Characteristics of Acacia mangium shoot apical meristems in natural and in vitro conditions in relation to heteroblasty

PDF version of the authors can be published in January 2013International audienceMorphological and histocytological characteristics of Acacia mangium shoot apical meristems (SAMs) were assessed in natural and in vitro conditions in relation to heteroblasty. In the natural environment, SAMs with a mature-phyllode morphology were much bigger, contained more cells with larger vacuolated area, or vacuome, and lower nucleoplasmic ratios than those from the juvenile type (Juv). In these latter, nuclei appeared more voluminous, evenly and lightly stained, with clearly distinguishable nucleolei and less abundant chromocenters. In vitro, where reversions from mature to juvenile morphological traits do occur unpredictably, heteroblasty was less obvious in the SAM characteristics examined. In vitro SAMs corresponding to the juvenile and mature types showed similarities with outdoor Juv SAMs, but could be distinguished from these latter by a much larger vacuome that might be induced by the culture conditions. These findings encourage pursuing the investigations at the chromatin and nucleolus level in SAM zones where heteroblasty-related differences have been detected

STUDY OF THERMOMECANICAL TREATMENTS USED FOR A CuZnAl INDUSTRIAL ALLOY

The use of CuZnAl industrial shape memory alloys requires to approach the questions of their stability and their transformation temperatures in the long run. We have investigated the influences that have education and time periodes between the several processing phases for several annealing times at 100°C. These three parameters have an effect not only on the alloy transformation temperatures but also on the evolution kinetic of these temperatures in the long run. This fact requires an exact characterization of the alloy state in order to master the industrial reproduction of such processings

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CHARACTERISATION OF THE MICROSTRUCTURAL STATE OF A CuZnAl INDUSTRIAL SHAPE MEMORY ALLOY

The thermomecanical treatments used for the industrial production have a great effect on the transformation temperatures of the CuZnAl shape memory elements. We characterize the microstructural state of samples submitted to several kinds of thermomecanical treatments. We used the transmission electron microscopy and X-ray diffraction. A particular effort was made on the observation of the alloy long range order state. The observations show different default structures and different long range ordered domain sizes according to the kind of treatment. The order state is characterized by a size and a number of long range ordered domains B2 and L21, but it seems to be necessary to estimate the short range order degree

INFLUENCE OF BETATIZATION HEAT TREATMENT ON MARTENSITIC TRANSFORMATION TEMPERATURE OF INDUSTRIAL COPPER BASED SHAPE MEMORY ALLOYS

The paper shows the effects of two types of long heat treatment at high temperature on copper based alloys with zinc or aluminium. The resulting increases of transformation temperatures seem to be governed both by loss processes and oxidation of the constitutive elements of the alloy. Different characterization techniques performed on heat treated samples demonstrate that the surface of the alloy plays an important role during betatization

Atomic Ordering and Martensitic Transformation in Cu-Zn-Al and Cu-Al-Ni Industrial Alloys

The isothermal relaxation process near room temperature in b Cu-Zn-Al and Cu-Zn-Al-Ni industrial alloys which follows a step quenching or an up quenching thermal treatment has been studied by isothermal calorimetric technique. The transition temperature Ms and its evolution have been obtained by differential scanning calorimetry and by detecting the acoustic emission. The dissipated energy of the sample measured during the relaxation process present a complex behaviour, characterized by a continuous slowing down. On the other hand, the evolution of Ms at the beginning of the phenomenon obeys a different law. We show that all measured evolutions are much more slow in the case of Cu-Zn-Al-Ni alloy, comparing to Cu-Zn-Al alloy. The presence of nickel, which slows diffusion processes can explain this behaviour, influenced by quenching rate and annealing time. We interpret the relaxation processes and the evolutions of Ms in term of atomic reordering (B2 and L21). These phenomena are so slow in Cu-Zn-Al-Ni alloys near room temperature that the equilibrium state of order cannot be reached