Papers by Author: Sergiy A. Firstov

Abstract: Regularities, features and mechanisms of deformation and fracture processes of new ceramic materials – porous (=3-35 %) two-phase titanium nanolaminate-composites Ti3SiC2/TiC, Ti3AlC2/TiC, Ti4AlN3/TiN (content of TiC or TiN – 5-70 % vol.) at 20-1300 оС are established. Composites are made by reaction sintering. On increase in mechanical properties and resistance to deformation they settle down in the following sequence: Ti3AlC2/TiC–Ti4AlN3/TiN–Ti3SiC2/TiC. In porous nanolaminate-composites containing less than 20 % TiC the increase in porosity  results in decrease in high-temperature strength pl and increase of plasticity . Appreciable increase of strength of porous composites is marked at content TiC>25-30 % (vol.).

Abstract: The influence of passing from a microcrystalline to a nanocrystalline structure on the mechanical properties of chromium deposited by magnetron sputtering is studied. The possibility of additional strengthening nanomaterials due to enrichment of grain boundaries by “useful” additives elements is established. A wide spectrum of materials in different structural states was investigated by the method of micromechanical tests. The notions of the “theoretical” hardness (largest hardness for the material) and “limit tool” hardness, connected with tool limitations in indentation, are introduced.

Abstract: Severe plastic deformation (SPD) techniques are the best for producing of massive nanostructured materials. The methods of equal channel angular pressure (ECAP) and twist extrusion (TE) are realized by simple shear uniform deformation without change of cross-section sizes of sample. In the case of roll forming (RF) the shear strain is localized in the near-surface layer of metal. Intensity of shear strain in the near-surface layer depends on variation of parameters of deformation and conditions of friction in a contact. Steel 65G (0.65C, 0.3Si, 0.6Mn, 0.3Cr, and 0.3Ni) was deformed by roll forming. Transmission electron microscopy (TEM) of “cross-section” samples was used for studying of gradient structure of deformed material. TEM investigation shown that cell substructure in a near-surface layer have been formed. The depth of deformed layer is approximately 40 micrometers. Average cell size in cross-section direction is about 100 - 200 nm. Thin nanostructure layer with cell size about 20-30 nm was detected. In our opinion such substructure formed due to effect of “good” impurities.