bluuebunny/crossref_metadata_2025 huggingface dataset:
The Powerful Jet and Gamma-Ray Flare of the Quasar PKS 0438–436
Authors: Punsly Brian , Tramacere Andrea , Kharb Preeti , Marziani Paola
Published: December 2018

PKS 0438–436, at a redshift of z = 2.856, has been previously recognized as possessing perhaps the most luminous known synchrotron jet. Little is known about this source since the maximum elevation above the horizon is low for the Very Large Array (VLA). We present the first VLA radio image that detects the radio lobes. We use both the 151 MHz luminosity, as a surrogate for the isotropic radio lobe luminosity, and the lobe flux density from the radio image to estimate a long-term, time-averaged, jet power,

. We analyze two deep optical spectra with strong broad emission lines and estimate the thermal bolometric luminosity of the accretion flow, L
bol = 6.7 ± 3.0 × 1046 erg s−1. The ratio

is at the limit of this empirical metric of jet dominance seen in radio-loud quasars and this is the most luminous accretion flow to have this limiting behavior. Despite being a very luminous blazar, it previously had no γ-ray detections until 2016 December 11–13 (54 hr) when FERMI detected a flare that we analyze here. The isotropic apparent luminosity from 100 MeV–100 GeV rivals the most luminous detected blazar flares (averaged over 18 hr), ∼5–6 × 1049 erg s−1. The γ-ray luminosity varies over time by two orders of magnitude, highlighting the extreme role of Doppler abberation and geometric alignment in producing the inverse Compton emission.
Vortex Flows in the Solar Atmosphere: Automated Identification and Statistical Analysis
Authors: Giagkiozis Ioannis , Fedun Viktor , Scullion Eamon , Jess David B. , Verth Gary
Published: December 2018

Vortices on the photosphere are fundamentally important as these coherent flows have the potential to form coherent magnetic field structures in the solar atmosphere, e.g., twisted magnetic flux tubes. These flows have traditionally been identified by tracking magnetic bright points (BPs) using primarily visual inspection. This approach has the shortcoming that it introduces bias into the statistical analyses. In this work we fully automate the process of vortex identification using an established method from hydrodynamics for the study of eddies in turbulent flows. For the first time, we apply this to detect intergranular photospheric intensity vortices. Using this automated approach, we find that the expected lifetime of intensity vortices is much shorter (≈17 s) compared with previously observed magnetic BP swirls. We suggest that at any time there are 1.48 × 106 such small-scale intensity vortices covering about 2.8% of the total surface of the solar photosphere. Lastly, we compare our results with previous works and speculate what this could imply with regards to estimating the global energy flux due magnetic tornadoes in the solar atmosphere with future higher resolution instrumentation.
Nonlinear Color–Metallicity Relations of Globular Clusters. VIII. Reproducing Color Distributions of Individual Globular Cluster Systems in the Virgo and Fornax Galaxy Clusters
Authors: Lee Sang-Yoon , Chung Chul , Yoon Suk-Jin
Published: December 2018

The color distributions of globular clusters (GCs) in individual early-type galaxies show great diversity in their morphology. Based on the conventional “linear” relationship between the colors and metallicities of GCs, the GC metallicity distributions inferred from colors and in turn their formation histories, should be as diverse as they appear. In contrast, here we show that an alternative scenario rooted in the “nonlinear” nature of the metallicity-to-color transformation points to a simpler and more coherent picture. Our simulations of the color distributions for ∼80 GC systems in early-type galaxies from the ACS Virgo and Fornax Cluster Surveys suggest that the majority (∼70%) of early-type galaxies have old (∼13 Gyr) and coeval GCs. Their variety in the color distribution morphology stems mainly from one parameter, the mean metallicity of a GC system. Furthermore, the color distributions of the remaining (∼30%) GC systems are also explained by the nonlinearity scenario, assuming additional young or intermediate-age GCs with a number fraction of ∼20% of underlying old GCs. Our results reinforce the nonlinearity explanation for the GC color bimodality and provide a new perspective on early-type galaxy formation in the cluster environment, such as the Virgo and Fornax galaxy clusters.
Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). I. Survey Description and First Results in the Coma Galaxy Cluster and Environs
Authors: Zaritsky Dennis , Donnerstein Richard , Dey Arjun , Kadowaki Jennifer , Zhang 张华 Huanian 年 , Karunakaran Ananthan , Martínez-Delgado David , Rahman Mubdi , Spekkens Kristine
Published: December 2018

We present a homogeneous catalog of 275 large (effective radius ≳5.″3) ultra-diffuse galaxy (UDG) candidates lying within an ≈290 square degree region surrounding the Coma Cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14,000 square degrees of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma Cluster. We conclude that the majority of our detections are at roughly the distance of the Coma Cluster, implying effective radii ≥2.5 kpc, and that our sample contains a significant number of analogs of DF44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The g − z color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma Cluster and a relative overabundance of blue UDG candidates in the lower-density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.
A Comprehensive Bayesian Discrimination of the Simple Stellar Population Model, Star Formation History, and Dust Attenuation Law in the Spectral Energy Distribution Modeling of Galaxies
Authors: Han Yunkun , Han Zhanwen
Published: December 2018

