Solidification Path Research Articles

Role of Ti-6Al-4V addition in modulating crack sensitivity, solidification microstructure and mechanical properties of laser powder bed fused γ-TiAl alloys

Solidification cracking is still the primary challenge for laser powder bed fusion (LPBF) without high-temperature preheating of γ-TiAl alloys. Circumventing the peritectic reaction and promoting β-solidification by adding the β-stablizing elements have been proved to be an effective way to suppressing the crack formation. In this work, we attempted a more economic method to realize β-solidification via the addition of Ti-6Al-4V (TC4) pre-alloyed powder. The results showed that the TC4 addition successfully changed the solidification path from L→L+β→L+α→α→α+γ→α2+γ to L→L+β→β→α+β→α2+β/B2. As a result, the solidified microstructure was mainly comprised of primary α2 phase and small amount of retained β/B2 (8.5 %) phase distributed along the molten pool boundary. What's more important was that the TC4 addition led to a 44.6 % decrease in crack density. Contributions to low hot cracking sensitivity were found to mainly origin from the relatively lower cooling rate, higher fraction of low-angle grain boundaries (LAGBs) and smaller dendrite coalescence undercooling induced by the TC4 addition. Besides, the smaller temperature interval (10.63K) in the final solidification stage (0.90<fs < 0.94) for the TC4/TiAl alloy was also conducive to facilitate the liquid feeding and dendrite coalescence.

Effect of al content on microstructure and corrosion resistance of Zn-Al-Mg alloy

In order to solve the solidification microstructure of Zn-1.7Al-1.1Mg alloy on the surface of steel plate during hot dip plating, the solidification path and microstructure of Zn-1.7Al-1.1Mg alloy were studied by Thermo-Calc thermodynamic software, differential thermal analysis (DSC) and scanning electron microscopy (SEM). The results show that during cooling from melting to room temperature, Zn-1.7Al-1.1Mg alloy begins to precipitate Zn-rich η phase at 386.5 °C, binary eutectic structure consisting of η phase and Mg2Zn11 at 350.0 °C, and ternary eutectic structure consisting of η phase, Al-rich metastable β phase and Mg2Zn11 at 343.4 °C,at 276.7 °C, β phase transforms into stable aluminum-rich α and η phases.

Microstructural Study of Containerless Solidification of Al–20wt%Ce Alloy

Containerless solidification of Al–20wt%Ce is investigated experimentally using the electromagnetic levitation (EML) and impulse atomization (IA) techniques. In the processed EML samples, small primary undercooling and minimal eutectic undercooling are shown. The microstructure consists of large primary Al11Ce3 dendrites surrounded by an α‐Al–Al11Ce3 eutectic. Phase fractions determined by neutron diffraction are similar to the values obtained from a Scheil–Gulliver solidification simulation. Larger IA powders (between 425 and 1000 μm) show a microstructure qualitatively similar to that of EML samples, implying that they follow a similar solidification path. Quantitatively, microstructural features are finer due to the higher cooling rates involved in the solidification process. Atomized particles with a size lower than 425 μm show a strikingly different microstructure, with a very fine eutectic giving way to large intermetallic plates surround by a regular eutectic. Microhardness testing of the structures shows a significant increase in hardness as the sample size decreases, going from 45.8 ± 3.6 HV for the EML sample (lowest cooling rate) to 142.2 ± 12.0 HV for particles in the 106–150 μm range (highest cooling rate).

Design of non-heat-treatable Al-Fe-Ni alloys with high electrical conductivity and high strength via CALPHAD approach

Electrical conductivity and strength are two critical properties concerned for rotors materials in electric vehicles. However, the two properties are often mutually exclusive in cast Al alloys. The present work proposes a novel non-heat-treatable Al-Fe-Ni alloy by considering the intermetallic compound’s content and morphology. With the modification of Ni and Fe content, the solidification path of designed alloy were calculated to predict the phase composition, which would greatly impact their performance. The as-cast Al-2Fe-1Ni (wt%) alloy exhibits comprehensive properties with an ultimate tensile strength of 131.2±2.5 MPa, an elongation of 20.2±3.6 % and an electrical conductivity up to 52.0±0.1 %IACS. The eutectic microstructure of Al13(Fe,Ni)4+α-Al in Al-2Fe-1Ni alloy accounts for over 90 %, much larger than the eutectic content in Al-0.4Fe-3.4Ni and Al-1Fe-1Ni alloys. The fine eutectics in Al-2Fe-1Ni alloy improve the second-phase strengthening effects and plastic deformation capability. In addition, the fibrous rod-like intermetallic reduces the electron scattering during the propagation process and leaves more space for free electron movement. The dominant second phase transforms from Al3Ni phase to Al9FeNi phase, further enhancing the thermal stability of the alloy. After aging treatment at 180 °C for 100 h, it shows no noticeable change in electrical conductivity and mechanical properties. It is hoped that this work can provide a new design approach for high-strength and high-conductivity Al alloys.

