Heterogeneous Nucleation Behavior in Al Deoxidized Liquid Iron

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.

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Nucleation and Pattern Formation of Coherent Islands During Epitaxial Growth of Ge on Si(110) Surfaces

MRS Proceedings ◽

10.1557/proc-440-377 ◽

1996 ◽

Vol 440 ◽

Author(s):

J. D. Weil ◽

Bi-Ke Yang ◽

C. G. Slough ◽

M. Krishnamurthy

Keyword(s):

Epitaxial Growth ◽

Buffer Layer ◽

Heterogeneous Nucleation ◽

Buffer Layers ◽

Dipole Orientation ◽

Nucleation Behavior ◽

Molecular Beam Epitaxial ◽

Passivating Oxide Layer ◽

Molecular Beam Epitaxial Growth ◽

Passivating Oxide

AbstractMolecular beam epitaxial growth of Ge on Si(110) surfaces reveals interesting aspects of the heterogeneous nucleation of coherent Ge islands. Cleaning of the Si substrate by desorption of a passivating oxide layer at high temperature creates surface pits. Two sets of experiments, including deposition of Ge on as-cleaned substrates, and surfaces with a thin Si buffer layer are compared to illustrate the nucleation behavior of Ge. Typical Ge deposition temperatures range from 600°C to 725°C.For Ge deposition on as-cleaned surfaces, the faceted edges of pits serve as preferential sites for the heterogeneous nucleation of coherent Ge islands. Experiments were also performed on surfaces with thin (˜20nm) Si buffer layers grown on the as-cleaned surface. Though the faceted pits have not been completely covered by the Si buffer layer, they have decreased in lateral size. In addition, the Si(110) surface shows ledges that are formed along specific crystallographic directions. Ge deposited on the Si buffer nucleates first at the corners of the pits, in an interesting dipole orientation, as well as along the ledges on the surface.

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The Study of Undercooling of Homogeneous Nucleation for Metallic Melting

Materials Science Forum ◽

10.4028/www.scientific.net/msf.561-565.1941 ◽

2007 ◽

Vol 561-565 ◽

pp. 1941-1944

Author(s):

Cheng Huang ◽

Bo Song ◽

Pei Zhao

Keyword(s):

Melting Temperature ◽

Liquid Iron ◽

Heterogeneous Nucleation ◽

Homogeneous Nucleation ◽

Mathematic Model ◽

Wetting Angle ◽

Calculation Results ◽

Maximum Undercooling

In this paper, the thermodynamic and kinetic requirements of heterogeneous and homogeneous nucleation of metallic melting were suggested. Based on the kinetic requirements of nucleation, the mathematic model of wetting angle of heterogeneous nucleation was developed, Based on the wetting angel model, it was predicted that the maximum undercooling of homogeneous nucleation for melts is two thirds of melting temperature. With the wetting angel model, the wetting angles of different catalysts in liquid iron were calculated, and calculation results are in agreement with that of other researchers.

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