When modeling and interpreting the spectral energy distributions (SEDs) of galaxies, the simple stellar population (SSP) model, star formation history (SFH), and dust attenuation law (DAL) are three of the most important components. However, each of them carries significant uncertainties that have seriously limited our ability to reliably recover the physical properties of galaxies from the analysis of their SEDs. In this paper, we present a Bayesian framework to deal with these uncertain components simultaneously. Based on the Bayesian evidence, a quantitative implement of the principle of Occam’s razor, the method allows a more objective and quantitative discrimination among the different assumptions about these uncertain components. With a Ks
-selected sample of 5467 low-redshift (mostly with z ≲ 1) galaxies in the COSMOS/UltraVISTA field and classified into passively evolving galaxies (PEGs) and star-forming galaxies (SFGs) with the UVJ diagram, we present a Bayesian discrimination of a set of 16 SSP models from five research groups (BC03 and CB07, M05, GALEV, Yunnan-II, BPASS V2.0), five forms of SFH (Burst, Constant, Exp-dec, Exp-inc, Delayed-τ), and four kinds of DAL (Calzetti law, MW, LMC, SMC). We show that the results obtained with the method are either obvious or understandable in the context of stellar/galaxy physics. We conclude that the Bayesian model comparison method, especially that for a sample of galaxies, is very useful for discriminating the different assumptions in the SED modeling of galaxies. The new version of the BayeSED code, which is used in this work, is publicly available at https://bitbucket.org/hanyk/bayesed/.
The Disk Substructures at High Angular Resolution Program (DSHARP). VIII. The Rich Ringed Substructures in the AS 209 Disk
Authors: Guzmán Viviana V. , Huang Jane , Andrews Sean M. , Isella Andrea , Pérez Laura M. , Carpenter John M. , Dullemond Cornelis P. , Ricci Luca , Birnstiel Tilman , Zhang Shangjia , Zhu Zhaohuan , Bai Xue-Ning , Benisty Myriam , Öberg Karin I. , Wilner David J.
Published: December 2018

We present a detailed analysis of the high angular resolution (0.″037, corresponding to 5 au) observations of the 1.25 mm continuum and 12CO 2 − 1 emission from the disk around the T Tauri star AS 209. AS 209 hosts one of the most unusual disks from the Disk Substructures at High Angular Resolution Project sample, the first high angular resolution Atacama Large Millimeter Array survey of disks, as nearly all of the emission can be explained with concentric Gaussian rings. In particular, the dust emission consists of a series of narrow and closely spaced rings in the inner ∼60 au, two well-separated bright rings in the outer disk, centered at 74 and 120 au, and at least two fainter emission features at 90 and 130 au. We model the visibilities with a parametric representation of the radial surface brightness profile, consisting of a central core and seven concentric Gaussian rings. Recent hydrodynamical simulations of low-viscosity disks show that super-Earth planets can produce the multiple gaps seen in AS 209 millimeter continuum emission. The 12CO line emission is centrally peaked and extends out to ∼300 au, much farther than the millimeter dust emission. We find axisymmetric, localized deficits of CO emission around four distinct radii, near 45, 75, 120, and 210 au. The outermost gap is located well beyond the edge of the millimeter dust emission, and therefore cannot be due to dust opacity and must be caused by a genuine CO surface density reduction, due either to chemical effects or depletion of the overall gas content.
The Disk Substructures at High Angular Resolution Project (DSHARP). VI. Dust Trapping in Thin-ringed Protoplanetary Disks
Authors: Dullemond Cornelis P. , Birnstiel Tilman , Huang Jane , Kurtovic Nicolás T. , Andrews Sean M. , Guzmán Viviana V. , Pérez Laura M. , Isella Andrea , Zhu Zhaohuan , Benisty Myriam , Wilner David J. , Bai Xue-Ning , Carpenter John M. , Zhang Shangjia , Ricci Luca
Published: December 2018

A large fraction of the protoplanetary disks observed with ALMA display multiple well-defined and nearly perfectly circular rings in the continuum, in many cases with substantial peak-to-valley contrast. The DSHARP campaign shows that several of these rings are very narrow in radial extent. In this Letter we test the hypothesis that these dust rings are caused by dust trapping in radial pressure bumps, and if confirmed, put constraints on the physics of the dust trapping mechanism. We model this process analytically in 1D, assuming axisymmetry. By comparing this model to the data, we find that all rings are consistent with dust trapping. Based on a plausible model of the dust temperature we find that several rings are narrower than the pressure scale height, providing strong evidence for dust trapping. The rings have peak absorption optical depth in the range between 0.2 and 0.5. The dust masses stored in each of these rings is of the order of tens of Earth masses, though much ambiguity remains due to the uncertainty of the dust opacities. The dust rings are dense enough to potentially trigger the streaming instability, but our analysis cannot give proof of this mechanism actually operating. Our results show, however, that the combination of very low

and very large grains

can be excluded by the data for all the rings studied in this Letter.
Effect of Iris Registration on Outcomes of LASIK for Myopia With the VISX CustomVue Platform
Authors: Moshirfar Majid , Chen Michael C. , Espandar Ladan , Meyer Jay J. , Christensen Dan , Christiansen Steve M. , Dave Sonal B. , Bedke Brent , Kurz Christopher
Published: December 2018

Purpose:

To compare visual outcomes after LASIK using the VISX STAR S4 CustomVue, with and without Iris Registration technology.

