Excess Energy Density Research Articles

Mechanical Properties and Interfacial Characterization of Additive-Manufactured CuZrCr/CoCrMo Multi-Metals Fabricated by Powder Bed Fusion Using Pulsed Wave Laser.

In this study, CoCrMo cuboid samples were deposited on a CuZrCr substrate using laser powder bed fusion (L-PBF) technology to investigate the influence of process parameters and laser remelting strategies on the mechanical properties and interface characteristics of multi-metals. This study found that process parameters and laser scanning strategies had a significant influence on the mechanical properties and interface characteristics. Samples fabricated with an EV ≤ 20 J/mm3 showed little tensile ductility. As the volumetric energy density (EV) increased to a range between 40 J/mm3 and 100 J/mm3, the samples achieved the desired mechanical properties, with a strong interface combining the alloys. However, an excessive energy density could result in cracks due to thermal stress. Laser remelting significantly improved the interface properties, especially when the EV was below 40 J/mm3. Variances in the EV showed little influence on the hardness at the CuZrCr end, while the hardness at the interface and the CoCrMo end showed an increasing and decreasing trend with an increase in the EV, respectively. Interface characterization showed that when the EV was greater than 43 J/mm3, the main defects in the L-PBF CoCrMo samples were thermal cracks, which gradually changed to pores with a lack of fusion when the EV decreased. This study provides theoretical and technical support for the manufacturing of multi-metal parts using L-PBF technology.

Effect of processing parameters on the defects, microstructure, and property evaluation of Ti-6Al-4V titanium alloy processed by laser powder bed fusion

In this study, we designed the processing windows for laser powder bed fusion (LPBF) of Ti-6Al-4V (Ti-64) alloy by using central composite design and made a detailed investigation into the influence of processing parameters on the defects. The purpose is to investigate the effect of defects on mechanical properties. It was found that insufficient energy density could lead to the formation of lack of fusion (LOF) defects and produce non-melted powders on the surface, while excessive energy density could lead to cracks that were detrimental to mechanical performance. In addition, the microstructural evaluation found that relatively low energy density could lead to shorter columnar prior-β grains, while prior-β grains in the sample processed by the high energy density extended almost the entire height of the cross-section, which could lead to the strong mechanical property anisotropy. The prior β grains are formed by heterogeneous nucleation on the partially melted material powder. As the energy input increases, all the powder powders in the molten pool can be melted so that these particles do not act as nucleation sites and the prior β grain can grow through more layers without forming new grains being able to nucleate. The prior β-grain in as-built Ti-64 samples consisted of acicular α’ martensite with myriads of lattice distortions, as a precursor to a phase transition, which lead to strong tensile strength and poor ductility. Annealing heat treatment promoted the improvement of the ductile performance of LPBF Ti-64. Overall, this study provides comprehensive views on the effects of processing parameters (laser power, scanning speed, and hatch distance) on the internal (pores and LOF) and external (unmelted powder, sintering neck, and crack), defects, microstructure, and tensile property evaluation of LPBF Ti-64, which offer insights for the development of additive manufactured titanium alloys with excellent mechanical property.

Microstructure and Mechanical Properties of Cermet Composite Coating on TC4 Surface

In order to improve the surface quality and performance of TC4, the TC4-HfC-TaC metal-ceramic composite cladding coating was prepared on the surface of TC4 by using different process parameters by laser cladding technology. Through digital testing equipment, the macro morphology, molten pool size, dilution rate, Rockwell hardness (HRC), geometry, microstructure and other comprehensive properties of the coating are studied and analyzed. The results show that the performance characterization of TC4-HfC-TaC cladding layer is closely related to the melting state of refractory carbide ceramic phase HfC and TaC powder, when the laser beam energy density is not enough to completely melt the ceramic phase powder, with the increase of energy density, the coating surface tends to be flat, the molten pool size and dilution rate increase, the hardness gradually increases, the metallographic structure is refined uniformly, and the surface quality is improved. Excessive energy density of the laser beam can easily lead to excessive dilution rate of the cladding layer, reduced coating hardness, coarse metallographic structure, and reduced surface quality. Finally, the best combination of process parameters was screened out: laser power 3000 W, scanning speed 300 mm/min, spot size 2.5 × 11.5 mm, rectangular spot lap rate 40%, preset powder thickness 1.5 mm, at which time the coating hardness increased to 63.22 HRC. It is about 2.1 times the hardness of TC4 substrate, with the best performance, and the metallographic structure is densely arranged fine cell-like crystals, with outstanding microscopic characteristics, which realizes the purpose of preparing high-quality TC4-HfC-TaC cermet composite cladding coating on the surface of TC4 titanium alloy.

