Some features of anisothermal solid-state transformations in alloy 718

This paper presents an attempt to use differential thermal analysis to study anisothermal precipitation of both the stable delta and the metastable gamma-second phases during cooling of alloy Inconel 718. Observation of the samples by scanning and transmission electron microscopy was carried out to identify the thermal arrests observed upon cooling. When the upper temperature of the cycle is above the solvus of the delta phase, a clear peak is observed that could be related to precipitation of gamma-second for all the cooling rates used in the present work. When this temperature is below the delta solvus, no thermal arrest can be observed, while when it is close to it two faint peaks were noted and associated with stable and metastable precipitation. The most striking result was that dissolution of the metastable gamma-second phase during the heating stage was found to proceed heterogeneously in the material, and this affected reprecipitation of the phases upon subsequent cooling

TEM Study of High-Temperature Precipitation of Delta Phase in Inconel 718 Alloy

Inconel 718 is widely used because of its ability to retain strength at up to 650◦C for long periods of time through coherent metastable γ” Ni3Nb precipitation associated with a smaller volume fraction of γ’ Ni3Al precipitates. At very long ageing times at service temperature, γ” decomposes to the stable Ni3Nb δ phase. This latter phase is also present above the γ” solvus and is used for grain control during forging of alloy 718.While most works available on δ precipitation have been performed at temperatures below the γ” solvus, it appeared of interest to also investigate the case where δ phase precipitates directly fromthe fccmatrix free of γ’’precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in δ plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases

Characterizing precipitation defects in nickel based 718 alloy

In the present study we examine the crystallographic structure of the ϒ, ϒ'' and δ phases present in nickel base 718 alloy. The chemical ordering of Nb atoms and possible planar faults that may be observed in ϒ'' precipitates are detailed. High resolution transmission electron microscopy (HRTEM) observations of various faults are reported. The decomposition of a matrix dislocation to form a locked V shaped configuration is shown. The observation along [110] type direction allows to identify the type of defect, which is observed as a pure geometric stacking fault

Contribution à l’étude de la précipitation des phases intermétalliques dans l’alliage 718

De nombreux alliages de structure doivent leurs propriétés mécaniques à la présence de précipités inter ou intragranulaires. Ainsi les superalliages à base nickel, de matrice austénique γ, sont souvent renforcés par des précipités de phases intermétalliques ordonnées. Au sein de l’alliage Inconel 718, outre la phase γ’ de structure L12 (cubique simple), on trouve des précipités de Ni3Nb sous la forme métastable γ" (D022 - tétragonal centré) ou sous la forme stable δ (D0a - orthorhombique). Le rôle des précipités γ’, γ" et δ sur les propriétés macroscopiques de l'alliage est connu et largement utilisé en contexte industriel. Cependant les mécanismes de précipitation et de transformation de ces précipités ne sont toujours pas complètement élucidés, ce qui a motivé ce travail. La microstructure de l’alliage a été caractérisée par microscopie optique (MO) et électronique (à balayage et en transmission ; MEB et MET) dans l’état de livraison et après des traitements thermiques isothermes et anisothermes. Les essais d’analyse thermique différentielle (ATD) nous ont permis de préciser les domaines de température de précipitation et de dissolution des différentes phases présentes (γ’, γ" et δ). Différents états de précipitation ont été obtenus à l’aide de traitements thermiques isothermes basés sur les diagrammes temps-températuretransformation (T.T.T.) disponibles dans la littérature. Les observations en MET « à haute résolution » des précipités des phases δ et γ’’ ont permis de caractériser certains des défauts structuraux présents dans ces précipités. Nous montrons ainsi que les défauts d’empilement au sein de la phase γ’’ peuvent servir de germes pour la précipitation de . Alors que la structure des interfaces δ/γ ainsi que les défauts d’orientation au sein des lamelles de δ suggèrent que la croissance de la phase δ a lieu directement à partir de la matrice . ABSTRACT : Many structural alloys are strengthened by the presence of precipitates in the grains or at grain boundaries. Nickel based superalloys often present an austenitic γ matrix in which ordered intermetallic phases precipitate. In the alloy Inconel 718, one can find γ’ L12 cubic ordered precipitates together with the compound Ni3Nb in its metastable form γ" (D022 - tetragonal) or the stable phase δ (D0a - orthorhombic). The incidence of those precipitates on macroscopic properties of the alloy 718 is well known and widely used in industrial applications. However the mechanisms responsible for the precipitation and transformation of these phases are not fully understood, which motivated the present study. The alloy microstructure has been observed by optical microscopy (OM) and electron microscopy (scanning and transmission, SEM and TEM) in the as received state as well as after heat treatment (isothermal and anisothermal). Differential thermal analysis (DTA) was used to determine the precipitation and dissolution temperatures of the phases γ', γ" and δ. Various precipitation microstructures were obtained by heat treatments based on available TTT diagrams. Some of the structural defects present in γ" and δ precipitates have been characterised by lattice imaging TEM observations. It is shown that stacking faults in γ’’ phase can act as a seed for the germination of . The structure of the δ/γ interface and the orientation defects in δ lamellae suggest that the growth of δ phase occurs directly from the matrix (and not by transformation of the γ’’ phase)