Methods:

In this retrospective study, LASIK was performed on 239 myopic eyes, with or without astigmatism, of 142 patients. Iris registration LASIK was performed on 121 eyes and non-iris registration LASIK was performed on 118 eyes. Primary outcome measures were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and manifest refraction.

Results:

At 6 months, the mean values for UCVA (logMAR) were 0.00±0.09 in the iris registration group and −0.01±0.11 in the non-iris registration group (
P
=.587). Seventy-nine percent of eyes in the iris registration group had UCVA of 20/20 or better compared to 78% in the non-iris registration group (
P
=.518). Ninety-two percent of eyes in the iris registration group and 90% in the non-iris registration group were within ±0.50 diopters (D) of emmetropia (
P
=.999). Mean postoperative absolute change in total root-mean-square higher order aberrations in the iris registration group and non-iris registration group was 0.22 µm and 0.19 µm, respectively (
P
=.6). At 3 months, the mean magnitude of error of surgically induced astigmatism was −0.09 in the iris registration group and −0.04 in the non-iris registration group (
P
=.25).

Conclusions:

Wavefront-guided LASIK with the VISX STAR S4 CustomVue laser system, independent of iris registration status, is effective, safe, and predictable. Under well-controlled surgical conditions, this study did not find any statistical significance supporting the better achievement of visual acuity, astigmatism correction, or the lesser induction of higher order aberrations using iris registration in comparison to a non-iris registration system. [
J Refract Surg
. 2009;25:493–502.]
Contrast Sensitivity Evaluation of Aspheric and Spherical Intraocular Lenses 2 Years After Implantation
Authors: Caporossi Aldo , Casprini Fabrizio , Martone Gianluca , Balestrazzi Angelo , Tosi Gian Marco , Ciompi Leonardo
Published: December 2018

Purpose:

To compare the quality of vision with aspheric and spherical intraocular lenses (IOLs) in pseudophakic patients after long-term follow-up.

Methods:

Two hundred eyes of 100 patients with bilateral cataracts were randomly assigned to receive spherical (Acrysof SN60AT [Alcon Laboratories Inc] or Sensar AR40e [Advanced Medical Optics Inc]) or aspheric IOLs (Acrysof SN60WF [Alcon] or Tecnis Z9000 [Advanced Medical Optics]). Ophthalmologic examination, including best spectacle-corrected visual acuity (BSCVA), pupil size, ocular dominance, contrast sensitivity under mesopic and photopic conditions, and wavefront analysis, was performed 2 months and 1 and 2 years after surgery.

Results:

No statistically significant differences among the four groups in terms of age, pupil diameter, postoperative BSCVA, corneal spherical aberration, and posterior capsular opacification were noted. At all followup examinations, contrast sensitivity results showed no significant differences between the two aspheric IOLs at all spatial frequencies. Under photopic conditions, significant differences (
P
<.05) between spherical and aspheric IOLs were detected for spatial frequencies of 12 and 18 cycles per degree (cpd) at 2 months and 2 years and 12 cpd at 1 year. Under mesopic conditions, significant differences (
P
<.05) were detected between spherical and aspheric IOLs for all spatial frequencies at 2 months; all spatial frequencies except 18 cpd at 1 year; and spatial frequencies of 3, 12, and 18 cpd at 2 years. In addition, aspheric IOLs had statistical reductions in total spherical aberration at all follow-up examinations (
P
<.01).

Conclusions:

This study confirms that implantation of a modified aspheric IOL improves functional visual performance at 2 years postoperative. [
J Refract Surg.
2009;25:578–590.]
Corneal Epithelial Thickness Profile in the Diagnosis of Keratoconus
Authors: Reinstein Dan Z. , Archer Timothy J. , Gobbe Marine
Published: December 2018

Purpose:

To illustrate the hypothesis that epithelial thickness profile maps could be used as an adjunctive tool to improve the sensitivity and specificity of keratoconus screening by presenting a case series of examples.

Methods:

The Artemis very high-frequency digital ultrasound arc-scanner was used to obtain epithelial thickness profiles in addition to a comprehensive ophthalmic examination to screen for keratoconus. Five case examples are presented; a normal eye, an eye with advanced keratoconus, and three cases where a diagnosis of keratoconus was uncertain based only on the ophthalmic examination.

Results:

The epithelial thickness profile in the normal eye was slightly thinner superiorly, consistent with that previously described for a normal population. The keratoconic eye demonstrated an epithelial doughnut pattern of epithelial thinning over the cone surrounded by an annulus of epithelial thickening. In case 1, an epithelial doughnut pattern confirmed the presence of keratoconus in an eye with an abnormal front surface topography. In case 2, the absence of an epithelial doughnut pattern excluded a diagnosis of keratoconus in a patient with an abnormal front surface topography. In case 3, the presence of an epithelial doughnut pattern coincident with an eccentric posterior elevation best-fit sphere indicated a diagnosis of keratoconus. The epithelium appeared to have compensated for the stromal surface cone, resulting in an apparently normal front surface topography.

