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ÓASM International 1059-9495/$19.00

Oxide Strengthening of Iron Oxidized with Air Kirill Kozlov, Victor Sagaradze, Natalya Kataeva, Sergey Afanasyev, Valery Shabashov, and Ivan Chernov Submitted: 19 February 2020 / Revised: 28 September 2020 / Accepted: 11 October 2020 As a result of surface oxide dissolution during ball mill grinding of oxidized iron powder, spark plasma sintering (at temperature of 1000 °C and a pressure of 80 MPa), cold rolling with 88% reduction and recrystallization annealing at 1100 °C (0.5 h), bulk iron samples, containing strengthening FexO oxides of 3.2 nm in size, were obtained. It is demonstrated that without any alloying elements, except for air oxygen, recrystallized oxide dispersion strengthened iron specimens possess enhanced strength characteristics (yield strength and ultimate tensile strength of 570 and 632 MPa, respectively). Keywords

electron microscopy, mechanical alloying, mechanical properties, Mo¨ssbauer spectroscopy, ODS, oxide nanoparticles, spark plasma sintering

1. Introduction Modern machine engineering requires cheap high-resistant steels without additional alloying elements. Cold and warm plastic deformation can provide enhancement of strength characteristics for such steels. However, deformation is sometimes impossible during production of complex-shaped items. Therefore, oxide dispersion strengthening (ODS), including iron nano-oxide strengthening, is one of prospective iron and plain steel strengthening techniques. A saturation of the structure by finely dispersed inclusions hampers the movement of dislocations, and an enhanced thermal stability of strengthening oxides, which (unlike carbides, nitrides, and intermetallic compounds) do not dissolve even when heated to pre-melting temperatures (Ref 1-7), leads to an increase in the strength and high-temperature strength of the synthesized materials. Production of ODS steels involves mechanical processing of the mixture of steel and oxide powders in a ball mill with subsequent high-temperature sintering of mechanically alloyed powder. During ball mill grinding, rather large initial oxides are grinded and dissolved in the steel powder (Ref 1-9). Then, the particles of strengthening oxides (iron, yttrium, titanium, etc.), 2-5 nm in size, precipitate under high-temperature sintering of mechanically alloyed powder (Ref 8). In the case of creation of ODS mechanically alloyed steels, in particular, for fast-neutron (fission) reactors, traditionally employed are the strengthening oxides of yttrium, titanium, and other elements (Ref 1-10). However, along with strengthening by oxides based on the additional alloying elements, it is allowed to use iron oxides, which are less stable (than, for instance, oxides of yttrium and

Kirill Kozlov, Victor Sagaradze, Natalya Kataeva, Sergey Afanasyev, and Valery Shabashov, M.N. Mikheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia; and Ivan Chernov, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow,