Defects and Diffusion in Metals - An Annual Retrospective VIII -

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Authors: I.S. Sandhu, D.K. Chaturvedi, Irina V. Belova, Graeme E. Murch
Abstract: In this paper Manning random alloy model has been extended to the binary nonstoichiometric intermetallic compound of the B2 structure. Two sub-lattices, that are dynamically independent in six-jump cycle (6JC) mechanism, are coupled together by taking into consideration the vacancy motion as a sequence of nearest neighbour jumps in random directions. The linear response expressions for the phenomenological transport coefficients are evaluated making use of the kinetic equation approach. The expressions for collective correlation factors are derived in terms of the equilibrium partial atomic concentrations and jump frequencies. Results are compared with Monte Carlo simulation results using the four-frequency model.
Authors: K.L. Gosain, D.K. Chaturvedi, Irina V. Belova, Graeme E. Murch
Abstract: Tracer diffusion in non-stoichiometric B2 intermetallic compounds having antistructural disorder is investigated using the six-jump-cycle (6JC) as a fundamental diffusion unit. For non-stoichiometric compositions, the antistructural atoms are assumed to be isolated and located at one of the six [110]-type and [100]-type sites (as only these sites are involved in the 6JC or 2JC). The jump frequencies for the 6JC involving a perfectly ordered configuration are calculated in terms of a four-frequency-model, using the meanfirst- passage concept of Arita et al. The jump frequency of an antistructural atom at [110] or [100]-type sites is taken to be the harmonic mean of frequencies of two successive nearestneighbour jumps of the same kind of atoms. The expressions for the tracer diffusion coefficients are derived for both atomic components at deviations from stoichiometry, assuming that the 6JC mechanism is valid. The results are compared with Monte Carlo simulations based on single vacancy jumps and found to be in fair agreement for compositions close to stoichiometry.
Authors: I.S. Sandhu, D.K. Chaturvedi, Irina V. Belova, Graeme E. Murch
Abstract: Tracer di f fusion by way of vacancies is invest igated in B2 intermetal l ics AB by means of a kinet ic equat ion approach. The model used is one wi th four inter sub-lat t ice frequencies where each sub-lat t ice is t reated as a random al loy. Coupl ing is achieved between the two types of cycles, i .e. , wi th the vacancy start ing on one sub- lat t ice and finishing on ei ther sub-lat t ice and wi th a vacancy start ing on the other sub-lat t ice and finishing on ei ther sub-lat t ice. An expression for the t racer cor relat ion factor is derived in terms of atom vacancy exchange frequencies and atomic concentrat ions. Resul ts from this expression are compared wi th Monte Car lo calculat ions and also resul ts f rom a previous Manning-type random al loy approach to the problem.
Authors: Jun Hui Li, Si Zong Min, Ji An Duan, Lei Han, Jue Zhong
Abstract: Vertical section features in bonding point were produced by ion-sputter thinning, and were tested by using TEM-F30. Lift-off characteristics at the interface of Ultrasonic bond are observed by using SEM (JSM-6360LV). Results show that thickness of Au/Al atomic diffusion interface was about 500 Nanometer under ultrasonic and thermal energy. Ultrasonic vibration activates dislocations at metal crystal lattice. Fracture morphology of lift-off interface was dimples. Tensile fracture appeared by pull-test not in bonded interface but in basis material, and bonded strength at interface was enhanced by diffused atom from the other side.

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