Conclusions:

An epithelial doughnut pattern appears to indicate the presence of an underlying stromal cone; the lack of an epithelial doughnut pattern would indicate that an abnormal topography was not due to keratoconus. In very early keratoconus, epithelial compensation can mask the presence of an underlying cone on front surface topography, ie, a diagnosis of keratoconus might be missed. [
J Refract Surg
. 2009;25:604–610.]
Teaching and Assessing Competency in Retinal Lasers in Ophthalmology Residency
Authors: Abràmoff Michael D. , Folk James C. , Lee Andrew G. , Beaver Hilary A. , Boldt H. Culver
Published: December 2018

Background and Objective:
The Accreditation Council for Graduate Medical Education has mandated that residency programs teach and assess six specific competencies (ie, medical knowledge, patient care, communication and interpersonal skills, professionalism, practice-based learning, and systems-based learning). To the authors’ knowledge, there is no standardized and widely used curriculum for teaching and assessing resident competencies in retinal lasers.

Methods:
The pertinent literature on resident education in retinal lasers is reviewed and specific “good practices” for teaching and assessing laser competency are presented.

Results:
Development and deployment of educational tools that teach and assess laser competency simultaneously; are reliable, reproducible, and valid; have low faculty time burden; and are affordable, generalizable, and fair are recommended.

Conclusion:
Retinal laser competency can be taught and assessed in ophthalmology residency training programs. Future research will be needed to provide evidence that these teaching and assessment tools produce improved educational and patient outcomes and provide verifiable, reliable, and valid evidence of resident competence in retinal lasers.
Annealing on Anisotropy and Mechanical Properties of an Al-Mg-Si Alloy
Authors: Yan Li Zhen , Zhang Yong An , Xiong Bai Qing , Li Zhi Hui , Li Xi Wu , Liu Hong Wei , Huang Shu Hui , Yan Hong Wei , Wen Kai
Published: December 2018

Intermediate annealing on anisotropy and mechanical properties of an Al-0.78Mg-0.90Si-0.65Zn-0.16Cu (wt. %) alloy was investigated by tensile test, optical microscope (OM) and electron back-scattered diffraction (EBSD). The results indicated that alloy sheet displayed various microstructure after without intermediate annealing, intermediate annealing treatment at 350°C for 2 h, 450°C for 2 h and 500°C for 5 min. Compared with the alloy without intermediate annealing, the alloy exhibited equiaxed grain with 35.0µm after annealing at 500°C for 5 min, grain orientation of the alloy was distributed randomly, and plastic strain ratio value of 45° direction was more than 0.6. The anisotropy of the sheet was significantly reduced. Annealing at 500°C for 5 min was suitable for the production process of automobile body sheets.
Two-Step Aging Behaviour of Solution Treated A356 System Alloy
Authors: Iijima Masahiko , Ozasa Tomoya , Ikeno Susumu , Matsuda Kenji , Saikawa Seiji
Published: December 2018

Al-7mass%Si-0.3mass%Mg alloy is widely applied to the automotive components, such as road wheel or suspension frame because of having higher ductility and corrosion resistance. Two-step aging behavior of solution treated Al-7mass%Si-0.3mass%Mg system alloy A356 cast into permanent mold and solution treated was investigated by micro-vickers hardness measurement, optical microscopy (OM) and transmission electron microscopy (TEM). The microstructure of as-cast state was consist of primary crystallized α-Al and secondary crystallized eutectic phases. Al-7mass%Si-0.3mass%Mg alloy after casting, the test specimens were heat treated for different pre-aging temperatures at 273K, 348K and 423K for various times after solution treatment at 813K for 36ks. After pre-aging treatment, the test specimens were heat treated for artificial aging at 523K for various times. The peak hardness increased almost the same value when the pre-aging temperature was 273K. On the other hands, positive effect of the final-aging was occurred after pre-aging at 348K and 423K with significantly increasing hardness in the under-aging region. The fine precipitates were observed in the specimen which was final aging at 523K after pre-aging at 348K and 423K.Such a positive effect is considered due to the influence of precipitated phase mainly such as clusters and /or G.P.zone.The present study aims to investigate the effect of pre-aged temperature on final-aged behavior in A356 system alloy.
The Effect of Crystal Orientation on Damping Capacity in Rolled AZ31 Magnesium Alloy
Authors: Kwak Ju Ho , Ko Min Seong , Kim Kwon Hoo
Published: December 2018

The effect of crystal orientation on damping capacity is studied on hot rolled AZ31 magnesium alloy. AZ31 magnesium alloys which was machined out parallel to rolled direction and perpendicular to rolled direction were investigated about the relationship between the initial texture and damping capacity. The specimens are annealed at 623 K and time ranging from 30 to 180 minutes. After heat treatment recrystallization is occurred. Then, average grain size and damping capacity are increased with increasing annealing time. Two types of specimens show different main component of texture and damping capacity respectively. It is found that initial texture was affected on damping capacity.
Al, Cu and Zr Addition to High Entropy Alloys: The Effect on Recrystallization Temperature
Authors: Colombini Elena , Garzoni Andrea , Giovanardi Roberto , Veronesi Paolo , Casagrande Angelo
Published: December 2018

