Containerless Processing Research Articles

Undercooling and demixing of copper-based alloys

Since the beginning of materials science research under microgravity conditions immiscible alloys have been an interesting subject. New possibilities to investigate such systems are offered by containerless processing techniques. Of particular interest is the ternary system Cu-Fe-Co, and its limiting binaries, Cu-Co and Cu-Fe. They all show a metastable miscibility gap in the regime of the undercooled melt. Within the ESA-MAP project “CoolCop”, different aspects of this alloy have been investigated; results obtained so far are reported here.

Microgravity Experiments on the Effect of Internal Flow on Solidification of Fe‐Cr‐Ni Stainless Steels

A new hypothesis has been developed to explain the effect of internal fluid flow on the lifetime of a metastable phase in solidifying Fe-Cr-Ni alloys. The hypothesis shows excellent agreement with available experimental results, but microgravity experiments are required for complete validation. Certain Fe-Cr-Ni stainless steel alloys solidify from an undercooled melt by a two-step process in which the metastable ferrite phase forms first followed by the stable austenite phase. Recent experiments using containerless processing techniques have shown that the lifetime of the metastable phase is strongly influenced by flow within the molten sample. Simulations using a commercial computational fluid dynamics (CFD) package, FIDAP, were performed to determine the time required for collision of dendrites and compared to experimental delay time. If the convective velocities are strong enough to bend the primary arms, then the secondary arms of adjacent dendrites can touch. The points of collision form low-angle boundaries and result in high-energy sites that can serve as nuclei for the transformation to the stable phase. It has been determined that the convective velocities in electrostatic levitation (ESL) are not strong enough to cause collision. However, in ground-based electromagnetic levitation (EML), the convective velocities are strong enough to cause the dendrites to deflect so that the secondary arms of adjacent dendrites collide. There is quantitative agreement between the numerically determined time to collision and the experimentally observed delay time in EML. The strong internal velocity due to convection within the EML samples is the reason for the observed difference in delay times between ESL and EML. Microgravity testing is essential because the significant change in nucleation behavior occurs between the ranges accessible by ground-based ESL and EML. Testing in microgravity using EML will permit a large range of internal convective velocities including those that are inaccessible in 1 g.

Rapid solidification: in situ diagnostics and theoretical modelling

We report on progress in direct experimental investigations of non-equilibrium crystallization in undercooled melts. Containerless processing is applied for undercooling and is combined with diagnostic means. The results of such experiments are utilized to critically assess physical models for rapid solidification. Existing models of rapid growth of solid into undercooled melts are reviewed. The sharp interface model is applied to quantitatively describe rapid dendrite growth of metals and alloys. It is extended to include effects of fluid flow in liquids induced by forced convection in electromagnetically levitated drops. Morphological transitions resulting in grain refinement via instabilities of growing dendrites are analyzed and used to evaluate the effect of fluid flow on grain refinement. Theoretical predictions given by sharp-interface model are compared with results of phase-field modeling and with new data of crystal growth dynamics measured with high accuracy. Depending on the undercooling prior to solidification the effects of solute diffusion, convective flow, solute trapping and microstructure evolution are demonstrated.

Glass transition and crystallization behavior of Zr 41Ti 14Cu 12.5Ni 10Be 22.5 glassy sphere solidified in a 52-m drop tube

Zr 41Ti 14Cu 12.5Ni 10Be 22.5 glassy spheres with diameter 80–1000 μm are prepared by containerless processing technique of a 52-m drop tube. Glass transition behavior and crystallization kinetics of the Zr 41Ti 14Cu 12.5Ni 10Be 22.5 glassy spheres solidified at various overheating temperatures are investigated. The experimental results indicate that the overheating temperature of droplets makes a notable impact on the glass transition and crystallization. The glassy sphere solidified at higher overheating temperature exhibits higher crystallization temperature, apparent activation energy of the glass transition and main crystallization reaction when heated.

