Early studies showed that the two-phase ordered alloy of semi-coherent β–Ni2AlTi (L21) and β–Ni(Al, Ti) (B2) exhibits excellent elevated-temperature creep strength, and the precipitation of the “rod-like” γ’–Ni3(Al, Ti) (L12) from either the β or the β’ phase improves the room-temperature ductility of the phases concerned. In the present investigation an attempt is being made to combine the above microstructural features in β’–β–γ’ three-phase alloys and for this purpose the composition Ni63Al22Ti15, near the β’–γ’ edge of the three-phase region in the recently estimated Ni–Al–Ti isotherm at 900 °C, has been selected for detailed study. The expected precipitation of both the β and the γ’ phases occurs in the dendritically solidified β’ phase after a 1100 °C/3 h homogenization and a 900 °C/115 h anneal, although the original interdendritic γ’ phase remains. The morphology of the two types of precipitates and their orientation relationships with the β’ parent phase have been examined using transmission electron microscopy and diffraction, and the experimentally obtained data compared with those predicted by Khachaturyan’s elastic strain energy theory. The β precipitates are nearly cuboidal in shape and are bounded by interface dislocations of aβ〈100〉 edge type. For the β precipitates, both morphology and orientation relation agree with those predicted by the theory. The γ’ precipitates were found to obey the Nishiyama–Wassermann orientation relationship with the parent phase. These precipitates are about 0.5 μm thick and elongated along their 〈211〉 directions, and in all cases consist of two twin-related variants, giving a sword-like morphology. The {i11} twin planes, parallel to the {1i0} of the parent phase, have been identified as the habits of the precipitation. The theory, however, predicts a habit of {0.732, 0, 0.681}γ’ type and a Baker–Nutting orientation relationship. This discrepancy has been attributed to the inapplicability of some assumptions made in the theory: equal elastic moduli between parent and product phases and a tetragonal transformation strain based on Bain’s model of the bcc → fcc transformation. The presence of diffuse streaks in the diffraction patterns of the parent phase, which can be correlated with the 〈110〉〈1i0〉 shear waves, suggests high elastic anisotropy and lends credit to Zener’s model. Crystallographic consideration shows that this model is feasible for the L21 → L12 transformation and explains the observed morphological features of the γ’ precipitates. Some earlier studies are also discussed.

DoITPoMS (Dissemination of Information Technology for the Promotion of Materials Science) is a web-based teaching and learning resource based in Cambridge University: www.msm.cam.ac.uk/doitpoms. Over a 6 year period we have developed freely accessible web-based libraries of Micrographs, and Teaching and Learning packages (TLPs). The Micrograph Library is a searchable collection of approximately 800 micrographs covering metallic, ceramic, composite and polymer systems. There is accompanying descriptive information, with links to a web-based Glossary of Materials Science and to relevant phase diagrams. There are now 32 TLPs, grouped into 7 broad themes. In establishing these TLPs we have designed and maintained the same basic format, in order to give the site a recognizable look and feel, but with the flexibility to include differing amounts of text, images, video clips, animations and external links, as well as interactive questions and answers. Many of these resources are now used within the Cambridge curriculum and elsewhere. Students have been involved in their development, so that they have been tailored to student requirements and are delivered in an appropriate format. They are also used by those teaching Materials Science, e.g. to illustrate how to set up and use specific laboratory practicals and demonstrations. We have strong links with the MATTER (Materials Teaching Educational Resources) initiative and the UK Centre for Materials Education at Liverpool, now part of the UK Higher Education Academy.

Tungsten trioxide films were deposited on (100) SrTiO3and R-plane (10 2) cut sapphire substrates by dc magnetron sputtering, using a tungsten target in an Ar/O2sputtering gas mixture at substrate temperatures ranging from 500 to 850 °C. Deposited films were characterized by x-ray diffraction using -2 scans and pole figure analysis. X-ray results showed that films deposited on both types of substrate were epitaxial. The equilibrium phase was monoclinic -WO3 , confirmed by Raman spectroscopy. Films on both substrates were (001) oriented. This preferred orientation improved as the deposition temperature was reduced. The in-plane orientation relationship of the films with the substrate was obtained from the pole figures.

