Full Density Research Articles

Twin-wire directed energy deposition-arc of Ti–48Al–2Cr–2Nb alloy: Feasibility, microstructure, and tensile property investigation

Due to low density and good high temperature performance, titanium aluminide has been continuously attractive for aerospace and automotive industries. In recent years, additive manufacturing of titanium aluminide has become a popular research area. The present work has first time fabricated commercial graded TiAl-4822 alloy using an innovative twin-wire directed energy deposition-arc (TW-DED-arc) process, which uses a unique twin-wire feeding method to produce the target alloy in-situ. According to experimental results, TW-DED-arc fabricated TiAl-4822 alloy possesses direct full density, homogeneous chemical composition, uniformed microstructure, and stable mechanical property. Also, the formation mechanism of layered microstructure consisting of alternative columnar and equiaxed grain regions has been investigated in detail. Even under as-fabricated condition, TW-DED-arc fabricated TiAl-4822 performs competitive tensile properties compared to the same alloy produced by casting and other additive manufacturing methods. Generally, successful TW-DED-arc buildup of TiAl-4822 provides a high-efficiency and low-cost route for the further development of titanium aluminide production.

Evaluation of injection molded gas and water atomized 316l stainless steel powder properties

This research investigates the features crucial to injection molding via the rheological behavior, injection molding, debinding, and sintering process of water and gas atomised 316L stainless steel powder utilizing a newly developed locally based binder system containing palm stearin. The critical powder loading for injection molding was 65vol% for gas atomisation and 62vol% for water atomisation. Due to the minimal interparticle friction and high packing density, the gas-atomised powder proved easier to shape. In contrast, the water-atomised powder has a high viscosity of the injection molding feedstock, a high interparticle friction, and a low packing density, all of which impede injection molding. The debinding of the binder was accomplished utilizing solvent and thermal methods. After debinding, samples were sintered in a high-temperature vacuum furnace at 1360 degrees Celsius. Results reveal that water-atomised powder can be sintered to 95% of its theoretical density, whereas gas-atomised powder can be sintered to near full density.

Sintered tungsten heavy alloys: Review of microstructure, strength, densification, and distortion

Tungsten heavy alloys are fabricated using liquid phase sintering to form inertial, electrical, radiation, or structural components. The compositions, initially developed a century ago, are based on various W-Ni-(Fe/Cu/Co/Mo) alloys. Two classes, and W-Ni-Fe and W-Ni-Cu, remain the most popular. Nickel is key to sintering densification, producing the majority of sintering shrinkage prior to liquid formation. Sintering densification and distortion depend on the gravitational environment. Normal gravity induces distortion after densification, while sintering in microgravity fails to reach full density yet distorts. Mechanical properties are adjustable via changes to the composition, sintering cycle, or post-sintering treatment. Increased strength, with a loss of ductility, comes with post-sintering deformation and aging treatments. As shown here, a range of mechanical property combinations are possible. Processing options designed to improve strength invariably result in a loss of ductility, and vice versa. Peak property combinations are attainable over a broad tungsten content range, reflecting convergence to a self-similar microstructure.

Atomic memory based on recoil-induced resonances

In this work, we perform a detailed theoretical and experimental investigation of an atomic memory based on recoil-induced resonance in cold cesium atoms. We consider the interaction of nearly degenerate pump and probe beams with an ensemble of two-level atoms. A full theoretical density matrix calculation in the extended Hilbert space of the internal and external atomic degrees of freedom allows us to obtain, from first principles, the transient and stationary responses determining the probe transmission and the forward four-wave-mixing spectra. These two signals are generated together at the same order of perturbation with respect to the intensities of pump and probe beams. Moreover, we have investigated the storage of optical information on the spatial modes of light beams in the atomic external degrees of freedom, which provided a simple interpretation for the previously reported nonvolatile character of this memory. The retrieved signals after storage reveal the equivalent role of probe transmission and four-wave mixing, as the two signals have similar amplitudes. Probe transmission and forward four-wave-mixing spectra were then experimentally measured for both continuous excitation and after storage. The experimental observations are in good agreement with the developed theory, and they open another pathway for the reversible exchange of optical information with atomic systems.