Potential reductions in ultra-processed food consumption substantially improve population cardiometabolic-related dietary nutrient profiles in eight countries

Background and aimsThe negative effect on dietary nutrient profiles is the most obvious mechanism explaining the higher risk of cardiometabolic diseases associated with increased dietary share of UPF observed in large cohort studies.We estimate the proportion of diets with excessive energy density, excessive free sugars or saturated fat contents and insufficient fiber that could be avoided, if UPF consumption was reduced to levels among lowest consumers across eight countries, as well as the proportion of diets with multiple inadequacies. Methods and resultsUsing nationally-representative cross-sectional surveys from Brazil (2008–09), Chile (2010), Colombia (2005), Mexico (2012), Australia (2011–12), the UK (2008–16), Canada (2015), and the US (2015–16), inadequate energy density (≥2.25 kcal/g) or contents of free sugars (>10% of total energy intake), saturated fats (>10% of total energy intake) and fiber (<25 g/2000 kcal) population attributable fractions were quantified.Substantial reductions in nutrient inadequacies would be observed ranging from 50.4% in Chile to 76.8% in US for dietary energy density, from 15.5% in Colombia to 68.4% in Australia for free sugars, from 9.5% in Canada to 35.0% in Mexico for saturated fats, and from 10.3% in UK to 37.9% in Mexico for fiber. Higher reductions would be observed for diets with multiple nutrient inadequacies: from 27.3% in UK to 77.7% in Australia for ≥3 and from 69.4% in Canada to 92.1% in US, for 4 inadequacies. ConclusionsLowering dietary contribution of UPF to levels among country-specific lowest consumers is a way to improve population cardiometabolic-related dietary nutrient profiles.

Melt pool feature analysis using a high-speed coaxial monitoring system for laser powder bed fusion of Ti-6Al-4 V grade 23

In laser powder bed fusion (LPBF), defects such as pores or cracks can seriously affect the final part quality and lifetime. Keyhole porosity, being one type of porosity defects in LPBF, results from excessive energy density which may be due to changes in process parameters (namely, laser power and scan speed) and/or result from the part’s geometry and/or hatching strategies. To study the possible occurrence of keyhole pores, experimental work and simulations were carried out for optimum and high volumetric energy density conditions in Ti-6Al-4 V grade 23. By decreasing the scanning speed from 1000 to 500 mm/s for a fixed laser power of 170 W, keyhole porosities are formed and later observed by X-ray computed tomography. Melt pool images are recorded in real-time during the LPBF process by using a high-speed coaxial Near-Infrared (NIR) camera monitoring system. The recorded images are then pre-processed using a set of image processing steps to generate binary images. From the binary images, geometrical features of the melt pool and features that characterize the spatter particle formation and ejection from the melt pool are calculated. The experimental data clearly show spatter patterns in case of keyhole porosity formation at low scan speed. A correlation between number of pores and amount of spatter is observed. Besides the experimental work, a previously developed high fidelity finite volume numerical model was used to simulate the melt pool dynamics with similar process parameters as used during the experiments. Simulation results illustrate and confirm the keyhole porosity formation by decreasing laser scan speed.

Invariant surface elastic properties in FCC metals and their correlation to bulk properties revealed by machine learning methods

We present a combination of machine-learned models that predicts the surface elastic properties of general free surfaces in face-centered cubic (FCC) metals. These models are built by combining a semi-analytical method based on atomistic simulations to calculate surface properties with the artificial neural network (ANN) method or the boosted regression tree (BRT) method. The latter is also used to link bulk properties and surface orientation to surface properties. The surface elastic properties are represented by their invariants considering plane elasticity within a polar method. The resulting models are shown to accurately predict the surface elastic properties of seven pure FCC metals (Cu, Ni, Ag, Au, Al, Pd, Pt). The BRT model reveals the correlations between bulk and corresponding surface properties in terms of invariants, which can be used to guide the design of complex nano-sized particles, wires and films. Finally, by expressing the surface excess energy density as a function of surface elastic invariants, fast predictions of surface energy as a function of in-plane deformations can be made from these model constructs.

