Solute Atoms In Metals Research Articles

The mechanism investigation of deep cryogenic treatment on high alloy martensitic steel by low frequency internal friction

Effects of deep cryogenic treatment (DCT) on the internal friction (IF) in high-carbon alloy steel are investigated. The temperature dependent internal friction (TDIF) of the quenched and DCT treated samples were measured in an inversed torsion pendulum with high vacuum by using free decay method. The TDIF of quenched sample is decomposed into four peaks: P1 at 342 K, P2 at 443 K, P3 at 492 K and P4 at 580 K. Peak P1 is attributed to the relaxation associated with the reorientation of interstitial solute atoms in metals under the application of oscillatory stress. Peak P2 is related to the carbides precipitation. Peak P3 is considered as the Snoek-Kê-Köster (SKK) peak, which is caused by both dislocations interaction and interstitial atoms decorating these dislocations. Peak P4 is attributed to retained austenite transformation basing on the peak disappearing while the samples carried out DCT treating.

Lattice distortion of solute atoms in metals studied by x-ray-absorption fine structure.

The analysis of the x-ray-absorption fine structure (XAFS) yields information about the local atomic arrangement of the absorbing atom. The technique was used to study systematically the lattice dilatation or compression caused by substitutional impurity atoms in the fcc metals Al, Cu, Ni, Pd, and Ag and the bcc metals Fe, Nb, and V. Measuring XAFS spectra at the {ital K} and {ital L} edges of a variety of metals, interatomic distances, coordination numbers, and Debye-Waller factors were determined. Using experimentally determined amplitudes and phases from appropriate model compounds, the accuracy of the analysis is about 0.5% for nearest-neighbor distances and about 10% for coordination numbers and Debye-Waller factors. For the 61 systems investigated, shifts of the first-neighbor-shell distance of up to 10 pm are found, while the shifts of higher shells are generally small. Systematic variations within the rows of the Periodic Table are observed, indicating the importance of electronic effects. The results are discussed in comparison with lattice-parameter measurements and band-structure calculations.

Lattice location of solute atoms by channeling

The lattice positions of solute atoms in metals and semiconductors were determined by the ion channeling method, and were related to interactions of the solute atoms with point defects and other solute atoms. Examples are given utilizing the techniques of Rutherford backscattering, nuclear reactions and characteristic X-rays. The following configurations are discussed: AlCu mixed dumbbells in Al, tetravacancy—In atom complexes in Al, In atom—As atom pairs in Si, split B interstitials in Si, octahedral and near-octahedral sites for N and D in Fe, and Zn-divacancy complexes in InP.

The determination of solute atom displacements in mixed dumbbell interstitials for the face-centered-cubic lattice

Interactions between irradiation-produced defects and solute atoms in metals have been investigated using the channeling technique. The interaction of interest in this investigation is the trapping of self interstitials by small solute atoms thus creating a [Formula: see text] mixed dumbbell, consisting of a host atom and a solute atom straddling a lattice site in the face-centered-cubic lattice. The displacement of solute atoms from lattice sites in the mixed dumbbell configuration was determined by comparing the experimentally observed normalized yields from solute atoms and from host atoms with the yields calculated analytically using the continuum approximation. The solute atoms in Al–Mn, Al–Cu, and Cu–Be mixed dumbbells were situated at 0.5 Å from the body-centered position, whereas the Ag atoms in Al–Ag dumbbells were 0.7 Å from this position. This result is consistent with the theoretical expectation that the smallest solute atoms are displaced the greatest amount in mixed dumbbells. In addition, experimentally obtained solute atom yields for [Formula: see text] and [Formula: see text] angular scans were compared with calculated scans. It was concluded that for large displacements of solute atoms into the flux peaking region, the analytical (continuum) calculation is a reliable method of determining solute atom displacements, either from the aligned yields or from the angular scans.

Interaction Between Localized States in Metals

The theory of localized magnetic states of solute atoms in metals is extended to the case of a pair of neighboring magnetic atoms. It is found that the simplified model based on the idea that the important interaction is the diagonal exchange integral in the localized state, which is exactly soluble in Hartree-Fock theory for isolated ions, is still soluble, and the solutions show both ferromagnetic and antiferromagnetic exchange mechanisms.

Interstitial Atomic Diffusion Coefficients

An attempt is made to interpret the temperature independent factor ${D}_{0}$ of the previously determined diffusion coefficients of interstitial solute atoms in metals. The primary uncertainty in the value of ${D}_{0}$ given by the standard reaction rate theory resides in an entropy factor $\mathrm{exp}(\frac{\ensuremath{\Delta}S}{R})$. When cognizance is taken of an additional strain in the lattice surrounding a solute atom as it passes over a potential energy divide, and of the increase in entropy associated with an increase in lattice strain energy, one can estimate a "theoretical" range within which these entropy factors should lie. All past observations except for C and N in $\ensuremath{\alpha}\ensuremath{-}\mathrm{Fe}$ are consistent with this theoretical range. The ${D}_{0}'\mathrm{s}$ for these two systems were, therefore, redetermined by more precise measurements, and are found to be an order of magnitude higher than the original values. The associated entropy factors are consistent with the theoretical range.