The equimolar Cr, Mn, Fe, Co and Ni alloy, first produced in 2004, was unexpectedly found to be single-phase. Consequently, a new concept of materials was developed: high entropy alloys (HEA) forming a single solid-solution with a near equiatomic composition of the constituting elements. In this study, an equimolar CoCrFeMnNi HEA was modified by the addition of 5 at% of either Al, Cu or Zr. The cold-rolled alloys were annealed for 30 minutes at high temperature to investigate the recrystallization kinetics. The evolution of the grain boundary and the grain size were investigated, from the as-cast to the recrystallized state. Results show that the recrystallized single phase FCC structures exhibits different twin grains density, grain size and recrystallization temperatures as a function of the at.% of modifier alloying elements added. In comparison to the equimolar CoCrFeMnNi, the addition of modifier elements increases significantly the recrystallization temperature after cold deformation. The sluggish diffusion (typical of HEA alloys), the presence of a solute in solid solution as well as the low twin boundary energy are responsible for the lower driving force for recrystallization.
Effect of Si Content on the Fatigue Fracture Behavior of Wrought Al-xSi-0.7Mg Alloy
Authors: Wang Guang Dong , Tian Ni , Li Chong , Zhao Gang , Zuo Liang
Published: December 2018

The wrought Mg-containing high-silicon aluminum alloy has become more attractive as an ideal structural material, because it has moderate strength and the ductility, high wear and corrosion resistance, low thermal expansion coefficient and low cost. However, as structural material, the fatigue properties and the fatigue fracture behavior of it should be paid much more attention to, especially the effect of Si content on the fatigue properties of wrought Mg-containing Al-Si alloy. In this paper, the wrought Al-(1.44%, 4.92%, 6.61%, 8.81% and 12.4%)Si-0.7%Mg alloy were prepared through DCC and homogenization treatment, and then hot-rolled and cold-rolled into 1.3mm sheets. The microstructure and fatigue fracture morphology of Al-(1.44~12.4)Si-0.7Mg-T4 alloy sheet after fatigue test were investigated by LSCM and SEM. The results showed that the size of Si particles in Al-(1.44~12.4)Si-0.7Mg alloy sheets was approximately the same, but the number of Si particles increased as the Si content increased. The size of recrystallization grain in Al-(1.44~12.4)Si-0.7Mg alloy sheets decreased from 47μm to 10μm when Si content increased from 1.44% to 12.4%, which indicates that increasing of Si content can refine the grain of Al-(1.44~12.4)Si-0.7Mg alloy sheets. With the increasing of Si content the propagation area of fatigue fracture surface of Al-(1.44~12.4)Si-0.7Mg alloy sheets in T4 temper became rougher, and crack propagation became more difficult. Moreover, dimples in the fast fracture area became larger in amount, smaller in size and more uniform in distribution.
Inhomogeneous Precipitation of the α-Phase in Ti15Mo Alloy Deformed by ECAP
Authors: Bartha Kristína , Veverková Anna , Stráský Josef , Minárik Peter , Veselý Jozef , Polyakova Veronika , Semenova Irina , Janeček Miloš
Published: December 2018

A metastable β-titanium alloy, Ti15Mo was subjected to equal channel angular pressing (ECAP). The resulting microstructure of the material is inhomogeneous consisting of micrometer size β-grains with deformed bands containing ultra-fine β-grains. The ECAP-deformed sample was subjected to thermal treatment in order to elucidate the difference in morphology of the α-phase precipitation in deformed and non-deformed materials. The α-phase formation is accelerated in areas with higher concentration of lattice defects. The detail investigation by transmission electron microscopy revealed equixed α-phase formation in deformed bands. In the transition area between deformed band and β-matrix grain boundary α-phase forms while in the interior of the β-grains the α-phase precipitation is suppressed.
Influence of Cr Content on Cellular Precipitation Behaviour of Ni-38Cr-3.8Al Alloy with Lamellar Structure
Authors: Koyanagi Yoshihiko , Takabayashi Hiroyuki , Yasuda Hiroyuki Y.
Published: December 2018

Ni-Cr binary alloys containing high amount of Cr demonstrate gamma/alpha-Cr lamellar structure by discontinuous precipitation (DP) reaction from grain boundary. The mechanism of DP reaction is caused by supersaturated Cr in the gamma phase. Supersaturated Cr concentration influences the driving force for the DP reaction and the lamellar spacing. Moreover, the Ni-based alloys with high Cr, containing Al, significantly increase the hardness and strength due to the very narrow lamellar structure. Al addition brings on Ni consumption in the matrix by precipitation of the gamma prime phase. Therefore, Cr supersaturates dramatically in the matrix. The wrought Ni-Cr-Al alloy, Ni-38Cr-3.8Al (mass%) , reaches extremely high tensile strength, which is over 2 GPa, after annealing treatment. Even though chemical composition of Ni-38Cr-3.8Al is simple, the microstructure is complex because it consists of the gamma/alpha Cr lamellar structure with the fine gamma prime particles. Therefore, in this study, we investigated the influence of Cr concentration on the cellular precipitation behaviour. In order to understand the influence of Cr concentration, Ni-34, 36 and 38Cr-3.8Al alloys were prepared. Forged bars were subjected to solution treatment in the gamma single phase region. Subsequently, the alloys were aged from 873K to 1073 K for various times. The cellular precipitation reaction is suppressed by a decrease in Cr concentration, particularly at low temperature annealing treatment condition. The hardness is low in lower Cr concentration alloys in all range of annealing treatment temperature. These results indicate that Cr concentration remarkably affects the driving force for the DP reaction.
Influence of Grain Size and Thermo-Mechanical Conditions on the Activation Energy for Super Plastic Flow in Ti-6Al-4V Alloy
Authors: Muñoz-Andrade Juan Daniel
Published: December 2018