Density reconstruction in convergent high-energy-density systems using x-ray radiography and Bayesian inference

X-ray radiography is a technique frequently used to diagnose convergent high-energy-density (HED) systems, such as inertial confinement fusion implosion, and provides unique information that is not available through self-emission measurements. We investigate the scope and limits of that information using a radiography simulation combined with the Bayesian inference workflow. The accuracy of density reconstruction from simulated radiographs of spherical implosions driven with 27 kJ laser energy is assessed, including the increase or decrease in accuracy due to the addition of Lagrangian marker layers, Poisson noise, and improved prior information. This work is the first to present the full uncertainty distributions inferred from radiography analysis in HED systems and demonstrates the importance of constructing the full posterior probability density, as opposed to a point estimate, due to the modal structure of the likelihood surface introduced by typical experimental noise sources. This general methodology can be used both for robust analysis of radiographic data and for an improved design of radiography experiments by modeling the full experimental system.

Powder Extrusion Printing and Sintering Densification Behaviors of Ultrafine 98W-1Ni-1Fe Alloy Powder

Powder extrusion printing (PEP) is an attractive fabrication technique for the automated mass production of engineering components with complicated shape and high-dimensional accuracy. This paper is concerned with PEP and sintering densification of ultrafine 98W-1Ni-1Fe powder. Three kinds of binder systems were designed. The influence of binder composition on the rheological behavior of the PEP feedstocks has been investigated. Results showed that all the feedstocks present pseudoplastic flow behavior. Compared with the FS-55 and FS-70 feedstocks, the FS-65 feedstock is more suitable for the PEP of ultrafine 98W-1Ni-1Fe powder due to its better comprehensive rheology and more homogeneous microstructure. The PEPed ultrafine 98W-1Ni-1Fe can be sintered to near full density at 1420 °C, which is much lower than traditional micro-scaled powder. The sintered 98W-1Ni-1Fe shows good mechanical performance due to its fine and uniform microstructure, its tensile strength can reach ~800 MPa, and its grain size is about 15 μm.

Small‐scale equidistribution of Hecke eigenforms at infinity

We investigate the equidistribution of Hecke eigenforms for PSL 2 ( Z ) ${\hbox{PSL}_2({\mathbb {Z}})}$ on sets that are shrinking toward the cusp. We show that at scales finer than the Planck scale they do not equidistribute while at scales more coarse than the Planck scale they equidistribute on a full density subsequence of eigenforms. On a suitable set of test functions we compute the variance showing an interesting transition behavior at half the Planck scale.

Evolution mapping: a new approach to describe matter clustering in the non-linear regime

ABSTRACT We present a new approach to describe statistics of the non-linear matter density field that exploits a degeneracy in the impact of different cosmological parameters on the linear dimensionless matter power spectrum, $\Delta ^2_{\rm L}(k)$. We classify all cosmological parameters into two groups, shape parameters, which determine the shape of $\Delta ^2_{\rm L}(k)$, and evolution parameters, which only affect its amplitude at any given redshift. With this definition, the time evolution of $\Delta ^2_{\rm L}(k)$ in models with identical shape parameters but different evolution parameters can be mapped from one to the other by relabelling the redshifts that correspond to the same clustering amplitude, which we characterize by the linear mass fluctuation in spheres of radius $12\, {\rm Mpc}$, σ12(z). We use N-body simulations to show that the same evolution-mapping relation gives a good description of the non-linear power spectrum, the halo mass function, or the full density field. The deviations from the exact degeneracy are the result of the different structure formation histories experienced by each model to reach the same clustering amplitude and can be accurately described in terms of differences in the suppression factor g(a) = D(a)/a. These relations can be used to drastically reduce the number of parameters required to describe the cosmology dependence of the power spectrum. We show how this can help to speed up the inference of parameter constraints from cosmological observations. We also present a new design of an emulator of the non-linear power spectrum whose predictions can be adapted to an arbitrary choice of evolution parameters and redshift.

Sintering of amorphous calcium phosphate to near-full density by uniaxial compaction at room temperature

Amorphous calcium phosphate is a metastable phase with excellent biocompatibility and resorbability. Despite these characteristics, its use is currently limited to the powder and coating forms; only moderate success has been achieved in its densification, which has prevented its use in the bulk form. Here, we show that amorphous calcium phosphate can be sintered to near full density by simple uniaxial die pressing at 1250–1500 MPa at room temperature. The relative densities of the samples that were compacted at 1250 and 1500 MPa exceeded 95 %. Their specific surface area was more than 1000 times smaller than that of the starting powder and their Vickers hardness exceeded 1.90 GPa. The microstructures of the samples consisted of a grain-like structure with grain sizes below 100 nm. These results could inspire new applications for amorphous calcium phosphate in the form of bulk ceramics.