A comparative EBSP study of microstructure and microtexture formation from undercooled Ni 99B 1 melts solidified on an electrostatic levitator and an electromagnetic levitator

Ni 99B 1 alloys were solidified by containerless processing at various melt undercoolings on an electrostatic levitator (ESL) and an electromagnetic levitator (EML). A scanning electron microscope in combination with an electron backscatter diffraction pattern mapping technique was employed to reveal microstructures and microtextures formed on these two facilities. The microstructure consists of well-developed primary dendrites with coarse secondary arms in the alloys solidified on the ESL at low and medium undercooling levels, whereas equiaxed grains are yielded in alloys solidified on the EML at almost the same undercoolings. Further analysis indicates that the melt flow induced by the electromagnetic field in the EML may play a significant role in promoting fragmentation of primary dendrites in the mushy zone and thus resulting in equiaxed grains. In contrast, the primary dendrites in the alloy processed on the ESL can fully develop in the absence of melt flow. The fluid flow in the sample on the EML can rotate, move, and displace surviving fragments, yielding a random distribution of grain orientation and thus leading to a random microtexture at low and medium undercoolings. At high undercoolings, refined equiaxed grains can be obtained on both the ESL and the EML and the influence of melt flow on refinement seems negligible due to the enhanced driving force in capillarity and solute effects. A great number of coherent annealing twins are formed, making the pole figures more complex and random.

Anomalous Permittivity during Crystallization of BaTi2O5 Glass

A 2 mm-diameter glass sphere of ferroelectric BaTi2O5 was produced from melt using containerless processing. Three successive phase transitions above the glass transition temperature, T g − end = 972 K, of BaTi2O5 were observed. At crystallization temperature, T α−onset = 994 K, the permittivity at 100 Hz jumped instantaneously by more than one order of magnitude, peaking at over 107. The interesting behavior at crystallization temperature has important technical implications for obtaining an excellent dielectric ceramics-glass through controlled crystallization of BaTi2O5 glass.

Kinetics of solidification of B2 intermetallic phase in the Ni–Al system

Solidification from the undercooled melt is dominated by nucleation and subsequent crystal growth. For chemically ordered intermetallics, the kinetics of crystal growth can be markedly different from that of disordered solid solutions, manifested as substantial interfacial undercoolings or anomalous partitioning behaviour. In the present work the electromagnetic levitation technique is applied, as a containerless processing route, to melt and deeply undercool Ni–Al alloy melts of various compositions – mostly within the homogeneity range of the B2 (β) phase. The ensuing rapid solidification of the undercooled specimen is directly observed by time-resolved temperature measurements and monitored by a high-speed video camera. This allows for direct investigations of crystal growth velocities as a function of composition and undercooling. The experimental results show that the growth of stoichiometric B2 phase (NiAl) is – contrary to common expectations – more sluggish as compared to that of Ni-rich alloys, despite the hindering effect of solute rejection on the growth rate which seems to occur only in the latter. These findings are interpreted within current models of crystal growth taking into account non-equilibrium effects due to partial ‘disorder trapping’ at the solid–liquid interface.

Fabrication of BaTi2O5 Glass−Ceramics with Unusual Dielectric Properties during Crystallization

A 2-mm-diameter glass sphere of ferroelectric BaTi2O5 was fabricated from melt using containerless processing. The glass structure was analyzed by high-energy X-ray diffraction using an incident ph...

Nonlinearities in the undercooled properties of Ti39.5Zr39.5Ni21

Using electrostatic-levitator (ESL)-based containerless processing combined with non-contact measuring techniques, surface tension and viscosity have been measured for Ti39.5Zr39.5Ni21, using the oscillating-drop method, in the superheated and metastable undercooled liquid states. Viscosity measurements show a non-Arrhenius behaviour that more closely matches a Vogel–Tamman–Fulcher trend, and a sudden divergence away from a high-temperature linear trend in surface tension has been observed for this composition. An overview of the measurement technique as well as the measurements are presented.

ガスジェット浮遊型電磁溶融プロセスによって作製したLa-Cu-Ni-Co-AlおよびNd-Fe-Co-Al系バルク状近似アモルファス合金

For Rare Earth-Transition Metal-Al with high undercooled liquid formability and glass-forming ability, bulk alloys have been produced with gas jet flow type electromagnetic levitation process, which is a new containerless process. A series of alloys of La80-xCu10Ni5Co5Alx (x=15, 20, 25 at%) were analyzed with respects to the supercooled solidification process, nucleation behavior of a crystalline phase, and the possibility of the formation of bulk amorphous alloys. In addition, the similar studies were carried out for the specimens containing SiC, which is reported to be effective to enlarge undercooling when used in the containerless process. The results show that the addition of SiC suppresses the nucleation of a crystalline phase, and thus, the undercooling (ΔT) increases in the range of ΔT=0.22 to 0.28 Tm, where Tm is the melting point. In addition, partially crystallized bulk amorphous alloys with a diameter of 6 mm are obtainable for the alloys with 0.2 mass% SiC addition when they are solidified at approximate cooling rate of 100 K/s. Furthermore, the SiC free alloys of La65Cu10Ni5Co5Al15 and Nd60Fe20Co10Al10 are also obtainable as partially crystallized bulk amorphous alloys.

