Besides the six established decagonal states of the Al-Co-Ni quasicrystal two more modifications have been discovered by means of transmission electron microscopy. One is a pentagonal quasicrystal with a superstructure found in specimens with a very high Co-content and quenched from the highest possible temperature lying within the stability field of decagonal Al-Co-Ni. Its electron diffraction patterns are characterized by a 5-fold rotation axis as a unique symmetry element as well as superstructure reflections similar to those of a related decagonal phase. the other is a one-dimensional quasicrystal closely related to decagonal Al-Co-Ni. the modulation length of 61 Å along the periodic direction in its pseudo 10-fold diffraction patterns can be assumed to be caused by a strong linear, uniform, phason strain in the material.

We report on the quantitative characterization of high-coercivity magnetic force microscopy tips for magnetic images using electron holography. In order to extract quantitative data from the reconstructed phase map, a simulation of the projected flux distribution of the magnetic field of the probe has been obtained considering the simple model of a distribution of macroscopic magnetic dipoles on the tip surface.

A stable one-dimensional quasicrystal has been found for Al-Co-Ni which is related closely to the decagonal phase in this system. It exists as a high-temperature state above 900 C in a range of compositions between approximately 71 and 71.5at.% Al between 18at.% and 22at.% Co. The modulation length along the periodic direction in its pseudo tenfold diffraction patterns is approximately 61A. We show that the 20A edge length defective rhomb tiling superimposed on to a corresponding high-resolution image, defined by centres of atomic clusters, can be considered as a subset of a phason-strained, 2.5A edge length Penrose tiling that has the observed period. An ideal 20A edge length tiling based on special configurations of this Penrose tiling can be chosen as a prototype for the observed experimental tiling.

A one-dimensionally periodic pentagonal quasicrystal with a superstructure has been found in the Al-Co-Ni system in a sample quenched from 1160oC at the composition Al71.5Co25.5Ni3. Its electron diffraction patterns are characterized by a fivefold rotation axis as a unique symmetry element as well as superstructure reflections similar to those of a related decagonal phase. The presence of this symmetry in electron diffraction patterns originates from strong dynamical scattering effects of electrons in relatively thick regions of the sample, in combination with the unique parallel arrangement of fivefold symmetric atom clusters. Differently, the superstructure reflections are caused by the long-range order of this new state which can be described by a random variant of a Penrose rhomb tiling.

The phase equilibria of the ternary Al-AlCo-AlNi system are demonstrated using isothermal sections at 1170, 1100, 1050, 900, 850, 730, End 600 degrees C. These are based on metallographic and TEM investigations and on several temperature-concentration sections, which are investigated using thermal analyses. The Scheil reaction scheme is used for explanation of the data. Eleven phases from the binaries Al-Co and AI-Ni and the three ternary phases Y-2 (Co2NiAl9), X and D were found at room temperature. The binary high-temperature phase Co4Al13(h) is stabilized in the ternary down to room temperature by Ni addition (YI). The phase field of D is composed of several modifications which can hardly be distinguished by light microscopy. These modifications are not considered in the present paper. 45 three-phase regions can be derived from the reaction scheme in the Al-AlCo-AlNi subsystem.

A subdivision of the stability region of decagonal Al-Co-Ni quasicrystals into eight different structural modifications is presented for the temperature against composition section along the maximum extension of the decagonal phase. The only methods identifying this subdivision are transmission electron microscopy techniques. Besides two decagonal superstructures (one of which also exists as a high-temperature modification), two variants of the basic decagonal state were observed. Also, a one-dimensionally periodic fivefold quasicrystal (together with its high-temperature superstructure modification) and a one-dimensional quasicrystal are parts of the quasicrystalline stability region. Both have a close structural relationship to the decagonal states. All samples investigated were obtained by quenching from the corresponding temperatures. The eight modifications can be differentiated by a set of attributes, especially by their characteristic diffraction patterns taken with the electron beam parallel to the unique periodic axis.

The phase equilibria of the ternary Al-AlCo-AlNi system were investigated around the decagonal phase. Isopleths with 70, 71.5 and 72.5 at.% Al and with 10 and 13 at.% Ni an elaborated with the aid of differential thermoanalysis, magnetothermal analysis, optical microscopy and transmission electron microscopy. These are based on results of samples of more than 80 different compositions and on data from other isopleths.

The constitution of the ternary Al-AlCo-AlNi system was investigated in the region from 55 to 70 at.% Al. Differential thermoanalysis, magnetothermal analysis, optical microscopy and transmission electron microscopy were applied. A liquidus projection surface of the stable diagram has been determined from heating experiments. The Scheil reaction scheme is reported for the investigated phase reactions. Isopleths with 57.5, 65 and 70 at.% Al and 19 at.% Ni are reported. These are based on results of more than 30 samples of different compositions and on data from other isopleths.

