Phase Selection in Sub-Rapidly Solidified Au-20Sn Alloys

2015 ◽  
Vol 817 ◽  
pp. 325-330
Author(s):  
Yu Hai Qu ◽  
Kai Jin Yang ◽  
Yan Tian Zhou ◽  
Yong Mao ◽  
Wei Zhang ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Copper Mold ◽  
Cooling Rates ◽  
Phase Selection ◽  
Graphite Mold ◽  
Injection Casting ◽  
Rapidly Solidified ◽  
Ausn Phase

The sub-rapidly solidified Au-20Sn eutectic alloys were prepared by four different solidification pathways, such as, graphite mold conventional casting, graphite mold injection casting, copper mold injection casting, and water-cooled copper mold suction casting. The precipitating sequences of competing primary phases of sub-rapidly solidified Au-20Sn alloys with four different cooling rates were investigated. The results show that phase selection process is related to the cooling rates during sub-rapid solidification process. The primary ζ'-Au5Sn phase with developed dendrites precipitate at low cooling rate (2.4×10−4.2×102K/min) and the morphologies of the primary ζ'-Au5Sn change to rosette-like at higher cooling rate (9.0×103K/min). While the cooling rate reaches to 3.5×104K/min, the primary ζ'-Au5Sn phase can be suppressed but δ-AuSn phase will precipitate prior to the ζ'-Au5Sn phase. On the basis of the classical nucleation theory and transient nucleation theory, the process of competitive nucleation between the ζ'-Au5Sn phase and the δ-AuSn phase were analyzed for sub-rapid solidified Au-20Sn alloy. The theoretical calculations are consistent with the experimental investigations.

scholarly journals Nucleation Behavior of a Single Al-20Si Particle Rapidly Solidified in a Fast Scanning Calorimeter

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2920
Author(s):  
Qin Peng ◽  
Bin Yang ◽  
Benjamin Milkereit ◽  
Dongmei Liu ◽  
Armin Springer ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Rapid Solidification ◽  
Heterogeneous Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Solidification Behavior ◽  
Nucleation Kinetics ◽  
Nucleation Behavior ◽  
Nucleation Undercooling ◽  
Primary Si

Understanding the rapid solidification behavior characteristics, nucleation undercooling, and nucleation mechanism is important for modifying the microstructures and properties of metal alloys. In order to investigate the rapid solidification behavior in-situ, accurate measurements of nucleation undercooling and cooling rate are required in most rapid solidification processes, e.g., in additive manufacturing (AM). In this study, differential fast scanning calorimetry (DFSC) was applied to investigate the nucleation kinetics in a single micro-sized Al-20Si (mass%) particle under a controlled cooling rate of 5000 K/s. The nucleation rates of primary Si and secondary α-Al phases were calculated by a statistical analysis of 300 identical melting/solidification experiments. Applying a model based on the classical nucleation theory (CNT) together with available thermodynamic data, two different heterogeneous nucleation mechanisms of primary Si and secondary α-Al were proposed, i.e., surface heterogeneous nucleation for primary Si and interface heterogenous nucleation for secondary α-Al. The present study introduces a practical method for a detailed investigation of rapid solidification behavior of metal particles to distinguish surface and interface nucleation.

Microstructure and Phase Selection of Undercooled Single-Phase Fe-Co Alloy

2010 ◽  
Vol 154-155 ◽  
pp. 1624-1628
Author(s):  
Ning Liu ◽  
Gen Cang Yang ◽  
Feng Liu
Keyword(s):  
Theoretical Calculation ◽  
Single Phase ◽  
Critical Value ◽  
Nucleation Theory ◽  
Experimental Result ◽  
Classical Nucleation Theory ◽  
Phase Selection ◽  
Maximum Undercooling ◽  
Bcc Phase ◽  
Selection Of

Fe-Co single-phase alloy melts with different Co contents were undercooled using fluxing method. The maximum undercooling DT = 457K (relative undercooling DT/Tm=0.259) was achieved in this work. At low undercooling (DT), single-phased microstructure was observed, but metastable bcc phase emerged in the as-solidified microstructure once DT exceeded a critical value, DTcrit. In the presence of classical nucleation theory, phase selection in the undercooled Fe-Co melt was investigated, and the theoretical calculation was coincided with the experimental result.

Nucleation Behavior and Solid-Liquid Interfacial Energy of Polytetrahedral Phases

1999 ◽  
Vol 580 ◽  
Author(s):  
Dirk Holland-Moritz
Keyword(s):  
Interfacial Energy ◽  
Orthorhombic Phase ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Phase Selection ◽  
Nucleation Behavior ◽  
Σ Phase ◽  
Selection Behavior ◽  
Liquid Interfacial Energy ◽  
Solid Liquid

AbstractAccording to classical nucleation theory the nucleation- and phase-selection behavior of undercooled meltallic melts is strongly dependent on the solid-liquid interfacial energy.A structural approach to the modelling of the interfacial energy for simple melt-crystal interfaces (fcc, hcp, bcc) was developed a number of years ago [1-4]. This approach is extended to polytetrahedral phases using numerical simulation. Results of these calculations are presented for different polytetrahedral structures: the tetragonal σ-phase in Ni-V, the monoclinic phase λ-Al13Fe4, the orthorhombic phase μ-Al5Fe2 and the icosahedral quasicrystalline I-phase in Al-Pd-Mn. The numerically estimated values for the solid-liquid interfacial energy are compared with results from experiments on the undercooling- and phase-selection behavior.

