstract Composite materials having lamellar structure are known to have a good combination of high strength and ductility. They are widely used in the fields of automobiles, civil engineering and construction, machines and many other industries. An application of lamellar microstructure for developing ultra-high strength steel wires was studied and discussed. Based on the experimental results, the relationships between the strength increase and microstructure development during the cold wire drawing were studied to reveal the strengthening mechanism. As cold drawing proceeds, the wire strength extremely increases, the microstructure changes from large single crystal lamellar structure to very fine polycrystalline lamellar one which has nano-sized grains, high dislocation density and amorphous regions. From the results obtained, it is concluded that heavy cold drawing technique is an effective method for lamellar composite to get high strength wires. Furthermore, formation process of the best microstructure for producing the ultra-high strength wires was also discussed.

Microstructural evolution of Cu-1 at% Ti alloy aged in a hydrogen atmosphere and its relation with the electrical conductivity

Copper alloys with titanium additions between 1 and 6at% Ti emerge currently as attractive conductive materials for electrical and electronic commercial products, since they exhibit superior mechanical and electrical properties. However, their electrical conductivity is reduced owing to the residual amount of Ti solutes in the Cu solid solution (Cu(ss)) phase. Since Cu shows only poor reactivity with hydrogen (H), while Ti exhibits high affinity to it, we were inspired by the idea that hydrogenation of Cu-Ti alloys would influence their microstructure, resulting in a significant change of their properties. In this contribution, the influence of aging under a deuterium (D(2)) atmosphere of Cu-1at% Ti alloys on their microstructure is investigated to explore the effects on the electrical conductivity. The specimens were investigated by means of transmission electron microscopy (TEM), field ion microscopy (FIM), computer-aided field ion image tomography (cFIIT), and atom probe tomography (APT). At an early aging stage at 623K in a D(2) atmosphere of 0.08MPa, ellipsoidal alpha-Cu(4)Ti precipitates are formed in the alloy, and during subsequent aging, delta-TiD(2) is competitively nucleated instead of growth of alpha-Cu(4)Ti particles. The co-precipitation of alpha-Cu(4)Ti and delta-TiD(2) efficiently reduces the Ti concentration of Cu(ss) matrix, particularly in the later aging stages in comparison to the aging in vacuum conditions. The electrical conductivity of the alloy aged in the D(2) atmosphere increases steeply up to 48% International Annealed Copper Standard (IACS) after 1030h, while it saturates to approximately 20% IACS in the alloy aged in vacuum. The outstanding increase of electrical conductivity during aging in D(2) atmosphere can be basically explained by the reduction of Ti solute concentration in Cu(ss) matrix.

APT analyses of deuterium-loaded Fe/V multi-layered films

Interaction of hydrogen with metallic multi-layered thin films remains as a hot topic in recent days. Detailed knowledge on such chemically modulated systems is required if they are desired for application in hydrogen energy system as storage media. In this study, the deuterium concentration profile of Fe/V multi-layer was investigated by atom probe tomography (APT) at 60 and 30K. It is firstly shown that deuterium-loaded sample can easily react with oxygen at the Pd capping layer on Fe/V and therefore, it is highly desired to avoid any oxygen exposure after D(2) loading before APT analysis. The analysis temperature also has an impact on D concentration profile. The result taken at 60K shows clear traces of surface segregation of D atoms towards analysis surface. The observed diffusion profile of D allows us to estimate an apparent diffusion coefficient D. The calculated D at 60K is in the order of 10(-17)cm(2)/s, deviating 6 orders of magnitude from an extrapolated value. This was interpreted with alloying, D-trapping at defects and effects of the large extension to which the extrapolation was done. A D concentration profile taken at 30K shows no segregation anymore and a homogeneous distribution at c(D)=0.05(2)D/Me, which is in good accordance with that measured in the corresponding pressure-composition isotherm.

