Triple and double twin interfaces in magnesium-the role of disconnections and facets.

Twin boundaries have been shown to deviate from the twinning planes in hcp metals, and facets have often been observed in twin interfaces. This study presents a twinning disconnection-based model for faceting in single, double and triple twin boundaries in magnesium. Primary twinning disconnections predicted via symmetry arguments are shown to produce commensurate facets in single twin boundaries, which are then transformed into commensurate facets in double twin boundaries via the action of secondary twinning disconnections.

A new approach to etching low-carbon microalloyed steels to reveal prior austenite grain boundaries and the dual-phase microstructure.

A modification to picric acid solutions has been undertaken to reveal the prior-austenite grain boundaries in microalloyed steels as a result of elemental segregation. It has been found the maximum addition of sodium dodecyl sulphate plus hydrochloric acid to fully reveal both the prior austenite grain boundaries and the final post-processed structures in these steels.

Microstructure and load bearing capacity of TiN/NbN superlattice coatings deposited on medical grade CoCrMo alloy by HIPIMS.

In recent years significant progress has been made in the application of various ceramic, namely Metal nitride (MeN) functional coatings to engineer the surfaces of medical implants utilising metal-on-metal (MoM) articulation. This article reports on the load bearing capacity and structural response of TiN/NbN superlattice coatings deposited on medical grade CoCrMo alloy substrate under the application of localised load and the subsequent crack formation mechanism. The coatings have been deposited by mixed High Power Impulse Magnetron Sputtering-Unbalanced Magnetron Sputtering (HIPIMS-UBM) process.

Effect of cryomilling time on microstructure evolution and hardness of cryomilled AZ31 powders.

The synthesis of nanostructured AZ31 powder by cryomilling was studied in this paper. The microstructural evolution during cryomilling, including the changes of particle morphology and internal grain size, was characterized via optical microscopy, SEM, TEM and XRD. Observations during the cryomilling produced four main findings.

Facile route to bulk ultrafine-grain steels for high strength and ductility.

Steels with sub-micrometre grain sizes usually possess high toughness and strength, which makes them promising for lightweighting technologies and energy-saving strategies. So far, the industrial fabrication of ultrafine-grained (UFG) alloys, which generally relies on the manipulation of diffusional phase transformation, has been limited to steels with austenite-to-ferrite transformation. Moreover, the limited work hardening and uniform elongation of these UFG steels hinder their widespread application.

The influence of hydrogen on plasticity in pure iron-theory and experiment.

Tensile stress relaxation is combined with transmission electron microscopy to reveal dramatic changes in dislocation structure and sub structure in pure α-Fe as a result of the effects of dissolved hydrogen. We find that hydrogen charged specimens after plastic deformation display a very characteristic pattern of trailing dipoles and prismatic loops which are absent in uncharged pure metal. We explain these observations by use of a new self consistent kinetic Monte Carlo model, which in fact was initially used to predict the now observed microstructure.

Exploring the mechanism of "Rare Earth" texture evolution in a lean Mg-Zn-Ca alloy.

The entire recrystallisation sequence and associated crystallographic texture evolution of Mg-0.8Zn-0.2Ca (wt.

Segregation mediated heterogeneous structure in a metastable β titanium alloy with a superior combination of strength and ductility.

In β titanium alloys, the β stabilizers segregate easily and considerable effort has been devoted to alleviate/eliminate the segregation. In this work, instead of addressing the segregation problems, the segregation was utilized to develop a novel microstructure consisting of a nanometre-grained duplex (α+β) structure and micrometre scale β phase with superior mechanical properties. An as-cast Ti-9Mo-6W alloy exhibited segregation of Mo and W at the tens of micrometre scale.

Spinel-rock salt transformation in LiCoMnO.

The transformation on heating LiCoMnO, with a spinel structure, to LiCoMnO, with a cation-disordered rock salt structure, accompanied by loss of 25% of the oxygen, has been followed using a combination of diffraction, microscopy and spectroscopy techniques. The transformation does not proceed by a topotactic mechanism, even though the spinel and rock salt phases have a similar, cubic close-packed oxygen sublattice. Instead, the transformation passes through two stages involving, first, precipitation of LiMnO, leaving behind a Li-deficient, Co-rich non-stoichiometric spinel and, second, rehomogenization of the two-phase assemblage, accompanied by additional oxygen loss, to give the homogeneous rock salt final product; a combination of electron energy loss spectroscopy and X-ray absorption near edge structure analyses showed oxidation states of Co and Mn in LiCoMnO.

3D analysis of thermal and stress evolution during laser cladding of bioactive glass coatings.

Thermal and strain-stress transient fields during laser cladding of bioactive glass coatings on the Ti6Al4V alloy basement were numerically calculated and analysed. Conditions leading to micro-cracking susceptibility of the coating have been investigated using the finite element based modelling supported by experimental results of microscopic investigation of the sample coatings. Consecutive temperature and stress peaks are developed within the cladded material as a result of the laser beam moving along the complex trajectory, which can lead to micro-cracking.

Stabilisation of Fe2O3-rich Perovskite Nanophase in Epitaxial Rare-earth Doped BiFeO3 Films.

Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.

Dynamic surface microstructural changes during tribological contact that determine the wear behaviour of hip prostheses: metals and ceramics.

It is often the dynamic microstructural changes induced by tribological contact that determine whether or not a material exhibits good wear resistance. It is well known that the mechanical properties of a surface are significantly different from the bulk, an effect amplified by wear induced plastic deformation and electrochemical effects. Despite the importance of these dynamic microstructural changes, there remains little quantitative understanding of how the surface microstructure changes during tribo-contact, and how this modifies the surface mechanical properties and chemical activity.

Characterization of worn alumina hip replacement prostheses.

Alumina hip replacement prostheses have been analyzed following in vitro simulated microseparation. The worn surfaces of the alumina acetabular cup and femoral head were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) which identified four different wear zones. Focused ion beam (FIB) cross-sectioning was used to section the worn surface and produce 3D reconstructions of the subsurface damage.

EELS characterisation of bulk CaCu3Ti4O12 ceramics.

CaCu3Ti4O12 (CCTO) is a cubic perovskite phase and sintered ceramics exhibit high permittivity at room temperature. Electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectrometry (EDS) data have been collected from samples of CCTO to relate the observed electrical properties to the microstructure and chemistry on the nanoscale. CCTO ceramics were sintered for 24h at 1115 degrees C in air, giving a grain size of 50-300 microm.