Ph. Vermaut

Ni49.8Ti42.2Hf8 shape memory alloy strips production by the twin roll casting technique

Abstract The twin roll casting technique has been used for the first time to produce semi-finished Ni49.8Ti42.2Hf8 shape memory alloy thin strips. Some cracks appear on these new products but can be removed by optimization of the operational parameters. The aspect, dimensions and thermodynamical behavior of the strips are studied and interpreted according to the operational parameters and the resulting microstructure, taking into account the complex heat and mass flows during the process.

Study of atomic displacement fields in shape memory alloys by high-resolution electron microscopy

Abstract The distortion of the atomic lattice is determined using a recently developed method of analysing high resolution electron microscope images. The analysis is carried out in terms of the individual lattice fringes which contribute to the image contrast. A perfect set of fringes has an amplitude and phase given by the corresponding Fourier component. A distorted lattice can be analysed by introducing the concept of a ‘local’ Fourier component, representing the local values of amplitude and phase as a function in position of the image. The local phase is used to determine the line of a perfectly coherent interface between two sets of lattice planes. The degree of self-accommodation of a series of martensitic plates in a Cu–Zn–Al shape-memory-alloy is studied by the phase analysis of an experimental high resolution image.

The microstructure of melt spun Ti–Ni–Cu–Zr shape memory alloys

Abstract NiTi base shape memory melt spun ribbons with a high substitution of Ni by Cu and Ti by Zr have been analysed. Depending of the chemical composition of the alloy, the ribbons are crystalline or amorphous. Transmission electron microscopy (TEM) studies in the as-cast state and after crystallization indicated that in the as-cast state the Ti 40 Ni 25 Cu 25 Zr 10 ribbons are constituted of two phases (Ti 2 Ni+amorphous phase) whereas the Ti 40 Ni 35 Cu 15 Zr 10 ribbons are fully amorphous and are single phase after crystallisation with a B2 structure. High resolution electron microscopy (HREM) observations have shown that the crystalline/amorphous phase interface is highly wavy even at the nanometric scale and that the B2 particles are single ordered domains.

A TEM study of a copper rich phase grown on an Al3Zr dispersoid in a spray formed AlSiC composite

A copper rich aluminium zirconium phase encountered in a spray formed Al/SiC composite has been investigated. It was found to grow epitaxially on the (001) faces of the Al{sub 3}Zr dispersoids. The measured concentrations by EDS, down to an accuracy of 1% did not correspond to a known compound, the new phase has a composition of Al{sub 7}Cu{sub 3}Zr{sub 2}. By careful diffraction and image simulation, and comparison with experimental results, the authors obtain a spatial group of P4/mmm and two very closely related atomic distributions inside the unit cell. The structure is close to that of Al{sub 3}Zr with the same a parameter, however the c parameter is 1.157 nm.

Symmetry properties of fast electron images and diffractions

The purpose of this paper is to present the properties of invariance for the interaction of fast electrons with a crystal and to deduce from them some symmetry rules for the interpretation of diffracting patterns or images. The small-angle approximation leads to a transformation of the propagation direction variable z into a time-like parameter. The symmetry operations which maintain z act as unitary operators and those which reverse z act as antiunitary operators.