The multi-principal element CrMnFeCoNi alloy, which solidifies as a single-phase solid solution with the face-centered cubic (fcc) structure, is thermally stable above 900 °C but is known to ...decompose into multiple phases at temperatures between 450 and 800 °C. Although the thermal stability of Cr-Mn-Fe-Co-Ni alloys can be altered by changing the composition, there is limited knowledge of the role of microstructure on the kinetics of precipitation from the supersaturated primary fcc phase. To fill this gap, we compared the thermal stability of monocrystalline and polycrystalline thin films of the equiatomic CrMnFeCoNi alloy during synthesis and after post-deposition annealing. At the processing temperature of 700 °C, the polycrystalline film undergoes substantial phase decomposition in 3 min, consistent with earlier results that a bulk alloy of similar composition decomposes into multiple phases at this temperature. In contrast, the monocrystalline film of the same composition remains single-phase both during synthesis and subsequent annealing at 700 °C for 5 h. X-ray diffraction investigations together with comprehensive transmission electron microscopy analysis revealed that the decomposition of the supersaturated primary phase is related to the presence of structural defects, in particular grain boundaries, which promote diffusion of Cr and Mn and subsequently destabilize the primary solid solution. Correspondingly, the absence of high-diffusivity grain boundaries in the monocrystalline alloy prevents its primary phase from decomposing. The fundamental role of grain boundaries on precipitation kinetics, manifested through the short circuiting of sluggish bulk diffusion in entropy-stabilized multi-principal element alloys, is discussed together with the possibility of controlling their thermal stability by microstructural design.
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The oxidation behavior of gas-atomized Al and Al alloy powder green compacts during heating prior to hot extrusion compaction was studied at laboratory and industrial scales by TGA, DSC, DTA, EDX, ...TEM and XRD methods. The effect of the heating of green compacts on the mechanical properties of the powder-extruded samples was assessed. Significant oxidation of Al and Al alloy powder green compacts takes place in the solid state during heating in air. The onset and intensity of oxidation were affected by the Mg content, the surface area of the powder and the volume of the powder green compacts. An exothermic heat associated with the oxidation of Al and Al alloy powders resulted in intense overheating of bulky powder green compacts during heating in air. The samples extruded from the powder green compacts heated in air exhibited reduced strength. The loss in strength was especially pronounced in the case of Mg-containing Al alloy powders. Mg diffuses from a powder metallic core toward the native Al2O3 surface layer present on as-atomized Al alloy powders; it reacts with oxygen present in air and in the Al2O3 surface layer where the MgO phase forms, eventually resulting in the depletion of Mg from the powder core. Materials extruded from Al powders depleted of Mg do not exhibit effective Al-Mg solid solution strengthening or strengthening by Mg-containing precipitates. Economically viable approaches to avoiding the detrimental effects of powder oxidation during the heating of green compacts prior to hot working consolidation are discussed.
High-induction Si-poor Fe-Nb-Cu-B-Si Finemet ribbons annealed in inert gas ambience are known to build oxides and prefer surface crystallization. Phosphorus-3 at% of P instead of B was substituted to ...see how it can influence these surface effects. The off-axis magnetic anisotropy caused by surfaces squeezing the ribbon interior was reduced and it was found out that the major source of the squeeze is the surface crystallization and not the oxides. Phosphorus appears to hamper preferentially the surface crystallization. The substitution also improves the magnetic softness of vacuum-annealed ribbons by grain size reduction. Slight reduction of saturation induction is a minor sacrifice to the improvements.
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•As-cast Fe-Co-Sn/P-B ribbons exhibited no Fe-oxides and impurities.•Surfaces of partially nanocrystallized ribbons affect their magnetic properties.•Magnetic characteristics reflect ...surface squeeze to ribbon interior.•After partial nanocrystallization Fe-oxides were observed on both surfaces.•P substitution impedes the formation of crystalline phase during annealing.
The properties of Fe-Co-Sn / P-B ribbons prepared by planar flow casting of the melt were investigated by various methods in as-cast and nanocrystallized state. To examine the influence of surfaces on ribbon’s magnetic properties was the major aim. As the surfaces and the ribbon interior possess slightly different properties, mutual macroscopic force is generated and it can affect the magnetic properties. The ribbon with P 2 at % and P-free one was annealed at two different temperatures to achieve partially nanocrystalline structure. P-free ribbon shows tilted hysteresis loop after annealing, what indicates a possible surface squeeze effect. The increase of coercivity after higher temperature annealing at 380 °C is due to the formation of a bcc-Fe phase with a larger grain size and higher crystallinity contents. Oxides, mainly Fe2O3 have been confirmed on surfaces of both the lower temperature (350 °C) annealed ribbons. P substitution appears to reduce the mutual force by impeding the formation of crystalline phase during 350 °C annealing.