SiO2-Bearing Fluxes Induced Solidification Path Transition in Weld Metals of EH36 Shipbuilding Steel

SiO2-Bearing Fluxes Induced Solidification Path Transition in Weld Metals of EH36 Shipbuilding Steel

An investigation on effect of tramp elements and solidification processing on homogenization kinetics of AA 7xxx series aluminum alloys

AA 7068 Aluminum alloy is produced via conventional solidification (CS) and controlled diffusion solidification (CDS) processing and homogenized at 450 °C for 6 and 12 h. Optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive x-ray spectroscope (EDS) were used to examine the as-cast and homogenized samples. It was found that although the CS sample is more chemically homogenized in the as-solidified state, the CDS sample exhibits a higher homogenization rate during the treatment. The calculated phase diagram (CALPHAD) methodology was employed to study the effect of silicon and iron on the solidification path and homogenization of the alloy. Silicon consumes magnesium atoms on the surface of the α-Al phase to form the Mg2Si phase. Therefore, the magnesium concentration on the α-Al phase required for the formation of the σ phase must be increased. Calculations shows that all the Mg atoms at this stage are completely supplied from the bulk of the αAl phase. It can be hypothesized that during the last stage of solidification, a solid/liquid diffusion couple can be created between the primary αAl and the remaining liquid for several minutes (4 min at a cooling rate of 0.2 oC/s). As a result of the activation of this couple, the Mg atoms diffuse from the α-Al bulk to its surface, and vacancies diffuse from the surface to the bulk, forming a line of Kirkendall voids. With CDS processing, the surface of the primary phase is less Mg-concentrated than that in the CS process and this significantly reduces the formation of the Mg2Si phase. Conversely, the vacancy and Mg concentration of the αAl phase in CDS is higher than that of CS and this lets other alloying elements other than Mg diffuse to the primary phase, decreasing the homogenization time. The presence of Si in the alloy leads to the formation of the Mg2Si phase, which significantly reduces the final Mg concentration in the α-Al phase after full homogenization. In the pure alloy, the Mg concentration is 2.42 wt%, while in the FeSi-containing alloy, it is reduced to 1.58 wt% due to solid solution and dispersion strengthening mechanisms. Through CDS processing, the negative impact of Si can be reduced by disrupting the mechanism of Mg2Si formation.

Effect of solidification path and volume shrinkage on cracking susceptibility at different cooling rates

Effect of solidification path and volume shrinkage on cracking susceptibility at different cooling rates

Effect of isothermal cooling on solidification behaviour of peritectic steel under in situ observation

In order to improve the volume shrinkage of peritectic steel during solidification, the solidification path of peritectic steel was changed by adjusting the cooling mode in this article. The solidification behaviour of peritectic steel under isothermal cooling conditions was studied by in situ observation experiment. The transformation shrinkage degree was reflected by sample surface roughness. The results show that the solidification path under the isothermal cooling is L→L+δ-Fe→δ-Fe→δ-Fe+γ-Fe without peritectic reaction. Moreover, the sample surface morphology was flat under isothermal cooling, and no granular morphology was observed. The surface roughness was 2.55 μm under isothermal cooling, which is much lower than that under different continuous cooling conditions. The surface roughness decrease indicates the solidification volume shrinkage is reduced. Therefore, the risk of cracking can be decreased by adjusting the cooling mode to control the solidification pattern of peritectic steel.

