Novel Co 20 Cr 15 Fe 26 Mn 17 Ni 22 ultra-fine grained high-entropy alloy

International audienceIn a non-equiatomic HEA from CoCrFeMnNi family, so-called A3S® alloy (austenitic superstainless steel), exceptional mechanical properties are observed. High yield strength (800 MPa) associated with significant elongation to fracture (35 %) and a stable austenitic paramagnetic structure (down to LN2 temperature) may be obtained in hot forged materials. Mechanical resistance (YS) of A3S is at least 200 MPa higher than that measured in equiatomic alloy (EA) of the same family. These properties come from a nanostructure, easily formed in the material after classical hot thermomechanical treatment (forging). Yet, mechanical resistance of A3S decreases strongly after a post-forging high temperature annealing: in this state, identical behaviors of A3S and EA are noticed. Effects of thermal conditions of forging and recrystallization annealing have been investigated in A3S. Only slight effect of temperature of forging (between 900 and 1100°C) has been shown. Surprising effects of recrystallization annealing have been found. Low temperature (up to 600°C for 48h) treatment leads to recrystallization with formation of fine (1 µm) grains. At higher temperatures (700-1100°C), recrystallization is blocked: only recovery followed by grain growth and formation of numerous twins is observed. Moreover, in this state, very high density of dislocations is conserved: they present ordered configurations with alignments in {111} planes. Formation of twins has major effect on mechanical behavior of both A3S and EA. Their absence stabilizes nanostructures and leads to high YS values while decrease of YS is accompanied by twins presence. Relative difficulty to form these defects in A3S (as compared to EA) is explained by high value of stacking fault energy, evaluated from TEM measurements of dislocations dissociation. Moreover, strong dependence of SFE on temperature has been shown: its lower value at high temperatures is in agreement with numerous twins observed

In-situ TEM straining experiments in Cantor’s alloy at room and LN2 temperatures

Cantor’s single-phase equiatomic FeNiCoCrMn alloy is a “high-entropy” alloy (or HEA) which crystallizes in the face-centered cubic (fcc) crystal structure. Its mechanical properties include high strength, particularly at low temperatures, good ductility and a large number of slip systems [1], on which its plasticity largely depends. To have a better understanding of these properties, in situ TEM straining experiments were carried out at room and liquid nitrogen temperatures, with a straining holder that applies mechanical stress on the specimen (locally measured using dislocations’ curvature) to analyze dislocation movements. According to previous studies, the planar slip of dislocations is responsible for the first stages of plasticity and twinning starts afterwards [1] [2] [3]. The strengthening mechanisms are a result of the classical dislocation/obstacle (grain boundary, twinning) interaction, but also of the local lattice distortions that may impede moving dislocations. These interactions seem to affect both perfect and partial dislocations. Please click Additional Files below to see the full abstract

Low seroprevalence and low incidence of infection with "Toxoplasma gondii" (Nicolle et Manceaux, 1908) in pediatric hematopoietic cell transplantation donors and recipients : polish nationwide study

Czyzewski, Krzysztof, Fraczkiewicz, Jowita, Salamonowicz, Malgorzata, Pieczonka, Anna, Zajac-Spychala, Olga, Zaucha-Prazmo, Agnieszka, Gozdzik, Jolanta, Styczynski, Jan (2019): Low seroprevalence and low incidence of infection with Toxoplasma gondii (Nicolle et Manceaux, 1908) in pediatric hematopoietic cell transplantation donors and recipients: Polish nationwide study. Folia Parasitologica (019) 66: 1-6, DOI: 10.14411/fp.2019.019, URL: http://dx.doi.org/10.14411/fp.2019.01

Febrile Neutropenia Duration Is Associated with the Severity of Gut Microbiota Dysbiosis in Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients

Febrile neutropenia (FN) is a common complication in pediatric patients receiving al-logeneic hematopoietic stem cell transplantation (HSCT). Frequently, a precise cause cannot be identified, and many factors can contribute to its genesis. Gut microbiota (GM) has been recently linked to many transplant-related complications, and may also play a role in the pathogenesis of FN. Here, we conducted a longitudinal study in pediatric patients receiving HSCT from three centers in Europe profiling their GM during the transplant course, particularly at FN onset. We found that a more stable GM configuration over time is associated with a shorter duration of fever. Moreover, patients with longer lasting fever exhibited higher pre-HSCT levels of Collinsella, Megasphaera, Prevotella and Roseburia and increased proportions of Eggerthella and Akkermansia at the engraftment. These results suggest a possible association of the GM with the genesis and course of FN. Data seem consistent with previous reports on the relationship of a so-called “healthy” GM and the reduction of transplant complications. To our knowledge, this is the first report in the pediatric HSCT setting. Future studies are warranted to define the underling biological mechanisms and possible clinical implications