Review—Electrochemical Phase Formation via a Supercooled Liquid State Stage: Metastable Structures and Intermediate Phases

Abstract

A review of experimental works proving the existence of the phenomenon of the electrochemical phase formation in metals and alloys via a supercooled liquid state stage is presented. The research findings focused on the electrochemical formation of metastable structures and intermediate phases, as well as on the structural features accompanying them. Electrochemical amorphous phase formation in metals and alloys, electrochemical quasicrystalline phase formation in metals, and electrochemical polymorphic phase formation in metals are discussed. Electrochemical hydrogen-related structure formation in metals, electrochemical high-defect crystalline phase formation in metals, and electrochemical texture-inhomogeneous structure formation in metals are considered. Electrochemical formation of intermediate phases in metals and alloys, electrochemical formation of eutectics in metallic alloys, and electrochemical formation of chemical compounds at the metallic cathode/electrodepositing metal interface are analyzed. Electrochemical reduction of ions in metals and alloys at a liquid cathode versus a solid chemically identical one, electrochemical phase formation of metals at chemically identical solid or liquid cathode, and electrochemical phase formation of alloys at chemically identical solid or liquid cathode are discussed.

Reorientation of grain crystal lattices in metals/alloys during electrocrystallisation under the action of force

“…[6][7][8][9] Based on the generalisation of the results of experimental and theoretical studies, the author of this work found that phase formation during the electrocrystallisation of metals/alloys occurs via the stage of supercooled liquid state. This finding, detailed in the review of the author's works, 10 fundamentally contradicts the existing concepts regarding the formation of phases in metals/ alloys during electrocrystallisation.…”

“…At the same time, numerous effects were experimentally demonstrated and explained based on the new ideas, in particular, the emergence of amorphous, quasi-crystalline and polymorphic phases in metals and alloys, the formation of intermediate phases in them (including carbides and hydrides), eutectics and other compounds. 10 In addition, many scientific facts have accumulated to date, which are difficult to satisfactorily explain on the basis of the existing ideas about the phase formation in electrocrystallised metals/alloys (e.g. an increase in the density of metals electrocrystallised under the action of small force exerted perpendicular to the crystallisation front 11 ; the wave-like flow of the surface layers of electrocrystallising metals under small force exerted parallel to the crystallisation front 12 ; change in the form of deposits of electrocrystallising metals under small force acting parallel to the crystallisation front, 13 etc.).…”

“…At the same time, numerous effects were experimentally demonstrated and explained based on the new ideas, in particular, the emergence of amorphous, quasi-crystalline and polymorphic phases in metals and alloys, the formation of intermediate phases in them (including carbides and hydrides), eutectics and other compounds. 10…”

Microstructure and tensile strength of electrodeposited Fe-rich bcc FeCoNi medium-entropy alloys

“…The same trend has also been reported in other works [30,31], whereas the as-electrodeposited FeCoNi MEA consists of a single bcc phase. The formation of nonequilibrium phases has been reported in some electrodeposited samples [24,25,26,35]. Especially, the formation of a bcc phase has been reported in the more extensive composition range upon adding saccharin to the solution in electrodeposited Fe-Co-Ni alloys [36].…”

“…It is a potential approach for fabricating alloys with fine-grains reaching the nanometre scale and bulk forms [21-23]. Moreover, heterogeneous microstructures, nonequilibrium phases, and supersaturated solid solutions have been identified in electrodeposited alloys [24-28]. Iron, cobalt, and nickel were employed as alloying elements for the present work, owing to their similar standard reduction potentials [29]: …”