Critical undercoolings for the formation of metastable phase and its morphologies solidified from undercooled Fe–Co melts

1999 ◽  
Vol 14 (5) ◽  
pp. 1679-1682 ◽  
Author(s):  
Li Mingjun ◽  
Song Guangsheng ◽  
Yang Gencang ◽  
Zhou Yaohe
Keyword(s):  
Phase Formation ◽  
Metastable Phase ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Solidification Behavior ◽  
Metastable Phase Formation ◽  
Bcc Phase ◽  
Co Alloys ◽  
Undercooled Melts

The maximum undercoolings of 304, 318, 308, and 296 K were achieved, respectively, in Fe-22, 26, 30, and 34 at.% Co alloys. The metastable bcc phase nucleated from melts when undercoolings exceeded critical ones. The critical undercoolings for the formation of metastable bcc phase from Fe-22, 26, 30, and 34 at.% Co melts were 104, 156, 204, and 248 K, respectively. The morphologies of as-obtained metastable bcc phase exhibited five typical patterns: dendrite cores with primary and second arms, well-developed second arms, and radiated, lath, and platelike structures. Based on the classical nucleation theory, the solidification behavior of the melts was analyzed with regard to the metastable phase formation when the melts were undercooled greater than critical undercoolings. The formation of various morphologies was also evaluated to consider the solidification behavior of the undercooled melts.

Metastable Phase Formation in Mechanically Alloyed Sm-Co-Fe

1997 ◽  
Vol 481 ◽  
Author(s):  
P. A. I. Smith ◽  
J. Ding ◽  
P. G. McCormick ◽  
R. Street
Keyword(s):  
Phase Formation ◽  
Metastable Phase ◽  
X Ray Diffraction ◽  
Mechanically Alloyed ◽  
Two Phase ◽  
Fe Content ◽  
Energy Of Mixing ◽  
Metastable Phase Formation ◽  
Free Energy Of Mixing ◽  
Bcc Phase

ABSTRACTA detailed phase analysis of mechanically alloyed (Sm0.18Co0.82)100-xFex powders has been performed using X-ray diffraction and Mössbauer spectroscopy. A two-phase structure develops as the Fe content is increased, with an increasing proportion of bcc Fe-Co in addition to amorphous Sm-Co-Fe. Both phases become richer in Fe, but Fe is concentrated in the bcc phase, due to a limited ability of Fe to substitute in amorphous Sm-Co. Changes in phase formation with increasing Fe content can be correlated with changes in the calculated free energy of mixing of amorphous Sm-Co-Fe.

Metastable phase formation in Ti–Al–Nb undercooled melts

2007 ◽  
Vol 55 (2) ◽  
pp. 681-689 ◽  
Author(s):  
O SHULESHOVA ◽  
T WOODCOCK ◽  
H LINDENKREUZ ◽  
R HERMANN ◽  
W LOSER ◽  
...  
Keyword(s):  
Phase Formation ◽  
Metastable Phase ◽  
Metastable Phase Formation ◽  
Undercooled Melts

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.

Metastable phase formation in reactively sputtered WxSiy films

1986 ◽  
Vol 4 (6) ◽  
pp. 3117-3120 ◽  
Author(s):  
J. S. Lin ◽  
R. C. Budhani ◽  
G. Pollock ◽  
C. V. Deshpandey ◽  
R. F. Bunshah
Keyword(s):  
Phase Formation ◽  
Metastable Phase ◽  
Metastable Phase Formation

scholarly journals Modeling of metastable phase formation diagrams for sputtered thin films

2016 ◽  
Vol 17 (1) ◽  
pp. 210-219 ◽  
Author(s):  
Keke Chang ◽  
Denis Music ◽  
Moritz to Baben ◽  
Dennis Lange ◽  
Hamid Bolvardi ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Formation ◽  
Metastable Phase ◽  
Metastable Phase Formation

Ostwald’s step rule: a consequence of growth kinetics and nano-scale energy landscape

2021 ◽  
Author(s):  
Patrick Meister
Keyword(s):  
Metastable Phase ◽  
Energy Landscape ◽  
Stable State ◽  
Dynamic Modelling ◽  
Atomic Scale ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Natural Environments ◽  
Mineral Formation ◽  
Nano Scale

<p>In his 1897 article on the formation and transformation of solid phases, Friedrich Wilhelm Ostwald described the phenomenon that hydrous sodium chlorate precipitates from an oversaturated solution, despite the fact that this phase is much more soluble than the non-hydrous salt. The fundamental concept, also known as Ostwald’s step rule, is best summarized on page 307 of his article (here translated to English):</p><p>“... Such phenomena also frequently occur during melting and condensation of steam and even in homogeneous chemical reactions, and I would like to summarize the previous experiences with this matter in the single phrase that during departure from any state, and the transition to a more stable one, not the under given circumstances most stable state is reached, but the nearest one.“</p><p>Despite its major importance for mineral formation under Earth’s surface conditions, this concept is still not fully understood on a mechanistic level. While Ostwald’s step rule is commonly explained with the classical nucleation theory, there are several inconsistencies, especially the conundrum that sometimes stable phases, such as dolomite or quartz, do not form as long as a metastable phase is supersaturated. I propose an alternative interpretation that would be consistent with Ostwald’s (1897) original formulation as well as with several observations from natural environments and laboratory experiments. If “nearest” (in German: “nächstliegend”) is not understood as “thermodynamically most similar”, but as the phase with the lowest kinetic barrier, Ostwald’s step rule should be always valid. The kinetic barrier is surface specific and independent of supersaturation, but it depends on the atomic scale interfacial energy landscape. This concept would better represent the power of Ostwald’s step rule to explain mineral formation processes and how they are affected by chemical and biological influences. New nano-scale analytical techniques in combination with advanced molecular dynamic modelling bear great potential to explain and appreciate the importance of Ostwald’s step rule.</p>

Metastable Phase Formation in Rapidly Solidified ZrO2-Al2O3 Powders

2003 ◽  
Vol 437-438 ◽  
pp. 407-410 ◽  
Author(s):  
X. Zhou ◽  
R.K. Sadangi ◽  
Bernard H. Kear ◽  
W.R. Cannon
Keyword(s):  
Phase Formation ◽  
Metastable Phase ◽  
Metastable Phase Formation ◽  
Rapidly Solidified
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