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Using undercooling technology combined with melt purification of glass and recirculation overheating, different undercoolings were successfully obtained for Cu60Ni38Co2 alloy samples. Applying high speed photography technique, the physical process of undercooled solidification was observed and relationship between undercooling and solidification rate was analyzed. Experimental results indicate the critical undercoolings exist in the structure evolution process. Electron backscatter diffraction (EBSD) analysis was applied to characterize the Cu60Ni38Co2 alloy sample with a maximum undercooling of 255K, revealing grain orientation and the corresponding orientation difference distribution. In addition, transmission electron microscopy (TEM) showed high density dislocation networks. Combining EBSD and TEM data analysis, an important conclusion was drawn: recrystallization is the main factor for grain refinement at high undercooling. This finding is of great significance for a deeper understanding of the structure evolution in the physical process of undercooled alloys.

As one of the representative patterns in nature and laboratory experiments, dendritic structures control the properties of a broad range of advanced materials. Dendrites arise during different phase and structural transformation processes. Generally, the formation of dendritic structures are stipulated by transport processes in bulk phases, together with thermodynamic properties and kinetic phenomena at the phase interfaces. The formation of a dendritic microstructure under the influence of external fields (electromagnetic and gravitational) is considered in this review. These fields involve the liquid and gaseous phases in a forced convective flow, causing the transfer of energy and matter in addition to the usual conductive (diffusion) transport. The formulated model takes into account rapid solidification from an undercooled liquid phase as well as intermediate and low growth velocities of dendritic crystals in pure one-component systems extended to binary mixtures and alloys. The areas of undercooling are identified, in which the influence of convection caused by the electromagnetic and/or gravitational field is most noticeable. The solidification regimes (from the diffusion-limited mode to the thermally and kinetically controlled mode) are reviewed in connection with the different liquid flow velocities that dictate various boundary conditions (conductive and convective) on the surface of growing crystals. A comparison of model predictions with experimental data and computational results provides the grounds for a discussion about the applicability of the formulated model to interpreting known and unexpected phenomena in the formation of a crystalline structure. By changing the power of the considered fields or reducing them almost to zero (for instance, in microgravity), it is possible to control the dispersion of a dendritic microstructure, as well as separate accompanying phases (eutectic, peritectic, monotectic, intermetallic phases, etc.) during the solidification of materials and, in the general case, during phase transformations. [ABSTRACT FROM AUTHOR]

The development of sector zoning in clinopyroxene is attributed to the influence of crystallisation kinetics imposed by magma undercooling (ΔT) and may reflect variations in magma cooling histories. Yet, the degree of compositional variations between sectors has not been explored as a potential recorder of crystallisation dynamics. Here, we investigate the distribution of major, minor, and trace elements between hourglass {−1 1 1} and prism { h k 0} sectors in clinopyroxene with distinct pre-eruptive histories at Mt. Etna, Italy. We analyse sector-zoned clinopyroxene crystals ranging in size from sub-mm to cm (i.e., microphenocrysts, phenocrysts, and megacrysts), from eruptions fed by the central conduits of the volcano (1669 and 2002–03 flank eruptions) and eruptions fed by eccentric dykes which bypass the central conduits, tapping deeper magma storage regions (1974 and 2002–03 flank eruptions). We focus on Cr-rich mantle zones, which crystallised upon eruption triggering mafic rejuvenation and are ubiquitous across our sample set. With decreasing crystal size (i.e., increasing ΔT), tetrahedral aluminium is more strongly partitioned between prism and hourglass sectors. This promotes the uptake of rare earth elements (REE) and high field strength elements (HFSE) into prism relative to hourglass sectors. Combining relative degrees of sector enrichment with ΔT estimates, we propose magma recharge, mush remobilisation and the onset of magma ascent imposed slightly higher ΔT in 1974 than in 2002–03 eruptions at Mt. Etna. Enhanced ΔT in 1974 could be related to vigorous mixing and rapid transport of magma with limited storage, resulting in crystals of smaller sizes. Crystal size populations vary across eruptions, but crystals within a given population (e.g., phenocrysts) return similar calculated ΔT and REE + HFSE sector enrichments, implying connectivity between magmatic environments in the mush system. We show that the magnitude of sector zoning in clinopyroxene can be employed to explore subtle differences in pre-eruptive dynamics in volcanic systems. As an example, we explore sector enrichment in clinopyroxene phenocrysts from the 2021 eruption at La Palma (Canary Islands) and megacrysts from Roman era activity at Stromboli (Italy). Results highlight the role of dynamic mixing and mush remobilisation before eruption in mafic alkaline settings and suggest changes in magma composition across alkaline systems influence clinopyroxene chemistry but do not influence sector enrichment. [ABSTRACT FROM AUTHOR]

