Papers by Keyword: Point Defect Relaxation

Abstract: The analysis of physicochemical mechanism of the influence of mechanical activation (MA) of a charge mixture on the subsequent self-propagating high-temperature synthesis (SHS) of intermetallic compounds is performed. Numerical estimates have revealed an insignificant role of the energy stored in solid reactants due to cold work during MA. The characteristic time of relaxation of non-equilibrium vacancies, which were generated in metals by MA, during heating in the SHS wave is estimated, and their insignificant influence on the reaction kinetics at high temperatures is demonstrated. It is shown that a strong effect of preliminary MA on SHS can be attributed only to deformation-enhanced solid-state diffusion during MA, which can lead to the formation of a supersaturated solid solution and thus affect the conditions for nucleation of a product phase (intermetallic compound) upon heating.

Abstract: It is known experimentally that solid-state interdiffusion is substantially enhanced during plastic deformation. This is especially noticeable in Mechanical Alloying (MA) which is used for producing a wide range of metastable materials (supersaturated solid solutions, amorphous phases, nanostructures) with unique properties. However, a physical mechanism of enhanced diffusion during MA is not clearly understood yet, and a comprehensive model of this complex phenomenon has not been developed so far. Moreover, the role of the diffusion process in MA is hotly debated in literature. In this work a new, self-consistent mathematical model of solid-state interdiffusion in a binary substitutional system A-B during periodic plastic deformation is developed. The model includes basic physical factors that affect diffusion, such as generation of non-equilibrium point defects by gliding screw dislocations during deformation and their relaxation in periods between impacts. The cross-link terms are considered, and interaction of point defects with edge dislocations and incoherent phase boundary A/B is taken into account. Computer simulation is performed using realistic data (e.g., quasi-equilibrium self-diffusion coefficients known in literature) and the process parameters typical of MA in a vibratory mill. A repeated “deformation-rest” cycle is considered. The results of modeling reveal the physical mechanism of the enhancement of solid-state diffusion by periodic plastic deformation during MA and demonstrate that within the frame of this approach supersaturated solid solutions can form within a reasonably short processing time.