•S-phase undergoes stress-induced decay and phase transitions at constant temperature.•The anisotropic lattice expansion and compression of the S-phase are analyzed.•The N displacement in both ...compression and nitriding is ruled by ηψϕKϕ=−Xψϕ.•The anisotropic factor transition (Aγ>1 to ASphase<1) governs the S-phase formation.•The evolution of elastic constants Sij with pressure was demonstrated.
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The nitrogen expanded austenite (γN or the S-phase), easily attainable by nitriding processes of FCC chromium-containing materials such as stainless steel (SS), Ni-based superalloys and CoCr alloys, discloses singular properties such as strong anisotropic expansion and crystal direction-dependent diffusion. These fundamental aspects were undertaken here from an experimental-theoretical approach. The S-phase was produced by plasma nitriding on SS 316L powder grains, and the material was submitted to quasi-hydrostatic compression-decompression experiments up to 30 GPa with in situ structural analyses. The experimental results agreed very well with a solid mechanics-based analysis. With this methodology – that was effective for modified surfaces – the anisotropic nitrogen reallocation in the lattice was found to obey a same linear relation during both compression (the S-phase decay) and nitriding (the S-phase formation). The transition from austenite with low nitrogen content – CN (the first-order expansion) to the S-phase (colossal saturated second-order) was featured by inversion of relative magnitudes, between 111 and 100, of the K〈ϕ〉=E〈ϕ〉31−2ν〈ϕ〉, elastic moduli E〈ϕ〉 and Poisson's ratios ν〈ϕ〉 (ϕ=hkl), all of them dependent on the orientation factor Γϕ. Rates of compression/expansion between 111 and 100 were affected accordingly. Such phenomena was concluded to arise from the inversion of the anisotropy factor, from Aγ>1 to AγN<1, which is an intrinsic property of the nitrided austenite and rules the aforementioned anisotropy inversions. Stress-induced nitrogen redistribution among crystal directions (at constant temperature) promoted changes in CN and affected elastic constants (Sij). It let the elastic modulus evolve with stresses applied on the solid. The elastic properties Sij and E〈ϕ〉 of the S-phase were determined at different pressure ranges, including pressures close to the atmospheric condition.
•Samples tested in Al die soldering tests showed similar behavior to industrial die molds.•Al corrosion tests present more pronounced corrosion than real molds and dies.•AlCrN PVD coating reduces the ...Al reaction and extraction stresses of H13 tool steel.•Dissolution of the H13 at stress concentration regions make the surface prone to fatigue failure.
High-pressure die casting (HPDC) is regularly used to produce aluminum components. The die-casting molds are subjected to severe localized corrosion due to contact with the hot melted aluminum (700 °C) and accelerated by the intense thermal cycling generated by the cooling system. The correct understanding of each failure mode that occurs during the operation of these molds can increase tool life and reduce operational costs. Different components used in aluminum components production were evaluated after completing their useful tool life, and the failure modes were compared with two high-temperature laboratory tests, molten aluminum corrosion and die soldering tests. The primary crack mechanism observed in the HPDC die was heat checking, with a surface reaction of the tool steel with the molten aluminum. PVD coating increases the die's tool life, reducing the reactivity with the molten aluminum, which was observed in both laboratory tests. Die soldering tests represent the die mold behavior in HPDC production, showing a similar intermetallic phase and crack formation. Laboratory corrosion tests showed a more aggressive corrosion behavior than that observed in molds and dies used in HPDC industrial production.
Mechanical properties of CuCrO2 delafossite oxide single crystals Monteiro, João Frederico Haas Leandro; de Souza, Gelson Biscaia; Jurelo, Alcione Roberto ...