Through the use of purification and recirculation superheating techniques on molten glass, the Ni65Cu33Co2 alloy was successfully undercooled to a maximum temperature of 292 K. High-speed photography was employed to capture the process of interface migration of the alloy liquid, allowing for an analysis of the relationship between the morphological characteristics of the alloy liquid solidification front and the degree of undercooling. Additionally, the microstructure of the alloy was examined using metallographic microscopy, leading to a systematic study of the microscopic morphological characteristics and evolution laws of the refined structure during rapid solidification. The research reveals that the grain refining mechanism of the Ni-Cu-Co ternary alloy is consistent with that of the binary alloy (Ni-Cu). Specifically, under low undercooling conditions, intense dendritic remelting was found to cause grain refinement, while under high undercooling conditions, recrystallization driven by accumulated stress and plastic strain resulting from the interaction between the liquid flow and the primary dendrites caused by rapid solidification was identified as the main factor contributing to grain refinement. Furthermore, the study highlights the significant role of the Co element in influencing the solidification rate and reheat effect of the alloy. The addition of Co was also found to facilitate the formation of non-segregated solidification structure, indicating its importance in the overall solidification process. [ABSTRACT FROM AUTHOR]

The experiment employed the use of melt purification and cyclic superheating technique to achieve maximum undercooling of Ni65Cu31Co4 alloy at 300K. Simultaneously, high-speed photography techniques were used to capture the process of alloy liquid phase interface migration, and analyzed the relationship between the shape characteristics of the front end of alloy solidification and undercooling. The microstructure of the alloy was observed through metallographic microscopy, and the micro-morphological characteristics and evolution of the rapidly solidified microstructure were systematically studied. It is found that the grain refinement mechanism of Ni-Cu-Co ternary alloy is similar to that of Ni-Cu binary alloy. Grain refinement at low undercooling is caused by intense dendritic remelting, while grain refinement at high undercooling is attributed to recrystallization, driven by the stress and plastic strain accumulated from the interaction of liquid flow and primary dendrites caused by rapid solidification. It also shows that the addition of the third element Co plays a significant role in solidification rate and re-ignition effect. [ABSTRACT FROM AUTHOR]

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The objective of the current work is to establish the conventional mechanisms of grain refining, and the effect of the refiner-modifier interaction in Al-based alloys on the resultant grain refining obtained. The different castings were carried out in preheated metallic molds with solidification rates of around 0.15 °C/s and 7 °C/s. As the nucleation sites (Al3Ti) change in composition depending on the percentage of Si in the alloy, the term “poisoning” frequently used to explain the loss or weakening of the power of the refiner, is misused. Addition of L12 metals e.g., Zr and Sc would contribute to constitutional undercooling, restricting the coarsening of α-Al grains as well as act as suitable sites for heterogeneous nucleation. The use of transition or ultra pure (99.99) metals would increase the degree of undercooling as well as nucleation of new grains due to precipitation of the second phase leading to the formation of a heterogeneous grain distribution. Thus, grain refining of binary alloys - partially or fully, may not be produced only through constitutional undercooling. It is suggested that, the use of 0.18%Sc has more-or-less the same grain refining efficiency of 0.15%Ti added in the form of Al–Ti–B master alloy i.e., reduction in the grain size by about 85% and an increase in the alloy strength by about 30%. For a given solidification rate, there is a grain refining threshold beyond which no further refining can be achieved. Apparently grain refining mechanisms are independent of solidification rate, only the extent of refining.

This work examined the performance of self-heating concrete under laboratory thermal conditions and outdoor real-time conditions during the fall and winter seasons. Snow-melting and freeze–thaw performance of low-temperature phase change materials (PCM) incorporated self-heating concrete slabs in various scales were evaluated. PCM exhibited high enthalpy of fusion (ΔHf≈170–180 J/g), long-term thermal stability, and desirable supercooling. The experimental program included (1) optimization of concrete mix designs for maximum PCM incorporation, (2) characterization of thermal properties of PCM-mortar specimens using longitudinal guarded comparative calorimetry (LGCC), and (3) large-scale PCM concrete slabs in outdoor conditions to evaluate the real-time thermal performance against freeze–thaw events and snow-melting efficiency. Two different approaches were used to incorporate PCM in concrete: (1) submersion of liquid PCM in porous lightweight aggregates (PCM-LWA); and (2) microencapsulated PCM (MPCM). Both PCM-LWA and MPCM concrete not only exhibited promising snow-melting capabilities but also lowered the number of freeze–thaw cycles during cold seasons. PCM-LWA concrete performed better in decreasing the number of freeze–thaw (F-T) cycles due to the undercooling phenomenon created by the LWA pore network confinement pressure, allowing gradual latent heat release; the undercooling phenomenon in PCM-LWA results in phase transformation in a wider low-temperature range (i.e., 3.94°C to −13.04°C). Therefore, the PCM-LWA concrete was effective in melting snow within a wider range of low temperatures. MPCM concrete was found to provide a rapid melting capability during a snowfall event due to its "one-shot" heat release phenomenon. Both LWA-PCM and MPCM concrete slabs demonstrated promising heat response and snow-melting capability. Snowfall and freeze–thaw cycles occur frequently during winter seasons in North American regions with cold climate, resulting in snow accumulation on concrete roads and flatworks as well as concrete freeze–thaw damage. In this paper, a "self-heating" concrete was developed via incorporation of low-temperature phase change material (PCM), and its promising snow removal and freeze–thaw improvements were validated. The self-heating concrete can be used to construct pavements, driveways, bridge decks, and any other types of flatworks. When the ambient temperature falls to ∼0°C , PCM will release desirable amounts of heat energy (ΔHf=170–180 J per g of PCM added) by changing its phase from liquid to solid. As a result, the accumulated snow and ice melts at a gradual pace. In addition, heat release from the incorporated PCM lowers the number of freeze–thaw cycles, improving freeze–thaw performance of concrete made elements in cold regions, which in turn improves concrete durability and service life by minimizing the susceptibility to freeze–thaw scaling and spalling. [ABSTRACT FROM AUTHOR]

