Role of Grain-Boundary Phase in Formation of Structure and Properties of Mechanocomposites Based on Copper and Iron

• Main Authors: Svetlana A. Kovaliova, Viktor I. Zhornik, Vladimir V. Shkurko
• Format: Article
• Language: English
• Published: National Academy of Sciences of Belarus, State Scientific Institution “The Joint Institute of Mechanical Engineering" 2019-09-01
• Series: Механика машин, механизмов и материалов
• Subjects: mechanochemical synthesis; mechanocomposite; grain boundary phase; dispersed hardening
• Online Access: http://mmmm.by/en/readers-en/archive-room-en?layout=edit&id=1499

The phenomenological description of the formation of mechanocomposites is proposed, which can be taken as model representations for obtaining the mechanocomposites from a wide range of metals with FCC and BCC lattice, as well as for forecasting of the structural state and properties of sintered composites based on them. The main stages of the formation of the mechanocomposite include: 1) dispersion of the material and increase of its reactivity due to defect formation; 2) fragmentation of the submicrostructure and formation of a “liquid-like” grain-boundary phase; 3) deformation and diffusion saturation of the boundary phase by the segregations and followed crystallization of new phases according to the mechanism of the emergence and growth of nuclei with the formation of nanostructural composites. The mechanocomposites formed at the last stage are characterized by the increased strength properties and structural stability due to dispersion hardening by intermetallic compounds. The results of studying of the structural-phase evolution of the composites formed in the Cu-Sn and Fe-Ga systems during the mechanochemical synthesis are presented. The interrelation of the phase separation process during the synthesis of mechanocomposites with the features of the grain-boundary phase structure is considered. It is shown that the volume fraction of the grain boundary phase is formed at the level of 20–50 vol.% in the process of mechanocomposite synthesis. The materials obtained by the thermobaric sintering on their basis retain the nanosized structure and are characterized by high microhardness values (for Cu–Sn ~ 3 GPa, and for Fe–Ga ~ 7 GPa). The formation of dispersed inclusions in the alloy at the increased temperature of the annealing makes it possible to reduce the rate of microhardness decrease during heating and to provide its values at the level 2.5 GPa after annealing at 700 °С.