Studying the relationship between microstructural interactions and resulting macroscopic material properties gives a more elaborate understanding on final material performance. The microstructural ...arrangement with characteristic length, relaxation, and thermal expansion behavior of regulated dimethacrylate networks is studied by differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis, and positron annihilation lifetime spectroscopy at a broad temperature range (250–380 K). The length scale ξ (Tg) of cooperative segmental rearrangement is decreased with increasing crosslinking and degree of freedom in regulated chain transfer agent (CTA)‐based networks. The macro and microscopic thermal expansion coefficients are determined in the glassy and rubbery state for three polymer systems—a dimethacrylate‐based reference (poly2M) and regulated photopolymers with CTAs (i.e., thiol, β‐allyl sulfone). The influence of CTAs on the free volume characteristics (i.e., free volume void size, the specific occupied volume V0, free volume number density per unit mass N′, and free volume fraction f) at the glass transition temperature Tg is correlated with the cooperative length, activation energy Ea,α, and mechanically effective crosslinking density. A more complex understanding of the revealed relations contributes to a more elaborate explanation of final material performance.
An extended positron annihilation lifetime spectroscopy (PALS) study is presented to investigate the microstructural properties of a dimethacrylate‐based reference poly2M and regulated networks (using chain transfer agents) below and above glass transition regarding their structural dynamic behavior. Macroscopic and mircoscopic thermal expansion of network structures are examined via thermomechanical analysis and PALS with an emphasis on possible mutual connections.
In this work, the phase behavior of cryoprotective mixtures based on dimethyl sulfoxide (DMSO) mixed with a lipid bilayer consisting of dimyristoyl phosphatidylcholine (DMPC) was studied. This system ...represented a model of a biological cell and its membrane. The aim of the work was to clarify the origin of the cryoprotective action of low-concentrated mixtures (1-10 vol%) DMSO in water, representing mixtures used in cryopreservation in cell therapy. The combination of experimental techniques of differential scanning calorimetry (DSC) and positron annihilation lifetime spectroscopy (PALS) allowed a study of crystallization behavior of water confined in liposomes imitating the intracellular environment. The ability of liposomes to show the fundamental aspects of water phase behavior seen during freezing of biological cells was proved. The presence of an amorphous freeze-concentrated phase of DMSO in the frozen state was confirmed and its possible crystallization into the DMSO trihydrate and ice during thawing was demonstrated. Correlation between the critical temperature range for the loss of cell viability during slow thawing and the temperatures of freeze-concentrated phase crystallization was found. Based on this finding, possible mechanisms of DMSO cryoprotection are discussed with support brought by results for the studied model system. Quantification of the ice phase fraction in the frozen mixtures revealed that even low concentrations of DMSO can induce a considerable decrease in the amount of ice present.
Ice-free phase formed by DMSO acting as a protective layer of lipid membrane.
Evolution of Complex Phases in Al-Fe-Si Systems Zigo, Juraj; Svec, Peter; Janickovic, Dusan ...
Materials research (São Carlos, São Paulo, Brazil),
11/2015, Letnik:
18, Številka:
suppl 1
Journal Article
Recenzirano
Odprti dostop
Phase transformations and composition of Al-Fe-Si, Al-Co-Si and Al-Ni-Si based rapidly quenched ribbons have been investigated. Different Al-Si based alloys with varying Si content and additions of ...third metallic element, namely Al sub(80) Si sub(20), Al sub(60) Si sub(40), Al sub(75) Fe sub(5) Si sub(20), Al sub(70) Fe sub(10) Si sub(20), Al sub(75) Co sub(5) Si sub(20), Al sub(70) Co sub(10) Si sub(20), Al sub(75) Ni sub(5) Si sub(20), Al sub(70) Ni sub(10) Si sub(20) were analyzed. Variation of phase composition with elemental composition was observed. Evolution of phases was determined by resistometry, differential scanning calorimetry (DSC). In situ X-ray diffraction (XRD) and transmission electron microscope (TEM) records were observed during isothermal and isochronal annealing.
The aim of this study is to characterize adsorbed liquid in montmorillonite structure for different levels of adsorption by both thermoanalytical and microstructural methods. Montmorillonite of Ca ...type is used for the analysis. Water desorption process occurring typically between 50 and 180 °C is analysed in details by thermogravimetric analysis. Thermal response of adsorbed water for the selected steps of desorption process is studied by differential scanning calorimetry. Corresponding characterization of free volume is performed by positron annihilation lifetime spectroscopy. An attempt to determine a correlation of characterization method results is provided.
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•Pre-freeze cell dehydration induced by polyethylene glycol 400 allows the application of rapid freezing cryopreservation.•Astable ice microstructure is formed during solidification ...with polyethylene glycol 400 in the freezing medium.•Ice formation is reduced, and eutectic crystallization of salts is entirely suppressed with polyethylene glycol 400.
An effort was made to design a simple and efficient protocol for the cryopreservation of human keratinocytes, a cell line relevant to tissue engineering. A possibility of simultaneously preventing the injury from intracellular ice formation and slow-freezing injury by introducing a macromolecular non-permeant polyethylene glycol 400 as a sole cryoprotectant with rapid freezing was recognized. Thermoanalytical and microstructural analysis of the potential cryoprotective mixture has been performed to test its efficacy in preventing cell cryoinjury mechanisms. The post-thaw cell recovery indicated successful cryopreservation with a similar recovery to the standard slow-freezing protocol with permeant dimethyl sulfoxide. The novel approach represents an alternative cryopreservation strategy that avoids intracellular cryoprotectant toxicity and offers a simple freezing procedure (plunging into liquid nitrogen) and a more practical cryoprotectant wash-out after the thawing. The cryopreservation protocol also brings up new possibilities for applying macromolecular additives as novel cryoprotectants.
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