E. Cesari

Poly(butylene terephthalate) poly(ethylene terephthalate) mixtures formed by ball milling

Mixtures of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) polymers were formed using ball milling technique and characterized by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). PET with different degrees of crystallinity was used in the solid-state mechanical milling process. Results suggest that PBT greatly influences the crystallization of amorphized PET by milling.

Thermomechanical cycling in Cu /Al /Ni-based melt-spun shape- memory ribbons

Temperature-induced transformations under constant tensile loads (thermomechanical cycling) have been performed on a set of Cu � /Al � /Ni-based shape-memory ribbons prepared by melt spinning. The rapidly solidified ribbons being already characterized in what concerns martensite and parent phase ageing and their effects on the thermal (stress free) martensitic transformation, the purpose of this study was to complete the characterization of the ribbons, particularly in their shape-memory effect. The results presented for a Cu */13.0 Al */4.0 Ni */0.3 Ti */0.05 B (wt.%) ribbon show larger recoverable strains in the strain � /temperature cycles (thus larger shape-memory effect) for ribbons aged at 200 8C than for the as-spun samples. The dependence of the transformation temperatures T on the applied load, quantified through the slope dT /ds , increases for aged alloys. Both results can be related to the recovery of internal stresses produced by the rapid solidification and some recovery of short-range disorder, both mechanisms favouring higher values of the effective transformation strain. This behaviour is in agreement with the evolution of transformation temperatures in stress free transformation and related microstructural changes produced by ageing the ribbons in parent phase. # 2003 Elsevier Science B.V. All rights reserved.

Amorphization of organic compounds by ball milling

We have applied the ball-milling technique to amorphize the organic compounds sucrose and poly(ethylene terephthalate). Differential scanning colorimetry and X-ray diffraction measurements show that the samples have been amorphized by milling. However, differential scanning colorimetry heating runs reveal some differences between the crystallization process of samples mechanically amorphized and those obtained by quenching.

Martensite stabilisation in Ni50Ti32.2Hf17.7

Thermal martensite stabilization, that is, the transient shift of the reverse transformation temperatures either after direct quench to martensite from parent phase, or after ageing in the martensitic state, has been studied for many years in Cu-based alloys, and mechanisms to explain this phenomenon as well as thermomechanical treatments to avoid it have been proposed. In this paper, results on martensite aging behavior in a Ni-Ti-Hf melt-spun ribbon are reported, confirming the occurrence of the above mentioned possibility of thermal stabilization in the Ni-Ti alloy system.

Thermogenese: Application des filtrages electronique et numerique inverses en calorimetre a conduction

Abstract The results of the application of the numerical and electronic inverse filtering to the same calorimetric output are presented. These two techniques, used to reduce the inertia of conduction calorimeters, give very similar results.

Martensite stabilization in Ni{sub 50}Ti{sub 32.2}Hf{sub 17.7}

Thermal martensite stabilization, that is, the transient shift of the reverse transformation temperatures either after direct quench to martensite from parent phase, or after ageing in the martensitic state, has been studied for many years in Cu-based alloys, and mechanisms to explain this phenomenon as well as thermomechanical treatments to avoid it have been proposed. In this paper, results on martensite aging behavior in a Ni-Ti-Hf melt-spun ribbon are reported, confirming the occurrence of the above mentioned possibility of thermal stabilization in the Ni-Ti alloy system.

Thermogenese: Application comparative de l'analyse harmonique et du filtrage inverse

Abstract Harmonic analysis, electronic and numerical filtering have been used to reduce the inertia of conduction calorimeters. The limitations of the different techniques and the instrumentation required for their application have been evaluated by studying several well-known thermogeneses. The techniques described largely extend the application of microcalorimetry to different fields such as kinetic studies, analytical chemistry and thermodynamics of solutions.

Effect of γ precipitates on the martensitic transformation in CuAlMn alloys

Abstract The effect of γ precipitates on the martensitic transformation has been studied for two CuAlMn alloys containing 13.7 wt.% Al and 1.55 or 3 wt.% Mn. Precipitates were made to grow by aging at 570 K. Subsequent thermally induced martensitic transformations were monitored by differential scanning calorimetry. Optical microscopy and transmission electron microscopy, including in-situ cooling-heating experiments, were carried out for microstructural studies and to ascertain the martensite-precipitate interaction. Precipitates grow faster in the alloy with lower manganese content because of its closer composition to that of the equilibrium γ phase. Precipitates cause substantial hardening, which increases with increasing aging time, being similar in martensite and in the parent phase. The evolution of characteristic transformation temperatures and heat of transformation is discussed in terms of matrix composition changes and stresses produced by the precipitates. Different precipitate-martensite interactions are related to the two γ′ martensite morphologies observed, one having large twinned plates in which the precipitates are embedded, and the other with fine heavily dislocated plates formed preferentially between the precipitates and predominating in samples with larger precipitates.

Description du comportement des calorimetres a conduction a l'aide de modeles

Abstract In the field of conduction calorimetry, several techniques give an interesting approach to thermogenesis by considering the calorimetric system as a “black box”: harmonic analysis, time-domain analysis, optimalization method, numerical and electronic filtering,… In order to design instruments well suited to kinetic problems and study the influence of geometrical and thermal parameters, it is necessary to develop physical models describing the behaviour of the apparatuses. In this paper, several such models are presented.

Effect of γ precipitates on the martensitic transformation of β CuZnAl studied by calorimetry

Abstract 1. i) The temperatures for forward transformation are always lower than standard ones in the domain of t ★ studied. This cannot be explained by a change in the composition of the β phase and therefore implies a relative stabilisation of β phase versus martensite. 2. ii) The temperatures for reverse transformation are lower than the standard ones for growing times t ★ ⩽ 20 s and higher for t ★ > / 40 s. A change of behaviour in this time interval is also present in acoustic emission results. It could be atributed to a change in the coherence of the precipitates. 3. iii) The cycle of hysteresis is always wider than the standard one. This is associated with an increase of friction. All the aforementioned effects are permanent. Therefore, it is possible to modify the martensitic transformation of shape memory alloys in a reproducible and controllable manner.