Study of phase evolution, mechanical, and tribological behaviour of a novel β-phase strengthened Ti-alloy with Fe and Co alloying via a laser material deposition route

A new Ti64-Fe-Co alloy was studied via a laser-material-deposition method. Associated with high growth restriction factors, β-eutectoid (Fe, Co) alloying minimizes anisotropy (due to the prior columnar β-grain growth) in the laseradditive -manufacturing (AM) built Ti-parts along with enhanced properties. Fe alloying for Ti64 via laser-AM results in superior strengthening with reduced ductility, where a good combination of strength and elongation properties can be achieved for a Ti-Fe-Co system. However, studies on Ti-Fe-Co-based systems via laser processing are limited. Co possesses a similar electronic property as Fe and the Ti-Fe system accompanies further solute addition. The effect of Co alloying the Ti64-Fe system was investigated in this study via a pre-placed laser-material-deposition method. A Ti64–5Fe-5Co alloy was formulated referring to CALPHAD simulations, along with a Ti64–10Fe composition. The new Ti-alloys were fabricated via both the laser-material-deposition and conventional vacuum arc melting routes, and the characteristics of the fabricated samples were examined. XRD analysis shows the evolution of the β-Ti phase with Fe and Co alloying, which agrees with the thermodynamic phase simulation results. The corresponding SEM micrographs depicted a β-phase dominant matrix with α-dendrites, and the solidification path was discussed. Considerable grain refinement was obtained for the laser-deposited alloys compared to the arc-melted ones, with an improved hardness value twice that of the commercial Ti64. A reduced stiffness for the laser-deposited Ti64–5Fe-5Co was observed from the load-vs-displacement characteristics, indicating matrix softening with Co alloying, which might benefit the elongation properties. The studied Ti-alloy shows a 30 % improvement in the dry-sliding wear characteristic with reduced fretting and abrasion compared to the commercial Ti64. The studied Ti-alloys were located in the theoretical d-electron space and new (Bo) ̅-(Md) ̅ vectors were introduced. Further studies on this would help in extending the applicability of laser-AM-built Ti-components.

Stability of Crystalline Compounds in Slag Systems Mainly Composed of Li2O-SiO2-CaO-MnOx

The challenge of obtaining sufficient raw materials is a major concern when it comes to extracting lithium from spent lithium-ion batteries. One way to address this is through pyrometallurgical processing, which leaves undesirable elements such as lithium, aluminum and manganese in the slag. The engineered artificial minerals approach focuses on the effective recovery of critical elements. Different slag systems have been studied in the literature, and understanding the phase relationships in the Li2O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Li}_2{\ ext {O}}$$\\end{document}-SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {SiO}_2$$\\end{document}-CaO-MnOx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {MnO}_x$$\\end{document} system can lead to optimization of the recycling process. In this context, the stability of undesirable silicates can affect the maximum separation of Li from the slag. In order to contribute to the development of the Li recycling process, the stability of crystalline compounds was experimentally investigated in the present work for different slag compositions. The melted and solidified microstructures were characterized by SEM/EDX, EPMA, and XRD. Phase diagram data of binary and ternary systems were used to describe the solidification paths. As a result of solidification, crystals of Li2SiO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Li}_{2}\ ext {SiO}_{3}$$\\end{document} and LiMnO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {LiMnO}_2$$\\end{document} were observed in a matrix consisting of Ca3Si2O7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Ca}_{3}\ ext {Si}_{2}\\hbox {O}_{7}$$\\end{document} and CaSiO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {CaSiO}_{3}$$\\end{document}.

Synergistic effect of Zr and Ti on microstructure and properties for Nb[sbnd]Si based in-situ composites

To reduce the adverse effects of highly active titanium elements in NbSi alloy, a series of high content of Zr and Zr for Ti substitution in NbSi based alloys are studied. The results show that the addition of Zr changes the solidification path from hypoeutectic to eutectic. The fracture toughness significantly enhances in 24Ti-xZr (x = 0, 4, 8, 16) alloys, owing to the increase of Nbss phases and microstructure refinement in the matrix. Moreover, the room-temperature compression properties increase in 24Ti-xZr alloys, resulting in the effect of significant solution strengthen. In 24Ti16Zr alloys, three-types of Nbss/Nb5Si3 eutectic are found, resulting in large supercooling degree and rapid cooling condition. The maximum KQ value and compressive strength are 12.47 MPa·m1/2 and 1800 MPa respectively in 24Ti16Zr alloys. The KQ values in Nb-16Si-(24-x)Ti-xZr (x = 4, 8, 16, 24) alloys enhance with element Zr increases to 16 at.% and then decline slightly, suggesting that appropriate substitution of Zr for Ti is effective for promotion of toughness. It's owing to the formation of complex Nbss/(Nb, X)5Si3 eutectic. The high-temperature compressive strength is also prepared (1200 °C), element Zr can provide a signally work hardening by making a strong cooperative deformation of Nbss and γNb5Si3 phases, and the highest true stress values are found in 8Ti16Zr alloys.