Applied physics. A, Materials science & processing,
03/2020, Letnik:
126, Številka:
3
Journal Article
Recenzirano
The mechanical properties of delafossite oxide single crystals were studied. The polycrystalline material, prepared by self-combustion urea nitrate process, consisted of distinguishable platelet-like ...single crystals with an area of around 100 μm
2
and 2 μm thick. All X-ray diffraction peaks were indexed as arising from CuCrO
2
delafossite oxide, with a rhombohedral structure and space group R-3m. The inspection of loading curves and imprints produced by nanoindentation on individual single crystals disclosed a ductile-like behavior, with no cracks at the 7 mN load employed. The deformation mechanisms were discussed and contrasted with the index of plasticity for this material. In the
ab-
plane, hardness was (6.6 ± 1.6) GPa and elastic modulus was (101 ± 20) GPa, while the values obtained for the
a(b)c-
plane were ~ 55 GPa and ~ 87 GPa, respectively. The great variation of hardness and elastic modulus when observing the several single crystals tested can be related to the lamellar nature of this material, as well as the fact that the bonding between the stacking planes was not really strong.
Salacia crassifolia traditionally known as “Bacupari-do-Cerrado” is used to treat kidney problems, and as a healing agent for coughs and malaria. The phytochemical study of the S. crassifolia roots ...led to the isolation of thirteen compounds: abruslactone-A (1), urs-12-ene-3β,25,30-triol (2), carioprystimerin (3), β-sitosterol (4), pristimerin (5), dispermoquinone (6), netzahualcoyonol (7), 20-hydroxy-20-epi-tingenone (8), 6-oxo-pristimerol (9), 9β,10β-epoxi-3β-hydroxy-1βH,4βH,5βH,7βH,11αH-guaian-12,8β-olide (10), 3-O-b-D-glucosyl-b-sitosterol (11), 4`-O-methylepigalocatechin (12) and cerebroside (13). The chemical structures of 1-13 were determined by IR, 1D/2D NMR together with X-ray diffractometry. Compounds 2 and 10 are herein described for the first time. Extracts of S. crassifolia and compounds 3, 5, 8 and 9 were evaluated on acetylcholinesterase inhibition, in vitro cytotoxic activity and in vivo toxicity tests using Caenorhabditis elegans model. All tested compounds inhibited acetylcholinesterase, and compounds 3, 8 and 9 demonstrated a greater potential when compared to the standard eserine. The tested compounds showed low cytotoxicity against the THP-1, K562 and MDA-MB-231 cancer cell lines. None of the tested compounds and extracts were toxic against C. elegans since the larvae survival rate in L1 stage was higher than 90%.
The superaustenitic stainless steel presents several technological applications, mainly in corrosive environments. The different phase precipitation might alter some of its mechanical properties. ...Such alterations affect several factors, including the working life of the material under adverse working conditions. In this study, Instrumented Indentation techniques, Tribology and X-ray diffraction (XRD) were used to evaluate alterations in regions close to the surface. The parameters analyzed were: hardness and elastic modulus (instrumented indentation), friction coefficient (tribology) and structural alterations of the unit cell of the identified phases (XRD - Rietveld Refinement). All properties analyzed were compared with those of common austenitic steel. The presence of σ-phase (space group P42mnm) and γ-austenite (space group Fm3m) were detected. Data analyzed indicated that the presence of σ-phase caused small alteration in properties such as hardness in regions close to the surface. In the regions farther from the surface (material bulk) data can be compared to that of conventional austenitic steel.
O aço inoxidável superasutenítico apresenta diversas aplicações tecnológicas, principalmente em ambientes corrosivos. A precipitação de diferentes fases pode alterar algumas de suas propriedades mecânicas. Tais alterações afetam vários fatores, incluindo a vida útil do material diante de condições de trabalho adversas. Neste estudo, medidas de Indentação Instrumentada, Tribologia e Difração de Raios X (DRX) foram utilizadas para avaliar possíveis alterações em regiões próximas à superfície em amostras tratadas termicamente. Os parâmetros analisados foram: dureza e módulo de elasticidade, coeficiente de atrito e alterações estruturais na célula unitária nas fases identificadas. Os resultados foram comparados com aço austenítico comum da família AISI 304. A presença das fases σ (grupo espacial P42mnm) e austenita-γ (grupo espacial Fm3m) foram detectadas. Os dados analisados indicaram que a presença da fase intermetálica σ contribuiu para pequenas alterações na dureza em regiões próximas à superfície e no coeficiente de atrito. Para regiões mais profundas (bulk) as propriedades analisadas foram semelhantes aos aços inoxidáveis comerciais.
