198,228 research outputs found
Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach
No full textNanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced to a sometimes-extraordinary grain size reduction via different severe plastic deformation (SPD) methods. In the present study, a dual strategy was followed to obtain a sound and stable nanostructured commercially pure cobalt. Powdered cobalt of 2 μm was compacted by ball-milling (BM) followed by spark-plasma sintering (SPS) to obtain a bulk metallic material whose relative mass density reached a value of 95.8%. This process constituted a bottom-up strategy to obtain ultrafine submicrometer-grained bulk cobalt, and a top-down strategy of subjecting the BM + SPS submicrometer-grained cobalt to a specific SPD technique, namely equal-channel angular pressing (ECAP). The latter was carried out in one to four passes following so-called route BC, reaching 98.4% density and a nanometric-grained microstructure. The material was microstructurally and mechanically characterized by TEM (transmission electron microscope) and nanoindentation. The obtained results are a representative solid example for obtaining nanostructured metallic materials using both grain-refining strategies, bottom-up and top-down
Skin effect in 125 to 10 μm-thick 5N-Al foils
No full textMicrostructure inhomogeneities between the core and the surface regions of cold rolled pure aluminum thin foils were documented and characterized by transmission electron microscopy. Different dislocation types were identified and these were recognized as responsible for the observed microstructure inhomogeneities. It resulted that as the foil thickness reduces to 10 mu m the core region tends to form single grains decorated by few tangled dislocations, while the surface regions are characterized by cell and grain boundaries
Médecine et religion. Collaborations, compétitions, conflits (XIIe-XXe siècles). Etudes réunies par M.P. Donato, L. Berlivet, S. Cabibbo, R. Michetti, M. Nicoud
No full textInstrumented Nanoindentation Tests Applied to Bulk Metallic Materials: From Calibration Issue to Pile-Up Phenomena
No full textInstrumented nanoindentation tests have reached an effective level of theoretical and
practical knowledge to become an interesting and useful tool for determining hardness, H, and local
elasticity (reduced Young’s modulus), Er, of a variety of materials, from coatings and thin films
to bulk metallic materials. Nanoindentation instruments are equipped with analysis software for
raw data for hardness and reduced Young’s modulus evaluation, generally based on the Oliver
and Pharr analysis method. On the other hand, it is widely known and recognized that prior data
acquisition, a tip-dependent calibration procedure of compliance, and area function are needed. With
this in view, an accurate and sound calibration protocol is here reported. Hardness and local elastic
modulus is measured on different bulk metallic materials, showing the distinctive strengths of using
nanoindentation. Finally, a local elastic-plastic phenomenon mostly induced by the nanoindentation
tip on ductile metallic material (i.e., pile-up) is also reported and modelled. This manuscript is thus
intended to favor and account for the importance of using the instrumented nanoindentation tests
for H and Er measurements of metallic materials
Carbon content driven high temperature γ-α2 interface modifications and stability in Ti–46Al–4Nb intermetallic alloy
No full textThe effect of carbon addition on the microstructure modifications and hardness response of a two-phase lamellar Ti–46Al–4Nb intermetallic alloy was studied. The alloy was heat treated as to have an initial tow-phase refined lamellar microstructure consisting of α2 laths and γ phase characterized by nanometric wide twinning. The effect of carbon in solid solution in the α2 phase and the onset of the H–Ti2AlC phase precipitation within the γ phase was addressed. A threshold carbon limit of C ≅ 3000 wt ppm was identified as lower limit solute concentration for the precipitation initiation of the H phase particles. The major alloy hardening factors were identified as the refined interlamellar spacing, the fine twinning and the amount of carbon in solid solution. The role of H phase formation on the alloy hardening with carbon content was addressed and it was essentially such to induce a hardening saturation effect
Minimum necessary strain to induce tangled dislocation to form cell and grain boundaries in a 6N–Al
No full textSevere plastic deformation (SPD) techniques are known to promote exceptional material properties by inducing significant modifications in the metallic material microstructure. In particular, severe plastic deformation (SPD) techniques are known to effectively refine the initial grain structure of f.c.c. and b.c.c. crystals to sub-micrometre levels. Pure metals are mostly appropriate to study the early stages of the microstructure modifications induced by SPD. This is chiefly due to the possibility to isolate the material strengthening due to dislocations from other possible microstructure features. To this purpose, a high-purity 6N-aluminum (99.9999% purity) was here used to study the minimum necessary strain to form crystal boundaries (that is, cell and grain boundaries). Cell and grain boundaries are formed from previously introduced tangled dislocations (TD), which constitute the microstructure modification features at the early stages of plastic deformation. In this study, the 6N–Al was subjected to high-pressure torsion (HPT) by which the minimum necessary strain, εeq, to form cell boundaries was identified. It was thus find that, TD started to evolve to cell boundaries at εeq = 0.05. This finding was validated by a second SPD technique, such as accumulative roll bonding (ARB). A microstructure strengthening model was applied and validated by nanoindentation measurements