Structural, spectroscopic, and dielectric characterizations of Mn-doped 0.67BiFeO 3 –0.33BaTiO 3 multiferroic ceramics

Abstract0.67BiFeO3-0.33BaTiO3 multiferroic ceramics doped with x mol% MnO2 (x = 2–10) were synthesized by solid-state reaction. The formation of a perovskite phase with rhombohedral symmetry was confirmed by X-ray diffraction (XRD). The average grain sizes were reduced from 0.80 μm to 0.50 μm as increasing the Mn-doped levels. Single crystalline nature of the grains was revealed by high-resolution transmission electron microscopy (HRTEM) images and electron diffraction patterns. Polar nano-sized ferroelectric domains with an average size of 9 nm randomly distributed in the ceramic samples were revealed by TEM images. Ferroelectric domain lamellae (71° ferroelectric domains) with an average width of 5 nm were also observed. Vibrational modes were examined by Raman spectra, where only four Raman peaks at 272 cm−1 (E-4 mode), 496 cm−1 (A1-4 mode), 639 cm−1, and 1338 cm−1 were observed. The blue shifts in the E-4 and A1-4 Raman mode frequencies were interpreted by a spring oscillator model. The dieletric constants of the present ceramics as a function of the Mn-doped levels exhibited a V-typed curve. They were in the range of 350–700 measured at 103 Hz, and the corresponding dielectric losses were in range of 0.43–0.96, approaching to 0.09 at 106 Hz.

Application of Focused Ion Beam to Atom Probe Tomography Specimen Preparation from Mechanically Alloyed Powders

Focused ion-beam milling has been applied to prepare needle-shaped atom probe tomography specimens from mechanically alloyed powders without the use of embedding media. The lift-out technique known from transmission electron microscopy specimen preparation was modified to cut micron-sized square cross-sectional blanks out of single powder particles. A sequence of rectangular cuts and annular milling showed the highest efficiency for sharpening the blanks to tips. First atom probe results on a Fe95Cu5 powder mechanically alloyed in a high-energy planetary ball mill for 20 h have been obtained. Concentration profiles taken from this powder sample showed that the Cu distribution is inhomogeneous on a nanoscale and that the mechanical alloying process has not been completed yet. In addition, small clusters of oxygen, stemming from the ball milling process, have been detected. Annular milling with 30 keV Ga ions and beam currents >or=50 pA was found to cause the formation of an amorphous surface layer, whereas no structural changes could be observed for beam currents <or=10 pA.

Tomography by Atom Probe Field Ion Microscopy

The Field Ion Microscope (FIM) introduced by E.W. Muller was the first instrument capable of imaging metal surfaces with atomic resolution in real space [1–7]. The FIM was originally employed to solve problems related to surface physics and crystallography. The field of application substantially widened when the imaging mode was supplemented by the atom probe mode. This technique finally gives the chemical composition of a sample volume with atomic spatial resolution, and the sensitivity of the chemical analysis does not depend on the atom species. These advantages led to increasing and fruitful use of the method in metal physics, materials science and engineering. While the in-depth resolution corresponds to the atomic plane distance parallel to the sample axis, the lateral resolution is essentially determined by the structure of position-sensitive ion detectors that monitor the original atom positions at the sample surface before field evaporation. Such detectors, although well known for many years in numerous areas of application, have been improved substantially for use in atom probes during the past decade. In parallel, fast and extended data acquisition and handling systems have also been developed. This chapter reviews this development and presents a number of results from materials research.

Ordering and site occupancy of D03 ordered Fe3Al-5 at%Cr evaluated by means of atom probe tomography.

Addition of ternary elements to the D0(3) ordered Fe(3)Al intermetallic phase is a general approach to optimise its mechanical properties. To understand the physical influences of such additions the determination of the probability of site occupancies of these additions on the lattice site and ordering parameters is of high interest. Some common experimental techniques such as X-ray diffraction or Atom Location by Channelling Enhanced Microanalysis (ALCHEMI) are usually applied to explore this interplay. Unfortunately, certain published results are partly inconsistent, imprecise or even contradictory. In this study, these aspects are evaluated systematically by atom probe tomography (APT) and a special data analysis method. Additionally, to account for possible field evaporation effects that can falsify the estimation of site occupancy and induce misinterpretations, APT evaporation sequences were also simulated. As a result, chromium occupies most frequently the next nearest neighbour sites of Al atoms and local ordering parameters could be achieved.