Microstructure Evolution in Rapidly Solidified Immiscible Alloys

2006 ◽  
Vol 508 ◽  
pp. 37-44 ◽  
Author(s):  
Michael Reuß ◽  
Lorenz Ratke ◽  
Jiu Zhou Zhao
Keyword(s):  
Cooling Rate ◽  
Nucleation Rate ◽  
Particle Diameter ◽  
Casting Process ◽  
Average Particle ◽  
Cooling Rates ◽  
Gravity Casting ◽  
The Difference ◽  
Rapidly Solidified ◽  
Mould Casting

We prepared Al-Bi alloys with our new aerogel counter gravity casting facility and Al-Pb alloys by simple mould casting with variable cooling rates. By counter gravity casting, it is possible to have directional solidification with flat isotherms and without forced melt flow during the casting process. Both methods allow studying the nucleation rate in liquid-liquid decomposition. The most important result is that a separation between monotectic and hypermonotectic particles is possible by using suitable cooling rates. The difference of the frequency maxima is a function, depending on cooling rate and starting composition. By casting experiments with variable cooling rates, we found that the average particle diameter is a function of the cooling rate, according to the theory of Ratke and Zhao, but the nucleation rate is higher than assumed in their theory.

scholarly journals Nucleation behaviour and microstructure of single Al-Si12 powder particles rapidly solidified in a fast scanning calorimeter

2021 ◽  
Author(s):  
Bin Yang ◽  
Qin Peng ◽  
Benjamin Milkereit ◽  
Armin Springer ◽  
Dongmei Liu ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Rapid Solidification ◽  
Heterogeneous Nucleation ◽  
Cooling Rates ◽  
Solidification Behaviour ◽  
Nucleation Undercooling ◽  
In Situ Investigation ◽  
Solidification Processes ◽  
Powder Particles ◽  
Rapidly Solidified

AbstractThe understanding of rapid solidification behaviour, e.g. the undercooling versus growth velocity relationship, is crucial for tailoring microstructures and properties in metal alloys. In most rapid solidification processes, such as additive manufacturing (AM), in situ investigation of rapid solidification behaviour is missing because of the lack of accurate measurement of the cooling rate and nucleation undercooling. In the present study, rapid solidification of single micro-sized Al-Si12 (mass%) particles of various diameters has been investigated via differential fast scanning calorimetry employing controllable cooling rates from 100 to 90,000 K s−1 relevant for AM. Based on nucleation undercooling and on microstructure analysis of rapidly solidified single powder particles under controlled cooling rates, two different heterogeneous nucleation mechanisms of the primary α-Al phase are proposed. Surface heterogeneous nucleation dominates for particles with diameter smaller than 23 μm. For particles with diameter larger than 23 μm, the nucleation of the primary α-Al phase changes from surface to bulk heterogeneous nucleation with increasing cooling rate. The results indicate that at large undercoolings (> 95 K) and high cooling rates (> 10,000 K s−1), rapid solidification of single particle can yield a microstructure similar to that formed in AM. The present work not only proposes new insight into rapid solidification processes, but also provides a theoretical foundation for further understanding of microstructures and properties in additively manufactured materials.

Microstructure and mechanical properties of slowly cooled Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 with ductile bcc phase

2002 ◽  
Vol 754 ◽  
Author(s):  
Uta Kühn ◽  
Jürgen Eckert ◽  
Norbert Mattern ◽  
Nicolle Radtke ◽  
Ludwig Schultz
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Alloy Composition ◽  
Glassy Matrix ◽  
Compression Tests ◽  
Copper Mold ◽  
Glass Forming ◽  
Injection Casting ◽  
Bcc Phase

ABSTRACTWe report about the preparation and properties of a Be-free Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 alloy with a glassy or a nanocrystalline matrix and ductile bcc precipitates, which were developed with the aim to improve the mechanical properties. The samples were prepared in form of rods by injection casting into a copper mold. The phase formation as well as the resulting microstructure and the mechanical properties of the different samples have been investigated upon cooling from the melt at different quenching rates. The formation of the bcc phase embedded in a glassy matrix is strongly governed by the alloy composition and the actual cooling rate during solidification, because the glass forming ability is much lower compared to Zr-based alloys containing Be. Already small reductions in cooling rate lead to precipitation of additional crystalline phases. Compression tests reveal that the in-situ glassmatrix composite undergoes work hardening and plastic deformation prior to failure. Surprisingly, also a nanocrystalline matrix leads to high elastic strain values. These features significantly improve the mechanical behavior of the composites compared to the monolithic glass.

scholarly journals Surface Crystallization in Mg-Based Bulk Metallic Glass during Copper Mold Casting

