Diffusion and Phase Transitions Accelerated by Severe Plastic Deformation

Abstract

Severe plastic deformation (SPD) can lead to the phase transformations in the materials. Even the SPD-treatment at ambient temperatureTSPD= 300 K is frequently equivalent to the heat treatment at a certain elevated temperature (effective temperature)Teff> 300 K. However, if the real annealing at effective temperature leads to the grain growth, SPD leads to strong grain refinement. SPD also accelerates the mass transfer in the materials. In this review the methods of determination for effective temperature after high-pressure torsion of metallic alloys are discussed as well as SPD-driven acceleration of diffusion.

Phase Transformations Induced by Severe Plastic Deformation

“…The SPD-driven mass transfer proceeds extremely quickly and in ambient conditions without substantial increase of sample temperature. 115,116) Usually, the time for establishment of steady-state by HPT is about 25 minutes. It varies by change of pressure, strain rate and HPT temperature, but not more than one order of magnitude.…”

“…It has been indeed observed in the direct measurements of vacancy concentration during HPT. 115,117) This concentration would be equal to the equilibrium concentration of lattice defects at a certain effective temperature T eff . 1) In case of CuCo system T eff amounts to T eff = 900°C (Fig.…”

Diffusive and Displacive Phase Transformations Under High Pressure Torsion

“…The SPD-driven phase transformations can also be analyzed when assuming [1] that the steadystate concentration of lattice defects during SPD is higher than that in the equilibrium at the temperature of SPD-treatment, TSPD, and pressure of the SPD-treatment, PSPD. It has been indeed observed in the direct measurements of vacancy concentration during HPT [115,117]. This concentration would be equal to the equilibrium concentration of lattice defects at a certain effective temperature Teff [1].…”

“…The SPD-driven mass transfer proceeds extremely quickly and in ambient conditions without substantial increase of sample temperature [115]. Usually, the time for establishment of steadystate by HPT is about 2-5 minutes.…”

Internal Interfaces in Severely Deformed Metals and Alloys: Coupling of Kinetics, Structure and Strain with Properties and Performance

“…2123) The original concept by Martin was found to be applicable to SPD-driven phase transformations, though with some important modifications. 22) The SPD processing accelerates the mass transfer in deformed materials and determines the value of ¦ in eq. ( 1).…”