The essential objective of this work is to establish the influence of grain size and thermo-mechanical conditions on the activation energy for super plastic flow (QSPF) in Ti-6Al-4V alloy by applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade, in the framework of the unified physics. The QM-RM allows the direct determination of the QSPF in advanced materials at instantaneous thermo-mechanical material working conditions. By applying, the QM-RM on the experimental results reported previously by some authors, it is shown for grain size of 6.1μm, that the calculated QSPF for grain boundary sliding is about 193 and 178 kJ/mol, at 850°C with an efficiency of power dissipation, η=0.65. These results are in closed agreement with the values of 204 and 174 kJ/mol reported previously for grain boundary self-diffusion energy of α-Ti. Nevertheless, for grain size of 0.6μm the calculated QSPF is 142 kJ/mol at 650°C, with an efficiency of power dissipation, η=0.61. As well, in order to understand the phenomenology and mechanics of SPF in Ti-6Al-4V alloy, the variation of the activation energy with the temperature; stress and strain rate is analyzed in association with coupled mechanisms during SPF, such as grain boundary sliding, cooperative grain boundary sliding and self-accommodation process related to the microstructure. In summary, the results of QSPF obtained in this work, by the QM-RM are in closed agreement with results reported previously by using the theoretical and conventional methodology set up by Mohamed and Langdon.
Behavior of Hydrogen in Tensile-Deformed Aluminum Alloys
Authors: Manaka Toshiaki , Itoh Goroh
Published: December 2018

Behavior of hydrogen in tensile-deformed Al-9mass%Mg and Al-5.8mass%Zn-2.4mass%Mg alloys was investigated by means of hydrogen microprint technique, HMPT, a method to visualize the microscopic location of hydrogen evolution from specimen surface as silver particles. Both in the two alloys, surface relief was formed at most grain boundaries by the stretching, while hydrogen evolution was observed at some grain boundaries. The evolution of hydrogen was discussed with parameters such as the angle between grain boundary on the specimen surface and tensile direction, the angle between grain boundary on the surface and slip line inside the grain, the height of the surface relief, and maximum gradient of the surface relief. The results indicated that the shear deformation along grain boundary caused transportation of hydrogen atoms with gliding dislocations to the surface, breakage of surface oxide film. In the Al-Zn-Mg alloy, it was suggested that the preferential deformation in the precipitate free zone was attributed to hydrogen evolution.
A Subsurface Fatigue Crack Generation Model in near Alpha Titanium at Low Temperature
Authors: Umezawa Osamu , Li Wei Bo
Published: December 2018

The subsurface fatigue crack generation processes in near α type titanium alloy were divided into four steps: (1) development of a saturated dislocation structure by cyclical micro-plastic strain accumulation, (2) generation of localized slip and/or microcracking to relax the stress concentration in the vicinity of a boundary, (3) microcrack growth and transition to main crack, and (4) crack propagation. The experimentals on transgranular facets formation in Ti-Fe-O alloy were reviewed and a subsurface fatigue crack generation model was discussed. The β platelets which were aligned between the recrystallized α grain and the recovered α grain were responsible for the microcrack generation to form (0001) tansgranular facet in the recrystallized α grains. A combination of the shear stress and tensile stress normal to the basal plane may give a trigger of the (0001) microcracking in the recrystallized α grain. The localized shear stress following slip off on the basal plane was activated at the microcrack tip in the recrystallizedαgrain, and the microcrack grew into the recrystallized α grain to form (0001) transgranular facet.
Thermo-Mechanical Treatment of Titanium Based Layered Structures Fabricated by Blended Elemental Powder Metallurgy
Authors: Prikhodko Sergey V. , Markovsky Pavlo E. , Savvakin Dmytro G. , Stasiuk Oleksandr , Ivasishin Orest M.
Published: December 2018

High specific strength of Ti-based alloys and composites makes them highly requested materials in various structural applications, especially when lightweight is desired in high-strength constructions. When these alloys are used in layered structures, far advanced set of characteristics that combine different mechanical properties often non-compatible in a single layer uniform structure can be attained; for instance, high hardness or moduli systems are usually lacking of sufficient toughness. Mechanical properties of individual layer in multilayered materials can be controlled by changing chemical composition and microstructure within each layer specifically. In present study layered materials were formed by combination of the layer of Ti-6Al-4V alloy and metal matrix composites on its base reinforced with fine TiB and TiC particles. Structures were fabricated using blended elemental powder metallurgy (BEPM). The effect of different post-sintering thermo-mechanical treatments on structure of layered BEPM materials was studied. Processing parameters were assessed in terms of their influence on materials’ porosity, grain size and structure, distribution of reinforcement particles and layers integration. The effect of above mentioned structural characteristics on hardness of layered materials was evaluated.
Cryogenic Sheet Metal Forming - An Overview
Authors: Grabner Florian , Gruber Belinda , Schlögl Carina , Chimani Christian
Published: December 2018