One-dimensionally periodic fivefold quasicrystals have been found in the Al-Co-Ni system. They are characterized by a fivefold rotation axis as a unique symmetry element in selected-area electron diffraction (SAED) patterns which is consistent with contrast features in high-resolution transmission electron microscopy (HRTEM) images. The compositions of the samples are Al72.5Co20Ni7.5 and Al72.5Co19Ni8.5 respectively. The break of the tenfold symmetry in the SAED patterns taken normal to the periodic axis, which contradicts Friedel's law, can be understood as being caused by dynamical scattering effects. In corresponding HRTEM images a homogeneously distributed pentagonal contrast feature due to an identical cluster is found in only one of the two orientations compatible with a tenfold aperiodic tiling. Based on a model with this fivefold-symmetric cluster in only one constant orientation, dynamical calculations of the electron diffraction patterns were made for a small patch of the structure. They corroborate the observation of a break of the tenfold symmetry in the SAED patterns for a specimen thickness of more than 30 nm.

High-resolution transmission electron microscopy images of decagonal Al-Co-Ni quasicrystals are presented, which show the existence of phason related stacking disorder along the periodic tenfold axis. The image contrast in the interior of hexagon-shaped tiles shows an inner vertex only if no phason defect is present. This interpretation of the high-resolution micrographs is substantiated by electron microscopic image simulations based on a realistic structure model.

Conventionally solidified samples of decagonal Al70Co11Ni19 annealed at 1050 degrees C for 12 h, studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM), display sharp spots in their diffraction patterns and almost no diffuse background scattering. Detailed geometric analysis of tilings constructed from rind superimposed onto HRTEM images show that the structure of these samples is very close to the perfect quasiperiodic structure of a Penrose pentagon tiling. This conclusion is corroborated by the observation that, for this structure, tilings in three sizes can be constructed using pattern matching based on semi(de)composition steps with a scaling factor tau. Moreover, these three tilings have a perpendicular space projection located in a window which is only very slightly-larger than the decagonal window of an ideal Penrose pentagon tiling.

In a decagonal quasicrystal with composition Al70Co15Ni15 two different types of superstructure have been found by electron microscopy techniques. One of these superstructures has previously been observed. The other newly characterized superstructure causes a ring-like zone of low diffraction intensities and, additionally, reflections at positions having half-integer indices. Both types of superstructure have a doubled period of 8.2 angstrom along the unique tenfold axis, which is suggested here to be due to Al/TM (TM = Co, Ni) ordering on different layers. The main structural elements are columns with a diameter of approximately 20 angstrom. During irradiation with a 300 keV electron beam both superstructures are transformed to a 'basic' decagonal structure with a 4.1 angstrom period, in which wheel-like contrast features with 20 angstrom diameter are absent. For the more disordered basic decagonal structure no conspicuous tiling can be found which can be superimposed onto the electron micrographs, while the new superstructure corresponds to a 'pentagon tiling' and the other superstructure to a tiling composed of the Penrose rhombs. The relation between the superlattice reflections and the real space order is discussed on the basis of these tilings.

Atomic structure models for decagonal Al-Co-Ni by Steurer et al., Hiraga ei al. and Burkov have been tested in image contrast calculations for high-resolution transmission electron microscopy (HRTEM) images. These models are not capable to account for special features present in the superstructures of decagonal Al-Co-Ni: pentagonal contrast around cluster centres, 8.2 Angstrom period along tenfold axis (as indicated by diffuse scattering layers in twofold diffraction patterns) and rearrangement of certain Al-atoms which occurs Juring an electron radiation induced order-disorder transformation. Therefore, a modified model has been developed based on HRTEM images, This new model presented here explains ail above-mentioned characteristics.

The crystalline textures of amorphous NiZr2 heated in a differential scanning calorimeter (DSC) at very low heating rates were studied by high-resolution transmission electron microscopy. Three differently heat-treated specimens were compared. One of these was taken out of the DSC just after a strong endothermal peak had occurred, which is unexpected for amorphous binary alloys. The remaining specimens were taken out of the DSC after termination of crystallization. All specimens have a polycrystalline texture, with an average grain size of 100 nm. The grains have the tetragonal Al2Cu-type structure, and each of these grains has a nanocrystalline domain texture consisting of rotation twin domains characterized by the following orientation relation: [001]1|[111]2; [110]1|[110]2. The boundary between any two nanocrystals intergrown according to this relation is a planar interface with index (110). The typical distance between such interfaces is 1–3 nm. It is concluded that all specimens are fully crystallized after the occurrence of the strong endothermal peak and that the orientation of the twin domains in the nanocrystalline texture results from medium-range bond orientational order assumed to be present in the amorphous starting material.