Search results for "RMET"

In-situ time resolved X-ray diffraction study of the formation of the nanocrystalline NbAl3 phase by mechanically activated self-propagating high-tem…

1999

The mechanically activated self-propagating high-temperature synthesis (MASHS) technique was used to produce a NbAl3 intermetallic compound. This process results from the combination of two steps: a mechanical activation of the Nb 3Al powder mixture which is followed by a self-propagating high-temperature synthesis (SHS) reaction, induced by the exothermal character of the reaction Nb3Al. An original experiment was designed to study in-situ the formation of the NbAl3 phase in the combustion front: time-resolved X-ray diffraction coupled with an infrared imaging technique and a thermocouple measurement were performed to monitor the structural and thermal evolution during the SHS reaction. Ow…

Effect of Microstructure on the High Temperature Oxidation and Pesting Behaviour of MoSi<sub>2</sub>

2004

One-Step Synthesis and Consolidation of Nanophase Iron Aluminide

2001

The simultaneous synthesis and densification of nanophase iron aluminide is investigated. Elemental nanophase reactants produced by mechanical activation were reacted by field activation with the simultaneous application of uniaxial pressure. The process was demonstrated in this work by the synthesis of dense nanometric FeAl. Iron and aluminum powders were co-milled in a specially designed planetary mill to obtain nanometric reactants and to avoid formation of any product phases. These powders were then subjected to high AC currents (1250–1500 A) and pressures in the range of 70–106 MPa. Under these conditions, a reaction was initiated and completed within a short period of time (2.5–3.5 mi…

Microstructural corrosion of aluminium alloys: a predictive finite element model based on corrosion-mimicking experiments

2013

The purpose of this study is to implement the basis of a finite element model (FEM) based on the resolution of the Nernst–Planck equation in order to progress in the predictive simulation of microstructural corrosion on aluminium alloys. Certain constituent intermetallic particles at the surface of aluminium alloys are considered as preferential sites for the initiation of structural corrosion resulting in localised trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alkalinization on 200 nm thick aluminium coatings, promoting their local dissolution in an a…

Dense nanostructured materials obtained by spark plasma sintering and field activated pressure assisted synthesis starting from mechanically activate…

2004

The preparation of highly dense bulk materials with a grain size in the range of a few to a few hundreds nanometers is currently the objective of numerous studies. In our research we have achieved a measure of success in this regard by using the methods of mechanically-activated, field-activated, pressure-assisted synthesis, MAFAPAS, which has been patented, and mechanically-activated spark plasma sintering, MASPS. Both methods, which consist of the combination of a mechanical activation step followed by a consolidation step under the simultaneous influence of an electric field and mechanical pressure, have led to the formation of dense nanostructured ceramics, intermetallics, and composite…

Simulation of pH-controlled dissolution of aluminium based on a modified Scanning Electrochemical Microscope experiment to mimic localized trenching …

2011

Abstract Some constituent intermetallic (IMPs) particles at the surface of aluminium alloys are considered as preferential sites for the initiation of structural corrosion resulting in localized trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alcalinisation on 200 nm thick aluminium coatings promoting their local dissolution in an aerated 0.1 M NaCl electrolyte. The local alcalinisation was induced by the oxygen reduction reaction on the tip of a SECM which mimics the surface of an isolated IMP. From a phenomenological point of view, reproducible cylindr…

Nanostructured metal/oxide coatings

2007

Al based nanocomposite coatings on Cu and glass substrates were obtained in the conditions of severe shear stresses by deformation scheme similar to that of friction. Structure, composition and micromechanical properties were investigated using AFM, XRD, SIMS, electron, optical microscopy and precision microindentation techniques. Coatings are characterized by the high microhardness and good adhesion to the substrates. This is determined by the formation of nanostructured Al-oxide composite stabilized by the presence of oxidized interlayers, which are barriers for the grain growth and intermetallic phase formation. The annealing in vacuum leads to the development of oxygen redistribution pr…

Mechanical Activation as a New Method for SHS

2006

The use of mechanical activation (the elemental powder mixture is milled for a short time at given frequency and impact energy) as a precursor to self-propagating high-temperature synthesis (SHS) results in the formation of nanostructured porous materials. The mechanical activation step was found necessary (i) to modify the thermal parameters of the combustion front (i.e. combustion front velocity, thermal heating rate…) in the cases of Mo-Si, Fe-Al, Ni-Si (ii) to initiate a combustion front in the case of systems having a low exothermicity. Nevertheless, the control of the mechanically activated mixture characteristics and, the understanding of the mechanical activation role on the SHS par…

Preparation and characterization of Pd2Sn nanoparticles

2007

We report a non-aqueous solution preparation of Pd{sub 2}Sn nanoparticles with sizes near 20 nm. The intermetallic compound with the Co{sub 2}Si structure has been characterized using transmission electron microscopy, Rietveld refinement of synchrotron X-ray and neutron powder diffraction, and real-space pair distribution function analysis of high-energy synchrotron X-ray scattering. We also present a description of the electronic structure of this covalent intermetallic using density functional calculations of the electronic structure.

Synthesis of niobium aluminides using mechanically activated self-propagating high-temperature synthesis and mechanically activated annealing process

1999

The mechanically activated self-propagating high-temperature synthesis (MASHS) technique and the mechanically activated annealing process (M2AP) were used to produce NbAl3 intermetallic compound. The MASHS process results from the combination of two steps: first, a mechanical activation of the Nb 3Al powders mixture; second, a self-propagating high-temperature synthesis (SHS). The M2AP process also results from the combination of two steps: the first is the same; the second consists of the annealing of as-milled powders. Based on X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDXS), the as-milled powders, MASHS, and M2AP end-pr…