Caractérisation des peuplements ligneux sur le tracé de la Grande Muraille Verte au Tchad

La connaissance des caractéristiques du peuplement ligneux du tracé de la Grande Muraille Verte (GMV) du Tchad permet de comprendre leur structure et fonctionnement afin de proposer des stratégies de gestion durable. C’est dans ce cadre que ce travail vise à caractériser la flore et la végétation ligneuses sur le tracé de la GMV du Tchad. La méthodologie utilisée consiste à déterminer la composition floristique et la structure du peuplement ligneux dans les trois sites retenus (Lac, Kanem et Bahr El Ghazal). Les inventaires floristiques ont permis de recenser 18 espèces réparties en 15 genres et 9 familles. La flore ligneuse est dominée par la famille des Mimosaseae. La densité des ligneux (34,67 ind.ha-1) et le recouvrement (1604,30 m².ha-1) sont plus importants au Lac et faible au Bahr El Ghazal (densité de 21,39 ind.ha-1 et recouvrement de 465,66 m².ha-1), quant à la surface terrière, elle est plus élevée au Kanem (3,39 m².ha-1). La distribution par classes de hauteur et de circonférence des ligneux révèle une prédominance des individus de la strate arbustive dans les trois sites. L’étude de la régénération naturelle montre que Acacia raddiana et Balanites aegyptiaca présentent le potentiel de régénération le plus élevé dans les trois sites. Globalement, les résultats obtenus montrent que les espèces les plus adaptées aux conditions écologiques de la GMV au Tchad sont Acacia raddiana et Balanites aegyptiaca et par conséquent, doivent être choisies pour la restauration de ces écosystèmes.© 2015 International Formulae Group. All rights reserved.Mots clés: Tchad, GMV, végétation, peuplement, structure, régénérationEnglish Title:  Characterization of the ligneous populatings on the route of the Great Green Wall in ChadEnglish AbstractThe knowledge of ligneous populating characteristics of the route of the Great Green Wall (GGW) of Chad helps to understand their structure and function in order to propose strategies for sustainable management. This study was carried out to characterize the flora and the tree vegetation present on the Chad  Great Green Wall (GGW) line. The methodology consisted in determining the floristic composition and the structure of the tree population in three sites: Lac, Kanem, and Bahr El Ghazal. The floristic inventories have identified 18 species distributed into 15 genera and 9 families. Trees are dominated by the Mimosaseae family. Their density (34.67 individuals ha-1) and their recovery (1604.3 m2 ha-1) are more important at Lac and lower at Bahr El Ghazal with 21.39 individuals ha -1 and 465.66 m2 ha-1, respectively. However, the basal area of the vegetation was more important at Kanem with 3.39 m2 ha-1. The distribution by classes of height and circumference of the trees indicates a predominance of the shrub layer in all the three sites. The study of the natural regeneration reveals that Acacia raddiana and Balanites aegyptiaca present the highest regeneration potential in the three sites. Globally, the results obtained in this study show that the most adapted species to the ecological conditions of the Chad’s GGW are Acacia raddiana and Balanites aegyptiaca. Consequently, these species must be considered during the restoration of the given ecosystems.© 2015 International Formulae Group. All rights reserved.Keywords: Chad, GGW, vegetation, population, structure, regeneratio

