Melting Experiments Research Articles

Testing solution models for phase equilibrium (forward) modeling of partial melting experiments

This study compares four sets of solution (or activity-composition) models using two internally consistent thermodynamic datasets for calculating isochemical phase diagram sections of six partial melting experiments covering a wide range of metasedimentary bulk compositions. Compared parameters are: (1) biotite-breakdown temperatures; (2) parageneses of Fe–Mg phases and Ti-oxides; (3) proportion of biotite, garnet, liquid and plagioclase; (4) Mg# of biotite, garnet and liquid and the anorthite content of plagioclase. Results reveal significant differences between sets that are mainly related to the construction of the biotite solution, with the model of Tajcmanova et al. (2009) yielding better results for the majority of investigated parameters. Owing to the success of the investigated set of solution models at reproducing the proxy that constitutes partial melting experiments, but also at reproducing natural observations as published elsewhere, it is suggested that this biotite model should be used in the Ti–Mn–Na–Ca–K–Fe–Mg–Al–Si–H–O system for phase equilibrium (forward) modeling of metasediments.

Mechanism of rapid compression-induced melt crystallization in selenium

Amorphous selenium (Se) can be easily prepared by quenching the melt, which indicates that the Se possesses the good glass-forming ability. However, crystallization occurs after rapidly compressing the melt within about 20 ms. In this work, we investigate the mechanism of rapid compression-induced crystallization from Se melt. Compressing Se melt experiments are carried out at the following temperatures: 513, 523 and 533 K. The melt is rapidly compressed under 2.4 GPa for about 20 ms. Different holding times, i.e. 0, 30, 60 min after solidification are adopted. The samples are quenched to room temperature and then unloaded to ambient pressure. The X-ray diffraction analysis of the recovered sample indicates that the crystallization product is the <i>t</i>-Se. It is found that with the prolongation of holding time, the grain size increases due to the continuous aggregation growth of crystal grains. By comparing with the isothermal crystallization products of amorphous Se and ultrafine Se powder, it is suggested that the rapid compression-induced solidification product should be <i>t</i>-Se crystalline. The speculation that the solidification product is amorphous Se and it crystallizes in the cooling process does not hold true. The amorphous Se cannot be prepared through the rapid compression process on a millisecond scale. It is related to the thermal stability of amorphous Se under high pressure. It is reported that the dependence of crystallization temperature <i>T</i><sub>x</sub> on pressure i.e. d<i>T</i><sub>x</sub>/d<i>P</i> for amorphous Se is about 40–50 K/GPa in a range of 0.1 MPa–1 GPa. However, the <i>T</i><sub>x</sub> of amorphous Se is almost constant in a range of 2–6 GPa. It means that the thermal stability of amorphous Se against crystallization does not increase with increasing pressure after 2 GPa. In this work, the temperature of 513–533 K in the experiments is higher than the <i>T</i><sub>x</sub> of amorphous Se. Therefore, the<i> t</i>-Se crystal is the stable phase and amorphous Se is unstable. The Se melt tends to crystallize in the supercooled liquid state after rapid compression. It is interesting to investigate the mechanism of d<i>T</i><sub>x</sub>/d<i>P</i> curve discontinuous change at around 2 GPa in the future. Both the Se melt after rapid compression and the amorphous Se before crystallization are in supercooled liquid state. We speculate that high pressure may result in the microstructure transition in supercooled liquid state Se.

SYBR Green I promotes melamine binding to poly-thymine DNA and FRET-based ratiometric sensing.

