Phase nucleation through confined spinodal fluctuations at crystal defects evidenced in Fe-Mn alloys

Abstract

Analysis and design of materials and fluids requires understanding of the fundamental relationships between structure, composition, and properties. Dislocations and grain boundaries influence microstructure evolution through the enhancement of diffusion and by facilitating heterogeneous nucleation, where atoms must overcome a potential barrier to enable the early stage of formation of a phase. Adsorption and spinodal decomposition are known precursor states to nucleation and phase transition; however, nucleation remains the less well-understood step in the complete thermodynamic sequence that shapes a microstructure. Here, we report near-atomic-scale observations of a phase transition mechanism that consists in solute adsorption to crystalline defects followed by linear and planar spinodal fluctuations in an Fe-Mn model alloy. These fluctuations provide a pathway for austenite nucleation due to the higher driving force for phase transition in the solute-rich regions. Our observations are supported by thermodynamic calculations, which predict the possibility of spinodal decomposition due to magnetic ordering.

The BCC-FCC Phase Transformation Pathways and Crystal Orientation Relationships in Dual Phase Materials From Al-(Co)-Cr-Fe-Ni Alloys

“…This topical Frontier's edition contains more details about this structure obtained along additive manufacturing routes with post-build annealing, as described by D. Vogiatzief et al and V. Rocio Molina Ramirez et al We point out, that nucleation triggered by the compositional modulations of a spinodal decomposition occurs in Fe-Mn alloys, being confined to crystalline defects (Da Silva et al, 2018). Furthermore, Loh et al, 2017 reported spinodal decomposition as the first step in a multistep nucleation of gold and silver nanocrystals in aqueous solutions.…”

Interfaces and defect composition at the near-atomic scale through atom probe tomography investigations

“…The reason for this electrical passivation might be the abovementioned atomic redistribution and segregation of alkali metals. 72 .…”

“…In Figure 7 (a), the structural information extracted from the partial crystallographic information available within the detector hit maps shown in (a) allow for full misorientation determination 27,29,33 . Figure 7 At 450°C, a miscibility gap in the FeMn appears in the phase diagram that can lead to a spinodal decomposition 72 . As the local composition of a microstructural feature reaches a certain threshold composition, compositional fluctuations along the linear defects and planar defects can be interpreted as a confined spinodal fluctuations.…”

Interplay of Chemistry and Faceting at Grain Boundaries in a Model Al Alloy

“…GBs are a type of lattice imperfection [1,2], with their own structure and composition, and as such impact a material's mechanical and functional properties [3]. Structural motifs and phases formed at chemically decorated GBs can be of a transient nature [4][5][6][7] or are local thermodynamic structural-chemical equilibrium states [8][9][10][11]. General GBs exhibit a wide range of local crystallographic structure and facet motifs.…”