Kurihina

In this work the authors calculated phase transformation kinetics in non-equilibrium solid solutions of binary alloys such as Fe-2 Cr (at.%), Fe-4 Cr (at.%), Fe-24Cr (at.%). In the literature [1] there is information on the impact of pre-heat treatment (PHT) on the size of iron nitrides after nitriding. Using the “Termodin” program [2, 3], they calculated cluster sizes, diffusion coefficients at temperatures of isothermal ageing, time of nucleation and time of the growth of the clusters, nucleation rate and growth rate of clusters which were formed at initial stages of decomposition of the supersaturated solid solution. Formation kinetics of a given volume fraction of the σ phase was also calculated. The obtained results allowed to control the structure of alloys, depending on heat treatment

The authors propose an energy method for calculating degradation rate of a non-equilibrium structure while in opeartion. With the use of differential scanning calorimetry it is possible to determine the presence of phase transformations in case of alloy aging, decay of supersaturated solid solutions, secondary crystallization and also assess heat content of the system during the transient process from the non-equilibrium state into the thermodynamic equilibrium state with extra energy release. Differentiating the current value of extra energy with respect to time, it’s also possible to determine the value of the chemical activity coefficient during phase transformations in alloys at working temperatures. Estimated dependence of the rate of energy dissipation χ on the initial value of a superfluous chemical potential was derived for the first time.

 The authors calculated the effect of temperature and time parameters of thermal pre-treatment of structural steels at the initial stages of formation of a fine structure before nitriding. With the program "Termodin" developed at the department "Materials science" in Bauman MSTU the authors calculated the critical radius of the nuclei of iron nitride, diffusion parameters, kinetic parameters of nucleation and growth phase Fe4N, time of formation of a given volume fraction of γ^/ phase during isothermal holding in the high holiday for binary alloys Fe-5, 6% N by mass. Kinetic curves of decomposition of the supersaturated solid solution with formation of a given volume fraction of γ^/ phase were built. The authors also calculated prediction modes of thermal pre-treatment on the size of hardening phases.

By the method of differential scanning calorimetry the authors studied phase transformations in the binary alloy Ni-Al (7%Al) formed at the disintegration of a supersaturated solid solution. It was shown that formation process of phase Ni3Al is connected with hidden crystallization heat release.

Computation of the phase change sequence during the incubation interval of oversaturated solid solution of Ni-Al alloy breakage      was carried out (93% Ni, 7% Al by weight). Quantity of conversion stages in the process of oversaturated solid solution breakage, atom’s superfluous chemical potential with every metastable phase equilibrium, mass content of precipitated phases, newly formed phases’ chemistry, gradient of Al atoms’ chemical potential between solution and nucleating phases could be determined with formed digram of non-equilibrium phase states.