K. Lücke

The kinetics of vacancy annihilation and short range order formation in Ni 11.4 at % Cr

Abstract In Ni-Cr alloys annealing after quenching from high temperatures leads to an increase of electrical resistivity which is attributed to a short range order state often denoted as K -state. Here the kinetics of the formation of the K -state in a Ni 10% Cr alloy is investigated by resistivity measurements for different quenching and annealing temperatures. The measurements are analyzed by an extended Schulze-Lucke method [22] which assumes that the rate of resistivity change is proportional to the vacancy concentration and that this rate as well as the rate of vacancy annihilation is described by a chemical rate equation. This analysis allowed a quantitative determination of the parameters determining the kinetics of short range order formation under different vacancy concentrations as well as the kinetics of annealing out of the quenched-in surplus vacancies. Among other quantities this treatment yielded the activation energies for vacancy formation H F = 1.16 eV, for vacancy migration H M = 1.56 eV and, as an independent cross check, for self diffusion H D = 2.73 eV in good agreement with H F + H M = 2.72 eV.

DISLOCATION PINNING EFFECTS IN OXIDIZED AND REDUCED COPPER AFTER ELECTRON IRRADIATION AT 4.2 K

Oxidized and reduced copper samples were irradiated at 4.2 K with 3 MeV-electrons. The observed pinning stages in both states are compared and discussed. Also a comparison with former irradiation experiments is given.

Influence of the Sample Pre-Treatment upon the Cold-Work Effects of Internal Friction in Copper

The influence of internally oxidizing and heavily (900°C) reducing annealing treatments upon the internal friction of high-purity copper at 1 Hz has been investigated. During heating after 7% deformation at 78 K the oxidized samples exhibit extremely large Hasiguti peaks P 1 (150 K) and P 2 (165 K), and in addition there is a weakly indicated peak P x (270 K). The dislocation pinning between 250 K is very small. The reduced samples, however, exhibit a very small P 1 , a reduced P 2 and an extremely large P x. In this case the pinning between 250 K and 300 K is also extremely large. The above pre-treatments were found to be reversible to a high degree.