Online tools for basic sequence manipulation, restriction analysis, PCR primers generation and evaluation
No full textThis book chapter describes the main online tools for the everyday basic sequence analysis needs of the bench scientist
Endoplasmic reticulum oxidoreductin 1-L beta (ERO1-L beta), a human gene induced in the course of the unfolded protein response
No full textOxidative conditions must be generated in the endoplasmic reticuinm (ER) to allow disulfide bond formation in secretory proteins. A family of conserved genes, termed ERO for ER oxidoreductins, plays a key role in this process. We have previously described the human gene ERO1-L, which complements several phenotypic traits of the yeast thermo-sensitive mutant ero1-1 (Cabibbo, A., Pagani, M., Fabbri, M., Rocchi, M., Farmery, M. R., Bulleid, N. J., and Sitia, R. (2000) J. Biol. Chem. 275, 4827-4833). Here, we report the cloning and characterization of a novel human member of this family, ERO1-Lβ. Immunofluorescence, endoglycosidase sensitivity, and in vitro translatlon/translocation assays reveal that the products of the ERO1-Lβ gene are primarily localized in the ER of mammalian cells. The ability to allow growth at 37 °C and to alleviate the 'unfolded protein response' when expressed in ero1-1 cells indicates that ERO1-Lβ is involved also in generating oxidative conditions in the ER. ERO1-L and ERO1-Lβ display different tissue distributions. Furthermore, only ERO1-Lβ transcripts are induced in the course of the unfolded protein response. Our results suggest a complex regulation of ER redox homeostasis in mammalian cells
Microstructure based strengthening model of a biocompatible WE54 alloy reinforced by SiC.
No full textA large number of magnesium alloys and magnesium-based composites are nowadays used as biocompatible light metallic materials. Example of their applications include bone-tissue screws, cardiac valves, orthodontic screws and components. In this sense, the biocompatibility, durability, and corrosion resistance and blood compatibility are key factors for the full availability of magnesium based alloys in the bioengineering field. On the other hand, minimal necessary mechanical properties necessary for their potential application in such a filed were investigated in the last three decades. With this respect, not only magnesium based alloys, but also magnesium composite alloys were tested for their biocompatibility. Oxides such TiO2, MgO, ZnO, ZrO2, TiB2, Al2O3, and also SiC showed sufficient biocompatibility and in addition, composite magnesium alloys added with such oxides or SiC are known to possess higher mechanical properties compared to their magnesium alloy counterparts. Among the different available metallurgical technologies to produce magnesium alloys, the powder metallurgy (PM) is surely one of the most promising one. With this regard, squeeze casting is one of the most reliable and cost-effective PM technique of production of magnesium based alloys and composites. In the present work, the microstructure and mechanical properties of WE54+15vol.%SiC under various compression temperature conditions, up to 300°C, were investigated by transmission electron microscopy (TEM). Microstructure inspections revealed the formation of stable cuboid secondary phase particles, and lamellae and irregular-shaped intermetallic phases. A microstructure-based strengthening model was proposed and compared to the experimentally obtained compression stress carried out at temperatures ranging 50-to-300°C. The most effective strengthening term was found to be the one coming from the refined grain structure. A further important strengthening contribution was constituted by the secondary phase particle precipitation within the Mg-matrix
Adiabatic heating and role of the intermetallic phase on the ECAP-induced strengthening in an Al-Cu alloy
No full textIn the present work, the strengthening effect of the Fe-rich intermetallic phases in a 2219 aluminum alloy subjectedto equal-channel angular pressing (ECAP) has been studied. Three different deformation conditions, correspondingto the as-extruded, ECAP/A-1 pass and ECAP/A-2 passes were considered. Mechanical and morphologicalcharacterizations have been performed by microhardness tests, light microscopy, transmission electron microscopyand scanning electron microscopy observations. All the contributions to the strengthening due to solid solution,dislocation boundary and secondary phase have been discussed. The electron microscopy study focused on theevaluation of the strengthening effect generated by the (Fe,Mn,Cr)3Si2Al15 intermetallic. This strengthening effect,generated by coarse precipitates such are the Fe-rich intermetallics, has also been correlated to the morphologicalparticle aspect. The ECAP-induced adiabatic heating strengthening contribution was also determined. Astrengthening combination model of all the microstructure terms was proposed and applied to this case to meet thealloy yield stress at the two different ECAP straining levels corresponding to the first and the second pass via route A
- …