The effect of laser surface melting on the microstructure, microsegregation and solidification path of service-aged ECY768 cobalt-based gas turbine nozzle

In this study, the laser surface melting of cobalt-based superalloy ECY768, which has been in service for 40,000 h at a temperature of 1000 °C, has been investigated. Subsequently, laser surface welding and post-welding heat treatment is performed on the samples. This study was conducted in order to restore the microstructure of the damaged service-aged gas turbine nozzle to as-cast state. The results showed that by performing laser surface remelting, the microstructure of as-cast state can be approached. Also, the results of this study have investigated the weldability, microsegregation and solidification path of this superalloy, and it can be used in the repairing this superalloy in the industry. Laser surface melting was performed using a continuous wave fiber laser at various speeds of 10, 12, 14, 20, 50, and 70 mm/s. The microstructure and phase characteristics of the samples were examined using optical and scanning electron microscopes. Upon analyzing the macrostructure of the weld metal, it was observed that the depth of the melt zone at the speed of 12 mm/s is 585 ± 40 μm. In the investigating the microstructure of the solidification modes, namely planar, cellular, columnar dendritic, and equiaxed dendritic, it was observed that microsegregation occurs during laser welding of the samples due to the presence of heavy elements such as tantalum and tungsten. The solidification distribution coefficient for tantalum was calculated to be 0.37, which increased to 0.60 after the solution annealing heat treatment, resulting in an improved segregation behavior. Characterizing the surface hardness profiles of laser-melted samples it was observed that the hardness in the melt zone significantly increased compared to the base metal. The results of the current research indicate that the weldability (resistance to various welding defects, especially hot cracks) of the cobalt-based superalloy ECY768 is acceptable, and this process can be used for rejuvenating service-aged ECY768 cobalt-based gas turbine nozzle.

Abnormal endothermic liquid–liquid phase transition upon cooling Pd40Ni40P20 melts

Liquid–liquid phase transition (LLPT) is the transformation of a liquid from one distinctive structure to another with the same composition. However, the origin of the structural variation at LLPT is still controversial. Here, we used ab initio molecular dynamics simulation to verify and investigate a high-temperature LLPT in a Pd40Ni40P20 melt; this melt showed a reduction in the nuclei interference of the conventional low-temperature LLPT. An abnormal endothermic LLPT was confirmed with flash differential scanning calorimetry, indicating a change in the atomic short-range-order structure around the P–P bond and a decrease in the number of specific icosahedral-like clusters, such as ⟨0 2 8 0⟩ and ⟨0 2 8 1⟩. The structural change of the P-centered clusters changed the solidification path through potential energy adjustments. Our results showed the structural mechanism of the unusual endothermic phenomenon and provided a different insight into regulating the properties of metallic glasses.

Solidification path and precipitation mechanism of a Ni-Cr-co-Mo based heat-resistant alloy

The solidification path and precipitation mechanism of the C-HRA-3 Ni-Cr-Co-Mo-based heat-resistant alloy are investigated by methods such as differential scanning calorimetry analysis, in-situ observations, quenching experiments, and scanning transmission electron microscopy. The results confirm that the primary solidification precipitates in the center of the C-HRA-3 alloy VAR ingot consist of Ti(C,N), M6C-M23C6 symbiotic phases, Ti(C,N)-M6C-M23C6 symbiotic phases and surrounding dispersed M6C and M23C6 carbides. The precipitation temperatures for Ti(C,N), M6C, and M23C6 are 1310 °C, 1280 °C, and 1230 °C, respectively. The C-HRA-3 alloy exhibits a wide solidification temperature range of 176 °C (1390 °C ∼ 1214 °C). Within 1390 °C ∼ 1355 °C, the γ phase grows vigorously, accompanied by a significant reduction in the fraction of liquid phase. At 1355 °C ∼ 1214 °C, the decrease in liquid phase fraction slows down, accompanied by significant enrichment of Mo, Cr, C and Ti elements. There is a clear functional relationship between the liquid phase percentage and temperature. M6C carbides undergo two heterogeneous nucleation mechanisms in the liquid phase. Due to the degradation of M6C carbides discharging Cr and C atoms, M23C6 carbides form at their edge. Dispersed M6C and M23C6 carbides nucleate at misfit dislocations around the symbiotic phases. Appropriately reducing the cooling rate during the stage above the precipitation temperature and increasing the cooling rate below the precipitation temperature can significantly reduce the volume percentage and size of the symbiotic phases.