Despite extensive efforts to improve energy efficiency in the automotive sector, the use of light-weight aluminium alloys for car bodies is impeded by formability limitations. Although it is a known phenomenon that Al alloys increase their strength and ductility at very low temperatures, it has not been attempted to exploit this effect to increase their overall formability at an industrial scale. Over the last four years, the cryogenic sheet metal forming behaviour of Al-alloys was extensively investigated to establish a process robust enough for manufacturing automotive parts at an industrial level. Initial experiments include tensile tests at temperatures down to –196 °C for characterisation of 5xxx and 6xxx series Al alloys, providing the mechanical material data for numerical design simulations of sheet metal forming processes at cryogenic temperatures. Numerical simulations will not be discussed in this publication. Furthermore, the necessary hardware for cryogenic sheet metal forming was developed and finally resulted in a semi-automated small scale industrial production site. The production of a miniaturized B-Pillar was demonstrated for 5xxx and 6xxx alloys. Due to the part’s demanding geometry, defect-free deep drawing process is possible at cryogenic temperature only. These results demonstrate that the use of Al alloys could be extended beyond their current applications in cars components. For example, the overall formability of 5xxx series alloys nearly doubles compared to room temperature. This paper shall give an overview over our work in the field of cryogenic aluminium sheet metal forming within the last couple of years.
Precipitation Kinetics of AA6082: An Experimental and Numerical Investigation
Authors: Herrnring Jan , Kashaev Nikolai , Klusemann Benjamin
Published: December 2018

The development of simulation tools for bridging different scales are essential for understanding complex joining processes. For precipitation hardening, the Kampmann-Wagner numerical model (KWN) is an important method to account for non-isothermal second phase precipitation. This model allows to describe nucleation, growth and coarsening of precipitation hardened aluminum alloys based on a size distribution for every phase which produces precipitations. In particular, this work investigates the performance of a KWN model by [1-3] for Al-Mg-Si-alloys. The model is compared against experimental data from isothermal heat treatments taken partially from [2]. Additionally, the model is used for investigation of the precipitation kinetics for a laser beam welding process, illustrating the time-dependent development of the different parameters related to the precipitation kinetics and the resulting yield strength.
Analytical Design of Superelastic Ring Springs for High Energy Dissipation
Authors: Spaggiari Andrea , Scire' Mammano Giovanni , Dragoni Eugenio
Published: December 2018

Classical ring springs are mechanical elements used in industrial applications and in transport for shock absorption and energy dissipation. They are constituted by a stack of internal and external metal rings (typically high strength steel), with tapered surfaces in contact with one another. Under the action of an axial load these surfaces slide, the rings are deformed circumferentially and energy is dissipated due to friction. The main advantages of these springs are the high specific energy stored and the large damping capacity due to sliding friction. Furthermore, the stiffness and damping are independent on the strain rate and the temperature, which limits or avoids the occurrence of any resonance problems. The superelastic materials, characterized by an almost flat stress plateau and large reversible deformation, can be used to replace traditional steels in ring springs giving a significant performance increase. Compared to the traditional version where energy is dissipated only due to friction, in superelastic ring springs there is an increase of the dissipated energy thanks to the internal hysteresis of the material. This paper studies analytically the ring springs in traditional material and in superelastic material, providing equations to dimension these mechanical elements, which enable the designer to customize this useful structural element.
An In Situ Observation of Slip Deformation in a Compressed Ti-Mo-Al Single Crystal
Authors: Hara Ryotaro , Tahara Masaki , Inamura Tomonari , Hosoda Hideki
Published: December 2018

The stress-induced martensitic transformation and slip deformation behavior were investigated by the compression test with an in-situ observation in a Ti-6Mo-10Al (mol %) alloy single crystal. Owing to the stress-induced martensitic transformation from the parent β phase to the α′′ martensite phase, the single crystal of α′′ martensite without internal twinnings was successfully obtained at room temperature. By further compression, the slip deformation occurred in the single crystal of α′′ martensite. The operated slip system in the α′′ martensite was analyzed by the two face trace analyses, and the slip direction was determined to be []o.
Superplastic GBS Constitutive Equation Incorporating Average Grain Misorientation Dependence
Authors: Carreño Fernando , Orozco-Caballero Alberto
Published: December 2018

Recent Al7075 severe friction stir processing (FSP) data gave new insights regarding the relationship among processing, microstructure and high temperature behaviour. Grain boundary sliding, GBS, usually operates with fine, equiaxed and highly misoriented grains although, so far, the variable misorientation is missing from the constitutive equation. A collection of very fine microstructures comprising various grain size and misorientation values is employed to evidence the relative importance of grain size vs misorientation in the superplastic behaviour of the processed alloy. This relationship is included into a new GBS constitutive equation incorporating the average misorientation as a variable.
Orientation Dependence on Fatigue Fracture Behavior of Pure Mg Single Crystals
Authors: Kido Yuta , Nakamura Akinobu , Tsushida Masayuki , Kitahara Hiromoto , Ando Shinji
Published: December 2018