Selective laser melting of Inconel 601 alloy using nanosecond fibre laser

The paper describes the impact of selective laser melting factors including using a nanosecond fibre laser, including laser powers, scanning speed, and thickness of layer, on the relative density and micro hardness Vickers of IN 601 samples was studied. Selective laser melting (SLM) is a commonly used powder bed fusion metal additive manufacturing (AM). Recent advances in additive manufacturing have attracted significant industrial interest, especially for producing metallic parts. Scanning electron microscopy (SEM), EDX and other techniques were utilized for studying the effect of speed of scanning and power of laser on densification behaviour, microstructural evolution and micro hardness of Inconel v alloy that was processed by SLM. With a VED of 3200 J/mm3, a scan speed of 250 mm/s with a 80 W, micro cracks of about 79-93 µm and voids of about (4.5 µm – 5.7) µm in diameter were realised. Moreover, the best hardness of 394 HV was attained with 80 W laser power. However, increasing the energy to more than the required values increased the porosity and decreased hardness. Using microsecond laser in SLM leads to the achievement of full density (almost 99.5%), whereas using nanosecond laser allows the achievement of less density (75-95%), which will be very useful for functions that require a porous structure and less weight, such as those in the aerospace applications, automotive industry and so on.

Deposition of a Porous Cu Layer by Electroplating and Feasibility Evaluation of Cu-Cu Die Attachment by Sinter Bonding Using Thermo-Compression

A porous Cu layer was deposited on a dummy Cu die and a dummy substrate, respectively, by electroplating to form a bondline that can endure high temperatures, such as 300 ℃. The plating at a current density of 40 mA/cm<sup>2</sup> in a plating solution containing a crystal controlling agent resulted in different porous layers from fine dendritic grains to coarse a typical grains and an increased layer thickness with increasing plating time. Die-attachment sinter bonding at 5 MPa and 300 ℃ in the air by thermo-compression using a 2-min-plated die and substrate after drying a reducing agent absorbed in the layer on a substrate. The boding for 1 min resulted in sufficient bondline shear strength of 26.6 MPa with an excellent microstructure of near full density. Identical bonding with exchanging nitrogen blowing increased the shear strength to 30.3 MPa with significantly reduced oxidation area in the inner edge of the die. The 1- and 3-min samples exhibited lower strength values owing to the local formation of large voids between non-uniform thickness of the deposited layers and the relatively less dense bondline structure, respectively.

Roles of Strong Scalar Couplings in Maximizing Glutamate, Glutamine and Glutathione Pseudo Singlets at 7 Tesla

For the H4 protons of glutamate (Glu), glutamine (Gln), and the glutamyl moiety of glutathione (GSH), the effect of the internal strong scalar coupling between the two nonequivalent H4 protons is far greater than that of the external couplings between the H3 and H4 protons. In this work, the roles of the internal and external scalar coupling terms in the dependence of Glu, Gln, and glutamyl GSH H4 peak amplitudes on the placement of the refocusing pulses of the point resolved spectroscopy sequence were investigated by full density matrix simulations. These strong coupling effects allowed practical and approximately simultaneous maximization of the sensitivity of the spectrally resolved Glu, Gln, and glutamyl GSH H4 pseudo singlets for spatially localized in vivo detection of Glu, Gln, and GSH in the human brain using magnetic resonance spectroscopy at the magnetic field strength of 7 Tesla.

In-situ alloying of Ti-5Fe titanium alloy using direct powder forging and the effect of the powder mixing method

This study investigates direct powder forging (DPF) as a new approach for the consolidation and in-situ alloying of the titanium alloy Ti-5Fe from loose powder. The absence of green compaction before thermomechanical processing and the effect of the powder blending method have been found to significantly influence the chemical and microstructure homogeneity. Two different powder mixing techniques were compared, ball milling (BM) and blended elemental (BE). After the initial heating stage, the BM sample has a uniform α+β lamella microstructure within the particles with a homogeneous iron distribution, unlike the BE sample, which shows a heterogeneous lamella microstructure, retained β-Ti (Fe-rich) and TiFe intermetallic compounds. Even if the BM samples exhibit a slightly higher density over the BE samples after the initial heating stage, all samples achieved full density and had a α+β lamella microstructure after the thermomechanical steps. However, for the BE sample, even if the DPF process was able to eliminate the intermetallic compounds, the thermomechanical process did not homogenize the iron, resulting in a heterogeneous and coarser microstructure. Based on the results, it can be concluded that DPF using a BM technique led to a fully homogenous and fully consolidated Ti-5Fe alloy. Therefore, direct powder forging has significant potential as an alternative fabrication strategy to produce the Ti-5Fe alloy. Moreover, this work can expand the opportunities for the development of the promising Ti-5Fe alloy.