Melamine binding to polythymine (poly-T) DNA has been widely used to develop biosensors for the detection of melamine. In this work, SYBR Green I (SGI) was used to stain the binding reaction, and using DNA melting experiments, it was confirmed that poly-T DNA formed intramolecular binding complexes to bind multiple melamine molecules. In addition, while this system was insensitive to ionic strength, longer DNA and lower pH favored the binding of melamine. A fluorescence resonance energy transfer (FRET) sensor was designed by labeling a TAMRA and a Cy5 fluorophore on the two ends of T30 DNA, respectively. In the presence of SGI, FRET-based ratiometric detection was achieved with an apparent Kd of 85 μM and a limit of detection of 10.7 μM melamine. Without SGI, the sensitivity of detection was decreased by 47-fold. Interference from Hg2+ can be masked by adding EDTA. Detection of melamine in milk was achieved with recovery rates from 87.0 to 101.7%. This study has provided both basic biochemical insights and a ratiometric sensor for highly sensitive and robust detection of melamine.

First principle calculations and low cost SLM processing of Ti–TiB composite materials

Abstract In order to obtain low cost, high-performance titanium matrix composite materials, first principle calculations and selective laser melting (SLM) experiments were conducted. Firstly, the properties of several typical reinforcements were compared by first principle calculations method, TiB was chosen as the ideal reinforcement. Secondly, the equilibrium lattice constants, mechanical properties and electronic structure of the titanium matrix and TiB reinforcement were calculated for estimating the properties of the composite materials. Calculation results show that both the elastic constants of Ti and TiB satisfy the mechanical stability conditions, and the bulk modulus, shear modulus, Young's modulus and hardness of TiB are all higher than those of Ti, which meets the reinforcing requirements. On this basis, SLM experiments were conducted to verify the calculations. Low cost, irregularly shaped hydrogenation-dehydrogenation titanium (HDH-Ti) and TiB2 powders were ball milled as the raw materials and printed. Microstructure and mechanical properties of the SLMed Ti–TiB composite materials with different addition content of TiB2 were analyzed, and the associated strengthening mechanism was discussed in detail.

Synthesis and properties of oligonucleotides bearing thymidine derivatives with 1,6-dioxaspiro[4.5]decane skeleton

Thymidine derivatives bearing spiroacetal moieties on the C4ʹ-position (5ʹR-spiro-thymidine and 5ʹS-spiro-thymidine) were synthesized and incorporated into oligonucleotides. The duplex- and triplex-forming abilities of both the oligonucleotides were evaluated from UV melting experiments. Oligonucleotides with the 5ʹS-spiro modifications could form thermally stable duplexes with complementary RNA and DNA; however, the 5ʹR-spiro modification significantly decreased the thermal stabilities of the duplexes and triplexes. Oligonucleotides with these spiro-thymidines showed significantly high resistance towards enzymatic degradation.

Predominantly recycled carbon in Earth's upper mantle revealed by He-CO2-Ba systematics in ultradepleted ocean ridge basalts

Basalts erupted within intra-transform spreading centers can be valuable probes of geochemical components in Earth's upper mantle, and provide constraints on the proportions of mantle carbon that are juvenile (primordial) vs. tectonically recycled. Here we present new results for submarine basalt glasses, erupted within the Garrett Transform Fault (GTF) and to its north and south along the East Pacific Rise (EPR). Analyses of 3He/4He, and He and CO2 concentrations in vesicles and glass were performed, through a series of crushing and melting experiments plus FTIR spectroscopy. Trace elements were analyzed by laser ablation ICP-MS.The GTF basalts provide further tests for the origin of volatile-undersaturated basalts using CO2/Ba and CO2/Nb systematics. CO2 is highly correlated with Ba and Nb in basalts erupted in the transform domain (n = 13, including 5 undersaturated basalts) and does not show the variability expected from mixing between undegassed and variably degassed melts. Rather, the melts appear to originate from a heterogeneous mantle source that was variably depleted through partial melting, and limited mixing of melts is involved in their generation. The CO2/Ba and CO2/Nb weight ratios of 106 ± 8 and 308 ± 27, respectively, are similar to values determined previously for a global suite of undersaturated mid-ocean ridge basalts (MORBs).The ridge and transform domains have distinct 3He/4He ratios. Along the nearby EPR, 3He/4He = 8.5 - 9.1 RA, while within the Garrett Transform Fault 3He/4He = 9.2 - 10.1 RA. These two basalt populations are also distinct in their Pb-Sr-Nd isotope compositions based on earlier regional studies. The distinct populations result from partial melting of two different mantle source compositions. Melting of depleted mantle containing a small amount (∼1 to 5%) of enriched, ancient heterogeneities occurs beneath the EPR. Melting of ultradepleted mantle (in which the heterogeneities have been removed by earlier melting beneath the EPR) occurs beneath the GTF. This explains the distinction between intra-transform and spreading ridge domains for 3He/4He, if the heterogeneities were enriched in U, Th and He and had low 3He/4He as would be found in tectonically recycled material. The enriched mantle component sampled by the EPR basalts has molar CO2/3He =2×109, and it dominates the CO2/3He ratio generally ascribed to the upper mantle source for mid-ocean ridge basalts. In contrast, the ultradepleted MORB mantle component sampled by the GTF basalts has CO2/3He =3×108 or less. This indicates that most of the carbon in Earth's upper mantle originates from tectonic recycling.