Amorphous Formation and Magnetic Properties of Nd-Fe-Co-Al Alloys by Gas Flow Type Levitation Process

It is reported that Nd-Fe-Co-Al amorphous alloys have high bulk amorphous formation ability and high coercivity by rapid solidification method. We have examined the undercooling solidification, bulk amorphous formation and high coercivity appearance by using containerless process. In this study, we investigated the undercooling, bulk amorphous formation and magnetic properties for Nd-Fe-Co-Al alloys which are levitated and solidified by using the gas jet flow and high cooling type electromagnetic levitation system. Therefore, the high undercooling degree was 66–152 K and the samples formed amorphous phase. The bulk samples, � 6 mm sphere, solidified at the cooling rate, about 100 K/s. In addition, the coercivity for Nd65Fe10Co15Al10 sample with bulk amorphous phase, 3.7 kOe, was the highest value in all samples. Also, the thermal stability for Nd65Fe10Co15Al10 sample was carried out by isothermal annealing experiments. The origin of high coercivity may be related to the amorphous phase. [doi:10.2320/matertrans.47.2842]

20304 大粒径浮遊液滴の流動挙動に関する研究(流れの計測と制御(1),OS6 流れの計測と制御)

The containerless processing conducted by droplet levitation techniques make it possible to manufacture new materials and conduct non-contact measurement of material properties under the microgravity. It is pointed out that surface deformation and internal flow of the large levitated droplet influence the containerless processing. However, there is few study about surface deformation and internal flow large levitated droplet by the acoustic wave. In the present study, at first, internal flow of levitated droplet are investigated by the ultrasonic standing wave under normal gravity environment. Finally, the levitation characteristic and internal flow of levitated droplet are investigated under the reduced gravity environment by using the aircraft.

Bulk Amorphous Formation and Magnetic Properties of Nd-Fe-Co-Al Alloys by the New Gas Jet Flow Type Levitating Process

The amorphous formation ability and the magnetic properties of Nd 60 Fe 30-x Co x Al 10 (x = 10, 15, 20 or 30) alloys in the containerless process were studied by the new gas jet flow type levitating process. The gas jet flow type levitating process enables solidification without any container wall by the inert gas jet. The samples were solidified at the cooling rate of around 100 K/s. Then, the undercooling of samples exhibits high values (AT = 60-150 K). From X-ray diffraction measurements, the Nd 60 Fe 30-x Co x Al 10 samples exhibit a typical broad diffraction pattern for an amorphous structure. The DTA curves of x = 10, 15 and 20 showed an exothermic peak due to the crystallization. That is, it was revealed that the Nd 60 Fe 30-x Co x Al 10 samples formed bulk amorphous. Also, the coercivity is 1.6, 3.3 and 3.6kOe for the Nd 60 Fe 20 Co 10 Al 10 , Nd 60 Fe 15 Co 15 Al 10 and Nd 60 Fe 10 Co 20 Al 10 , respectively. From the thermomagnetic curves, the Curie temperature is determined to be 463, 482 and 482 K for the Nd 60 Fe 20 Co 10 Al 10 , Nd 60 Fe 15 Co 15 Al 10 and Nd 60 Fe 10 Co 20 Al 10 , respectively. In the M-H loops and the thermomagnetic curves, this difference between x = 10 and x = 15, 20 may depend on the microstructure.

Thermophysical property measurements of liquid metals by electromagnetic levitation

Electromagnetic levitation is a useful technique for containerless processing of liquid metals. In combination with non-contact diagnostic tools it can be used for completely non-invasive measurements of thermophysical properties of metallic melts. Considerable progress has been made in this field in recent years. This paper reviews methods and results, including those obtained in microgravity.

Machine vision for high-precision volume measurement applied to levitated containerless material processing

By combining the best practices in optical dilatometry with numerical methods, a high-speed and high-precision technique has been developed to measure the volume of levitated, containerlessly processed samples with subpixel resolution. Containerless processing provides the ability to study highly reactive materials without the possibility of contamination affecting thermophysical properties. Levitation is a common technique used to isolate a sample as it is being processed. Noncontact optical measurement of thermophysical properties is very important as traditional measuring methods cannot be used. Modern, digitally recorded images require advanced numerical routines to recover the subpixel locations of sample edges and, in turn, produce high-precision measurements.