2014 ◽  
Vol 2014 ◽  
pp. 1-4 ◽  
Author(s):  
Xin Wang
Keyword(s):  
Metallic Glass ◽  
Cooling Rate ◽  
Bulk Metallic Glass ◽  
Casting Process ◽  
Copper Mold ◽  
Copper Mold Casting ◽  
Internal Part ◽  
Mold Casting ◽  
Injection Casting ◽  
Cast Surface

The localized crystallization of Mg54Cu28Ag7Y11bulk metallic glass (BMG) in the injection casting process using a copper mold was investigated. It has been found that several crystalline phases were formed close to the as-cast surface but did not exist in the internal part of the BMG plate. It is abnormal that the as-cast surface is partially crystallized with higher cooling rate than that of inside. Overheating of the melt and nucleation induced by the surface of copper mold play key roles in the abnormal crystallization. It is suggested that the function of copper mold to trigger heterogeneous nucleation cannot be totally ignored, although it provides the high cooling rate for the glass formation during casting.

Crystallization of Supercooled Zr41Ti14Cu12Ni10B23 Melts During Continuous Heating and Cooling

1998 ◽  
Vol 554 ◽  
Author(s):  
Jan Schroers ◽  
Andreas Masuhr ◽  
Ralf Busch ◽  
William L. Johnson
Keyword(s):  
Cooling Rate ◽  
Bulk Sample ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Continuous Heating ◽  
Glass Forming ◽  
Heating And Cooling ◽  
Diffusion Limited ◽  
Surface Nucleation ◽  
The Difference

AbstractThe crystallization behavior of the bulk glass forming Zr41Ti14Cu12Ni10Be23 liquid was studied under different heating and cooling rates. Investigations were performed in high purity graphite crucibles since heterogeneous surface nucleation at the container walls does not effect the crystallization of the bulk sample. A rate of about 1 K/s is sufficient to circumvent crystallization of the melt while cooling from the equilibrium melt. In contrast, upon heating a rate of more than 150 K/s is necessary to avoid crystallization of Zr41Ti14Cu12Ni10Be23 samples. The difference between the critical heating and cooling rate is discussed within classical nucleation theory and diffusion limited crystal growth. The calculated difference of the critical heating and cooling rate can be explained by the fact that nuclei formed during cooling and heating are expose to different growth rates.

scholarly journals Analysis of isothermal and cooling-rate-dependent immersion freezing by a unifying stochastic ice nucleation model

2016 ◽  
Vol 16 (4) ◽  
pp. 2083-2107 ◽  
Author(s):  
Peter A. Alpert ◽  
Daniel A. Knopf
Keyword(s):  
Experimental Data ◽  
Cooling Rate ◽  
Surface Area ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Freezing Process ◽  
Nucleation Kinetics ◽  
Rate Dependent ◽  
Immersion Freezing

Abstract. Immersion freezing is an important ice nucleation pathway involved in the formation of cirrus and mixed-phase clouds. Laboratory immersion freezing experiments are necessary to determine the range in temperature, T, and relative humidity, RH, at which ice nucleation occurs and to quantify the associated nucleation kinetics. Typically, isothermal (applying a constant temperature) and cooling-rate-dependent immersion freezing experiments are conducted. In these experiments it is usually assumed that the droplets containing ice nucleating particles (INPs) all have the same INP surface area (ISA); however, the validity of this assumption or the impact it may have on analysis and interpretation of the experimental data is rarely questioned. Descriptions of ice active sites and variability of contact angles have been successfully formulated to describe ice nucleation experimental data in previous research; however, we consider the ability of a stochastic freezing model founded on classical nucleation theory to reproduce previous results and to explain experimental uncertainties and data scatter. A stochastic immersion freezing model based on first principles of statistics is presented, which accounts for variable ISA per droplet and uses parameters including the total number of droplets, Ntot, and the heterogeneous ice nucleation rate coefficient, Jhet(T). This model is applied to address if (i) a time and ISA-dependent stochastic immersion freezing process can explain laboratory immersion freezing data for different experimental methods and (ii) the assumption that all droplets contain identical ISA is a valid conjecture with subsequent consequences for analysis and interpretation of immersion freezing. The simple stochastic model can reproduce the observed time and surface area dependence in immersion freezing experiments for a variety of methods such as: droplets on a cold-stage exposed to air or surrounded by an oil matrix, wind and acoustically levitated droplets, droplets in a continuous-flow diffusion chamber (CFDC), the Leipzig aerosol cloud interaction simulator (LACIS), and the aerosol interaction and dynamics in the atmosphere (AIDA) cloud chamber. Observed time-dependent isothermal frozen fractions exhibiting non-exponential behavior can be readily explained by this model considering varying ISA. An apparent cooling-rate dependence of Jhet is explained by assuming identical ISA in each droplet. When accounting for ISA variability, the cooling-rate dependence of ice nucleation kinetics vanishes as expected from classical nucleation theory. The model simulations allow for a quantitative experimental uncertainty analysis for parameters Ntot, T, RH, and the ISA variability. The implications of our results for experimental analysis and interpretation of the immersion freezing process are discussed.

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