Optimisation en fluage et fatigue-fluage d'aciers martensitiques à 9%Cr par traitement thermo-mécanique

National audienceL'utilisation des aciers martensitiques à 9-12%Cr est envisagée dans les futurs réacteurs nucléaires de génération IV. En service, ils seront soumis à du fluage à haute température ainsi qu'à des sollicitations de fatigue-fluage. Or de récents travaux sur l'acier commercial P91 ont montré que des sollicitations cycliques de fatigue combinées au fluage conduisent à un adoucissement rapide du matériau, lié à un grossissement de sa microstructure. Des traitements thermomécaniques ont donc été réalisés dans le but d'affiner et de stabiliser la microstructure de cet acier. Le traitement thermomécanique présenté ici conduit à une martensite plus fine, émaillée de nombreux et fins précipités de type MX. Le P91 optimisé montre un net gain en termes de propriétés mécaniques par rapport à l'acier P91 à réception : sa dureté est plus élevée de 100 Hv, sa limite d'élasticité conventionnelle est supérieure de 430 MPa à 20°C et de 220 MPa à 550°C, sa durée de vie en fluage à 650°C est 20 fois supérieure et son adoucissement à 650°C est légèrement moins rapide

Relationship between microstructure and mechanical behaviour of thermomechanically optimised 9-12% Cr steels

International audienceThe development of Generation IV fission nuclear reactors and fusion nuclear reactorsrequires materials able to resist to high temperature (650°C) creep, but also to creep-fatigue.Martensitic 9-12%Cr steels are candidate materials for these applications.Recent studies on commercial P91 steel showed that cyclic loadings coupled to high temperature creep loadings lead to a strong softening effect, which affects the steelmechanical strength. This effect is due to the decrease of the dislocations density and thecoarsening of martensitic microstructure.Thermomechanical treatments, including warm-rolling in austenitic phase and tempering,have been applied to P91 in order to refine its microstructure and to improve its precipitationstate. The temperature of rolling was set at 600°C, and those of annealing at 650°C and700°C, thanks to MatCalc calculations.Microstructural observations proved that the warm-rolling and the following tempering lead toa finer martensite pinned with numerous small precipitates. In terms of mechanical propertiesimprovement, the hardness of thermomechanically treated P91 is higher than that of asreceivedP91. The yield strengths are higher than that of P91 (around 400 MPa at 20°C; andmore than 200 MPa at 550°C). Preliminary creep resu lts show that these treatments improvethe creep lifetime by at least a factor 8

Determinação do ciclo estral em catetos Pecari tajacu: aspectos colpocitológicos e clínicos.

Este trabalho teve por objetivo estudar o ciclo estral do cateto, aplicando a colpocitologia como método diagnóstico. As amostras da citologia vaginal foram coletadas em dez fêmeas adultas, durante três vezes na semana, por seis meses. Verificou-se que a duração média do ciclo estral para esta espécie foi de 28,45 ± 5,45 dias. Observou-se diferença estatística (p<0,01) em relação à frequência dos diferentes tipos celulares na mesma fase do ciclo estral. No proestro foi verificado o aumento de células intermediárias e superficiais. A fase de estro caracterizou-se pela elevação significativa de células superficiais em relação aos demais tipos celulares e pela ausência de leucócitos. Durante este período, a genitália externa estava hiperêmica, edemaciada e com muco. No metaestro houve um decréscimo de células superficiais, quando comparado com o proestro e com o estro, e uma elevação significativa de células intermediárias, presença de leucócitos, de células de metaestro e de foam. Na fase de diestro, houve um aumento de células intermediárias, e um decréscimo no número de leucócitos. Conclui-se que, por meio da colpocitologia, é possível diferenciar as fases do ciclo estral em catetos

Curva de crescimento do caititu (Tayassu tajacu) criado em cativeiro na Amazônia.

Resumos apresentados no VIII Salão de Iniciação Científica - Ed. Internacional, VIII Mostra Científica - Ed. Internacional e I Feira de Extensão - Ed. Internacional, Uruguaiana, 2008

Produção e reprodução de animais silvestres - o caititu (Tayassu tajacu).

CONERA

Ovarian folliculogenesis in collared peccary, Pecari tajacu (Artiodactyla: Tayassuidae).

The sustainability and production of collared peccary (Pecari tajacu) has been studied in the last few years; however, further information on its reproduction is necessary for breeding systems success. Understanding folliculogenesis aspects will contribute to effective reproductive biotechniques, which are useful in the preservation and production of wildlife. The aim of this study was to evaluate the ovarian folliculogenesis in collared peccary. Ovaries from six adult females of collared peccary were obtained through ovariectomy and analyzed. These were fixed in aqueous Bouin’s solution and sectioned into 7µm slices, stained with hematoxilin-eosin and analyzed by light microscopy. The number of pre-antral and antral follicles per ovary was estimated using the Fractionator Method. The follicles, oocytes and oocyte nuclei were measured using an ocular micrometer. Results showed that the length, width, thickness, weight, and the gross anatomy of the right and left ovaries were not significantly different. However, the mean number of corpora lutea was different between the phases of the estrous cycle (p<0.05), with the highest mean in the luteal phase. Primordial follicles were found in the cortex; the oocytes were enveloped by a single layer of flattened follicular cells. In the primary follicles, proliferation of the follicular cells gave rise to cuboidal cells (granulosa cells). The secondary follicle was characterized by two or more concentric layers of cuboidal cells (granulosa), beginning of antrum formation, and the presence of pellucid zone and theca cells. Antral follicles were characterized by a central cavity (antrum), the presence of cumulus oophorus and theca layers (interna and externa). In the right ovary, the values of the primordial and primary follicles were similar, but significantly different from the secondary ones (p<0.05). In the left ovary, significant differences were observed between all follicles in the follicular phase (p<0.05); the mean number of primordial and primary follicles was similar in the luteal phase. The mean number of pre-antral follicles and antral follicles in the follicular phase was higher in the left ovary (p<0.05). The mean number of antral follicles in the luteal phase was similar in both ovaries. We also found significant differences in mean diameter of preantral follicles, oocyte, granulosa layer and oocyte nucleus during the estrous cycle. In the antral follicles a significant difference was observed only in follicular diameter (p<0.05). The predominance of active primordial and primary follicles was found in both phases; otherwise the secondary follicles and antral follicles showed a high degree of degeneration. The results obtained in the present work will strengthen the development of biotechnology programs to improve the productive potential and conservation of the collared peccar

Manejo reprodutivo e produtivo do caititu (Tayassu tajacu) em cativeiro.

Resumos do III Congresso Norte Nordeste de Reprodução Animal (CONERA)