Solute trapping in rapid solidification

Abstract

Sulfide partial melting and galena–tetrahedrite intergrowth texture: An experimental study

AbstractGalena–tetrahedrite intergrowth textures have been observed in some quenched run products of melting experiments conducted at 500 and 600°C in the systems ZnS–PbS–FeS–Cu2S–Sb2S3 and ZnS–PbS–FeS–Cu2S–Sb2S3–As2S3, using the evacuated silica-tube method. At 600°C the intergrowth formed an interface between sulfide melt and galena, whereas at 500°C it existed as inclusions partially embedded or completely embedded within tetrahedrite. At 600°C tetrahedrite was absent in PbS-bearing experiments, instead galena and melt were a part of the equilibrium phase assemblage. From the disposition of the galena–tetrahedrite intergrowths at 500°C it is evident that droplets of galena–tetrahedrite melt coexisted with tetrahedrite or tetrahedrite + galena and gave rise to these intergrowths upon quenching. The intergrowths coexisting with galena probably represent compositions on the galena-rich liquidus in the galena–tetrahedrite binary and those coexisting with tetrahedrite represent points on the tetrahedrite-rich liquidus. A eutectic at galena:tetrahedrite = ~30:70, very close to 500°C is apparent. It is clearly indicated that galena–tetrahedrite intergrowths can be formed by sulfide partial melting, and could be used as a potential indicator of partial melting in metamorphosed sulfide ore deposits.

Biophysical insights into the interaction of two enantiomers of Ru(II) complex [Ru(bpy)2(7-CH3-dppz)]2+ with the RNA poly(U-A⁎U) triplex.

To determine the factors affecting the stabilization of RNA triple-stranded structure by chiral Ru(II) polypyridyl complexes, a new pair of enantiomers, ∆-[Ru(bpy)2(7-CH3-dppz)]2+ (∆-1; bpy = 2,2'-bipyridine, 7-CH3-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) and Λ-[Ru(bpy)2(7-CH3-dppz)]2+ (Λ-1), have been synthesized and characterized in this work. Binding properties of the two enantiomers with the RNA poly(U-A⁎U) triplex (where "-" denotes the Watson - Crick base pairing and "⁎" denotes the Hoogsteen base pairing) have been studied by spectroscopy and hydrodynamics methods. Under the conditions used in this study, changes in absorption spectra of the two enantiomers are not very different from each other when bound to the triplex, although the binding affinity of ∆-1 is higher than that of Λ-1. Fluorescence titrations and viscosity experiments give convincing evidence for a true intercalative binding of enantiomers with the triplex. However, melting experiments indicated that the two enantiomers selectively stabilized the triplex. The enantiomer ∆-1 stabilize the template duplex and third-strand of the triplex, while it's more effective for stabilization of the template duplex. In stark contrast to ∆-1, Λ-1 stabilizes the triplex without any effect on the third-strand stabilization, suggesting this one extremely prefers to stabilize the template duplex rather than third-strand. Besides, the triplex stabilization effect of ∆-1 is more marked in comparison with that of Λ-1. The obtained results suggest that substituent effects and chiralities of Ru(II) polypyridyl complexes play important roles in the triplex stabilization. Complexes Λ/Δ-[Ru(bpy)2(7-CH3-dppz)]2+ (Λ/Δ-1; bpy = 2,2'-bipyridine, 7-CH3-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) were prepared as stabilizers for poly(U-A ∗ U) triplex. Results suggest the triplex stabilization depends the chiral structures of Λ/Δ-1, indicating that [Ru(bpy)2(7-CH3-dppz)]2+ is a non-specific intercalator for poly(U-A ∗ U) investigated in this work.