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored. The non-equilibrium solidification structure of the under cooled alloy samples were analyzed. It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process. Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed. High-density defects were observed, such as dislocations, stacking faults networks, and twinning structures. The standard FCC diffraction pattern represents that it is still a single-phase structure. Based on the metallographic diagram, EBSD and TEM data analysis, it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization. In addition, the laser cladding technology is used to coat Co-based alloy (Stellite12) coating on 304 stainless steel substrate; the microstructure of the coating cross-section was analyzed. It was found that the microstructure of the cross-section is presented as columnar crystals, planar crystals, and disordered growth direction, so that the coating has better hardness and wear resistance. By electrochemical corrosion of the substrate and coating, it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film, which improved the corrosion resistance of the coating. [ABSTRACT FROM AUTHOR]

Understanding the sluggish kinetics is of great significance for improving the properties of multi-principal element alloys (MPEAs). In this paper, the crystal growth in undercooled CoNi, CoNiFe and CoNiPd alloys was studied by molecular dynamics (MD) to show atomistic insights into sluggish crystal growth kinetics. The added Fe and Pd lead to a decrease in the crystal growth velocity and more significant sluggish crystal growth kinetics was observed in CoNiPd. After minimizing the instantaneous potential energy of atoms adjacent to the Solid/Liquid (S/L) interface, it was found that the decreased crystal growth velocity as the number of principal elements could be accounted by the accompanying change of inherent structure. The exploration of bulk undercooled liquid showed that the diffusion kinetic in liquid does not play a critical role on the sluggish crystal growth kinetics. Besides, the investigation of atomic structure in front of the smooth S/L interface revealed that the sluggish crystal growth kinetics induced by properties of element was associated with the atomic spontaneous ordering degree.

Employing molten glass purification and cyclic overheating technologies, a Cu60Ni40 alloy was modified by introducing trace amounts of Co element. Through this process, we aimed to understand how the addition of Co element influences the microstructure morphology of the alloy. By combining the BCT model and metallographic analysis, the intrinsic factors of microstructure transformation in the alloy were studied. In the case of small undercooling, solute diffusion dominates dendritic growth, but the undercooled melt is limited to a narrow range of growth, resulting in the formation of coarse dendritic morphology in Cu–Ni alloy. As the undercooling increases, the growth of dendrites is gradually controlled by both solute diffusion and thermal diffusion, and the remelting effect of dendrites is also gradually enhanced. During rapid solidification with lower undercooling, the dendrites formed by the undercooled melt can be remelted to form numerous crystal seeds. Within a moderate undercooling range, dendrites grow directionally due to thermal diffusion and exhibit specific characteristics. At high undercooling, the dendrites' directional growth, primarily driven by thermal diffusion, undergoes stress fragmentation.

Applying molten glass purification and cyclic superheat methods, deep undercooling treatment was performed on a Ni88Cu6Co6 alloy system. The alloy was undercooled to an undercooling as high as 300 K and the corresponding microstructure characteristics were analyzed systematically. Compared with the Ni88Cu12 system, the addition of a minor amount of Co had a pronounced impact on the grain refinement mechanism of Ni88Cu6Co6 system. Grain refinement observed at low undercooling was attributed to the dendritic melting mechanism. On the other hand, in the high undercooling region, the recrystallization process played a dominant role in refining the microstructure. Through the present analysis, the characteristic undercoolings of microstructure evolution had been determined. In addition, BCT model was applied to study the free growth of an undercooled Ni88Cu12 alloy, and by comparing Ni88Cu12 and Ni88Cu6Co6 alloys, we aimed to find the effect of Co on the microstructure refinement mechanisms of deeply undercooled Ni–Cu alloys.

Al 2 O 3 /ZrO 2 eutectic bulks (20 mm in diameter) with different Y 2 O 3 contents (0–4.5 mol %) were grown using the conventional casting method. Variations in the microstructural characteristics and colony tip growth behavior caused by Y 2 O 3 addition in the central equiaxed grain zone were investigated. As Y 2 O 3 was added to the Al 2 O 3 /ZrO 2 binary eutectic, except for a decrease in colony size, the colony tip radius reduced drastically and then increased slightly. Colony growth behavior can be well predicted using the Lipton–Glicksman–Kurz (LGK) model. A critical Y 2 O 3 content (0.5–1.1 mol%) exists below which the eutectic colony growth is accelerated owing to the Y 2 O 3 addition, but slowed down otherwise. However, the average interphase spacing and ZrO 2 rod diameter inside the colonies varied with Y 2 O 3 content, converse to the growth rate. [ABSTRACT FROM AUTHOR]

