Defects and Diffusion in Metals XII

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Authors: S.M. Klotsman, G.N. Tatarinova, Alexander N. Timofeev
Abstract: The volume diffusion of nonmagnetic homovalent atomic probes (APs) from the IIIB group of the periodic table of the elements (PTE)Sc, La, and Th in Whas been studied by the method of secondary ion mass spectrometry. The Arrhenius dependences have the following parameters: the coefficients DSc - (D0)Sc = (1.4  0.3)10-4 m2s-1 and QSc = (546±4) kJ/mole; the coefficients D¬La - (D0)La = (1.6  0.8)×10-6 m2s-1 and QLa = (41010) kJ/mole; and the coefficients DTh - (D0)Th = 4.4×10-6 m2s-1 and QTh = 447 kJ/mole. It has been found that the coefficients D5dAP(Tm)W of the bulk diffusion of transition 5d APs in W coincide at its melting point (Tm)W. The enthalpies, QWSc,La,Th, of the volume diffusion of nonmagnetic homovalent APs from the IIIB group of PTE increase linearly with decreasing relaxation volumes, , of these APs, which interact with vacancies in W. The sums, (Q + E)WSc,La,Th, of the bulk diffusion enthalpies, QWSc,La,Th, and the relaxation energy, (E)WSc,La,Th, of the environments of homovalent APs diffusing to W are nearly constant.
Authors: Emad A. Badawi, M.A. Abdel-Rahman, Alaa El-Deen A. El-Nahhas, M. Abdel-Rahman
Abstract: Many Aluminum-based alloys are strengthened by using a heat-treatment process known as age-hardening. The aim of this work was to produce a high-strength 6xxx-series Aluminum alloy by adjusting the processing conditions, namely solutionizing and artificial aging. It consists of heating the alloy to a temperature at which the soluble constituents will form an homogeneous mass via solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable, depending upon the composition. After solution treatment and quenching, hardening is achieved either at room temperature (natural aging) or via a precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature, long-term processes. Temperatures range from 115 to 190C; times vary from 5 to 48 h. The choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces an optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6066 wrought aluminum alloys was studied. Their effects were investigated in terms of microstructure using positron annihilation lifetime techniques and monitoring the mechanical properties by mean of Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, and gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater resistance it has to deformation. The Vickers hardness of 6066 alloy has its maximum value (98) when aged for (10) hours at (175C) after quenching at 530C; so this temperature is the solution temperature of this alloy .The hardness conformed to reference values.
Authors: L. Bendjeddou, M.Y. Debili
Abstract: It is the intention of this paper to present the results of a study of Al-Fe-Ti (26-50Fe-2wt%Ti) cast alloys. We have examined the solidification structure over a wide range of iron contents. Using X-ray diffraction and quantitative microstructural analysis, we have characterized the alloy microstructure and identified second-phase crystallographic structures. The hardness of the alloys was also determined. The solidification structure was modified by the addition of Ti to Al1-xFex alloys.
Authors: S. Lallouche, M.Y. Debili
Abstract: This work deals with Al-Cu thin films, deposited onto glass substrates by RF (13.56MHz) magnetron sputtering, and annealed at 773K. The film thickness was approximately the same 3-4µm. They are characterized with respect to microstructure, grain size, microstrain, dislocation density and resistivity versus copper content. Al (Cu) deposits containing 1.8, 7.21, 86.17 and 92.5at%Cu have been investigated. The use of X-ray diffraction analysis and transmission electron microscopy lead to the characterization of different structural features of films deposited at room temperature (< 400K) and after annealing (773K). The resistivity of the films was measured using the four-point probe method. The microstrain profile obtained from XRD thanks to the Williamson-Hall method shows an increase with increasing copper content.