Effects of the powder, laser parameters and surface conditions on the molten pool formation in the selective laser melting of IN718

Abstract A series of single-track selective laser melting (SLM) experiments was carried out on IN718 plates with and without a powder layer and with different laser processing parameters (power and scan velocity) and surface conditions (original surface and sand blasted surface). The impacts of the powder, laser parameters, and surface conditions on the molten pool (MP) formation in SLM were systematically investigated through characterizations of the geometry of the resolidified MP, including width, depth, and area. Clear-cut correlations between the dimensions of the MP and the parameters were deduced from the measured data, such as between width/depth of the MP and the power of the laser beam, or between the area of the MP and the laser energy density. We also show that without a powder layer, an increased roughness of the surface consistently increases the MP cross-section area, whereas it has no impact for the cases with powder layer. Finally, the occurrence of defects, such as insufficient melting, unstable MP, and porosities/keyhole effect, is investigated and linked to the SLM parameters. We propose a processing map that defines the range of laser velocity and power for a defect-free solidification of the MP and the occurrence of the different types of defects.

A phenolic hydroxyl in the ortho- and meta-positions on the main ligands effect on the interactions of [Ru(phen)2(o-HPIP)]2+ and [Ru(phen)2(m-HPIP)]2+ with the poly(U)·poly(A)*poly(U) triplex

The association of two ruthenium(II) complexes [Ru(phen)2(o-HPIP)]2+ (Ru1; phen = 1,10–phenanthroline, o-HPIP = 2-(2-hydroxyphenyl)-imidazo[4,5-f][1,10] phenanthroline) and [Ru(phen)2(m-HPIP)]2+ (Ru2; m-HPIP = 2-(3-hydroxyphenyl)–imidazo[4,5-f][1,10]phenan-throline) with the RNA poly(U)·poly(A)⁎poly(U) triplex has been investigated by spectrophotometric titrations and melting experiments in this work. All experimental data reveal an intercalative triplex-binding mode of the two complexes, whereas the binding constant for Ru1 is significantly higher than that for Ru2. Circular dichroism spectroscopic investigations show that the two complexes could bind to the chiral environment of the triplex, but the triplex perturbation effects induced by Ru1 are more marked. Thermal denaturation experiments demonstrate that both Ru1 and Ru2 display a large binding preference and stabilizing effect for the third strand over the Watson–Crick base-paired duplex of the triplex. However, the third-strand stabilizing effect of Ru1 is much more effective than that of Ru2. The obtained results suggest that positions of the phenolic group on the main ligands have significant effect on the binding of the two complexes with poly(U)·poly(A)⁎poly(U) triplex

Sensitivity of Thermal Predictions to Uncertain Surface Tension Data in Laser Additive Manufacturing

