Papers by Keyword: Pure Metals

Abstract: Tracer diffusion is one of most reliable techniques for providing basic kinetic data in solids. In the present review, selected direct methods, in particular the radiotracer measurements as a superior technique due to its high sensitivity, Secondary-Ion-Mass-Spectroscopy (SIMS) profiling, X-Ray Diffraction measurements and Rutherford Backscattering Spectrometry are presented and discussed. Special attention is put on the radiotracer technique describing the currently used sectioning techniques in detail with a focus on the experimental applications and complications. The relevant experimental results are exemplary shown. Furthermore, the most recent developments and advances related to the combined tracer/inter-diffusion measurements are highlighted. It is shown that this approach offers possibilities to provide the concentration-dependent tracer diffusion coefficients of the constituting elements in multi-component alloys in high-throughput experiments. Possibilities of estimating the tracer diffusion coefficients following different types of diffusion couple methods in binary and multicomponent systems are briefly introduced. Finally, specificity of SIMS analysis of diffusion in fine-grained materials are carefully analyzed. If applicable, a direct comparison of the results obtained by different techniques is given.

Abstract: Precursor phenomena of melting in pure metals (In, Pb, Bi and Sn) and alloys of the systems Pb-Bi and In-Sn with different compositions have been investigated by means of Mechanical Spectroscopy (MS), i.e. dynamic modulus and damping measurements. MS tests evidenced that a sharp drop of dynamic modulus E takes place in a temperature range ΔT before the formation of the first liquid: the modulus variation ΔE and the corresponding temperature range ΔT depend on the specific metal or alloy. The modulus drop is consistent with a relevant increase of interstitial concentration (self-interstitials assuming the dumbbell configuration), as predicted by the Granato’s theory of melting. The increase of damping in the same temperature range of modulus drop supports this explanation. Owing to their dumbbell configuration self-interstitials interact with the flexural vibration of samples and the periodic re-orientation under the external applied stress leads to energy loss and damping increase. The increase of self-interstitials has the effect to weaken interatomic bonds (modulus drop) and favours the collapse of crystal lattice (melting).

Abstract: In the present work 99.98% commercial pure copper, 99.5% commercial pure nickel and 99.5% commercial pure aluminum were imposed on high strain levels of ~24, ~8 and ~44 by equal channel angular pressing (ECAP) via route Bc, respectively. Microstructures and mechanical properties are investigated by TEM observations, tensile tests and microhardness tests. It shows that grain sizes of pure copper, pure nickel and pure aluminum has been severed refined from several tens of microns into several hundreds of nanometers after ECAP processing, however, microstructure of copper are mainly consisted of equiaxed (sub) grains with illegible grains/ (sub) grains boundaries after processed by ECAP, while it is featured as lamellar boundaries in that of pure nickel and as elongated grains in that of pure aluminum underwent a same strain level of ECAP. Results of mechanical properties show that yield strength and microhardness increase as strain increase up to a max value in copper, and then begin to decrease slightly, while mechanical properties of the other two increase as strain increases in nickel up to a strain level of ~12, and as in aluminum, yield strength and microhardness increase as strain increase in a relative low strain level, and then reach an saturation value.

Abstract: We highlight some of the most salient recent advances in point defects studies obtained from atomic-scale simulations performed in the framework of the density functional theory. The refinement of the theory, combined with its efficient numerical implementations and the (until now) everlasting growth of computer power allowed the transition from qualitative (in the beginning of the 90’) to quantitative results. Some of the longstanding controversies in the field have been tackled, and as far as aluminum is concerned, it has been shown that the curvature in the Arrheniusplot is due to anharmonic effects rather than to a two-defect diffusion mechanism. The anomalous diffusion in the b (bcc) phase of the group-IV elements has been related to the strong structural relaxation around vacancies, which significantly reduces their formation energy. Self-interstitials have been studied in materials of technological interest, their structure and mobility have been analyzed allowing a better interpretation of experimental results and an improved understanding of processes occurring under irradiation. Dilute interstitial solid solutions have been investigated. The strong binding between C and vacancies in bcc Fe may partially explain the observed influence of low amounts of C on Fe self-diffusion; the attraction of H to stacking faults in a Zr should favor planar dislocations glide. Intermetallics involving Fe (Fe-Al, Fe-Co) behave like highly correlated systems requiring methodological improvements of the DFT for a quantitative description. However, valuable trends concerning the structural point defects (those that allow nonstoichiometric compositions at low temperature) as well as the temperature dependence of point defects concentrations have been obtained.