The growth of single crystal/highly textured films of oxides on metals has become of considerable interest recently as a building block to the exploitation of conductors of YBCO based HTS materials. This study describes work in which oxide films are deposited by pulsed laser ablation onto previously deposited, single crystal metal thin films. The metal films are sputter deposited onto single crystal oxide substrates in a linked, but separate, UHV chamber. The samples are then transferred to the laser ablation chamber. Different levels of oxidation are used in the laser ablation process. In its most novel form, the oxide films are grown using a sub-millisecond oxygen pulse synchronised with the ablating laser pulse. In this way the overall oxygen exposure of the metal is minimised and controlled. Other background gases have been introduced to change the environment of the growing oxide films. Epitaxial (002) SrTiO3 has been grown directly on (002) Ni, with a 0.48 degrees rocking curve; this work is being extended to YSZ and CeO2 where there is a greater tendency to grow with a(lll) orientation.

The aim of this work is the fabrication of heterostructures of epitaxial oxides and metals for device applications. The epitaxial metals are deposited on R-plane sapphire substrates by de magnetron sputtering in a linked UHV system. The oxide layer is then grown on top of this metal layer in a linked UHV pulsed laser deposition (PLD) system using a pulsed oxygen jet to provide oxidation of the ablation products while minimising oxidation of the metal layer. Isolating the oxide deposition from the metal deposition avoids contamination of the sputtering process which enables, very high quality, single crystal metal films to be produced. In this preliminary study the length of the oxygen pulse was varied during the initial growth of MgO on Nb to investigate when the epitaxial oxide nucleation became significantly degraded. The full width half maximum (FWHM) of the X-ray diffraction rocking curve was used as a gauge of the quality of the epitaxy (Nb: 0.33 degrees--0.92 degrees; MgO: 0.81 degrees--3.43 degrees). The results suggest that oxidation of the surface of the metal does indeed affect the epitaxy of the MgO overlayer with an oxygen pulse length greater than 3 ms. The purity of the metal base layers was examined by residual resistance ratio (10 K to 293 K) and found to be in the range of 75 for a clean Nb film to 1.1 for a heavily oxidised Nb film. (C) 1997 Elsevier Science Ltd. All rights reserved.

Room temperature giant magnetoresistance (GMR) has been investigated for Co/Cu(1 1 1) multilayers grown by DC magnetron sputtering. The effect of annealing on the magnetic structure of multilayers with a nominal copper thickness of 0.9 nm has been studied, a strong linear correlation between the GMR and the volume fraction of ferromagnetic regions is observed. Such behaviour has been used to elucidate the scattering mechanism responsible for the GMR of this system, and suggests that s-d scattering into the split d-band of cobalt is the dominant mechanism responsible for the GMR of Co/Cu multilayers. This is in contrast to systems like Fe/Cr where experimental studies on the effect of interfacial mixing indicate that interfacial scattering resulting from spin-dependent interface potentials contributes strongly to the observed GMR.

We have prepared (111) Co/Cu multilayers using d.c. magnetron sputtering which exhibit room temperature giant magnetoresistances (GMR) around 65%. These values are similar to the record for this system, but more than 20% higher than those reported by other workers. Such big differences are not fully explained, and have been attributed to difficulties in finding the optimum growth conditions. Here we present results on the effect of annealing one of these very high GMR multilayers. The aims of this study were to relate changes in the multilayer structure to the magnetic properties of the sample and the GMR. By using X-ray characterisation and vibrating sample magnetometer measurements we have found that large changes in the GMR are associated with a reduction in the volume fraction of antiferromagnetic alignment, while there was very little (if any) change in the quality of the layering.

Theoretical attempts to interpret the giant magnetoresistance (GMR) phenomenon exhibited by magnetic multilayers differ in their conclusions as to where the scattering occurs. Here we present results which show that changes in the GMR produced by annealing (111) Co/Cu multilayers are due to changes in the bulk density of states available for scattering. Further, we find no changes in the scattering potential at the interfaces between the layers.

Structural deviations from ideal layering can have a marked effect on the physical properties of multilayers. Using X-ray diffraction and cross-sectional transmission electron microscopy as the structural probes, we have systematically identified the presence of a variety of structural imperfections in sputtered Co/Cu multilayers. By constructing a structural model which realistically represents the multilayer structures, we attempt to extract structural data on the regularity of layering and interfacial roughness through the fitting of low-angle X-ray diffractograms.

Qualitative and quantitative characterisation of Co/Cu multilayers prepared by magnetron sputtering have been performed using X-ray diffraction. To gain information on the quality of the layering within the samples, both specular and off-specular (diffuse) measurements have been made, with the experimental scans interpreted using numerical techniques. We find inter-facial roughness that is partially correlated through the multilayer stack.