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys. [ABSTRACT FROM AUTHOR]

The Invar alloy has excellent properties, such as a low coefficient of thermal expansion, but there are few reports about the rapid solidification of this alloy. In this study, Invar alloy solidification at different undercooling (ΔT) was investigated via glass melt-flux techniques. The sample with the highest undercooling of ΔT = 231 K (recalescence height 140 K) was obtained. The thermal history curve, microstructure, hardness, grain number, and sample density of the alloy were analyzed. The results show that with the increase in solidification undercooling, the XRD peak of the sample shifted to the left, indicating that the lattice constant increased and the solid solubility increased. As the solidification of undercooling increases, the microstructure changes from large dendrites to small columnar grains and then to fine equiaxed grains. At the same time, the number of grains also increases with the increase in the undercooling. The hardness of the sample increases with increasing undercooling. If ΔT ≥ 181 K (128 K), the grain number and the hardness do not increase with undercooling. [ABSTRACT FROM AUTHOR]

Deep undercooling rapid solidification experiments of Cu–Ni–Co alloys were carried out using the molten glass purification cycle superheat method. 130 K, 177 K and 277 K undercooling degrees were obtained and analysed for Cu55Ni43Co2 alloy. The crystallographic information obtained by EBSD and the dynamics of the solidification front taken by high speed photography were analysed and it was concluded that both the formation of relatively rounded equiaxed grains during the first refinement and the subsequent formation of finer subcrystals were due to the release of a large amount of solidification energy during the solidification process. The re-glow stage releases a large amount of latent heat of solidification resulting in the remelting of the dendrites. TEM tests were carried out on Cu55Ni43Co2 alloy with a maximum undercooling of 277 K. It was found that part of the substructure showed a high density dislocation network. By analysing the effect of increasing undercooling on the microstructure evolution, combined with the EBSD and TEM characterisation data, it was found that the stress-induced recrystallization mechanism was the dominant factor in the grain refinement mechanism at large undercooling.

The present work systematically studied nonequilibrium solidification microstructure and its morphology evolution with undercooling of Cu60Ni40 binary alloy and Cu60Ni35Co5 ternary alloy, and the characteristic undercooling degree of alloy evolution was determined. Combining with BCT model, dendritic growth of undercooled Cu–Ni alloy was studied. On the basis of the above, a new ternary single-phase alloy was formed by adding minor Co element into Cu60Ni40 alloy. Subsequently, a comparative analysis was conducted on Cu60Ni40 and Cu60Ni35Co5 alloys, exploring the effect of Co element on the evolution of microstructure of deeply undercooled Cu–Ni alloys.

Traditional recrystallization technology is based on recrystallization annealing after artificial plastic deformation. In the present study, we found that rapid solidification through deep undercooling can induce substantial plastic deformation and recrystallization. Applying cycle superheating combined with molten glass purification technologies, Ni88Cu6Co6 alloys were highly undercooled to a maximum undercooling of 300 K. Microstructure characteristics and its evolution varying with bulk undercooling during the rapidly solidified process were analyzed. The grain-refined microstructure that appeared at low undercooling regimes was caused by dendrite remelting. The dominant factor of grain refinement microstructure appearing in the high-undercooling regime was recrystallization. It was found that, after annealing rapid solidification microstructure of Ni88Cu6Co6 alloy with a undercooling of 240 K at 1223 K for 12min, the partially recrystallized rapid solidification microstructure was further refined by recrystallization. This study has opened up a new recrystallization technology and is worthy further research.

This article mainly used the deep undercooling technology to treat Cu60Ni40, Cu60Ni38Co2, and Cu60Ni35Co5 alloys to obtain different undercoolings. By using high speed cameras, the rapid solidification process was recorded to analyze the relationship between its evolution law and the magnitude of undercooling. When observing its microstructure, it was also found that there was a critical undercooling degree throughout its entire solidification process. The influence of Co element addition on solidification rate, recalescence effect, and critical undercooling of copper based single-phase alloys under undercooling conditions was explored. EBSD analysis was conducted on the refined microstructure of the alloy that achieved the maximum undercooling, and the significance of grain orientation and orientation difference distribution was found. TEM tests were conducted on a Cu60Ni38Co2 alloy with a maximum undercooling of 259 K, and it was found that there are high-density dislocation networks in some areas within them. Finally, the Vickers hardness of the above alloys was measured and recorded using a microhardness tester (HVS-1000Z), and the evolution between microhardness and undercooling, as well as the changes in microhardness under critical undercooling, were analyzed. Based on the analysis of EBSD, TEM, and microhardness data above, it is found that grain refinement at high undercooling is dominated by recrystallization.

A transition of dendrite growth kinetics from stable hcp to metastable fcc phases was observed for refractory Re95W5 alloy in an electrostatic levitation state, which attained a liquid undercooling up to 872 K (0.26TL). Stable hcp dendrite dominated in the single recalescence for pure Re in the whole of its undercooling regime, but prevailed for Re95W5 alloy only in the specific range of 159–867 K undercooling. The rapid dendrite growth velocity displayed a power-law relationship with the degree of undercooling. Once the refractory alloy melt was undercooled beyond 867 K undercooling, metastable fcc dendrite grew primarily from the liquid phase in the first recalescence, which was followed by a complete 'fcc to hcp' solid-state transformation in the second recalescence. An abrupt change of growth kinetics took place to depress the dendrite growth velocity drastically from 41.8 m·s−1 for stable hcp phase at 867 K undercooling to 10.9 m·s−1 for metastable fcc phase at 872 K undercooling. [ABSTRACT FROM AUTHOR]

Both Cu60Ni38Co2 and Cu60Ni40 alloy were naturally cooled after rapid solidification from the liquid phase. The transformation law of the microstructure characteristics of the rapidly solidified alloy with the change of undercooling (ΔT) was systematically studied. It is found that the two alloys experience the same transformation process. The refinement structures under different undercoolings were characterized by electron backscatter diffraction (EBSD). The results show that the characteristics of the refinement structure of the two alloys with low undercooling are the same, but the characteristics of the refinement structure with high undercooling are opposite. The transmission electron microscopy (TEM) results of Cu60Ni38Co2 alloy show that the dislocation network density of low undercooled microstructure is lower than that of high undercooled microstructure. By combining EBSD and TEM, it could be confirmed that the dendrite remelting fracture is the reason for the refinement of the low undercooled structure, while the high undercooled structure is refined due to recrystallization. On this basis, in the processing of copper base alloys, there will be serious work hardening phenomenon and machining hard problem of consciousness problems caused by excessive cutting force. A two-dimensional orthogonal turning finite element model was established using ABAQUS software to analyze the changes in cutting speed and tool trajectory in copper based alloy ultrasonic elliptical vibration turning. The results show that in copper based alloy ultrasonic elliptical vibration turning, cutting process parameters have a significant impact on cutting force. Choosing reasonable process parameters can effectively reduce cutting force and improve machining quality. [ABSTRACT FROM AUTHOR]

An understanding of the solidification characteristics of the melt pool during laser powder bed fusion, L-PBF, metal printing is essential to ensure the manufacture of sound parts. This is the main theme of this article where it is attempted to unlock the solidification black box through calculation/measurement of the main solidification parameters of cooling rate, growth rate, temperature gradient, and undercooling. The very small melt pool size and its rapid cooling hinder the application of conventional tools to extract such information. A knowledge of these parameters and their effect on the microstructure and morphology of constituent phases could help to better control the L-PBF process and indeed all the fusion-based additive manufacturing routes, to fabricate high-quality parts. Al12Si alloy solidification during the L-PBF fabrication route is examined to highlight the extreme changes in solidification parameters and their effect on the morphology and size of eutectic Si. This is because the morphology of Si controls the mechanical properties of the finished part. The Al–Si eutectic has a divorced architecture attributed to the difficulty associated with Si growth resulted from rapid solidification. The generation of a temperature gradient of about 7700 °C/mm resulted in cooling rates in the range of 1.1 × 106 °C/s and a growth rate of 140 mm/s. Such values were then used to predict the morphology of eutectic Si based on the traditional approach. [ABSTRACT FROM AUTHOR]

Thermobarometry provides a critical means of assessing locations of magma storage and dynamics in the lead-up to volcanic eruptions and crustal growth. A common approach is to utilise minerals that have compositions sensitive to changes in pressure and/or temperature, such as clinopyroxene, which is ubiquitous in mafic to intermediate magmas. However, clinopyroxene thermobarometry may carry significant uncertainty and require an appropriate equilibrium melt composition. In addition, the degree of magma undercooling (Δ T) affects clinopyroxene composition and zoning, with common sector zoning potentially obfuscating thermobarometry results. Here, we use a set of crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy) at Δ T  = 25–233 °C, P = 400–800 MPa, H2O = 0–4 wt % and fO2 = NNO + 2, with clinopyroxene crystals defined by Al-rich zones (prisms and skeletons) and Al-poor zones (hourglass and overgrowths) to assess common equilibrium models and thermobarometric approaches. Under the studied conditions, our data suggest that the commonly applied Fe–Mg exchange (cpx-meltKdFe–Mg) is insensitive to increasing Δ T and may not be a reliable indicator of equilibrium. The combined use of DiHd (CaMgSi2O6 + CaFeSi2O6) and EnFs (Mg2Si2O6 + Fe2Si2O6) models indicate the attainment of equilibrium in both Al-rich and Al-poor zones for almost all investigated Δ T. In contrast, CaTs (CaAl2SiO6) and CaTi (CaTiAl2O6) models reveal substantial deviations from equilibrium with increasing Δ T , particularly in Al-rich zones. We postulate that this reflects slower diffusion of Al and Ti in the melt compared with Ca and Mg and recommend the concurrent application of these four models to evaluate equilibrium between clinopyroxene and melt, particularly for sector-zoned crystals. Thermobarometers calibrated with only isothermal–isobaric experiments closely reproduce experimental P–T at low Δ T , equivalent to natural phenocrysts cores and sector-zoned mantles. Models that also consider decompression experiments are most accurate at high Δ T and are therefore suitable for outermost phenocryst rims and groundmass microlites. Recent machine learning approaches reproduce P–T conditions across all Δ T conditions. Applying our experimental constraints to sector-zoned microphenocrysts and groundmass microlites erupted during the 1974 eccentric eruption at Mt. Etna, we highlight that both hourglass and prism sectors are suitable for thermobarometry, given that equilibrium is sufficiently tested for. The combination of DiHd, EnFs, CaTs and CaTi models identifies compositions closest to equilibrium with the bulk melt composition, and results in smaller differences in P–T calculated for hourglass and prism sectors compared with applying only DiHd and EnFs equilibrium models. This provides a framework to assess crystallisation conditions recorded by sector-zoned clinopyroxene crystals in mafic alkaline settings. [ABSTRACT FROM AUTHOR]