Abstract To understand the process-microstructure relationships in additive manufacturing (AM), it is necessary to predict the solidification characteristics in the melt pool. This study investigates the influence of Marangoni driven fluid flow on the predicted melt pool geometry and solidification conditions using a continuum finite volume model. A calibrated laser absorptivity was determined by comparing the model predictions (neglecting fluid flow) against melt pool dimensions obtained from single laser melt experiments on a nickel super alloy 625 (IN625) plate. Using this calibrated efficiency, predicted melt pool geometries agree well with experiments across a range of process conditions. When fluid mechanics is considered, a surface tension gradient recommended for IN625 tends to overpredict the influence of convective heat transfer, but the use of an intermediate value reported from experimental measurements of a similar nickel super alloy produces excellent experimental agreement. Despite its significant effect on the melt pool geometry predictions, fluid flow was found to have a small effect on the predicted solidification conditions compared to processing conditions. This result suggests that under certain circumstances, a model only considering conductive heat transfer is sufficient for approximating process-microstructure relationships in laser AM. Extending the model to multiple laser passes further showed that fluid flow also has a small effect on the solidification conditions compared to the transient variations in the process. Limitations of the current model and areas of improvement, including uncertainties associated with the phenomenological model inputs are discussed.

Identification of Phase Fraction–Temperature Curves from Heat Capacity Data for Numerical Modeling of Heat Transfer in Commercial Paraffin Waxes

The area-proportional baseline method generates phase fraction–temperature curves from heat capacity data of phase change materials. The curves describe the continuous conversion from solid to liquid over an extended temperature range. They are consistent with the apparent heat capacity and enthalpy modeling approach for the numerical solution of heat transfer problems. However, the curves are non-smooth, discrete signals. They are affected by noise in the heat capacity data and should not be used as input to continuous simulation models. This contribution proposes an alternative method based on spline approximation for the generation of consistent and smooth phase fraction–temperature, apparent heat capacity–temperature and enthalpy–temperature curves. Applications are presented for two commercial paraffins from Rubitherm GmbH considering heat capacity data from Differential Scanning Calorimetry and 3-layer-calorimetry. Apparent heat capacity models are validated for melting experiments using a compact heat exchanger. The best fitting models and the most efficient numerical solutions are obtained for heat capacity data from 3-layer-calorimetry using the proposed spline approximation method. Because of these promising results, the method is applied to melting data of all 44 Rubitherm paraffins. The computer code of the corresponding phase transition models is provided in the Supplementary Information.

Partial Melting of the Lower Oceanic Crust: Implications for Tracing the Slab Component in the Source of Mid‐Ocean Ridge Basalts

AbstractThe potential role of the lower oceanic crust in the source region of mid‐ocean ridge basalts has been examined by a series of partial melting experiments on three natural pyroxenite xenoliths entrained in alkali basalts well representing the lower oceanic crustal material at 1 GPa, 1100–1300°C. Layered experiments were also performed to simulate the reaction between lower oceanic crust‐derived melts and surrounding dunite and have successfully enabled the melt infiltration. Melt compositions are consistently basaltic and vary significantly as a function of melt fraction, and these lower oceanic crust‐derived melts are characterized by high Eu/Eu*, Nb/Ta, and Ba/Th values, especially for experiments conducted at 1300°C. No reaction zone is observed in layered experiments, and our results demonstrate that the compositional variations caused by the reaction with dunitic mantle in the lower oceanic crust‐derived melts are relatively minor at 1 GPa. Our melting experiments show that melting of the lower oceanic crust can provide trace element characteristics such as positive Sr and Eu anomalies and consistent Nb/Ta and Zr/Hf ratios, but it cannot account for the wide major element compositional variations (e.g., high FeOT and TiO2 contents) in mid‐ocean ridge basalt (MORB). Some component other than the surrounding dunite in the upwelling mantle flux is needed to substantially modify the major element compositions of the lower oceanic crust‐derived melts. It is quite likely that these lower oceanic crust‐derived melts could be extracted from the upwelling mantle while still preserving their trace element and isotopic imprintings.

