Structure and mechanical properties of iron subjected to surface severe plastic deformation by attrition: II. Mechanical properties of nano- and submicrocrystalline iron

Abstract

Depth sensing indentation is used to study the effect of grain refinement to submicro and nan ograins on the mechanical properties (hardness, plasticity, Young's modulus) of armco iron subjected to severe plastic deformation by attrition in argon. In contrast to fcc metals, where the hardness increases and the plastic ity decreases as the grain size decreases to 20 nm, the hardness of bcc iron decreases from 5.8 to 3.7 GPa and plasticity δ A increases from 0.82 to 0.87 as the grain size decreases from 50 to 20 nm.

Microstructure and Strength Properties of Submicro and Nanocrystalline Nickel under Friction

“…Multiple reflections are located around diffraction rings, which are shown on this picture. This type of electron diffraction pattern is similar to that one of [6] and it confirms formation of grain-type fine-dispersed microstructure with large-angle disorientations.…”

Structure and mechanical properties of iron after surface severe plastic deformation under friction with simultaneous nitrogen saturation: II. The mechanical properties of nano- and submicrocrystalline iron saturated with nitrogen during deformation

“…As the grain decreases further (from 200 to 50 nm), the hard Mechanical characteristics of various regions in the iron surface layer after SPDF with simultaneous nitrogen saturation and after furnace nitriding ness is unchanged and remains high, which is a devia tion from the Hall-Petch relationship, and the hard ness substantially decreases in the layer region with grain sizes d < 50 nm. In this case, the hardness of the layer region of the α Fe[N] solid solution with grain sizes of 20-50 nm obtained after SPDF with simulta neous nitrogen saturation almost coincides with the hardness after SPDF in argon [6] for the same grain size. As the grain size decreases to 10 nm, the hardness of nanocrystalline nitrogen ferrite is almost unchanged (3.6 ± 0.5 GPa).…”

“…Using the nanoindentation method, it was stated in [6] that the hardness of fcc metals only increases and plasticity decreases with decreasing the grain sizes to 20 nm. The opposite effect, namely, a decrease in the hardness (from 5.8 to 3.7 GPa) and an increase in the plasticity parameter δ A (from 0.82 to 0.87) has been revealed in bcc iron produced by SPDF in a neutral atmosphere (argon) as the grain size decreases from 50 to 20 nm.…”

“…(The technique of preparation and the structure formation in iron dispersed and sat urated with nitrogen are described in detail in part I of this work [22].) In connection with a gradient structure of the sur face layers and their high dispersion, the mechanical behavior of iron and a set of their mechanical charac teristics (Young's modulus E, hardness H h , and plas ticity characteristic δ A ) were found using a Nano Indenter II device equipped with a Berkovich pyramid during continuous indentation at a load of 10 mN, as in the case of iron after SPDF in a neutral medium (argon) [6]. For comparison, we also tested a sample saturated with nitrogen with no deformation during conventional furnace nitriding.…”

“…Recent studies show that ultradisperse mate rials obtained by severe plastic deformation (SPD) exhibit unusual physical and mechanical properties as compared to polycrystalline materials [1][2][3][4][5][6]. The experimental data on the deformation behavior of materials due to refinement of grains to submicro and nanometer scale sizes, a decrease in Young's modu lus as compared with usual polycrystalline materials, and the deviations of experimental results from the Hall and Petch concepts relative to the hardening role of grain boundaries that act like barriers prevent ing dislocation motion are reviewed in a number of works [1-3, 7, 8].…”