The Yalguba Ridge volcanic rocks form part of the Middle Paleoproterozoic (ca. 1.97 Ga) volcano-sedimentary sequence within the Karelian Craton in the Fennoscandian Shield. Yalguba variolitic textures are known worldwide and have been previously considered to originate from liquid immiscibility. The present study reveals two new variolite types recognized in the Yalguba sequence: (1) Variolites with unzoned varioles have distinct chemical and mineralogical compositions of varioles and matrix that support an origin by liquid immiscibility. They were recognized in quenched zones of pillows, so it might be assumed that melt separation caused by liquid immiscibility occurred before magma emplacement. The difference from the previously described variolites lies in the variole microtexture and might be caused by the various cooling conditions. (2) Spherulitic variolites have varioles composed of andesine–oligoclase spherulites embedded in the cryptocrystalline matrix with oligoclase–anorthoclase composition, thus the variole and matrix have similar chemical and mineralogical composition. The mineralogical and textural features of these variolites suggest that the spherulites have a primary magmatic origin due to the rapid cooling of superheated magma. The variety of variolitic textures in the Yalguba section might be caused by the different H2O saturation of parental magma and cooling conditions. [ABSTRACT FROM AUTHOR]

In this study, to improve pulverization of Fe–Si alloy, the evolution of its microstructure under container and containerless solidification conditions were investigated using electromagnetic levitation melting technology. The results indicated that the microstructure changed from dendritic crystals during container solidification to equiaxed crystals with containerless solidification. With an undercooling of 280K obtained by containerless solidification, the pulverizing sensitive elements (Al, P) disperse better in FeSi2 phase. The equiaxed Si grains with relatively uniform grain size obtained under ΔT=280K are distributed in random orientation. High angle grain boundaries are significantly more present with the increase of misorientation within FeSi2 grains. This texture is closely related to recrystallization in favor of grain refinement, which is attributed to the melt oscillation and dendrites remelting-recrystallization effects occurring in containerless solidification.

Applying cycle superheating and molten glass purification technologies, Cu60Ni35Co5 alloys were deeply undercooled to maximum undercoolings of 284 K. The microstructure characteristics and its evolution varying with bulk undercooling during the rapidly solidified process were analyzed. It was found that, after minor addition of element Co, crystal refinement mechanisms of the undercooled Cu60Ni35Co5 system was similar to those of the Cu–Ni sytem. Crystal refined microstructure appearing at the low undercoolings was result of dendrite remelting mechanism; the dominant factor of grain refinement microstructure appearing at high undercooling regime was resultant from the recrystallization process. Driving force of stress induced strain energy for recrystallization could be divided into two parts, one was the thermal stress generated by the solidification latent releasing in the recalescence process, and the other was accumulated stress and plastic strain resultant from interaction between primary dendrite and liquid flow driven by rapid solidification.

Molten glass purification and cycle superheating technologies were used to make Ni65Cu35, Ni65Cu33Co2 and Ni65Cu31Co4 alloys obtain maximum undercoolings of 320 K, 292 K and 300 K respectively. In order to analyze the relationship between morphological characteristics of solidification front and undercooling change during migration of solid–liquid interface, a high-speed camera was used to capture pictures of the recalescence process. Observing the microstructure of the undercooled alloys using metallographic microscope, the characteristics and evolution of microstructure during rapid solidification process of undercooled liquids were analyzed. It was found that grain refinement mechanisms of highly undercooled Ni–Cu–Co alloys was the same as those of the Ni–Cu alloys. Dendrite remelting leads to the grain refinement at low undercooling, while the dominant factor of grain refinement at high undercooling is recrystallization process induced by stress. The internal driving force can be divided into two parts: one is the thermal stress generated by the releasing of solidification latent heat during recalescence process, and the other is the stress and strain accumulated by interaction of liquid flow and primary dendrite during rapid solidification. We also found that addition of third element Co not only played an important role in solidification rate and recalescence effect, but also significantly improved the average hardness of grain refined microstructure, which was about 80% higher than that of as cast alloy. The addition of trace Co was also conducive to the formation of non-segregation solidification microstructure.