Energy considerations for nonlinear equatorial water waves

&lt;p style='text-indent:20px;'&gt;In this article we consider the excess kinetic and potential energies for exact nonlinear equatorial water waves. An investigation of linear waves establishes that the excess kinetic energy density is always negative, whereas the excess potential energy density is always positive, for periodic travelling irrotational water waves in the steady reference frame. For negative wavespeeds, we prove that similar inequalities must also hold for nonlinear wave solutions. Characterisations of the various excess energy densities as integrals along the wave surface profile are also derived.&lt;/p&gt;

On the energy of nonlinear water waves.

This article presents results concerning the excess kinetic and potential energies for exact nonlinear water waves. In particular, it is proven, for periodic travelling irrotational water waves, that the excess kinetic energy density is always negative, whereas the excess potential energy density is always positive, in the steady reference frame. A characterization of the total excess energy density as a weighted mean of the kinetic energy along the wave surface profile is also presented.

Optimization of acoustic parameters for ultrasonic separation of emulsions with different physical properties.

Ultrasound is an emerging and promising method for demulsification, which is highly affected by acoustic parameters and emulsion properties. Herein, a series of microscopic and dehydration experiments are carried out to investigate the parameter optimization of ultrasonic separation. The results show that the optimal acoustic parameters highly depend on the emulsion properties. For low frequency ultrasonic standing waves (USWs), mechanical vibrations not only facilitate droplet collision and coalescence, but also disperse the surfactant absorbed on the interface to decrease the interfacial strength. Therefore, low frequency ultrasound is suitable for separating emulsions with high viscosity and high interfacial strength. Increasing the energy density to produce moderate cavitation can increase demulsification efficiency. However, excessive cavitation results in secondary emulsification. In high frequency USWs, the droplets migrate directionally and form bandings, thereby promoting droplet coalescence. Therefore, high frequency ultrasound is favorable for separating emulsions with low dispersed phase content and small droplet size. Increasing the energy density can accelerate the aggregation of droplets, however, excessive energy density causes acoustic streaming that disturbs the aggregated droplets, resulting in reduced demulsification efficiency. This work presents rules for acoustic parameter optimization, further advancing industrial applications of ultrasonic separation.

Removal characteristics of shop-primer paint by laser energy density in Q-switching fiber laser cleaning

In this study, we performed laser cleaning using a Q-switching fiber laser to remove the shop-primer paint and the oxide layer. An analysis of the surface cleaned by laser was carried out at various energy densities. The results showed that the oxide layer on the steel surface was not removed at a relatively low energy density, whereas the base metal was damaged under excessive energy density. We confirmed that it was essential to select an appropriate energy density for efficiently removing only the paint and the oxide layer without damaging the base metal in laser cleaning.

Effects of Co2 and Nd:YAG Laser Remelting of the Ti6Al4V Alloy on the Surface Quality and Residual Stresses

Abstract The titanium alloys are materials susceptible to tribological wear and the laser treatment can be applied in surface treatment processes to obtain for example higher hardness level. From the other side, it is important to take into consideration, that hardness increase that can be connected with cracks. The aim of this research was to investigate the effects of different lasers and the process parameters on the form and level of residual stresses in the Ti6Al4V alloy, which determine the initiation and propagation of cracking. Two lasers were used, the CO2 and Nd:YAG lasers. The specimens were remelted in liquid nitrogen, water or calm air at different pre-heating temperature. The different laser power and scan rates were applied. The increase in energy density increased the number of cracks, the change of an environment and pre-heating affected alo the surface cracking. The cracks observed after remelting with Nd:YAG laser were longer than those observed after treatment with CO2 laser. The compressive stresses after the CO2 laser treatment, and tensile stresses after treatment with the Nd:YAG laser, were found. The appearance of cracks was attributed to an excessive energy density. The different distribution of heat energy inside and around the laser tracks was discussed as the origin of presence either tensile or compressive stresses in the alloy treated with different lasers.

Quasilocalized excitations induced by long-range interactions in translationally invariant quantum spin chains

We show that long-range ferromagnetic interactions in quantum spin chains can induce spatial quasi-localization of topological magnetic defects, i.e., domain-walls, even in the absence of quenched disorder. By means of matrix-product-states numerical techniques, we study the non-equilibrium evolution of initial states with one or more domain-walls under the effect of a transverse field in variable-range quantum Ising chains. Upon increasing the range of these interactions, we demonstrate the occurrence of a sharp transition characterized by the suppression of spatial diffusion of the magnetic defects during the accessible time scale: the excess energy density remains localized around the initial domain-wall positions, hindering thermalization. This quasi-localization is accurately reproduced by an effective semiclassical model, which elucidates the crucial role that long-range interactions play in this phenomenon. These predictions can be tested in current experiments with trapped ions.

