Objective
Multicomponent mutual and reactive diffusion plays a major role in many important technological processes. For example, recently discovered possibility of obtaining multicomponent bulk metallic glasses by moderate quenching rate from the liquid state is clearly caused by peculiarities of diffusion process connected with nucleation in multicomponent systems. Contrary to binary systems, diffusion properties of ternary and multicomponent alloys remain much less investigated. Even less investigated is the reactive diffusion in ternary systems. To develop the general description of these processes one has to investigate in details some model systems with limited number of intermediate phases (in this case Cu-Ni-Sn and Cu-Ni-In). Emphasis is to be made on the initial stages since they determine the resulting phase spectrum and the morphology of diffusion zone.
Following main tasks can be formulated:
1) to investigate the course of the diffusion paths at the early stage of interdiffusion in ternary systems (taking Kirkendall shift and void formation into account) possibly leading to the formation of a metastable inhomogeneous solid solution; to investigate the evolution of diffusion zone structure with increasing annealing time;
to investigate (by means of theory, real and computer experiments) the nucleation of ternary intermediate phases and the growth of precipitates in the diffusion zone taking into account stress generation and relaxation processes;
to develop the theory and software for the evolution of the two-phase zones including the possibility of periodic layer formation and to compare it with experimental results.
Following research activities (which are the continuation of preliminary joint work of research teams) are planned:
1. Creation of methods and software for calculation of diffusion paths for inter diffusion in the stable and metastable solid solutions using information on self-diffusivities and Gibbs energies;
2. Development of the theory of intermediate phase nucleation in the concentration gradients of ternary systems, including optimisation of nucleus shape, calculation of nucleation barriers, incubation times, nuclei size distribution);
3. Simulation of two-phase zone evolution, including growth and competition of intermediate phase precipitates.
Experimental study of interdiffusion and accompanying phenomena in ternary systems Cu-Ni-Sn and Cu-Ni-In as well as for component binary systems for comparison with theory of new phase nucleation and growth.
Experimental study of two-phase zone evolution for abovementioned systems and for systems demonstrating the periodic layer formation.
Expected results:
Criteria for the diffusion path prediction during reactive diffusion in ternary systems;
Methods of predicting the time sequence for appearing phases, including incubation times;
Prediction of the two-phase zone morphology as a function of initial compositions and diffusion parameters;
Software for predicting the two-phase zone evolution, including nucleation at the early stages.
Topic(s)
Call for proposal
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38402 Saint Martin d'Heres
France