The Role of Blueschist Stored in Shallow Lithosphere in the Generation of Postcollisional Orogenic Magmas

AbstractIn regions with small ocean plates and continental blocks, such as the Mediterranean in the Cenozoic and modern Indonesia, many blueschists may be stored at shallow depth in the mantle lithosphere that is newly formed during the amalgamation of small continental blocks and oceans. Melting of these blueschists at low pressures in the mixed lithosphere of this type during postcollisional relaxation may be involved in the generation of postcollisional orogenic magmas. Here, we have conducted a series of melting experiments on three blueschist samples with differing protoliths at 800–850°C, 2 GPa to investigate phase relations, mineral compositions, and trace element partitioning (using laser ablation‐inductively coupled plasma‐mass spectrometry [LA‐ICP‐MS]/nanoscale secondary ion mass spectrometry [NanoSIMS]), including the first results for clinozoisite. Dacitic/rhyolitic melts (SiO2 60 to 66 wt%) containing ~13 wt% volatiles are produced in all runs. Mn‐rich and Mn‐poor almandine garnets exhibit distinct rare earth element (REE) distribution patterns, while Mn‐rich garnets are effective preconcentrators of heavy REEs (HREEs) for later metamorphic processes. Melts produced from fluid‐affected blueschists of terrigenous origin show the most large‐ion lithophile element (LILE) enrichment, whereas those from terrigenous blueschists with no fluid history exhibit the lowest K/Th and Ba/Th and strongest Ce/Pb and Nb/U fractionations. Melts of blueschists derived from mid‐ocean ridge basalt (MORB) have relatively consistent, MORB‐like Ba/Th and Nb/U (~3) but the lowest Ce/Pb ratios (3.3). V/Sc and Zr/Hf ratios remain constant at ≥850°C regardless of the origin of the blueschist. Dehydration melting in new mantle lithosphere where blueschist is stored at shallow depth will significantly affect trace element behavior and should be considered carefully when examining chemical cycling and magmatism in postcollisional orogenic settings.

Nanoparticles and metal foams for heat transfer enhancement of phase change materials: A comparative experimental study

This paper presents an experimental work addressing the low thermal conductivity of phase change materials (PCMs), which is a major challenge associated with PCMs, when used as thermal energy storage solutions. This study experimentally compares the effectiveness of using copper oxide nanoparticles and copper metal foams, together and separately, for improving the performance of a selected PCM (RT44HC) during melting and solidification processes and for different heat transfer configurations. Four samples of pure PCM (as the base case), PCM-nanoparticle, PCM-metal foam, and PCM-nanoparticle-metal foam were tested. Two types of melting experiments were conducted: at constant temperature and with constant heat flux heat sources. The solidification experiments were conducted with a constant temperature heat sink. The results of the experiments showed that, compared to the base case of pure PCM, the heat transfer rate inside the PCM-nanoparticle, PCM-metal foam, and PCM-nanoparticle-metal foam composites increased by, respectively, about 13%, 17%, and 24% during melting with constant temperature heat source, about 24%, 26%, and 65% during solidification with constant temperature heat source, and about 7%, 11%, and 12% during melting with constant heat flux heat source. This study also shed light on some other challenges associated with using PCM as well as the role and the practicality of applying above-mentioned thermal techniques in addressing them.

Investigation of V–N Micro-alloying Using Nitrogen Bottom Blowing

Herein, a novel method of V–N micro-alloying was developed by adding ferrovanadium and nitrogen bottom blowing. For comparison, melting experiments were carried out by directly adding ferrovanadium nitride. Results indicate that nitrogen content increases rapidly and can reach the actual production level via nitrogen bottom blowing. TEM observations show that carbonitrides precipitate along the dislocation line, on the boundary of cementite and ferrite–cementite, and the ferrite grain boundary. Meanwhile, higher the nitrogen content in the steel, more the precipitates and higher dispersion will form, which indicates that addition of ferrovanadium first is better than blowing nitrogen first. Furthermore, the size, distribution and dispersion of carbonitrides obtained via the method of firstly adding ferrovanadium are comparable with that of directly adding ferrovanadium nitride. The results reveal that it is feasible to realize V–N micro-alloying by adding ferrovanadium and nitrogen bottom blowing.

