Papers by Keyword: Bulk Nanomaterials

Abstract: The tendency of the aluminum alloy D16 system Al-Cu-Mg to natural (NA) and artificial aging (AA) after hardening and high pressure torsion (HPT) under a pressure of 6 GPa at room temperature was studied using optical metallography, scanning electron microscopy, electrical conductivity tests. The dependences of microhardness and electrical conductivity were constructed depending on the exposure time. It is shown that heat treatment (HT) (hardening + HPT + NA) leads to an increase of hardening of the alloy D16 compared to standard HT (T4) in 2,3 times, at preservation of level of conductivity.

Abstract: The structure and properties of discs from cast coarse-grained D16 alloy have been investigated with the help of optical metallography and transmission electron microscopy, after the traditional heat treatment (HT) modes or subjected to high pressure torsion (HPT) under pressure in 6 GPa at room temperature. Standard HT modes included: Т4 (hardening 495°С + natural aging at room temperature for 5 days) and Т6 (hardening 495°С + artificial aging at 185°С for 10 hours). It is shown that after HT of alloy D16 according to modes T6 and Т4, the sizes of the structural elements, compared with the original, decreased by about 4,8 times and the microhardness increased by 1,6 times. It is shown that after one or ten rotates of HPT in D16 alloy the sizes of structural elements, in comparison with initial, decreased by 393 and 899 times, and microhardness increased by 2,4 and 2,9 times, respectively. Detection of hardening hard, brittle and high-alloy copper γ2- phases (Cu₉Al₄) indicates the passage in the HPT process of the decomposition of a supersaturated solid solution (dynamic aging) in the planes of a local shift.

Abstract: Nanostructuring of metals and alloys by severe plastic deformation techniques is an effective way of enhancing their mechanical and functional properties. The features of the nanostructured materials produced by severe plastic deformation (SPD) are stipulated by forming of ultrafine-sized grains as well as by the state of grain boundaries. The concept of grain boundary (GB) design of ultrafine-grained metals and alloys is developed for enhancement of their properties by tailoring grain boundaries of different types (low-angle and high-angle ones, special and random, equilibrium and nonequilibrium) and formation of grain boundary segregations and precipitations by SPD processing. The paper presents experimental data demonstrating the super-strength and “positive” slope of the Hall-Petch relation when passing from micro-to nanostructured state in a number of metallic materials subjected to severe plastic deformation. The nature of the superior strength is associated with new strengthening mechanisms and the difficulty of generation of dislocations from grain boundaries with segregations. This new approach is used for achieving the enhanced strength in several commercial Al and Ti alloys as well as steels subjected to SPD processing.

Abstract: The data are presented for Ni selfdiffusion and Au heterodiffusion in nanocrystalline Ni. Volume diffusion coefficients are much greater than those for a coarse – grained polycrystals extrapolated from high temperatures. Interface diffusion parameters were calculated based on the assumption that B – kinetic regime is realized at temperature range more than 448 K, while C – kinetic regime is realised at temperatures less than 423 K. The consistency of obtained results with the proposed cluster diffusion model is discussed. Diffusion in Au – Cu thin films (from several tens to several hundreds nanometers) was studied with the use of the Rutherford Back Scattering, RBS, under the kinetic regime B (448 – 523 K). The RBS spectra were transformed in the concentration depth profiles for both volume and grain boundary (GB) diffusion. The triple products Pn = snδDn (sn is the enrichment coefficient, while δ is the nanograin boundary width) were calculated using Whipple model. As a result of this analysis the s – value for Cu – Au system was determined to be of the order of unity. The paper is focused on a difference between GB diffusion parameters in nano – and coarse grained materials.