Effect of Zn7Sb2O12 pre-synthesis on microstructure and properties of ZnO varistor ceramics

In this work, the Zn7Sb2O12 spinel phase is pre-synthesized at 980, 1000, 1020, 1040, and 1060 °C by mixing ZnO and Sb2O3 in a molar ratio of 7:1. ZnO varistors are prepared by replacing Sb2O3 with the Zn7Sb2O12 spinel phase. The effect of the Zn7Sb2O12 spinel on the electrical properties and microstructure of ZnO varistors is studied. The results show that Sb2O3 can produce free electrons and reduce the number of oxygen vacancies (VO⋅⋅) and grain size during the reaction process. The ZnO varistors prepared by replacing Sb2O3 with the Zn7Sb2O12 spinel phase have full grain growth and high density. In addition, ZnO varistors prepared by the Zn7Sb2O12 spinel phase replacing Sb2O3 can not only reduce the sintering temperature by 60 °C but also reduce the reverse voltage gradient rate of ZnO varistors from 7.85% to 1.2% on the basis of stable electrical properties and improve the impact stability of ZnO varistors. This method has the advantages of no change in formula composition and being a simple process and can provide ideas for the preparation of multilayer chip ZnO varistors.

Assessment of the Retinal Vessels in Keratoconus: An OCT Angiography Study.

This study investigated vascular density and foveal avascular zone (FAZ) parameters using optical coherence tomography angiography (OCT-A) in patients with keratoconus (KC). Participants with KC and healthy controls were included and underwent best-corrected visual acuity (BCVA), keratometry, anterior segment OCT, and macular OCT-A examinations. Of the 70 subjects (mean age 42.9 ± 15.31 years), 79 KC and 47 healthy eyes were included. Significant reductions in the KC group were recorded for the FAZ area, with a mean (±SD) of 0.19 ± 0.12 vs. 0.25 ± 0.09 mm2 p < 0.001. Central vascular density in KC patients was lower compared with the controls: 6.78 ± 4.74 vs. 8.44 ± 3.33 mm−1 p = 0.049; the inner density was also decreased in the study group (13.64 ± 5.13 vs. 16.54 ± 2.89 mm−1, p = 0.002), along with the outer density (14.71 ± 4.12 vs. 16.88 ± 2.42 mm−1, p = 0.004) and full density (14.25 ± 4.30 vs. 16.57 ± 2.48) p = 0.003. Furthermore, BCVA was positively correlated with central vascular density (R = 0.42 p = 0.004, total R = 0.40, p = 0.006) and inner density (R = 0.44, p = 0.002) in patients with KC but not in controls. Additionally, we found a correlation between K2 and inner vascular density (R = −0.30, p = 0.043) and central epithelium thickness and outer density (R = 0.03, p = 0.046). KC patients had lower macular vascular density and a smaller FAZ than healthy participants. The BCVA in KC patients was correlated with the vascular density.

Analytical framework for non-equilibrium phase transition to Bose–Einstein condensate

The theoretical description of non-equilibrium Bose–Einstein condensate (BEC) is one of the main challenges in modern statistical physics and kinetics. The non-equilibrium nature of BEC makes it impossible to employ the well-established formalism of statistical mechanics. We develop a framework for the analytical description of a non-equilibrium phase transition to BEC that, in contrast to previously developed approaches, takes into account the infinite number of continuously distributed states. We consider the limit of fast thermalization and obtain an analytical expression for the full density matrix of a non-equilibrium ideal BEC which also covers the equilibrium case. For the particular cases of 2D and 3D, we investigate the non-equilibrium formation of BEC by finding the temperature dependence of the ground state occupation and second-order coherence function. We show that for a given pumping rate, the macroscopic occupation of the ground state and buildup of coherence may occur at different temperatures. Moreover, the buildup of coherence strongly depends on the pumping scheme. We also investigate the condensate linewidth and show that the Schawlow–Townes law holds for BEC in 3D and does not hold for BEC in 2D.

Production of Dense Cu-10Sn Part by Laser Powder Bed Fusion with Low Surface Roughness and High Dimensional Accuracy.