Morphology and phase distributions of molten core in a reactor vessel

Investigations on the morphology and phase equilibrium characteristics of corium were performed by a series of experiments in parallel with thermodynamic phase equilibrium analyses. Melting and solidification experiments were performed using corium consists of U, Zr, ZrO2, SS, and B4C. TROI-49 and TROI-50 experiments with corium compositions representing Pressurized Water Reactor (PWR), whose compositions are similar to those of MA-3 and MA-4 of OECD MASCA (Material Scaling) Program while amount of mass is 5 times more, resulted in two-layered structure with oxide rich layer on top of metal rich layer. Experiments of FK-1 and FK-2 with a mixture of UO2, ZrO2, Zr, SS and B4C at a representative Fukushima Daiichi Nuclear Power Plant (FDNPP) corium composition resulted in a formation two-layered structure of corium with upper layer rich in metal and lower layer rich in oxide. Zirconium diboride phase trapped boron and mainly distributed in the metallic layer. Predictions by thermodynamic calculations for the equilibrium phase distribution and chemical compositions of each phase using the NUCLEA thermodynamic database with a focus on U-Zr-O-Fe system were in good agreement with the experimental results. Agreement in terms of U/(U+Zr) was quite close while there were dispersions in oxygen and steel components. The temperatures for the formation of two immiscible liquids calculated by the NUCLEA for FK-1 and FK-2 was 300 K higher than the experimental observation. This point has to be looked at for improving the NUCLEA models for corium containing B4C, by introducing a non-zero boron solubility in the ceramic phase. The agreement between the NUCLEA predictions and the results of experiments clearly indicate that thermodynamic equilibrium phases play an important role in governing the core damage progression, which is important not only for the severe accident management but also for decommissioning and defueling process for the Fukushima Daiich damaged reactors.

Micromechanics-based damage model for liquid-assisted healing

This work presents a damage evolution framework including liquid-assisted healing. The model incorporates contributions from void size, void pressure, surface tension and liquid pressure. Experimental motivation for the damage-healing model is provided with in-situ melting experiments, where the evolution of the void distribution under monotonic tension is illustrated. The damage evolution is based on nucleation and growth of voids, which are modeled in a unified creep and plasticity framework. The proposed damage formulation introduces a void collective, which computes the void distribution in the material and allows to describe void collapse using the Rayleigh-Plesset equation. The necessary conditions for healing are discussed with use of model results. Particularly, the role of external load during healing, the dependence on liquid viscosity and surface tension are investigated.

Role of operating and environmental conditions in determining molten pool dynamics during electron beam melting and selective laser melting

Abstract Electron beam melting (EBM) and selective laser melting (SLM) are representative powder bed fusion additive manufacturing methods. Because EBM and SLM have different operating and environmental conditions, such as ambient pressure of the chamber, initial temperature, and heat source, they have different molten pool dynamics. In this study, single-bead melting experiments using EBM and SLM were performed in conjunction with computational thermal-fluid dynamics simulations in high-energy conditions to highlight the differences in the molten pool dynamics of EBM and SLM. The experimental results reveal that SLM is more likely to melt in the keyhole mode than EBM under nominally identical line energy. The simulations showed that the instantaneous maximum temperature of the SLM molten pool is much lower than that of the EBM molten pool. An increase in the preheating temperature is found to strengthen the vapor recoil pressure; however, the vapor recoil pressure under vacuum is maintained at a considerably low level in EBM. Compared to EBM, the high atmospheric pressure and multiple laser reflections during SLM significantly enhance the effect of the vapor recoil pressure on the melt surface. The findings of this study can be useful for the formulation of appropriate processing strategies for the two processes.