Alloys processed by laser powder-bed fusion show distinct microstructures composed of dislocation cells, dispersed nanoparticles, and columnar grains. Upon post-build annealing, such alloys show ...sluggish recrystallization kinetics compared to the conventionally processed counterpart. To understand this behavior, AISI 316L stainless steel samples were constructed using the island scan strategy. Rhodonite-like (MnSiO
3
) nanoparticles and dislocation cells are found within weakly-textured grains in the as-built condition. Upon isothermal annealing at 1150 °C (up to 2880 min), the nucleation of recrystallization occurs along the center of the melt pool, where nuclei sites, high stored elastic energy, and local large misorientation are found in the as-built condition. The low value of the Avrami coefficient (
n
= 1.16) can be explained based on the non-random distribution of nucleation sites. The local interaction of the recrystallization front with nanoparticles speeds up their coarsening causing the decrease of the Zener-Smith pinning force. This allows the progression of recrystallization in LPBF alloys, although sluggish. These results allow us to understand the progress of recrystallization in LPBF 316L stainless steel, shedding light on the nucleation mechanisms and on the competition between driving and dragging pressures in non-conventional microstructures. They also help to understand the most relevant microstructural aspects applicable for tuning microstructures and designing new LPBF alloys.
Graphical abstract
A novel additive manufacturing approach is proposed to produce an electrical steel (Fe-3.5%Si) by laser powder bed fusion (LPBF) followed by conventional thermomechanical processing. The aim of this ...proof-of-concept study is to develop a new processing route for grain-oriented electrical steels from LPBF-processed plates with strong texture and SiO
2
nanoparticles followed by cold rolling and long-term annealing to trigger abnormal grain growth. The slabs were processed with two different scanning strategies; e.g., with (90R) and without 90° rotation (0R) between layers aiming at intensifying the as-built textures near-Goss and/or cube components. The as-built slabs were cold rolled to 83% reduction and annealed for subsequent monitoring of primary recrystallization and abnormal grain growth. Goss or near-Goss nuclei were identified for both strategies after cold rolling. Abnormal grain growth occurred more intensely in samples with a 90° rotation between layers. Goss-oriented grains are bounded by high-angle boundaries with peak misorientations of 50° in 90R and 37.5° in 0R strategy. Porosity in 0R is three times higher than in 90R, while the total fraction of CSL boundaries is similar for both strategies (about 6%). Boundary mobility seems to be higher in 90R, which explains easier grain boundary depinning from oxide nanoparticles than in 0R strategy. In comparison with grain-oriented commercial products, increased total magnetic losses can be explained by thickness effects, porosity and deviation from ideal Goss orientation.
Graphical Abstract
Aerospace and automotive industries utilize advanced high strength steels due to their exceptional mechanical strength and ductility. Laser beam welding has shown potential in reducing the melted ...zone, heat affected zone, and process time for these steels. This study focused on dissimilar welding between DP 780 and 300M steel sheets, commonly used in the automotive and aerospace industries, respectively. The aim was to expand the range of possibilities and innovations by enabling the use of these steels in both applications. The study investigated the optimal process parameters, microstructure, and mechanical properties for the laser welding process. It also examined the influence of intercritical quenching and tempering on the microstructure and mechanical properties of the laser welded steels. The materials underwent dilution and different phase transformations due to the welding process and heat treatments, as revealed by microstructural characterization. The weld showed a notable increase in hardness, however without compromising toughness. The fractures during tensile testing occurred in the DP 780 steel, far from the MZ and HAZ. Heat treatments increased ultimate tensile strength, but lowered ductility. Welding affected the fatigue life, especially in the intercritically quenched joint, which showed a quasi-cleavage crack growth mechanism and a decrease in fracture toughness.
AISI 317 L stainless steel replaces 316 L grade in some applications due to its superior mechanical strength and corrosion resistance. Aiming at expanding its applicability to structural ...applications, ongoing studies are dedicated to overcoming the trade-off between strength and ductility. The stacking fault energy decreases with deformation temperature and favors stacking faulting, (nano)twinning and strain-induced martensite (SIM) formation, resulting in severe microstructural fragmentation. The effect of temperature on deformation behavior of AISI 317 L steel was investigated in samples rolled at room temperature to thickness reductions of 50% and 85% and at 77 K to reductions in thickness of 10% and 50%. The microstructural evolution was followed by scanning electron microscopy, Vickers microhardness, X-ray diffraction, magnetization, electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The nucleation sites in the early stages of the transformation sequence γ → ε → α’ were identified in the 10% cryorolled sample. The highest volume fraction of α’-martensite reached 45.8% in the cryorolled steel to 50% rolling reduction. Much lower fractions were obtained for samples rolled to 10% reduction at 77 K (2%) and at room temperature to 50% (0.3%) and 85% reductions (1.6%). The texture components after cryorolling were Goss and Brass for austenite; rotated cube, α- and γ-fibers for δ-ferrite and α’-martensite. The ε-martensite presents the typical texture of hcp metals with a c/a ratio above the ideal value and 〈0001〉 − oriented tilted about 21° from the normal direction towards the rolling direction. The results show cryorolling as an effective method for enhancing SIM formation and promoting severe microstructural refinement in AISI 317 L stainless steel.