This study describes the results of the sequencing and analysis of segments of Blocks II and III of the RNA polymerase L gene of Rabies virus isolates from different reservoir species of Brazil. The ...phylogenetic relations of the virus were determined and a variety of species-specific nucleotides were found in the analyzed areas, but the majority of these mutations were found to be synonymous. However, an analysis of the putative amino acid sequences were shown to have some characteristic mutations between some reservoir species of Brazil, indicating that there was positive selection in the RNA polymerase L gene of Rabies virus. On comparing the putative viral sequences obtained from the Brazilian isolates and other Lyssavirus, it was determined that amino acid mutations occurred in low-restriction areas. This study of the L gene of Rabies virus is the first to be conducted with samples of virus isolates from Brazil, and the results obtained will help in the determination of the phylogenetic relations of the virus.
Rabies virus (RABV) isolates from two species of canids and three species of bats were analyzed by comparing the C-terminal region of the G gene and the G-L intergenic region of the virus genome. ...Intercluster identities for the genetic sequences of the isolates showed both regions to be poorly conserved. Phylogenetic trees were generated by the neighbor-joining and maximum parsimony methods, and the results were found to agree between the two methods for both regions. Putative amino acid sequences obtained from the G gene were also analyzed, and genetic markers were identified. Our results suggest that different genetic lineages of RABV are adapted to different animal species in Brazil.
Under nitrogen plasma immersion ion implantation, the energy density per pulse EPulse/A was found to be proportional to the amount of the N-expanded austenite phase (γN) in a superaustenitic ...stainless steel, as previously seen for an austenitic-ferritic alloy. Since γN occurs in a range of stoichiometries, the parameter was also contrasted with the ion fluence Γ, which affects the retained dose. Γ varies inversely with EPulse/A and influences oppositely the properties of the modified surfaces. The temperature was the same among the treatments (320 °C) to rule out thermal diffusion as an extra variable. The increase of EPulse/A (for applied voltages 6.2–10.4 kV) produces thicker layers (1.4–2.2 µm), as an increase in lattice defects and stresses enhances N-diffusion, while high Γ values favor the N-saturation at the top surface for the opposite reason. The lowest Epulse/A (6.2–9.5 kV) result in brittle cases with a possible thin nitrides layer on top, whereas γN prevails in the ductile layer produced by the highest one (10.4 kV). The N-concentration governs the strength against plastic deformation: hardness varies up to 32% from the highest (6.2 kV) to the lowest Γ treatment (10.4 kV). In summary, the correlation of Epulse/A with Γ is indispensable for controlling properties of the modified surfaces for performance purposes.
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●The energy density per pulse EPulse/A controls the γN amount in superaustenitic SS.●At the same PIII temperature, the layer thickness grows with EPulse/A (1.4-2.2 µm).●The role of implantation defects and lattice stresses in the N diffusion is evidenced.●EPulse/A and ion fluence Γ vary inversely and rule synergistically the surface properties.●The N-concentration in the layer increases with Γ and governs its mechanical strength.
The H-cathodic charging applied to a superaustenitic stainless steel produces a metastable H-expanded phase by interstitial solid solution, which discloses parallels with the austenite N-expanded ...(S-phase). The ∼1 μm modified layer comprises a high expansion region γH followed by a low expansion γe domain, the former presenting a lattice parameter 3% higher than the austenite γ. The complete decay γH → γe → γ occurs around 1-day time. The mechanical properties change accordingly: hardness increases twofold and elastic modulus 17% with H-inlet, returning progressively to the pristine values after hydrogen diffuses out from the modified layer, mainly towards the outer surface. This is consistent with a competitive effect, where the solid solution strengthening overcomes the H-enhanced plasticity in the initial period of decomposition. Moreover, the prevalence of one of these phenomena in plastic deformations is strain-rate dependent: high strain rates result in hindered dislocation mobility, whereas the material discloses embrittlement under low strains.
•Cathodic hydrogenation produces H-expanded phase in superaustenitic stainless steel.•The H-expanded phase comprises low (first order) and high (second order) expansions.•Hardness and elastic modulus, higher than austenite, decay with the metastable phase.•Solid solution strengthening dominates over enhanced plasticity in indentation tests.•The mechanical response of the H-expanded austenite is strain rate-dependent.
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