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Multiple power ultrasounds were employed to investigate the phase transition process of ternary Al81.5Cu14.7Bi3.8 immiscible alloy by various exerting modes. As the ultrasonic sources increased, the liquid phase separation pattern transformed from (Bi)-rich layered macrosegregation into the uniform distribution of secondary (Bi) droplets. Meanwhile, the primary (Al) phase evolved from coarse dendrites into plenty of small spherical grains and also tended to be uniformly dispersed. The subsequently formed ternary (Al) + (Al2Cu) + (Bi) monotectic structure, featured by the alternative (Al) and (Al2Cu) lamellar structure with fine (Bi) grains distributed, was coarsened first and then refined. Numerical simulations showed that the transient cavitation and the acoustic streaming strength were significantly enhanced by increasing ultrasonic beams, with the fourfold ultrasounds producing the most prominent effects on the phase separation process. The intensive and enlarged cavitation areas greatly accelerated the nucleation of both the secondary liquid phase and primary solid phase, which refined the growing (Bi) droplets and (Al) dendrites. The strength and morphology of acoustic streaming were the key factors in offsetting Stokes motion and carrying the growing grains to various regions, resulting in a uniform microstructure. Furthermore, increasing ultrasonic sources improved the friction and wear properties of the solidified alloy, which indicated that the Al81.5Cu14.7Bi3.8 immiscible alloy may become an excellent wear-resistant material owing to the uniform monotectic structure fabricated by the fourfold ultrasounds. [ABSTRACT FROM AUTHOR]

The metastable liquid properties and chemical bonds beyond 2000 K remain a huge challenge for ground‐based research on liquid materials chemistry. We show the strong undercooling capability, metastable liquid properties and surface wave patterns of refractory Nb−Si and Zr−V binary alloys explored in space environment. The floating droplet of Nb82.7Si17.3 eutectic alloy superheated up to 2338 K exhibited an extreme undercooling of 437 K, approaching the 0.2TE threshold for homogeneous nucleation of liquid‐solid reaction. The microgravity state endowed alloy droplets with nearly perfect sphericity and thus ensured the high accuracy to determine metastable undercooled liquid properties. A special kind of swirling flow was induced for liquid alloy owing to Marangoni convection, which resulted in the spiral microstructures on Zr64V36 alloy surface during liquid‐solid phase transition. The coupled impacts of surface nucleation and surface flow brought in a novel olivary shape for these binary alloys. Furthermore, the chemical bonds and atomic structures of high temperature liquids were revealed to understand the liquid properties in outer space circumstances. [ABSTRACT FROM AUTHOR]

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]

The rapid eutectic growth kinetics of undercooled liquid Ti27Ni25Co20V14Nb14 high-entropy alloy (HEA) was investigated by electromagnetic levitation (EML) and drop tube (DT) techniques. The maximum liquid undercoolings attained 207 K (0.14 TL) at levitated state and 385 K (0.25 TL) under free fall condition, respectively. During EML experiments, a microstructural transition from regular lamellar eutectic to anomalous eutectic was achieved by controlling the liquid undercooling above 62 K. An increase in volume fraction of anomalous eutectic and significant grain refinement were modulated by further elevating the liquid undercooling. The maximum growth velocity of lamellar eutectic was measured as 1.47 mm s−1, whereas that of anomalous eutectic reached 35.64 mm s−1 at the largest undercooling of 207 K. Under microgravity condition, the microstructure transformed twice by adjusting alloy droplet diameters. Two critical diameters were determined, and the corresponding undercooling thresholds were calculated as 73 K and 251 K, respectively. When the droplet diameter decreased to 705 μm, the "lamellar eutectic–anomalous eutectic" microstructure transition occurred, which was similar to that under EML condition. Notably, a coarse structure consisting of primary hcp-NbV grains and intergranular anomalous eutectic was formed in tiny alloy droplets with less than 95 mm diameter, which is attributed to the independent nucleation of hcp-NbV phase. Furthermore, the crystalline orientation relationship between B2-TiNi and hcp-NbV phases was determined as 11 2 ¯ 3 ¯ hcp // 111 B 2 and 1 1 ¯ 00 hcp // 110 B2 in lamellar eutectic by TEM analysis. The alloy microhardness was remarkably enhanced after containerless rapid solidification, which resulted mainly from the crystalline grain refinement. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-8 was synthesized in a containerless state via acoustic levitation. The cavitation effect of ultrasound affected the coordination connection of organic ligands in acoustically levitated droplets and they exhibited a conspicuous difference in the particle size distribution as compared with those under normal conditions. Herein, methanol was chosen as the solvent to investigate the influence of droplet evaporation on acoustic levitation synthesis. The kinetic parameters of droplet evaporation such as geometrical morphology transformation, concentration change and temperature evolution were measured for the levitation state. Surface evaporation resulted in the drastic deformation of the droplet during ZIF-8 synthesis and caused its vertical vibration and shape oscillation. The abrupt change of the levitation state aggravated the sound field effect on the containerless synthesis and caused a decrease of particle size distribution. A two-dimensional axis-symmetry model was used to visually simulate the sound field distribution during acoustic levitation synthesis based on the finite element method. The fabricated ZIF-8 was able to remove phthalic acid in wastewater through adsorption, and its kinetic features followed a pseudo second-order rate model. [ABSTRACT FROM AUTHOR]