It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σa) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σa =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.
Cube{100}<001> Grains Nucleation during Annealing of S-Oriented Aluminum Single Crystal
Authors: Miszczyk Magdalena M. , Paul Henryk
Published: December 2018

The crystallographic aspects of nucleation of cube grains during annealing have been analyzed in (234)[20-28 11] - oriented aluminum single crystal. The samples were plane strain compressed in a channel-die up to logarithmic strains of 0.5 (40%) and then annealed to develop initial and final stages of primary recrystallization. The deformed and annealed samples were analyzed using scanning electron microscopy equipped with EBSD facility. Local orientation measurements reveled that significant part of the sample deforms homogeneously with only small deviation from the initial crystal orientation. The heterogeneities were thin bands of localized strain in which the crystal lattice rotate towards another variant of S orientation. After annealing the orientations identified inside deformed/recovered areas were similar to that observed in the sample just after deformation. The crystal lattice of recrystallized grains exhibit a well-defined clockwise and anticlockwise rotations around the axes grouped near all normals of the {111} planes of the deformed/recovered state. The cube grains were observed in both homogeneously and heterogeneously deformed areas despite the cube-oriented nuclei surrounded by high angle boundary were not present in the as-deformed structure.
Critical Conditions of Cold Cracking in High Strength Steel Weld Based on the Local Stress Distribution and Hydrogen Accumulation
Authors: Sato Yuya , Murakami Yoshiaki , Satoshi Igi , Ishikawa Nobuyuki
Published: December 2018

In this study, the occurrence of cold cracking in high strength steel welds were investigated in terms of residual stress and hydrogen diffusion behavior. The y-groove weld cracking test of TS780MPa grade steel plate was conducted with intentionally introducing hydrogen into the shielding gas during the gas-metal arc welding (GMAW). Since local stress is one of the most important factors for the cold cracking, residual stress distribution in the weld joint was measured by the neutron diffraction using TAKUMI in J-PARC. The root region, which is usually the crack initiation site in the y-groove cold cracking test, was under a multi-axial stress state and showed highest tensile residual stress in the transverse direction. It was considered that hydrogen diffusion and accumulation could be enhanced in the high stressed root region, resulting in cold cracking. Therefore, hydrogen diffusion behavior and stress distribution in the y-groove weld joint was investigated by a coupled thermo elastic plastic and hydrogen diffusion analyses. Hydrogen accumulation occurred in the root region where showed highest hydrostatic stress. The point where showed the hydrogen accumulation was well corresponded to the crack initiation site. It was indicated that local hydrogen concentration after welding was another important key factor for the cold cracking. From these investigations, it was essential to take the combination of local hydrogen concentration and residual stress distribution near the root region into account for the highly precise estimation of cold cracking.
The Effect of Oxygen on the Phase Composition and Heat Treatment Behavior of Ti-V Alloys
Authors: Nagasawa Hitomi , Ikeda Masahiko , Ueda Masato
Published: December 2018

Titanium and its alloys possess high specific strength, excellent corrosion resistance and good biocompatibility [1] [2]. Since oxygen is an unavoidable impurity in such materials, it has been adopted as an alloying element in the development of low-cost titanium alloys. Therefore, it is important to investigate the role of oxygen in these alloys, especially in β-type alloys. In the present study, the effects of oxygen on the electrical resistivity, Vickers hardness and heat treatment behavior of a Ti-20mass%V alloy which is the lowest concentration for which the fully retained β phase is obtained were assessed. The electrical resistivity and Vickers hardness of solution-treated and quenched specimens increased with increasing oxygen content, due to the dissolution of oxygen into the β phase and solid solution hardening, respectively. Upon isothermal aging at 673 K, the addition of O accelerated a-phase precipitation. The addition of O was found to suppress the appearance of the athermal ω phase in the solution-treated and quenched state.
Ultrasonic Rheocasting for Refinement of Mg Alloys Reinforced with LPSO Phase
Authors: Lü Shu Lin , Yang Xiong , Hao Liang Yan , Wu Shu Sen
Published: December 2018

In this work, ultrasonic rheocasting was used to refine the microstructures of Mg alloys reinforced with long period stacking ordered (LPSO) phase. The semisolid slurries of Mg-Zn-Y and Mg-Ni-Y alloys were prepared by ultrasonic vibration (UV) and then formed by rheo-squeeze casting under high squeeze pressure (~ 400 MPa). The effects of UV and squeeze pressure on microstructure and mechanical properties of the Mg alloys were studied. The results reveal that UV and rheo-squeeze casting can significantly refine the LPSO structure and alpha-Mg matrix in Mg alloys, but they cannot change the phase compositions of the alloys or the type of LPSO phase. When the squeeze pressure is 400 MPa, the average thickness of LPSO phase is decreased, and the block LPSO structure is completed eliminated and uniformly distributed at the grain boundaries. Compared with the gravity cast alloys without UV, mechanical properties of the rheocast Mg alloys were enhanced and reached the maximums when the squeeze pressure was 400 MPa.