Ostwald ripening of nanodispersed phases in metal alloys

Abstract

The review analyzed the kinetics of Ostwald ripening of nanodispersed phases in metal alloys provided that the growth (dissolution) of the nanoparticles of the strengthening phase is controlled simultaneously with matrix diffusion, diffusion through the dislocation tubes and the rate of transition of atoms through the interphase boundary (Wagner's mechanism of growth). It is established that the general principle of different mechanisms of growth (dissolution) of nanoparticles in the process of ripening is not its single action, but simultaneous. The number of mechanisms involved in growth (one, two, three) depends on a lot of factors, in particular: the chemical composition of the nanodispersed phases, the conditions of exploitation (changes in mechanical loads, regimes of temperature, the outdoor environment), technological conditions of synthesis etc. It has been shown that when the growth (dissolution) of nanoparticles in the Ostwald ripening process is controlled simultaneously with the matrix diffusion and the diffusion coefficient through the dislocations , then the corresponding function of particles size distribution depends on one parameter which varies within the limits , where – determines the relation between the diffuse and dislocated fluxes. In the case when three mechanisms of growth (dissolution) simultaneously, the general flux which corresponds to the mass transfer between the particles and the matrix consists of three parts , where the kinetic component is determined with the kinetic coefficient . At present, the corresponding function of the nanoparticles size distribution depends on two parameters and which determine the relationship between the diffuse ( ) and the kinetic flux ( ). The possibility of realizing the proposed mechanisms of growth of nanoparticles in the Ostwald ripening process can be confirmed or rebutted with comparing experimental and theoretical data. Results of the comparison of experimental histograms with theoretically computed curves point to the realism of the proposed coarsening mechanisms of dispersed phase nanoparticles in the process of ripening.

Keywords

• наночастинка, оствальдівське дозрівання, теорія ліфшица-сльозова-вагнера, нанокристал, кластер, функція розподілу за розмірами