In-Situ Nuclear Magnetic Resonance Investigation of Strain, Temperature, and Strain-Rate Variations of Deformation-Induced Vacancy Concentration in Aluminum

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin–LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.

Au-In System Studied with Perturbed Angular Correlation Method

The Au-In system was the subject of our comprehensive study with the perturbed angular correlation technique. Bulk samples of all intermetallic phases shown in the phase diagram were prepared to determine the hyperfine interaction parameters and their temperature dependence. A polymorphic phase transformation in the AuIn phase at about 630 K and a new metastable modification of Au$\text{}_{7}$In$\text{}_{3}$ after quenching the sample of 30 at.% In from temperature above 700 K were found. In addition, formation of the Au-In phases of different stoichiometries at the interfaces of thin Au/In films was observed. It turned out that the starting composition of bilayer samples, i.e. the thickness ratio of the Au and In layers, strongly influenced the stoichiometry of the formed compounds

Au-In System Studied with Perturbed Angular Correlation Method

The Au-In system was the subject of our comprehensive study with the perturbed angular correlation technique. Bulk samples of all intermetallic phases shown in the phase diagram were prepared to determine the hyperfine interaction parameters and their temperature dependence. A polymorphic phase transformation in the AuIn phase at about 630 K and a new metastable modification of Au$\text{}_{7}$In$\text{}_{3}$ after quenching the sample of 30 at.% In from temperature above 700 K were found. In addition, formation of the Au-In phases of different stoichiometries at the interfaces of thin Au/In films was observed. It turned out that the starting composition of bilayer samples, i.e. the thickness ratio of the Au and In layers, strongly influenced the stoichiometry of the formed compounds

Perturbed γ-γ Angular Correlation Studies of Isostructural Ag5\text{}_{5}Zn8\text{}_{8} and Ag5\text{}_{5}Cd8\text{}_{8} Intermetallic Compounds

Perturbed γ-γ angular correlation spectroscopy was applied to study hyperfine interaction parameters for $\text{}^{111}$In probes in intermetallic compounds of D8$\text{}_{2}$ structure. The perturbed γ-γ angular correlation spectra measured in Ag$\text{}_{5}$Zn$\text{}_{8}$ and Ag$\text{}_{5}$Cd$\text{}_{8}$ phases reflect a number, population and symmetry of nonequivalent substitutional sites occupied by the indium probes. The temperature dependences of the observed electric field gradients were measured in the temperature range 37-500

Experimental and ab initio study of the electric field gradients at Ta and Cd impurities in TiAl3

The hyperfine quadrupole interaction parameters and their temperature dependence for Hf-181/Ta-181 probe in TiAl3 compound were determined using the time differential perturbed angular correlation (TDPAC) method. in addition, ab initio calculations using the augmented plane wave plus local orbitals (APW+ lo) method as implemented in the WIEN2k code, within the framework of the density functional theory(DFT) have been performed. Through the comparison of the calculated and measured electric field gradients (EFG) it was established that Ta occupies Ti 2(a) position, while Cd probe is settled at the Al 4(d) site. (c) 2009 Elsevier B.V. All rights reserved

Structural characterization of the Zr4Al3 and Hf4Al3 compounds by means of hyperfine interaction studies

Electric-field gradients have been measured in the isostructural intermetallic compounds ${\rm Zr}_{4}{\rm Al}_{3}$ and ${\rm Hf}_{4}{\rm Al}_{3}$, using radioactive $^{181}{\rm Hf}/^{181}$Ta hyperfine probes. In both compounds, two well-defined electric-field gradients have been observed, whose temperature dependence follows the $T^{3/2}$ rule in the temperature range 30$\hbox{--}$1170 K. Using the full-potential augmented plane-wave + local-orbitals formalism, the electric-field gradients have been calculated. On the basis of the 181Ta hyperfine interaction parameters, the possible Hf/Zr lattice sites have been assigned. In this way the controversy concerning the lattice structure of these compounds deduced from X-ray diffraction has been solved

Electric field gradients at Ta and Cd in Ti(2)Pd compound

The hyperfine quadrupole interaction parameters and their temperature dependences for (181)Ta and (111)Cd probes in Ti(2)Pd compound were determined experimentally by means of the perturbed angular correlation (PAC) technique. In addition, ab initio calculations using all-electron augmented plane wave plus local orbitals (APW + lo) method have been performed. Through the comparison of the calculated and measured electric field gradients (EFG) it was established that both Ta and Cd occupy 4(e) Ti position in the Ti(2)Pd compound. (C) 2008 Elsevier B.V. All rights reserved