Martensitic transition of Cu-13.2Al-3Ni (wt.%) shape memory alloy studied by isothermal mechanical spectrometry

Anelastic and elastic properties of polycristalline Cu-13.2Al-3Ni (wt.%) samples have been studied both during the transition and in the martensitic state. In order to eliminate any transient effect, the measurements have been performed in isothermal conditions over a large frequency range (10-3 Hz to 40 Hz) for temperatures between 293 K and 473 K. The damping determined at low frequency exhibits peculiar behaviour. First, an high damping level has been measured in the as quenched state. Then, ageing in the martensitic phase leads to the irreversible diminishing of the internal friction. This effect has been ascribed to the pinning of the variant interfaces by quenched vacancies. A second important result indicates that the direct transition (austenite → martensite) manifests by a sharp increase of the damping while the reverse transition (martensite → austenite) does not affect the internal friction all along the heating. These effects, compared to those previously observed on NiTi alloys, have been attributed to the freeze of the interface mobility by interactions with structural defects. Complementary MET study has pointed out a likely role of the dislocations and/or NiAl precipitates in the freezing process

Influence of martensite variant orientation on their mobility in a CuAlNi alloy

The study has been performed on a Cu-13.6Al-3.1Ni (wt. %) single crystal. Two specimens have been submitted to a treatment at 1133 K during 10 min. followed by a water quench at room temperature. One sample was longitudinally strained, with a residual deformation of 4.5 %. Then, the internal friction has been measured in isothermal conditions over a large frequency range from 40 Hz to 10-4 Hz for measurement temperatures ranged between 294 K and 497 K. The damping measured at high frequency (>10-2 Hz) on the two samples is quite similar and is not changed significantly during the transitions (direct and reverse). On the contrary, at low frequency two effects are evidenced. First of all, on cooling, a sharp damping increase is observed from the beginning of the direct transformation on both samples. The damping is then, continuously decreased down to the martensite state. These evolutions have been ascribed to the fractal growth of the martensite. Second, during the first reverse transition, i.e. the first heating, the damping measured in the strained sample exhibits a maximum. This effect is diminished for the second reverse transition and is not present on the unstrained sample. The damping increase is discussed taking into account the incidence of the variant orientation on their mobility and the likely motion of structural defects introduced by the straining

First stages of martensitic growth studied by TEM in a Cu-Al-Ni single crystal and associated mechanical spectroscopy instabilities

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

TEM study of the austenitic phase of high Ms CuAlNi alloys

CuAlNi shape memory alloys, with Ms close to 130 °C (in the as-quenched state) have been studied on single crystalline and polycrystalline samples. The specimens have been quenched after heat treatment at 850 °C. The structural study discussed in the present paper has been performed using electrical resistivity and TEM (Transmission Electron Microscopy) analysis. The electron diffraction patterns show that the austenite of the two as-quenched samples is a disordered and body-centred cubic structure. Then, after one annealing at 165 °C performed in the TEM, the polycrystalline austenite reorders in a facecentred cubic structure (L21-type), while the single crystalline austenite (annealed at 172 °C) stays in the disordered state. Nevertheless, during the heating of the single crystal sample above AF, ordered precipitates appear in the parent phase along the former martensite- martensite interface traces. In addition, precipitates of the Cu9Al4 (γ2) phase are evidenced in the two samples after annealings below 172 °C. These observations, the structural difference between the single- and the polycrystalline austenite and the low temperature precipitation of the γ2 phase, are quite original and have to be discussed by taking into consideration previous investigations performed on similar alloys

Measuring tempo: a descriptive analysis of the development pattern in EP

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Evolution de la structure cristalline et des propriétés mécaniques de nitrure Ti1-xAlxN en fonction de la teneur en Al

International audienc

Adhesion of rhodium films on metallic substrates

Rhodium coated metallic films were prepared by magnetron sputtering on metallic substrates. All films were elaborated in same conditions on copper, molybdenum and stainless steel. Adhesion strength tests were carried out by scratch test. The results reveal that the adhesion strength between the film and the substrate is influenced by the hardness of the substrate. Increase of deposition temperature improves the adhesion of the coating. In addition, pre-treatment of substrates by a filtered cathodic vacuum arc and the layer thickness have has some effects on the final adhesion strength. (c) 2008 Elsevier B.V. All rights reserved

Structural investigation of thin films of Ti1-x AlxN ternary nitrides using Ti K-edges X-ray Absorption Fine Structure

International audienc