Abstract
Measurements have been made of the thermal conductivity of specimens of Cu + 10 at. % Al and Cu + 10 at. % Au in (i) the fully annealed state (ii) the deformed and aged at liquid helium temperatures state and (iii) aged under room-temperature conditions. Results have reflected an increase in the dislocation thermal resistivity for the room-temperature aged specimens by a factor of 5.6 for the Cu + 10 at. % Al and 4.6 for the Cu + 10 at. % Au alloy. Measurements of residual electrical resistivity on a sample of Cu + 10 at. % Al in the three different states have confirmed that the changes observed in the thermal conductivity results are not due to changes in the electronic thermal conduction. The changes in the lattice resistivity are therefore interpreted as due to formation of Cottrell atmospheres for the room-temperature aged specimens, - the observed enhanced thermal resistance due to solute atmosphere formation is in qualitative agreement with the theoretical predictions of Ackerman and Klemens, (1971). Further, the Ackerman and Klemens annealing temperature dependence of the scatteri.ng for the deformed alloys in which Cottrell atmospheres have already formed and attained equilibrium with the dislocations, was experimentally tested in this research work. Good correlation between theory and eKxperiment was achieved and moreover, the results confirmed the experimental work of Mitchell et al., (1971). Measurements on a Cu + 10 at. % Al sample deformed at liquid helium temperatures and aged at several higher cryogenic temperatures have shown that the dislocation thermal resistivity increases vd.th increasing ageing temperatures. This is interpreted as due to systematic segregation of solute atoms to the dislocations as the ageing temperature is raised. An average value for the scattering in the deformed but not aged Cu + 10 at, % Al samples has been determined to be 0.31 x 10-7 W -1 cm3 k3 and is considered to be representative of the scattering in the pure copper - the value is in agreement to that predicted by Charsley et al., (1968), from their extrapolated curve of scattering after room-temperature ageing versus aluminium content in copper alloys and to those for Leaver, (1969), for alpha-brass. A knowledge of the scattering in the pure metal was used to determine dislocation densities in the Cu + 10 at. % Au specimen deformed at liquid helium temperatures and thus an accurate value for the scattering in the Cu + 10 at. % Au aged at room-temperature was deduced. This was used to deduce more accurately the dislocation densities introduced in the Cu + 10 at. % Au specimen of Leaver, (1969), which was plastically deformed at room-temperature by between 2 and 12% tensile strain. It has been shown that Leaver underestimated his dislocation densities. Critical consideration of the 1971 theory of Ackerman and Klemens has been presented. It has been concluded that reasonable qualitative correlation between theory and experiment exists for the specimens tested but quantitative agreement is very poor.