Design of eutectic high-entropy alloys in the Co-Cr-Ni-V-Ti-Al system using Scheil solidification path optimization

The design strategy for eutectic high-entropy alloys (EHEA) is still in need of further exploration. This paper explores a new design approach using data computation, combining the simple mixing enthalpy method with a computed phase diagram approach based on a high-entropy alloy database. By calculating the thermodynamic empirical parameters of existing FCC/BCC-type eutectic alloy systems, the proportion range of alloy elements for eutectic design was narrowed. Ultimately, by analyzing the solidification path through the Scheil model, six eutectic compositions were obtained for the Co-Cr-Ni-Ti-V-Al alloy system that satisfy theoretical concepts. Microscopic characterization revealed that the actual alloy’s microstructure has only minor differences from the theoretically calculated results, with the main phase compositions of the alloys being FCC and BCC phases, aside from minor metal precipitates and third phases. However, significant differences were observed in the microstructures and mechanical properties of the six alloys. The research results demonstrate that this new design theory shortens the EHEA design cycle, enhances design accuracy and provides guidance for the eutectic design of target alloy systems.

Liquidus surface projection and isothermal section at 1500 °C of (Mo-5Nb)-Ti-C pseudo-ternary system

The liquidus surface projection and isothermal section at 1500 °C of the (Mo-5Nb)-Ti-C pseudo-ternary system were experimentally determined. X-ray diffraction analysis and scanning electron microscopy in conjunction with electron-probe microanalysis were carried out to analyze the solidification behavior and phase constituents. The replacement of 5 at.% Mo with Nb was found to negligibly affect the solidification path or the formation of new phases. However, the quasi-peritectic point U2 shifted closer to the (Mo-5Nb)-C border in the liquidus surface projection than in the Mo-Ti-C system. The BCC single-phase region, BCC + TiC two-phase region, and BCC + Mo2C + TiC three-phase region were determined in the isothermal section at 1500 °C. The replacement of 5 at.% Mo with Nb was found to expand the BCC + TiC two-phase region and narrow the BCC + Mo2C + TiC three-phase region by stabilizing the TiC phase. Therefore, the addition of Nb to the Mo-Ti-C system expanded the compositional range of the BCC + TiC two-phase region, leading to variable properties of TiC-dispersed BCC-based alloys and BCC-TiC cermets.

Effect of Preparation Process on the Microstructure and Characteristics of TiAl Pre-Alloyed Powder Fabricated by Plasma Rotating Electrode Process

TiAl pre-alloyed powder is the foundation for additive manufacturing of TiAl alloys. In this work, TiAl pre-alloyed powder was prepared using a plasma rotating electrode process (PREP). The effects of electrode rotating speeds and current intensity on the microstructure and characteristics of TiAl pre-alloyed powder have been investigated in detail. The results show that the electrode rotating speeds mainly affected the average particle size of the powder (D50). As the electrode rotating speed increased, the D50 of the powder decreased. The current intensity mainly affected the particle size distribution of the powder. As the current intensity increased, the particle size distribution of the powder became narrower, which was concentrated at 45~105 μm. In addition, the current intensity had a significant effect on the sphericity degree of the powder with the particle size &gt; 105 μm, but it had little effect on that &lt;105 μm powder. TiAl pre-alloyed powder with a particle size &gt; 45 μm demonstrated a dendritic + cellular structure, and the &lt;45 μm powder had a microcrystalline structure. The powder was mainly composed of the α2 phase and γ phase. There were two kinds of phase structure inside the powder, namely the α2 + γ lamellar microstructure (particle size &lt; 45 µm) and the α2 + γ network microstructure (particle size &gt; 45 µm). The phase structure of the powder was related to the solidification path and cooling rate of molten droplets in the PREP. The average thickness of the α2 + γ lamellar was about 200 nm, in which the lamellar γ phases were arranged in an orderly manner in the α2 phase matrix with a thickness of about 20 nm. The network phase structure was corrugated, and the morphology of the γ phase was not obvious.

