Review: Transition metal-based nanolamellar phases

This paper is the state-of-the-art review of the transition metal-based nanolamellar phases of the (hmcn)k types (h – hexagonal close-packed motif; c – cubic close-packed motif; m, n, and k – integers). These nanolamellar phases are emerging materials, which possess extraordinary properties, as a result of their crystal structure, where planar defects (stacking faults and/or twins) are an inherent part of their crystal structure. On the other hand, the stacking faults and/or twins are nanostructuring elements, which define nanostructure-properties relationships. The thickness of nanolamella, which is formed by two parallel adjacent stacking faults on a nanometer scale, is ∼1 nm. The density of stacking faults can reach 1015 cm−3 that approach the density of grain boundaries in nanostructured materials. Formation of the nanolamellar phases is a result of structural phase transformation in consequence of ordering of interstitial C/N-atoms and vacancies in metalloid sub-lattice of the non-stoichiometric NaCl-type carbides/nitrides, resulting in the structural phase change associated with regular ordering of stacking. No any review has been published from that time of the discovery of the stunning phases, which are a novel segment of nanostructured materials. The aim of this paper is to advance the research, development, and applications of the transition metal-based nanolamellar phases. tedly the formation of the ζ-phases occurs as a result of regular removal of every fourth non-metal layer followed by shearing of transition metal layers to yield the sequence … ↑ A γ B α C β A ↑ C β A γ B α C ↑ B α C β A γ B ↑ … , where A, B, and C are transition metal close-packed atomic layers, and α, β, and γ are non-metal (carbon or nitrogen) close-packed atomic layers. The formation of the ε-phases occurs similarly, i.e. … ↑ A γ B α C ↑ B α C β A ↑ C β A γ B ↑ … where ↑ indicates the removal of the C/N-atomic layers in the metalloid sub-lattice and appearance of stacking faults bounded with Shockley partial dislocations with Burgers vector b = a/6〈1 1 2〉. perimental facts are that both mechanical and physical properties of the nanolamellar ζ/ε-phases differ from their parent NaCl-type carbides and nitrides. The microhardness of the ζ/ε-phases is lower than that of their parent NaCl-type carbides and nitride, namely 8.8 GPa for the ζ-Hf4N3-(hcch)3, 16.5 GPa for the ζ-Ta4C3-(hcch)3, 14.5 GPa for the ε-Ta3C2-(hch)3, and 19 GPa for the ζ-V4C3-(hcch)3. The brittle-to-ductile transition for the Ta4C3-(hcch)3 phase demonstrates the significant plasticity of the Ta4C3-phase in comparison with non-stoichiometric NaCl-type tantalum carbide. The general trend is that the ζ/ε-phases are remarkably ductile than their mono-carbides and mono-nitride. The thermo-electromotive force for the Ta4C3-(hcch)3 phase is lower than that for tantalum mono-carbide within temperature range between 100 °C and 1100 °C. The specific resistivity of the Ta4C3-(hcch)3 phase was found to be significantly higher than that of TaC0.98 at the temperature range between 200 °C and 1000 °C. For example, at room temperature the resistivity of stoichiometric tantalum mono-carbide is 24–27 μΩ cm in comparison with 160–170 μΩ cm for the Ta4C3-(hcch)3. eview chapter is the first attempt to glean sparse data related to the ζ-phases of transition refractory metal carbides and nitrides. The review is devoted to the 50th anniversary as the research and development on this fascinating topic of the nanolamellar materials were begun by Lesser and Brauer [38,39] in 1958–1959.