Tin-bronze alloys with a tin content of at least 10 wt% have excellent mechanical properties, wear resistance, and corrosion resistance. Among these alloys, Cu-10Sn was investigated in this study for production with the laser powder bed fusion process with a 500W Yb:YAG laser. In particular, a design of experiment (DoE) was developed in order to identify the optimal process parameters to obtain full density, low surface roughness, and high dimensional accuracy. Samples were characterized with Archimedes’ method and optical microscopy to determine their final density. It was shown that the first method is fast but not as reliable as the second one. A first mechanical characterization was performed through microhardness tests. Finally, a set of process parameters was identified to produce fully dense samples with low surface roughness and high accuracy. The results showed that the volumetric energy density could represent an approach that is too simplified, therefore limiting the direct correlation with the physical aspects of the process.

A Description Logic Based Ontology for Knowledge Representation in Process Planning for Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) provides a rapid and cost-effective solution for fabricating metallic parts with near full density and high precision, strength, and stiffness directly from metallic powders. In LPBF, process variables are widely recognised as fundamental factors that have important effect on the quality of the built parts. However, activity of designing process variables for LPBF, i.e., process planning for LPBF, still heavily depends on knowledge from domain experts. This necessitates a knowledge base that enables the capture, representation, inference, and reuse of existing knowledge. In this paper, a description logic (DL) based ontology for knowledge representation in process planning for LPBF is presented. Firstly, a set of top-level DL entities and specific DL entities and semantic web rule language (SWRL) rules for part orientation, support generation, model slicing, and path planning are created to construct the ontology. The application of the ontology is then illustrated via process planning on an LPBF part. Finally, the benefits of the ontology are demonstrated through a few examples. The demonstration results show that the ontology has rigorous computer-interpretable semantics, which provides a semantic enrichment model for LPBF process planning knowledge and enables automatic consistency checking of the ontology, knowledge reasoning on the ontology, and semantic query from the ontology. This would lay solid foundation for development of a process planning tool with autonomous decision-making capability.

Impact of bias nonstationarity on the performance of uni- and multivariate bias-adjusting methods: a case study on data from Uccle, Belgium

Abstract. Climate change is one of the biggest challenges currently faced by society, with an impact on many systems, such as the hydrological cycle. To assess this impact in a local context, regional climate model (RCM) simulations are often used as input for rainfall-runoff models. However, RCM results are still biased with respect to the observations. Many methods have been developed to adjust these biases, but only during the last few years, methods to adjust biases that account for the correlation between the variables have been proposed. This correlation adjustment is especially important for compound event impact analysis. As an illustration, a hydrological impact assessment exercise is used here, as hydrological models often need multiple locally unbiased input variables to ensure an unbiased output. However, it has been suggested that multivariate bias-adjusting methods may perform poorly under climate change conditions because of bias nonstationarity. In this study, two univariate and four multivariate bias-adjusting methods are compared with respect to their performance under climate change conditions. To this end, a case study is performed using data from the Royal Meteorological Institute of Belgium, located in Uccle. The methods are calibrated in the late 20th century (1970–1989) and validated in the early 21st century (1998–2017), in which the effect of climate change is already visible. The variables adjusted are precipitation, evaporation and temperature, of which the former two are used as input for a rainfall-runoff model, to allow for the validation of the methods on discharge. Although not used for discharge modeling, temperature is a commonly adjusted variable in both uni- and multivariate settings and we therefore also included this variable. The methods are evaluated using indices based on the adjusted variables, the temporal structure, and the multivariate correlation. The Perkins skill score is used to evaluate the full probability density function (PDF). The results show a clear impact of nonstationarity on the bias adjustment. However, the impact varies depending on season and variable: the impact is most visible for precipitation in winter and summer. All methods respond similarly to the bias nonstationarity, with increased biases after adjustment in the validation period in comparison with the calibration period. This should be accounted for in impact models: incorrectly adjusted inputs or forcings will lead to predicted discharges that are biased as well.

Generalized pole figures from post-processing whole Debye-Scherrer patterns for microstructural analysis on deformed materials.

Debye-Scherrer patterns, obtained from X-ray diffraction experiments using synchrotron light in transmission geometry, were analysed to construct generalized pole figures, and further used as input for an orientation distribution function inversion algorithm. By using Langford's method for separating strain and size contributions to peak broadening, it was possible, for the first time, to obtain full domain size and dislocation density generalized distribution functions (GDFs). This method was applied to cold-rolled and annealed interstitial-free steel. The predictions made using GDFs were corroborated by electron backscatter diffraction measurements and were also consistent with what was previously known for this kind of material under these conditions.