The present analysis addresses the solidification and thermodynamic parameters involved during the solidification of aluminum (Al)-based alloys as presented in the literature using different systems viz., binary aluminum-boron (Al-B) and aluminum-titanium (Al-Ti) systems, ternary aluminum-titanium-boron (Al-Ti-B) and aluminum-titanium-carbon (Al-Ti-C) systems, as well as taking into consideration the silicon-titanium-aluminide (Si-TiAl3) interaction in Al-based alloys containing Si. The analysis is supported by recent metallographic evidence obtained by the authors on A356.2 alloys. The sections on thermodynamic aspects cover the different models proposed concerning nucleation and growth on a newly formed Al grain. The value of the recalescence parameter reduces gradually with the increase in the Ti added. At a level of 0.20 wt%, this parameter becomes zero. If the concentration of grain refiner exceeds a certain amount, the grain size becomes minimal. Another parameter to be considered is the interaction between the grain refiner and traces of other metals in the base alloy. For example, Al-4%B can react with traces of Ti that may exist in the base alloy, leading to the reaction between boron and titanium to form titanium diboride (TiB2). Grain refinement is achieved primarily with TiB2 rather than aluminum diboride (AlB2), or both, depending on the Ti content in the given alloy. [ABSTRACT FROM AUTHOR]

Crystal morphology is controlled by several physicochemical parameters such as the temperature, pressure, cooling rate, nucleation, diffusion, volatile composition, and viscosity. The development of different crystal morphologies is observed as a function of the cooling rate in many different rock types (i.e., glassy volcanic rocks, and archeometallurgical slags). Crystallization is a two-stage kinetic process that begins with the formation of a nucleus and then continues with the accumulation of ions on it. The shapes of the crystals depend on the degree of undercooling (ΔT), and euhedral crystals, having characteristic forms that reflect their crystallographic internal structure, that grow just below their liquidus temperature. In this study, crystal morphologies in different minerals (e.g., quartz, sanidine, olivine, pyroxene, magnetite, etc.) that had developed in silicic volcanic rocks (spherulites) and slags from ancient mining were investigated and characterized using optical microscopy, X-ray diffraction, and Fourier-transform infrared (FTIR), Raman, and scanning electron microscope-energy dispersive X-ray fluorescence (SEM-EDX) spectroscopic techniques. Depending on the increase in the cooling rate, quartz, feldspar, olivine, pyroxene, and magnetite minerals were found to crystallize in subhedral, skeletal, dendritic, spherical, bow-tie and fibrous forms in glassy volcanic rocks and archeometallurgical slags. [ABSTRACT FROM AUTHOR]

Both Cu60Ni38Co2 and Cu60Ni40 alloy were naturally cooled after rapid solidification from the liquid phase. The transformation law of the microstructure characteristics of the rapidly solidified alloy with the change of undercooling (ΔT) was systematically studied. It was found that the two alloys experienced the same transformation process. The refinement structures under different undercoolings were characterized by electron backscatter diffraction (EBSD). The experimental results show that the characteristics of the refinement structure of the two alloys with low undercooling are the same, whereas, the characteristics of the refinement structure with high undercooling are opposite. The transmission electron microscope (TEM) results of Cu60Ni38Co2 alloy show that the dislocation network density of low undercooled microstructure is lower than that of high undercooled microstructure. By combining EBSD and TEM, it can be confirmed that the dendrite remelting fracture is the reason for the refinement of the low undercooled structure, while the high undercooled structure is refined due to recrystallization. [ABSTRACT FROM AUTHOR]

In this study, a series of Bridgman casting experiments were conducted to study the physical processes occurring in 2D grain selectors with different geometric parameters. The corresponding effects of the geometric parameters on grain selection were quantified by using an optical microscopy (OM) and a scanning electronic microscopy (SEM) equipped with electron backscatter diffraction (EBSD) function. Based on the results, the influences of the geometric parameters of the grain selectors are discussed, and an underlying mechanism accounting for the experimental results is proposed. The critical nucleation undercooling in the 2D grain selectors during grain selection was also analyzed. [ABSTRACT FROM AUTHOR]

The present article addresses solidification parameters, and includes analyses of the macrostructure and microstructure in the light of the results obtained from the thermal analysis, from which it is possible to conclude that undercooling (TS) and recalescence (TR) temperatures increase with the initial increase in titanium (Ti) concentration. If the concentration reaches approximately 0.25%, a rapid decrease in these temperatures is observed. Thereafter, the temperatures increase again with the further increase in Ti concentration, and eventually become constant. These temperatures also vary depending on the superheating and casting temperature. The ∆T parameter (i.e., TS − TR) decreases with the Ti concentration and, from a concentration of around 0.20% Ti, this parameter becomes zero. The grain size decreases with the Ti concentration. If the concentration exceeds about 0.20%, the grain size becomes the minimum. Another parameter to be considered is the interaction between the grain refiner and the traces of other metals in the base Al alloy. For example, Al-4%B can react with traces of Ti that may exist in the base alloy, leading to the reaction between boron (B) and Ti to form TiB2. Grain refinement is achieved primarily with TiB2 rather than AlB2, or both, depending on the Ti content in the given alloy. [ABSTRACT FROM AUTHOR]

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys.

