The martensitic transition of a Cu-Al-Ni single crystal has been studied by isothermal mechanical spectroscopy and in situ transmission electron microscopy (TEM) observations. A damping instability (with time) has been found at low frequency at the beginning of the transition. At the same time, TEM study has evidenced the presence of thin martensite plates which appear just at the beginning of the (massive) martensite formation and growth. The martensite plate growth rate is quite low and non continuous. While high internal friction in the transition domain is usually associated with the mobility between martensite/austenite interfaces, the present internal friction anomaly has been ascribed to the unstable motions of the first martensite plates.

Two shape memory Cu-Al-Ni alloys, a polycrystal and a single crystal, exhibiting a martensitic transformation close to 130 °C (in the as-quenched state) have been studied. Specimens have been quenched after heat treatment at 850 °C. The structural evolutions of the high temperature phase (austenite) have been studied for thermal treatments performed below 200 °C. Investigations have been carried out using electrical resistivity measurements, TEM (Transmission Electron Microscopy) observations and X-ray diffraction analysis. The main structural modifications are observed in the polycrystalline alloy and concern first, the reordering process of the austenite structure (B2 $\to$ L21), and second, the precipitationof the (Cu9Al4) γ 2 phase. In the single crystal alloy, the evolutions are veryslight and localized on the structural defects. Particular attention is paid to the role ofthe quenched-in vacancy elimination on the observed mechanisms. In addition, the incidenceof the structural evolution on the transformation temperatures is also discussed.

The elastic and anelastic properties of AgNi multilayers prepared by sputtering were investigated during the course of anneal cycles. The respective temperature variations of some of the elastic constants and moduli were followed by Brillouin scattering and dynamical methods based on use of a torsion pendulum and a vibrating-reed system. The last two enabled to investigate the internal damping associated with the presence of two-dimensional defects. It appears that the motion of interfaces and grain boundaries is inhibited by the high defect density. In contrast, substantial effects associated with the motion of the magnetic domain walls were evidenced. Concurrently, internal stresses were studied by in situ deflection measurements. Flow stress values on the order of 1 GPa were observed. Dilatometry experiments showed that a large part of the non-recoverable modifications in the state of stress induced by thermal cycling originates in the densification of the material.

Silver-nickel multilayers were prepared by sputtering at 100 K. X-ray diffraction, electrical resistivity and dimensional variation measurements were performed to structurally characterize these stratified materials, both in the as-prepared state and during the course of annealing cycles. Clearly, polycrystalline superlattices with marked (111) texture perpendicular to the strata are formed. We studied the elastic properties of these superlattices by performing uniaxial tension tests. No deviation from linear elasticity was observed, whatever the period. Young's modulus was found to be 130±15 GPa for all the periods studied. Thus no significant functional dependence of Young's modulus on the stacking periodicity exists in the AgNi superlattice, in the range of periods explored, 2.6 to 18 nm.