Completeness of information in electronic compared with paper-based patients’ records in a maternity setting in Dakar, Senegal

Background: Evaluate the consistency of information in paper-based records when registered in parallel with an electronic medical record.Methods: The study was performed at PMSHC in Dakar Senegal. From the end of year 2016, patients’ files were recorded on both paper-based and electronically. Additionally, previous records were electronically registered. To investigate the completeness of records before and after the electronic recording system has been implemented, information about some maternal and fetal/neonatal characteristics were assessed. When the variable was recorded, the system returned 1, unrecorded variables were coded as 0. We then calculated, for each variable, the unrecorded rate before 2017 and after that date. The study period extended from 2011 to June 2019, a nearly ten-year period. Data were extracted from E-perinatal to MS excel 2019 then SPSS 25 software. Frequencies of unrecorded variables were compared with chi-squared test at a level of significance of 5%.Results: A total of 48,270 unique patients’ records were identified during the eight-year period.  Among the study population, data for patients’ age, address and parity were available most of the time before and after 2017 (0.5% missing data versus 0.3% for age and 2.6% versus 1.3% for home address and from 0.3% to 0.0% for parity). However, phone number, maternal weight, maternal height, last menstrual period and blood group were found to be missing up to 96% before 2017. From 2017, these rates experienced a sudden decrease at a significant level: from 82.4% to 27.8% for phone number, from 96% to 56.3% for maternal weight and from 60.1% to 21.3% for blood group. Regarding newborns’ data, it was found that fetal height, head circumference and chest circumference were missing up to just under 25% before 2017. After that date, their completeness improved and flattened under 5%.Conclusions: Structured and computerized files reduce missing data. There is an urgent need the Ministry of health provides hospitals and health care providers with guidelines that describes the standardized information that should be gathered and shared in health and care records

Evaluation of the Prognostic Value of IFN-γ Release Assay and Tuberculin Skin Test in Household Contacts of Infectious Tuberculosis Cases in Senegal

BACKGROUND: Chemoprophylaxis of contacts of infectious tuberculosis (TB) cases is recommended for TB control, particularly in endemic countries, but is hampered by the difficulty to diagnose latent TB infection (LTBI), classically assessed through response to the Tuberculin Skin Test (TST). Interferon-gamma release assays (IGRA) are proposed new tools to diagnose LTBI, but there are limited data on their ability to predict the development of active TB disease. To address this, we investigated the response to TST and IGRA in household contacts of infectious TB cases in a TB high-burden country and the potential correlation with development of TB. METHODOLOGY/PRINCIPAL FINDINGS: Prospective household contacts study conducted in two health centres in Dakar, Senegal. A total of 2679 household contacts of 206 newly detected smear and/or culture positive index TB cases aged 18 years or greater were identified A TST was performed in each contact and an ESAT6/CFP10 ELISPOT assay performed in a random sample of those. Contacts were followed-up for 24 months. TB was diagnosed in 52 contacts, an incidence rate of 9.27/1000 person-years. In univariable analysis, the presence of positive TST (> or = 10 mm) and ELISPOT (>32 SFC/million PBMC) responses at baseline were associated with active TB during follow-up: Rate Ratio [RR] = 2.32 (95%CI:1.12-4.84) and RR = 2.09 (95%CI:0.83-5.31), respectively. After adjustment for age, sex and proximity to index case, adjusted RRs were 1.51 (95%CI:0.71-3.19) and 1.98 (95%CI:0.77-5.09), respectively. Restricting analysis to the 40 microbiologically confirmed cases, the adjusted RR for positive ELISPOT was 3.61 (95%CI:1.03-12.65). The median ELISPOT response in contacts who developed TB was 5-fold greater than in those who did not develop TB (p = 0.02). CONCLUSIONS/SIGNIFICANCE: TST and IGRAs are markers of a contact of the immune system with tubercle bacilli. In a TB endemic area, a high ELISPOT response may reflect increased bacterial replication that may subsequently be associated with development of TB disease and may have a prognostic value. Further longitudinal data are needed to assess whether IGRAs are reliable markers to be used for targeting chemoprophylaxis