Cryorolling at 77 K favors strain-induced martensite formation. Display omitted
•Cryorolling at 77 K favors the formation of strain-induced martensite (SIM).•Dislocation slip and twinning are the main deformation mechanisms during rolling at RT.•KAM analysis indicates an equivalent strain partitioning among the phases.•Magnetic measurements quantified the volume fraction of α’-martensite.•The volume fraction of ε- and α’-martensite increases with strain.
The 15-5PH (UNS S 15500) stainless steel combines high mechanical strength, ductility, and good corrosion resistance for aircraft and aerospace applications. This set of properties and its high ...added-value applications make it an excellent choice for additive manufacturing processes such as laser powder-bed fusion (LPBF). However, there is a need to understand the complex microstructure developed in LPBF-processed parts, which may show particularities such as columnar solidification, preferential orientation, different kinds of porosities, chemical segregation along the melt pools, metastable phases, and oxide nanoinclusions. We report the microstructural characterization of LPBF-processed 15-5PH stainless steel in the as-built condition and after aging. Low porosity (<1%), high hardness (420 HV0.1), and a large amount of retained austenite (15%) were found in the as-built samples. The microstructure shows the usual “fish scale”-like morphology. Grain size and hardness vary depending on the location within the melt pools. Reconstruction of the parent grains from EBSD maps indicates a microstructural refinement due to in situ reaustenitization of parts of the previous consolidated layers, where these heat-affected zones are harder and present larger amounts of retained austenite. After aging, as-built samples were harder and more resistant to overaging than annealed or wrought counterparts. Transmission electron microscopy reveals a large amount of nanometric crystalline silicon-oxide inclusions, indexed as cristobalite. The combination of fine-grained martensite, coherent Cu-rich clusters, nanometric oxide particles, and retained austenite makes LPBF-processed 15-5PH stainless steel a very promising material for high-end structural applications.
•Texture-free, low-porosity, and high-hardness 15-5PH steel was processed by LPBF.•The intrinsic thermal cycling during processing leads to grain refinement.•Interstitial pick-up was not observed during the manufacturing process.•The austenite fraction in the as-built condition is higher than in the wrought material.•A large number of oxide crystalline nanoinclusions is dispersed in the material.
Austenite reversion, i.e., a’-martensite → γ phase transformation in UNS S32304 lean duplex steel was investigated. The material was cold rolled to a true strain (ε) of 1.61 and subjected to ...continuous annealing up to 1000 °C with a heating rate of 3 °C/min. From the dilatometric curve, an unexpected thermal expansion at around 545 °C was found within the temperature range where the austenite reversion occurs. Based on this unexpected behavior, additional samples were annealed at the same heating rate until key temperatures. Besides dilatometry, microstructural changes were followed by means of magnetic measurements at room temperature, Vickers microhardness testing, high-resolution electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). From EBSD data, a protocol was developed to distinguish the different constituents in the material during the austenite reversion, i.e., α'-martensite, ferrite, and both reversed and untransformed austenite. The driving force for the austenite reversion was calculated using thermodynamic calculations. The a’-martensite → γ transformation begins at about 545 °C and ends at almost 800 °C. In the early beginning, the austenite reversion is governed by a shear mechanism. At higher temperatures, at about 725 °C, KAM (kernel average misorientation) distributions and texture of both reversed and untransformed austenite show evidence of a diffusion-controlled austenite reversion mechanism. These results are supported by thermodynamic calculations and microstructural evidence revealed by ECCI.
•UNS S32304 duplex steel (e = 1.61) shows unexpected behavior in dilatometry at 545 °C.•Shear-dominated austenite reversion explains the anomalous thermal expansion at 545 °C.•The austenite reversion is diffusion-controlled at 725 °C.•Ms and Hc magnetic parameters are very sensitive to austenite reversion.•Hc reflects the increase of a’/g interfaces during austenite reversion.
