I. V. Ratochka

Diffusion — Induced creep of polycrystalline and nanostructured metals

Abstract Kinetic mechanisms of phenomena to be induced by the diffusion on the grain boundaries in polycrystalline and nanostructured (NS) materials have been analyzed. By way of example of nickel and copper nanostructured (grain size 100÷300 nm) it was shown that the effect of diffusion induced loss of strength by creep was much observed at temperatures low than 400 K in comparison with polycrystalline condition with grain size 20 μm. It was supposed that the physical reason for the decrease in the temperature for the effect to manifest itself is much higher value of diffusion coefficients of impurities in nanostructures.

Investigation of possibility to get superplastic state of nanostructured copper

Abstract The possibility of realisation of superplastic state of nanostructured (NS) copper (grain size 0.1–0.3 μm) produced by equal-channel angular pressing has been studied during creep and tensile tests in vacuum and under the influence of aluminium grain boundary diffusion fluxes from external source (coating). The creep acceleration effect for NS copper under the influence of aluminium grain boundary diffusion fluxes is found. The effect takes place in a lower temperature range as compared with fine-grained copper. It has been established that at 473K strong increase of strain rate sensitivity (m = ∂ lgσ ∂ lg ϵ) takes place during deformation of copper under influence of aluminium diffusion fluxes (m = 0.5) in comparison with pure copper (m = 0.19)

The Aspects of Practical Application of Ultrafine-Grained Titanium Alloys Produced by Severe Plastic Deformation

The mechanical and physical properties of ultrafine-grained titanium alloys produced by severe plastic deformation are considered. It is found that the formation of ultrafine-grained structure in these materials causes a significant enhancement in their mechanical properties at room temperature and in their resistance to hydrogen embrittlement as well as a change in their acoustic properties. Moreover, superplasticity is realized in these materials at less elevated temperatures relative to the respective coarse grained counterparts. It is shown that the above changes in material properties permit optimization of conditions by the production of items from the titanium alloys, e.g. medical implants having the requisite strength and stepped waveguides having long life even in the high power density conditions of an ultrasound system.

The Features of Deformation Behavior of Ultra-Fine Grained Titanium and Aluminum Alloys under Conditions of High Strain Rate Superplasticity

The stress-strain curves at high strain rate superplasticity were analyzed for Ti-6Al-4V and aluminum 1420 industrial alloys in ultra-fine grained state produced by severe plastic deformation. For both alloys the observed strengthening effect can be caused by grain growth under the above mentioned conditions resulting to increase of grain boundary sliding resistance. In the case of aluminum alloy the grain recovery can be accompanied by significant change in phase composition which is also stimulates the recrystallization process.

High-temperature creep of nickel under conditions of grain-boundary diffusion of impurities from the surface

AbstractComparative investigations of the effect of diffusion streams of copper atoms (a weakly segregating impurity) and silver atoms (a strongly segregating impurity) from the surface in the high-temperature plastic deformation of nickel have been carried out. It has been established that in the high-temperature plastic deformation of nickel, when there are diffusion streams of copper and silver from the surface, there is a reduction in the creep resistance of nickel due to an increase in the contribution of grain-boundary slip to the overall deformation. Two stages, characterized by different values of the rate sensitivity factor m, are observed on the curve of the stress against the rate of deformation over a certain temperature range for each impurity. In the region of deformation rates of

Variation of apparent creep activation energy in plastic deformation of molybdenum in diffusion contact with nickel

\dot \varepsilon< 2.5 \cdot 10^{ - 6}

A comparative study of grain-boundary diffusion of copper in ultrafine-grained and coarse-grained nickel

sec−1, m≊0.2, and for