Solidification velocity of undercooled Fe–Co alloys

Abstract

The goal of this work was to investigate intra-alloy relationships, as they pertain to rapid solidification, which can be applied to computational materials modeling. Those relationships can be utilized to improve the accuracy of predictive modeling by leveraging previous experimental results. With that in mind, FeeCo samples were prepared with 30e50 at.% cobalt and they were processed via electrostatic levitation (ESL) or electromagnetic levitation (EML). The samples were levitated, melted, and allowed to cool and solidify in a vacuum for ESL testing and under He gas for EML testing. If sufficient undercooling was achieved, the sample solidified via double recalescence. In that event, the metastable dephase would grow into the undercooled liquid, and then the stable gephase would grow into a combination of the metastable phase and remaining undercooled liquid, or mushy zone. The velocities of the solid phases growing into undercooled liquid were analyzed with current dendrite growth theories. The purpose of the growth velocity analyses was twofold: 1) Assess the validity of current dendrite theory as it applies to the FeeCo system. 2) Evaluate the kinetic growth coefficient, m, assuming a constant kinetic rate parameter, V o. The results of the analyses indicate that it is reasonable to assume that the kinetic rate parameter, V o , is constant for a given phase within an alloy system if DH f =T 2 m does not vary significantly within the system, or within the composition range of interest. The average growth velocities of the stable phase into the mushy zone, V gd , for the Fee30, 40, and 50 at.% Co compositions are 1.6, 2.4, and 4.9 m/s, respectively, which scale with the thermal driving forces of the transformations, DT gd , which are 10 K, 24 K, and 40 K, respectively.

In situ study of non-equilibrium solidification of CoCrFeNi high-entropy alloy and CrFeNi and CoCrNi ternary suballoys

“…A double recalescence occurring during solidification of deeply undercooled Fe-based melts has been observed earlier, e.g., in Fe-Co alloys by Rodriguez et al [36] and Herman et al [37], and in the Fe-Cr-Ni system by Koseki and Flemings [38], and Matson et al [39]. Based on the thermodynamics considerations and microstructure analysis of the solidified samples it was concluded about a transient crystallization with the formation of a metastable bcc phase followed by a stable fcc phase.…”

Highly Stable Electrochemical Supercapacitor Performance of Self-Assembled Ferromagnetic Q-Carbon

“…Therefore, undercooling is directly proportional to regrowth velocity at constant kinetic growth. 16,41 A small undercooling induces a low regrowth velocity of 1−2 ms −1 , and it promotes the generation of graphite. The amorphous regrowth becomes energetically beneficial above a critical velocity in contrast to nanodiamond nucleation and the complete amorphization of the melt developed above the critical velocity of ∼16 ms −1 .…”

Use of Thermophysical Properties to Select and Control Convection During Rapid Solidification of Steel Alloys Using Electromagnetic Levitation on the Space Station

“…8 It is desirable for this delay to be as long as possible such that most of the casting has experienced double recalescence. This nucleation and growth competition behavior is also observed in a wide range of commercially important alloy systems including FeNi, 9 FeC, 10 FeCo, 11 TiAl,…”