A Aloke Paul

Intrinsic diffusion in Ni3Al system

Abstract Interdiffusion experiments were performed between different Ni–Al two-phase alloys. A method is given to estimate the tracer diffusion coefficient of one of the constituents in a binary alloy knowing the tracer diffusion coefficient of the other species. The procedure is based on the so-called Darken-Manning analysis. The tracer diffusion coefficient of Al was determined in this way in Ni3Al: D Al ∗ =5.05×10 −7 −1.117×10 −7 +2.28×10 −6 exp −243±16 KJ / mol RT m 2 s Our results are compared with others available in the literature. The values for the self diffusivity of Al calculated from interdiffusion experiments give consistent result. All these measurements support the theory that diffusion of the minor element occurs through a vacancy mechanism in Ni3Al.

Formation of AB2-intermetallics by diffusion in the Au–Sb–Bi system

Abstract Binary diffusion couples, in which one single-phased product layer is growing between pure elements, were employed to study the diffusion properties of Au 2 Bi- and AuSb 2 -intermetallics at 230 and 330xa0°C. The position of the Kirkendall-marker plane inside the reaction zones revealed that in this temperature range the minority element is the faster diffuser in the Laves-phase Au 2 Bi as well as in AuSb 2 . The concept of integrated diffusion coefficient is used to describe the growth kinetics of the intermetallic compounds. The integrated diffusion coefficient in an intermetallic is related to the tracer diffusivities of the components and the thermodynamic stability of the phases involved in the interaction. The tracer diffusion coefficients were deduced from the interdiffusion experiments. The isothermal cross-section through the ternary phase diagram Au–Sb–Bi at 230xa0°C was constructed by means of the diffusion couple technique. No ternary phases are found in this system. Both intermetallic compounds Au 2 Bi and AuSb 2 are in equilibrium with the (Sb,Bi)-solid solution. The solubility of Sb in the Laves-phase Au 2 Bi was found to be negligible. Up to about 10.5 at.% of Bi can be dissolved in the AuSb 2 -phase, the Bi-atoms substituting Sb in the cubic lattice of AuSb 2 .

Bifurcation and trifurcation of a Kirkendall plane during multiphase interdiffusion

A Kirkendall-effect mediated behaviour of inert (fiducial) markers situated before the interaction at the original interface of a diffusion couple can be complex in both spatial and temporal domains. It was found that the Kirkendall plane can bifurcate and even trifurcate in a multiphase reaction zone. This can be rationalised in terms of Kirkendall velocity construction as well as from a purely chemical point of view considering diffusion-controlled interactions at the interphase interfaces. The physico-chemical approach is also used to explain significance of the Kirkendall effect in the morphogenesis of interdiffusion systems.

The Kirkendall Effect in Multiphase Interdiffusion

The Kirkendall effect mediated migration of inert inclusions during multiphase diffusion can be rationalized using a Kirkendall velocity construction. It is demonstrated that the Kirkendall plane locations inside the diffusion zone can be identified by grain morphology changes within the microstructure of the reaction products. The latter is the result of different nucleation processes at both sides of the Kirkendall plane.

Physico-Chemical Analysis of Compound Growth in Binary Interdiffusion Systems

A diffusion-controlled growth of intermetallic phases and the role of the Kirkendall effect in morphological evolution of the product phase layers can be described in terms of an alternative theory considering chemical reactions at the interphase interfaces. Application of this “physicochemical” treatment to diffusional growth of intermediate phases with fairly wide homogeneity ranges is illustrated by the example of interaction in the Ag-Zn system. The model is purely phenomenological, and its use is convenient, since no explicit assumption of the underlying diffusion mechanism is required.

The Kirkendall plane in binary interdiffusion systems

There is now a considerable body of experimental evidence to indicate that in a volumediffusion controlled interaction the Kirkendall plane need not be unique. The Kirkendall plane can microstructurally be stable as well as unstable (it does not exist!). Under predictable circumstances, it can also bifurcate and even trifurcate. This can be rationalised in terms of Kirkendall velocity construction as well as from a purely chemical point of view considering diffusion-controlled interactions at the interphase interfaces. The physico-chemical approach is also used to explain significance of the Kirkendall effect in the morphogenesis of interdiffusion systems.