Laurence Ryelandt

Reactive Growth of Yba2cu3o7-x Layers On Y2bacuo5 Substrates

YBa2Cu3O7-x thick films were grown via a solid/liquid reaction between Y2BaCuO5 and a mixture of 3 BaCuO2 + 2 CuO. The morphology of the 123 films was found to be related to the microstructure of the parent solid phase. The reaction kinetics has been investigated and the growth mechanisms are discussed in relation with the density of the substrates.

Effect of the homogenisation conditions on the extrudability and high temperature fracture resistance of AA6063 aluminium alloy

Homogenisation is an essential step in the preparation of aluminium billets for extrusion. It is designed to produce an homogeneous solid solution and to transform the beta-Al5FeSi particles to the more equiaxed and thus more acceptable cubic alpha-Al-12(Fe-x,Mn1-x)(3)Si variety. The effect of the homogenisation conditions on high temperature surface damage and fracture is investigated through full scale industrial extrusion experiments on AlMgSi alloy. The transformation of AlFeSi intermetallic particles from the beta-Al5FeSi thin plate like shape to the more rounded alpha-Al-12(Fe,Mn)(3)Si form, quantified by EDS measurements, is shown to postpone the formation of surface defects. Transmission Electron Microscopy (TEM) analysis of extruded samples close to the location of extrusion defects, reveals that damage initiates by microcracks within the brittle beta-Al5FeSi particles or due to incipient melting caused by the eutectic transformation Al + beta-Al5FeSi + Si --> Liquid at 578degreesC. These microcracks open by plastic deformation around the cracked brittle phase and, after sufficient growth, coalesce into a large crack.

Neutron diffraction analysis of the evolution of phase stresses during plastic straining of aluminium matrix composites reinforced with a continuous, random planar network of fibres

Composites consisting of a pure Al matrix reinforced with a continuous network of 20 or 30 vol % of continuous fibres of Inconel 601 exhibit a tensile ductility of more than 10%, The fibre orientation distribution presents transverse isotropy with low misorientation with respect to the isotropy plane. The evolution of phase stresses during in-plane tensile testing was investigated by neutron diffraction, using Al-111 signal for the matrix and Ni-111 signal for the fibres. The phase stresses were obtained using computed diffraction elastic constants. Analysis of the variation of the fibre stresses as a function of composite strain allowed distinguishing four successive regimes corresponding to different straining behaviours of the phases.

Critical assessment of the process of growth of a YBa2Cu3O7-delta layer on Y2BaCuO5

A layer of YBa2Cu3O7-delta (123) can be grown on a Y2BaCuO5 (211) substrate by reaction with a mixture of 3BaCuO(2) + 2CuO. This reaction has been studied in the temperature range of 930 to 980 degrees C. The reaction is never complete but levels off when the CuO present in the reactant mixture is exhausted, The liquid dissolves an excess of CuO and the 211 substrate becomes covered by co-precipitation of 123 grains and CuO inclusions. The formation of 124 and related polytypoids is favoured by the Cu-rich stoichiometry of the reactant liquid. The growth of the 123 grains follows a parabolic law. The presence of a thermal gradient during reaction does not affect the orientation of the grains but has an influence on the thickness of the 123 layer.

Multiscale characterisation of the plasticity of Fe-Mn-C TWIP steels

It is known for a long time that mechanical twinning occurring in FCC metal can bring about a very large work hardening rate. It is believed that deformation twins increase the work-hardening rate by acting as obstacles for gliding dislocations. This mode of plastic deformation is active, among others, in the Hadfield steel known for a very long time [1]. Fe-Mn-C grades exhibiting mechanical twinning present a renewed interest for some years since some applications are expected in the automotive industry. Several kinds of TWIP (Twinning Induced Plasticity) steels are now intensively studied.

Microscale characterisation of deformed microstructures of TRIP-assisted and multiphase

The improvement of the mechanical behaviour of high performance steels brings about a renewed interest for the work hardening rate resulting from deformation-induced martensitic transformation or mechanical twinning. Even if these mechanisms are known for quite a long time, the deformation – transformation interactions that they induce is not yet fully characterised and understood. This study aims at characterising the microstructure evolution of a Fe-Mn steel grade during straining thanks to TEM and high resolution OIM. Particular patterns of austenite – e and a’ martensite are found.