Accelerated Diffusion and Phase Transformations in Co–Cu Alloys Driven by the Severe Plastic Deformation

Abstract

The cast Co5.6 mass% Cu and Co13.6 mass% Cu alloys were subjected to severe plastic deformation (SPD) by the high-pressure torsion (HPT). The HPT treatment drastically decreases the size of the Co grains (from 20 µm to 100 nm) and the Cu precipitates (from 2 µm to 10 nm). The metastable fcc-Co disappeared, and supersaturated Co-based solid solution present in the as-cast alloys completely decomposed after HPT. Only the phases stable below 400°C remained after severe plastic deformation (i.e. almost pure hcp-Co and fcc-Cu grains). The applicability of the concept of effective temperature originally developed for materials under irradiation for the SPD-accelerated diffusion is discussed.

Interfacial mixing of nickel vanadium multilayers induced by cold rolling

“…This comparison implies that the effective diffusion coefficient induced by deformation can be enhanced by about 30 orders of magnitude compared to the diffusivity due to thermal diffusion. Similar large enhancements of an effective diffusivity have also been reported elsewhere such as a promotion of 22 orders of magnitude in Cu-Co alloys by high pressure torsion [17]. If this promoted diffusion coefficient is considered as a thermal activation effect, the corresponding effective temperature can be calculated from Eq.…”

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

“…57) Grain re nement by SPD processing accompanies other microstructural changes in a complicated way. These change includes phase transformation, 58,59) redistribution of impurity and solute elements, 60,61) the morphology change of precipitation by partial dissolution and physical fragmentation, [62][63][64][65] residual dislocation density, 66,67) texture, [68][69][70][71] etc. Effect of these changes is superimposed on grain size effect on corrosion, and this may cloud the underlying law dominating grain-size-dependency, if any, generic to SPD.…”

Phase Transformations in Ti–Fe Alloys Induced by High‐Pressure Torsion

“…[26,27] If one would compare the phases in alloys before and after SPD with an equilibrium phase diagram, one could estimate the so-called effective temperature for the SPD treatment. [28,29] The investigation of peculiarities of phase transformations in the SPD-treated Ti-Fe alloys was the goal of this work.…”