Cryogenic atom probe tomography (cryo-APT) is being developed to enable nanoscale compositional analyses of frozen liquids. Yet, the availability of readily available substrates that allow for the ...fixation of liquids while providing sufficient strength to their interface, is still an issue. Here we propose the use of 1-2 microns thick binary alloy film of gold-silver (AuAg) sputtered onto flat silicon, with sufficient adhesion without an additional layer. Through chemical dealloying, we successfully fabricate a nanoporous substrate, with open-pore structure, which is mounted on a microarray of Si posts by lift out in the focused-ion beam, allowing for cryogenic fixation of liquids. We present cryo-APT results obtained after cryogenic sharpening, vacuum cryo-transfer and analysis of pure water on top and inside the nanoporous film. We demonstrate that this new substrate has the requisite characteristics for facilitating cryo-APT of frozen liquids, with a relatively lower volume of precious metals. This complete workflow represents an improved approach for frozen liquid analysis, from preparation of the films to the successful fixation of the liquid in the porous network, to cryo-atom probe tomography.
Cited2 is a transcriptional modulator with pivotal roles in different biological processes. Cited2-deficient mouse embryos manifested two major defects in the developing eye. An abnormal ...corneal-lenticular stalk was characteristic of Cited2 -/- developing eyes, a feature reminiscent of Peters' anomaly, which can be rescued by increased Pax6 gene dosage in Cited2 -/- embryonic eyes. In addition, the hyaloid vascular system showed hyaloid hypercellularity consisting of aberrant vasculature, which might be correlated with increased VEGF expression in the lens. Deletion of Hif1a (which encodes HIF-1α) in Cited2 -/- lens specifically eliminated the excessive accumulation of cellular mass and aberrant vasculature in the developing vitreous without affecting the corneal-lenticular stalk phenotype. These in vivo data demonstrate for the first time dual functions for Cited2: one upstream of, or together with, Pax6 in lens morphogenesis; and another in the normal formation of the hyaloid vasculature through its negative modulation of HIF-1 signaling. Taken together, our study provides novel mechanistic revelation for lens morphogenesis and hyaloid vasculature formation and hence might offer new insights into the etiology of Peters' anomaly and ocular hypervascularity.
1 RIKEN, Brain Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan;
2 Division of Neural Systems, Memory and Aging,
University of Arizona, Tucson, Arizona 85724; and
3 Japan Science ...and Technology Program, Core
Research for the Evolutional Science and Technology Program (CREST);
and 4 Tokyo Denki University, Hatoyama, Saitama
350-0394, Japan
Yamaguchi, Yoko,
Yoshito Aota,
Bruce L. McNaughton, and
Peter Lipa.
Bimodality of Theta Phase Precession in Hippocampal Place
Cells in Freely Running Rats. J. Neurophysiol. 87: 2629-2642, 2002. The firing of hippocampal principal cells
in freely running rats exhibits a progressive phase retardation as the
animal passes through a cell's "place" field. This "phase
precession" is more complex than a simple linear shift of phase with
position. In the present paper, phase precession is quantitatively
analyzed by fitting multiple (1-3) normal probability density
functions to the phase versus position distribution of spikes in rats
making repeated traversals of the place fields. The parameters were
estimated by the Expectation Maximization method. Three data sets
including CA1 and DG place cells were analyzed. Although the
phase-position distributions vary among different cells and regions,
this complexity is well described by a superposition of two normal
distribution functions, suggesting that the firing behavior consists of
two components. This conclusion is supported by the existence of two distinct maxima in the mean spike density in the phase versus position
plane. In one component, firing phase shifts over a range of about
180°. The second component, which occurs near the end of the
traversal of the place field, exhibits a low correlation between phase
and position and is anti-phase with the phase-shift component. The
functional implications of the two components are discussed with
respect to their possible contribution to learning and memory mechanisms.
There has been considerable research which has focused on clarifying the origin of pain in patients with atypical odontalgia (AO), also known as "idiopathic toothache", and on identifying effective ...treatment, but there has been limited success so far. In this study, we assessed the outcomes of treatment and attempted to identify factors that could account for pain remission in patients with AO.
Data for 165 patients diagnosed with AO from June 2015 to August 2017 were retrospectively reviewed. The patients' sex, age, duration of pain, and psychiatric history were collected, along with information on pain intensity, depressive status, and catastrophizing scores. Responses at 4 and 16 weeks from the start of treatment were observed. The associations between potentially associated factors and outcome were investigated using Bayesian model averaging.
A 30% reduction in pain was reported by 38 patients (46.3%) at 4 weeks and by 54 patients (65.9%) at 16 weeks. The pain intensity decreased as the depression and catastrophizing score improved; all of the changes were statistically significant (
<0.001). Four elements, that is, patient sex, depression score at baseline, pain score at 4 weeks, and change in the catastrophizing score, explained 52.5% of the variation in final outcome between individual patients.
Our findings confirm the efficacy of tricyclic antidepressants (TCAs) as a treatment for AO and indicate that other medications, especially aripiprazole used in combination with a TCA, may be useful. A considerable number of patients, especially women, those with lower levels of depression at baseline, and those who responded to 4 weeks of treatment, achieved pain relief.
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