The Sn-8.8 wt. % Zn eutectic alloy was produced by using casting furnace and vacuum melting furnace. Then cast alloys were directionally solidified upwards with a constant temperature gradient (G=4.16 K/mm) at different solidification rates (V=8.3-166.0 μm/s) in a Bridgman type controlled directional solidification furnace. The undercooling (ΔT) values are calculated with the Jackson-Hunt model by using the solidification rate, eutectic spacing (λ) and system parameters (K1 and K2). At a constant temperature gradient (G=4.16 K/mm) with the increasing of solidification rate from 8.3 μm/s to 166.0 μm/s, undercooling increased from 0.87 K to 3.89 K. At minimum undercooling of 0.87 K, the rod eutectic spacing is obtained 3.22 μm while the eutectic spacing is obtained 0.72 μm at the 3.89 K. The results were compared with the literature. [ABSTRACT FROM AUTHOR]

In the realm of undercooled eutectic alloys, the nucleation (i.e., copious vs. single) and the growth (i.e., coupled vs. decouple) modes, particularly the formation of anomalous eutectics, remain subjects of intense debate. This study delves into the crystallographic orientation relationships (ORs) during rapid solidification of an undercooled Co-24 at.% Sn eutectic alloy, where the high-temperature eutectic phases (β-Co 3 Sn 2 and α-Co) persist to room temperature. A significant finding is the consistent observance of the same eutectic OR, i.e., 11 2 ̅ 0 β − Co 3 Sn 2 // 1 1 ̅ 1 α − Co and 0001 β − Co 3 Sn 2 // 110 α − Co , across various undercooling conditions from low to high and eutectic morphologies from lamellar to anomalous. This consistency underscores a unified growth mode of coupled eutectic growth. Furthermore, the observance of twin OR, i.e., 11 2 ̅ 1 < 11 ̅ 26 > , 11 2 ̅ 2 < 11 23 ̅ > or 11 2 ̅ 4 < 22 43 ̅ > , between β-Co 3 Sn 2 phases in diverse eutectic colonies, spanning from low to intermediate undercooling, and would also be the case of high undercooling, reinforces a single nucleation mode except under exceedingly low undercooling. Building on these insights, the anomalous eutectic colonies are suggested to be formed from a single origin where coupled eutectic growth of eutectic seaweeds or eutectic dendrites instead of dual origins. This study not only illuminates the underlying mechanisms of rapid solidification in undercooled eutectic alloys but also paves the way for innovative microstructure modulation strategies. [Display omitted] • The 11 2 ̅ 0 β − Co 3 Sn 2 // 1 1 ̅ 1 α − Co , 0001 β − Co 3 Sn 2 // 110 α − Co eutectic OR is followed independently with undercooling and microstructures. • Twin ORs are obeyed between β-Co 3 Sn 2 in different eutectic colonies except for very low undercooling. • The single nucleation mode is the case if undercooling is not very low and the coupled eutectic growth mode is followed. • Anomalous eutectics are formed from coupled eutectic growth but not uncoupled dendrite growth. [ABSTRACT FROM AUTHOR]

Multi-principal element alloys (MPEAs) have attracted growing attention owing to the vast compositional field and the comprehensive properties. In this work, Fe 7 (CoNi) 77 B 16 MPEA was undercooled by vacuum melting furnace with low (61 K, 95 K), medium (115 K, 148 K), and high undercoolings (200 K). The maximum growth velocity of the alloy was 0.21 m/s due to the sluggish kinetics effect. The regular eutectic transformed to anomalous eutectic and the primary dendrite refined from 9.1 μm to 3.5 μm with the increase of undercooling. Meanwhile, the phase selection behavior at high undercooling was observed between the stable (Fe, Co, Ni) phase and the metastable (Fe, Co, Ni) 23 B 6 phase. The hardness of primary phase and compressive strength of the undercooled MPEAs were increased to 952.19 HV and 2061.72 MPa, which is much higher than the as-cast alloy. The enhancement of the mechanical properties was attributed to microstructure evolution. The decrease in plasticity resulted from the increasing volume fraction of brittle intermetallic phases. This study helps to theoretically understand the solidification mechanism of the Fe-Co-Ni-B MPEAs and provides a promising way to enhance the mechanical properties of the novel MPEAs. • The growth velocity of primary dendrite is determined. • Regular eutectic transforms to anomalous eutectic. • The microstructure refines with the increase of undercooling. • Phase selection occurs at high undercooling. • Mechanical properties enhance due to non-equilibrium solidification. [ABSTRACT FROM AUTHOR]

The mechanism of grain refinement in undercooled Ni 3 Ga melts was investigated. An in situ diagnosis of the dendrite growth velocity using a high-speed camera indicates direct crystallization of the Ni 3 Ga compound and disorder trapping at a critical undercooling of 68 K and 120 K, respectively. An EBSD analysis shows a grain-refined microstructure for samples with undercoolings of 120 K and 148 K in contrast to a coarse-grained microstructure for the sample with an undercooling of 89 K. HRTEM investigation shows a mixture of a disordered solid solution and the ordered Ni 3 Ga compound in the atomic-scale microstructure of each sample in agreement with X-ray and neutron diffraction analyses. Microhardness tests show that disorder trapping reduces the mechanical strength of the samples in spite of grain refinement. It is concluded that disorder trapping promotes plastic deformation of the Ni 3 Ga compound and that grain refinement is induced by recrystallization after rapid solidification processing. [Display omitted] [ABSTRACT FROM AUTHOR]