Solidification paths of Al-Cu-Sn alloys: Comparison of thermodynamic analyses and solidification experiments using in situ X-radiography

The increasing importance of Al-Cu-Sn alloys as materials for producing self-lubricating bearing materials in automotive industries requires the development of uniform microstructures with improved performance, which could be achieved by a precise control of solidification processes. Adding Sn to Al-Cu binary alloy could dramatically alters the solidification path, generating liquid phase separation and monotectic reaction. In this paper, Al-10 wt% Cu-X wt% Sn (with X = 0; 5; 10 and 20) alloys have their solidification paths investigated by three different complementary approaches. Firstly, the solidification paths were calculated by using the CALPHAD method through Thermo-Calc software revealing the sequence of transformations that could occur during the solidification of these alloys, from the formation of the initial α-Al dendrites to the final eutectic reaction. Secondly, experimental thermal analysis was carried out by DSC (Differential Scanning Calorimetry), which reveals the successive events that occur during the controlled melting and cooling of these alloys. Thirdly, directional solidification was performed on all alloys, with in situ and real-time observations achieved through the utilization of X-radiography. The comparison between the various approaches showed a suitable correspondence between the history of the alloy solidifications computed by Thermo-Calc and those obtained experimentally (DSC and directional solidification experiments). Additional information about the dynamics of each reaction was obtained during the directional solidification experiments in terms of microstructures, segregation, and the genesis of the liquid phase separation that occurred for high Sn-content alloys.

Magma titanium and iron contents dictate crystallization timescales and rheological behaviour in basaltic volcanic systems

Magma ascending through Earth’s crust undergoes complex chemical and physical changes that may induce crystallization, a process that contributes to lead the magmatic system toward a thermodynamic state of equilibrium. The diverse cooling and deformative regimes suffered by magmas heavily influence crystallization rates, solidification timescales, and consequently, the rheological evolution of magma. This, in turn, significantly impacts the dynamics of volcanic plumbing systems and the associated eruptive styles. Here, we investigate the rheological changes in Stromboli magma (Italy) during disequilibrium crystallization under non-isothermal subliquidus conditions. By systematically varying the cooling rate (1-10 °C/min) and the shear rate (1-10 s−1), we find that cooling rates significantly influence the solidification path of the basalt, whereas shear rates have a subordinate effect. By comparing our results with literature data on basalts from Mt. Etna (Italy), characterized by higher TiO2 and FeOtot contents, we observed distinct timescales and rates of solidification, contributing to unique eruptive dynamics in these volcanic plumbing systems.

Influence of alloy solidification path on melt pool behavior in additive manufacturing

Numerical models used to study transport phenomena in laser-powder bed fusion processes often rely on assumptions and simplifications to reduce their computational expense. One common simplification is in the description of latent heat evolution during the solid-liquid phase change (i.e., the solidification pathway), justified by the fact that the mushy zone thickness is similar to the numerical grid spacing used for continuum transport models. The lack of resolution of transport phenomena in the mushy zone motivates the use of computationally convenient solidification paths such as linear or sigmoidal relationships over pathways derived from fundamental solidification theory such as equilibrium or Scheil models. In the present work, an uncertainty quantification (UQ) framework is used to analyze the influence of solidification pathway selection on the solidification dynamics and melt pool geometries in laser based additive manufacturing (AM) of IN625. Results show the solidification pathway has a quantifiable influence on the cooling rate at the liquidus isotherm, mushy zone thickness, and solidification time. Due to similarities in the latent heat evolution at the beginning of solidification, the equilibrium and Scheil models predict similar cooling rates near the liquidus isotherm, however the wider freezing range of Scheil leads to a wider mushy zone compared to equilibrium. The non-physical latent heat release profiles of sigmoidal and linear paths lead to significant overpredictions of cooling rates at the liquidus isotherm compared to equilibrium and Scheil. These results indicate that careful consideration should be given to the choice of solidification pathway to ensure reliable model predictions.