Miloš Hamerský

Creep of Al-3wt.%Mg as measured with the incremental loading method

Abstract The deformation behaviour of Al-3wt.%Mg polycrystals was studied in the temperature interval from 295 to 674 K on a creep apparatus, applying the incremental loading method. The temperature dependences of the stresses which first cause plastic strain as well as the stress sensitivities of the strain rate indicate that different deformation mechanisms are operating. At temperatures below 0.5 T m , the intersection of forest dislocations is the most likely rate-controlling mechanism, superimposed at the lowest applied temperatures by effects of dynamic strain ageing. Above 0.5 T m there is diffusion-controlled high-temperature dislocation creep. The differences in results due to the use of the method and its limitations are discussed.

Discontinuous creep curves of Cd+0·44 at.% Zn alloy single crystals

The creep behaviour of Cd+0·44 at.% Zn alloy single crystals is described. Contrary to the Cd single crystals discontinuous creep curves have been observed, which do not occur at 78 K. The low- temperature limit of this effect is 130 K approximately. The characteristics of these discontinuous creep curves are discussed on the assumption that the Portevin-Le Chatelier effect is acting in the Cd+0·44 at.% Zn alloy.

Thermally activated process in deformed alpha titanium

Deformation behaviour of alpha titanium has been studied in the temperature range 295 to 914 K. The temperature dependence of the yield stress exhibits an athermal region at temperatures 500–750 K. A non-monotonous temperature dependence of the stress sensitivity parametern, estimated in stress relaxation tests, is observed in the same temperature interval. Possible mechanisms of thermally activated deformation and dynamic strain ageing are considered.

Thermoactivated creep and stress relaxation in Cd + 0·08 at% Sn single crystals

The activation area of plastically deformed Cd + 0·08 at% Sn single crystals was determined from differential creep test and stress relaxation at temperatures 78 K, 200 K and 295 K. The activation areaA depends on the resolved shear stress, τ,A*∼τ−r wherer is dependent on temperature and the testing method used. For temperatures above 0·3Tm recovery during stress relaxation should be considered.

Conditions for the initiation of strain bursts in the Portevin-Le Châtelier effect

In tests carried out at constant stress rate, the Portevin-Le Chatelier effect is manifested as a discontinuity in the load-elongation (stress-strain) curves in form of strain bursts which obey similar rules as serrations in constant-strain-rate tests. Experiments were conducted with an aluminium alloy containing 3 wt.% magnesium. The samples were solution treated at 400 C for 15 minutes and quenched in water. Tensile tests were carried out at different stress rates {dot {sigma}} at room temperature where the Portevin-Le Chatelier effect is well pronounced.

Internal Friction in Cd+Zn Alloy Single Crystals

Internal friction measurements were used for the examination of Cd + Zn alloy single crystals. It was established that the interaction energy between solute Zn atoms and dislocations in basal planes is 0·12 eV.