Link between liquid structure and the nucleation barrier for icosahedral quasicrystal, polytetrahedral, and simple crystalline phases inTi−Zr−Nialloys: Verification of Frank’s hypothesis

Comprehensive undercooling experiments on a large number of simple crystalline, polytetrahedral, and icosahedral quasicrystalline phase forming compositions in $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Zr}\text{\ensuremath{-}}\mathrm{Ni}$ alloys have been carried out using electrostatic levitation (ESL) techniques for containerless processing. Consistent with Frank's hypothesis, a direct correlation was found between the reduced undercooling [$\ensuremath{\Delta}{T}_{r}=({T}_{l}\ensuremath{-}{T}_{r})∕{T}_{l}$, where ${T}_{r}$ and ${T}_{l}$ are the nucleation and liquidus temperatures, respectively] and the icosahedral short-range order in the solid. The reduced undercooling is less for liquids that form the icosahedral quasicrystal ($i$ phase) than for those that form the hcp $C14$ Laves polytetrahedral phase. For many compositions near $21\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%$ Ni, the primary nucleation of a metastable $i$ phase instead of a stable $C14$ Laves phase demonstrates that the interfacial free energy between the liquid and the $i$ phase is smaller than between the liquid and the $C14$ Laves phase, indicating icosahedral local order in the undercooled liquid. This is in agreement with a classical-nucleation-theory-based estimate of the interfacial free energy and the work of formation of the critical cluster from the undercooling data. Taken together with high-energy x-ray diffraction studies of the undercooled liquid, these results demonstrate that the local structure of liquids in $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{Zr}\text{\ensuremath{-}}\mathrm{Ni}$ alloys is icosahedral, as postulated by Frank over a half century ago.

Experimental evidence of crystal fragmentation from highly undercooled Ni99B1 melts processed on an electrostatic levitator

Employing an electrostatic levitator (ESL) equipped with a CO2 laser heating setup, we solidified Ni99B1 bulk crystals through containerless processing at high undercoolings and observed grain-refined microstructures. The electron backscatter diffraction pattern (EBSP) and analysis of the twin directions were accomplished, from which the primary growth traces with a cellular-like structure were revealed on a macro-millimeter scale. In comparison with the strong mechanical electromagnetic stirring in a sample processed on an electromagnetic levitator, the ESL provides a quite quiescent state for the melt, which enables identification of the primary growth traces after solidification. The present observation supplied experimental evidence that the refined microstructure in the Ni99B1 alloys at the high undercooling regime was due to fragmentation of the primary growth crystal, rather than dynamic nucleation.

Phase selection during solidification of undercooled Ti–Fe–Si–O melts

The alloy system Ti–Fe–Si–O forms a large variety of stable and metastable solid phases. By non-equilibrium solidification from the metastable state of an undercooled melt different solidification pathways are accessible. In this work the phase selection behavior during solidification of Ti–Fe–Si–O melts was investigated as function of undercooling and alloy composition using the combination of the containerless processing technique of electromagnetic levitation and energy dispersive diffraction of synchrotron radiation. This allows direct determination of the crystal structure of the solid phases formed during solidification.

Liquid phase separation of Co–Cu alloys in the metastable miscibility gap

Liquid phase separation has been investigated in the Cu–Co system using electromagnetic levitation (EML) and processing in drop tube. Owing to the rapid solidification in both methods, properties of the liquid are maintained after solidification. In the Co–84.0 at.% Cu alloy the evolution of droplet dispersions versus cooling rate has been experimentally determined. In drop tube experiments, the experiment duration is short, and ends before collisions of droplets and coagulation become important at a given fluid flow motion. Terrestrial EML processing subjects the liquid to a strong fluid flow, which leads to a bimodal droplet size distribution. Containerless processing in the TEMPUS facility during parabolic flight reduces the fluid flow and, thus, coagulation of droplets.

Shape Recovery of a Levitated Aspherical Droplet From 2D Image Information

This paper presents an image processing technique in order to predict the shape of a levitated aspherical droplet. The technique is of great importance to containerless materials processing. A majority of the electromagnetic levitation techniques utilizes two cameras at right angles to observe both transversal and frontal views. This allows obtaining two images of the droplet at instant time. In many cases, the portion of the frontal image is missing due to the heating coil. The newly developed technique allows restoration of the missing portion of the image information. The through image can be reconstructed by combining the recovered shapes. A special computer program is generated to simulate a normalized volume of the droplet.