Phase transformations in the {beta} phase of a number of nickel-rich Ni-Al-Ti alloys between 600 and 700 C have been studied by transmission electron microscopy. When titanium content is increased to about 10 at.%, no martensite forms upon quenching to room temperature, and new metastable phases with either 4H or 6R long-period stacking variations were found upon short-term annealing. This contrasts with the behavior of Ni-Al or Ni-Al-Ti alloys with low titanium contents, in which the appearance of 3R and 7R martensites is followed by formation of Ni{sub 5}Al{sub 3} upon annealing in the same temperature range.

Analyses using a LIMA-2A laser microprobe of Fe3Al 3 at.% X and metal oxide samples are reported. The results are compared to the local thermodynamic equilibrium (LTE) model in which the relative sensitivity factor (RSF) is predicted to depend on the ionisation potential.The RSF depended on the ionisation energy for metals in Fe3Al 3 at.% X as expected, but not for non-metals. The agreement for non-metals was enhanced if they were plotted at a corrected ionisation energy given by the ionisation energy of the element in the same row of the periodic table with the electronic configuration (noble gas+s2+one electron) i.e. for silicon the corrected ionisation energy is that of aluminium. A possible explanation of this is that the metallic sea of electrons in the Fe3Al has altered the electronic state of the dopant element X if X is not itself a metal.Analyses on metal oxides with differing oxidation states showed that the RSF depended on the electronic state of the metal. Thus lending weight to the hypothesis that the production of ions from a sample depends on the electronic structure of the element in the matrix rather than in isolated form.

The recently developed Arrhenius formula of modified Sutherland equation was applied to calculate the self- and impurity diffusivities in liquid Al, Ce and Ni. Based on the measured tracer and chemical diffusivities available in the literature together with the reliable thermodynamic parameters of the liquid phase in the Al–Ce–Ni system and the atomic mobilities of binary Al–Ni melts, the atomic mobilities in Al–Ce–Ni melts were evaluated using the DICTRA (diffusion-controlled transformations) software package. Comprehensive comparisons between the calculated results and the experimentally measured data show that most of the diffusivities from different sources can be well reproduced by the atomic mobilities obtained in the present work. The atomic mobilities were further verified by comparing the model-predicted concentration profiles and the measured ones in two liquid Al–Ce–Ni diffusion couples.

The crystallography and nucleation of the Cr phase (alpha) from both beta-Ni(Al, Ti) and gamma'-Ni3(Al, Ti) in an alpha-beta-gamma' three-phase alloy are investigated using analytical electron microscopy. The alpha-particles in beta are spherically shaped and oriented parallel with the parent phase. Those in gamma' are lath-shaped with a well-defined habit plane of (121BAR)gamma'/(312BAR)alpha, a growth direction close to [111BAR]alpha/[101BAR]gamma', and are related to gamma' by the Kurdjumov-Sachs (K-S) orientation relationship. It is shown that alpha particles can nucleate only from the disordered-gamma phase which was stabilized at higher temperatures. The heterogeneous nucleation and distribution of alpha-particles in gamma' are interpreted in terms of a transformation sequence. Modification of the microstructure by rapid solidification is also discussed.

As part of a comprehensive study of 3-phase alloys in the Ni-Al-Ti system incorporating the beta (B2, NiAl type), beta' (L2(1), Ni2AlTi type) and gamma' (L1(2), Ni3Al type) phases, the phase equilibria for this part of the ternary diagram were modelled by CALPHAD methods. The approach used and the results obtained are presented, and compared with an experimental determination by analytical electron microscopy of the 3-phase equilibrium triangle at 900-degrees-C. The calculated/experimental 3-phase triangle differs significantly from earlier estimates. The theoretical model is also used to predict phase formation sequences for several alloys in the 3-phase triangle and these are critically compared with observed microstructures. An unusual graded antiphase domain structure seen in one alloy is interpreted.

Article Structural Relaxation in Fe40Ni40B20 Metallic Glass: Evolution of Resistivity at Temperature in Electrically Self-Heated Specimens* was published on January 1, 1988 in the journal Zeitschrift für Physikalische Chemie (volume 157, issue 1).

The concept of an activation energy spectrum (AES) has been successfully applied by many authors in modelling the kinetics of structural relaxation displayed by many physical properties of metallic glasses. In this paper it is shown that a combination of a constant, physically reasonable value of v0 with broad gaussian spectra of activation energies can provide a good fit to observed isothermal kinetic data. It is also found that temperature-dependent gaussian spectra can be used to model the results of non-isothermal experiments, e.g. constant heating rate differential scanning calorimetry. The origin of the temperature dependence of these spectra is related to the behaviour of a distribution of two level systems. Finally it is confirmed from a study of reversible and irreversible changes of electrical resistivity and from a comparison of the relaxation kinetics of several properties of one glass, that separate spectra are needed to account for reversible and irreversible processes.