Authors: Li Qun Chen, Tao Yu, Zheng Chen Qiu
Abstract: The optimal geometries and mechanical properties of a kink with P are studied by applying density functional theory to the ½[111](1¯10) edge dislocation in bcc iron. The calculated impurity segregation energy shows that the P atom can be potentially trapped by the kink, and the doping P preferably segregates to the core region of the ½[111](1¯10) edge dislocation rather than to the <100>(010) edge dislocation. The analysis of the electronic structure indicates that the sideward motion of the kink is impeded owing to strong a interaction between P and neighboring Fe atoms. That is, the P induces a pinning effect on the ½[111](1¯10) edge dislocation. The hybridizations between P and Fe come from P 3p and Fe 3d4s4p. The p and d states have an obvious orientation, which may not be favorable to the toughness of iron. The localized effect of the P-kink complex distinctly affects the electronic structure as well as the energy of the system.
Authors: Amitava Ghorai
Abstract: In fast diffusion, the impurity diffusion coefficient is much greater than the self-diffusion coefficient. The pair mechanism is here considered to explain fast diffusion. Formulations for the formation of the pair are based upon pseudopotential theory.
Authors: Xue Mei Li
Abstract: The local distortion of the impurity Ni+ center in magnesium oxide is theoretically studied by analyzing its electron paramagnetic resonance g factor from the formula of a 3d9 ion under octahedra with tetragonal elongation deformation. The defect center is suggested to exhibit the relative elongation along the four-fold axis by about 0.05 Å of the Jahn-Teller nature. The observed isotropic g factor ( 2.2391) is attributable to the dynamical average of the anisotropic g values under tetragonal elongation due to the dynamical Jahn-Teller effect.
Authors: Kameshwar Kumar, Nagesh Thakur, S.C. Katyal, Pankaj Sharma
Abstract: In the present communication, a study was made of the compositional variation of physical properties: average coordination number (), average number of constraints (Ncon), number of lone-pair electrons (L), mean bond energy (), cohesive energy (CE), average heat of atomization (Hs), glass transition temperature (Tg), density (ρ) and theoretical energy gap (Eg) for Te15(Se100-xBix)85 (x = 0, 1, 2, 3, 4, 5at%) glassy alloys. The mean bond energy and the cohesive energy have been calculated using the chemical bond approach (CBA). The glass transition temperature was calculated using the Tichy-Ticha approach, and has been found to increase with Bi content. The mean bond energy is found to be proportional to the glass transition temperature and the average coordination number. It has been found that the average coordination number, average number of constraints, mean bond energy and density increase, whereas the cohesive energy, average heat of atomization and theoretical energy gap decrease with increasing Bi content in Se-Te alloys.
Authors: Frank Wirbeleit
Abstract: Boron diffusion after implant and anneal has been studied extensively in the past, without de-convoluting the Boron diffusion behavior by the initial post implant Boron concentration profile, which is done in this work first time. To support the de-convolution approach, the local density diffusion (LDD) model is selected, because this model is based on just one single arbitrary diffusion parameter per atomic species and host lattice combination. The LDD model is used for Phosphorus and Arsenic diffusion so far and an extension to simulate Boron diffusion in presence of Boron clusters is presented here. As the result, maximum Boron penetration depth post different rapid thermal anneals and the quantification of diffusing and clustering (non-diffusing) Boron in silicon and silicon-germanium host lattice systems are given.
Authors: Min Quan Kuang, Shan Xiang Zhang, Pei Xu
Abstract: The electron paramagnetic resonance parameters (g-factors and the hyperfine structure constants) for the Cu2+ center in lanthanum magnesium nitrate (LMN) are theoretically studied from the conventional perturbation formulas of these parameters for a 3d9 ion in tetragonally elongated octahedra. The studied complex is found to exhibit the slight tetragonal elongation (characterized by the relative elongation ratio ρ  4%) due to the Jahn-Teller effect, which may entirely conceal the original trigonal distortion of the host Mg2+ site in LMN. The conventional formulas containing only the metal orbital and spin-orbit coupling contributions are proved to be valid for the Cu2+ center in view of the weak covalency and ligand spin-orbit coupling interactions. This defect is also compared with the similar Cu2+ center of the Jahn-Teller nature on the octahedral interstitial site in the CdSe nanocrystals.

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