Extreme Energy Density Confined Inside a Transparent Crystal: Status and Perspectives of Solid-Plasma-Solid Transformations

It was demonstrated during the past decade that an ultra-short intense laser pulse tightly-focused deep inside a transparent dielectric generates an energy density in excess of several MJ/cm. Such an energy concentration with extremely high heating and fast quenching rates leads to unusual solid-plasma-solid transformation paths, overcoming kinetic barriers to the formation of previously unknown high-pressure material phases, which are preserved in the surrounding pristine crystal. These results were obtained with a pulse of a Gaussian shape in space and in time. Recently, it has been shown that the Bessel-shaped pulse could transform a much larger amount of material and allegedly create even higher energy density than what was achieved with the Gaussian beam (GB) pulses. Here, we present a succinct review of previous results and discuss the possible routes for achieving higher energy density employing the Bessel beam (BB) pulses and take advantage of their unique properties.

A Computational Study on Porosity Evolution in Parts Produced by Selective Laser Melting

Selective laser melting (SLM) is a powder-bed additive manufacturing process that uses laser to melt powders, layer by layer to generate a functional 3D part. There are many different parameters, such as laser power, scanning speed, and layer thickness, which play a role in determining the quality of the printed part. These parameters contribute to the energy density applied on the powder bed. Defects arise when insufficient or excess energy density is applied. A common defect in these cases is the presence of porosity. This paper studies the formation of porosities when inappropriate energy densities are used. A computational model was developed to simulate the melting and solidification process of SS316L powders in the SLM process. Three different sets of process parameters were used to produce 800-µm-long melt tracks, and the characteristics of the porosities were analyzed. It was found that when low energy density parameters were used, the pores were found to be irregular in shapes and were located near the top surface of the powder bed. However, when high energy density parameters were used, the pores were either elliptical or spherical in shapes and were usually located near the bottom of the keyholes.

Diode area melting single-layer parametric analysis of 316L stainless steel powder

Diode area melting (DAM) is a novel additive manufacturing process that utilises customised architectural arrays of low power laser diode emitters for high speed parallel processing of metallic powdered feedstock. The laser diodes operate at shorter laser wavelengths (808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient energy absorption for specific materials. This investigation presents a parametric analysis of the DAM process, identifying the effect of powder characteristics, laser beam profile, laser power and scan speed on the porosity of a single-layer sample. Also presented is the effect of process energy density on melt pool depth (irradiated thermal energy penetration capable of achieving melting) on 316L stainless steel powder. An analysis of the density and the melt depth fraction of single layers is presented in order to identify the conditions that lead to the fabrication of fully dense DAM parts. Energy densities in excess of 86 J/mm3 were theorised as sufficient to enable processing of fully dense layers.

High-energy continuum generation in an array of thin plates pumped by tunable femtosecond IR pulses

We report the generation of octave-spanning supercontinuum pulses in an arrangement of thin transparent plates pumped by 60 fs infrared pulses tunable from 1.2 to 1.75 $$\upmu \mathrm{m}$$ . We demonstrate that the multiple plate technique allows scaling up the energy of the continuum to the level of hundreds of $$\upmu \mathrm{J}$$ while avoiding optical damage and beam breakup due to multiple filamentation. We investigate the spatial and temporal structures of the continuum by performing XFROG and frequency-resolved angular spectra measurements and confirm that the continuum wave packet is well-behaved in time and space and possesses an estimated spectral energy density in excess of 10 nJ/nm throughout the range, which exceeds that of continua generated in bulk solids by more than two orders of magnitude. Finally, we demonstrate for the first time that the carrier-envelope phase stability of the multi-plate continuum is comparable to that of a continuum generated in a bulk medium.

Energy distribution design on the photovoltaic cell array of the SSPS-OMEGA concept

Solar energy collection and conversion is of great significance to the power transmission of the Space Solar Power Station (SSPS), and has influences on the overall system, technologically and economically. For the proposed SSPS-OMEGA concept, the original conceptual design had non-uniform energy distribution and excessive energy density in local areas, which would cause decreases in its optical and electric performance. Aiming at this point, firstly, this paper evaluates the optical performance of the OMEGA concept via ray trace technique. Secondly, the generatrix geometry design of the photovoltaic (PV) cell array based on Bézier curve is carried out to obtain optimal optical performance available for efficient response to sunrays. After that numerical examples achieve good collection efficiency and suitable energy distribution. Finally, modular construction for the main concentrator and its influence on optical performance are investigated. Moreover, the effect of the orbital motion and tracking error are analyzed to provide reference for the realization of the OMEGA.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures.

Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 108 J cm-3 and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world's largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 × 1019 W cm-2, we demonstrate energy penetration depths of several micrometers, leading to UHED plasmas of that size. Relativistic three-dimensional particle-in-cell simulations, validated by these measurements, predict that irradiation of nanostructures at intensities of >1 × 1022 W cm-2 will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 × 1010 J cm-3, equivalent to a pressure of 0.35 Tbar.

Smooth and fast versus instantaneous quenches in quantum field theory

We examine in detail the relationship between smooth fast quantum quenches, characterized by a time scale $\delta t$, and {\em instantaneous quenches}, within the framework of exactly solvable mass quenches in free scalar field theory. Our earlier studies \cite{dgm1,dgm2} highlighted that the two protocols remain distinct in the limit $\delta t \rightarrow 0$ because of the relation of the quench rate to the UV cut-off, i.e., $1/\delta t\ll\Lambda$ always holds in the fast smooth quenches while $1/\delta t\sim\Lambda$ for instantaneous quenches. Here we study UV finite quantities like correlators at finite spatial distances and the excess energy produced above the final ground state energy. We show that at late times and large distances (compared to the quench time scale) the smooth quench correlator approaches that for the instantaneous quench. At early times, we find that for small spatial separation and small $\delta t$, the correlator scales universally with $\delta t$, exactly as in the scaling of renormalized one point functions found in earlier work. At larger separation, the dependence on $\delta t$ drops out. The excess energy density is finite (for finite $m\delta t$) and scales in a universal fashion for all $d$. However, the scaling behaviour produces a divergent result in the limit $m\delta t \rightarrow 0$ for $d\ge4$, just as in an instantaneous quench, where it is UV divergent for $d \geq 4$. We argue that similar results hold for arbitrary interacting theories: the excess energy density produced is expected to diverge for scaling dimensions $\Delta > d/2$.

Packaging Design and Assembly for Ultrahigh Energy Density Microbatteries

For commercially available lithium ion batteries, the package structures can account for as much as 70% of its volume. In a multiyear effort, we have developed designs, fabrications, and assembly processes for ultrahigh energy density microbatteries of 5 and 1 mm3. Over the course of the research, the packaging system evolved due to changes or limitation specific to the battery system itself. During the study, improvements in the construction of the housing for the cathodes were made. Anodized aluminum cans fabricated through our in-house micromachining facility replaced the electroformed gold cans used in earlier experiments. Throughout the iteration of the can design, a flange around its open end, which would be used for sealing, was present, and both designs were fabricated as arrays. The ability to fabricate the housings in an array format lends it to be implemented into a scalable production assembly process. Materials evaluated for the cover ranged from copper foil to the final design of metalized sapphire with a plated through via. One area which needed to be addressed was reducing the temperature of the assembly process due to a change in the cell materials. This resulted in developing a low-temperature hermetic sealing process. The seal between the cover and can was made using a novel composite ring of indium and epoxy. The indium provided the hermeticity needed for the battery chemistry and the epoxy provided mechanical robustness. Most of our experience was with sealing temperatures of 100°C, but the sealing temperature is only limited by the cure temperature of the epoxy. One experiment was conducted to look at the reliability of the seal. A dozen 1-mm3 cells were filled with lithium and sealed. They were aged in laboratory ambient environment and periodically weighed. There was no weight gain in any of the cells over the course of several months, but one cell that was opened at the end of the experiment rapidly gained weight as the lithium corroded. The microbattery cell developed in this program used a lithium cobalt oxide cathode in the form of a porous sintered compact. Its bottom surface was coated with a gold film so that it could be thermocompression bonded to a gold bump on the bottom of the can. Following bonding, the cathode assembly was spray coated with a polymer separator. The anode was a piece of lithium metal bonded to the battery cover. After the cover was sealed to the battery can, the cell was filled with electrolyte and charged. Then a plug was inserted in the via through the cover to seal the battery. Batteries assembled in this manner exhibited energy densities in excess of 200 Wh/L for the smaller volumetric package.