Defect and Diffusion Forum Vols. 251-252

Abstract: Micro-structural change caused by the corresponding change in creep properties of Cu-8.5at.%Al alloy was studied. It was found that a micro-structural observations reveal the formation of different types of defect features during creep of the investigated alloy at intermediate temperatures between 0.46-0.72Tm, where Tm is the absolute melting point. SEM was used to characterize the studied alloy by quantitative micro-analysis. It allowed the observer to defect the micro-structural features such as dislocation that were generated from deformation and could move interagranularly by glide and climb. Clearly, the development of this microstructure could be attributed to the grain refining effect of the Al indicating the role of the applied stress at this alloy. The results show that the creep rupture strength of Cu-8.5at.%Al alloy in the power law creep damage mechanism. This due to the constraint introduced on the matrix creep flow by the Al phase rather than the devolvement of high threshold stress values. While the increase in the length of Al filaments and reduction in interfilament spacing with increasing draw ratio increase the constraint on the creep flow of the matrix, they also enhance the creep damage caused by the diffusion mechanisms because of the easy diffusion paths along the Al filaments and the reduction in the matrix grain size.

Abstract: SEM observations and Vickers-hardness tests were performed to identify the irradiation effects. γ- irradiation effect during the aging hardening process can be explained depending on the composition of the alloy and is used to derive quantitative information on the kinetics of the transformation precipitates. Increasing the Cu content of an Al-Cu alloy can improve the aging hardness. The present results of hardness behavior with SEM observations of surveillance specimens at different doses suggest that the radiation-induced defects are probably complex valance-solute clusters. These clusters act as nuclei for the precipitation of θ-Al2Cu type. This can be effectively utilized to study the systematic of nucleation of precipitates at vacancy-type defects. γ-irradiation probably play the key role in defects responsible for material strengthening and embrittlement.

Abstract: As the critical constructive analysis, with using the thermodynamic and crystal-chemical approaches, of the related experimental data is shown, the anomalous (with respect to the Al selfdiffusion characteristics (DAl - the self-diffusion coefficient, D0Al - the entropy (frequency) factor of the self-diffusion coefficient, QAl – the self-diffusion activation energy (enthalpy)) quantities of D*, D0*, Q* of the transition impurity Fickian diffusion in Al in many cases can be of the apparent character (related to the known Oriani model), whereas the normal quantities of D, D0, Q (i.e., close to DAl, D0Al, QAl), and the anomalously low quantities of D⊥, Q⊥, D0⊥ can be as the true characteristics of the impurity Fickian diffusion in the normal Al lattice (bulk) and in the compound-like nanosegregation (CLNS) structures at dislocations, respectively.

Abstract: Urgent open questions and their solution ways are considered of the thermodynamic stimuli and mechanisms of the enhanced Fickian diffusion mass-transport providing the unusual structuralphase transformations in metallic materials undergoing the intensive cold deformation, those can not be described in the framework of the conventional phase diagrams.