Thesis Topics

Interdiffusion and the Kirkendall effect in solid-state (Chirantan Ghosh, Ph.D. project)
Research is in progress to develop a better understanding on the Kirkendall effect related to interdiffusion in solid-state. Main aim here will be to modify the physico-chemical approach, which was recently developed by us. Reaction/dissociation at the interface interphases will be considered to combine with flux equations. This approach can replace diffusion-based approach to determine diffusion parameters with an extra benefit that one can explain morphological evolutions during interdiffusion.

This model is applied to study interactions between lead free solder alloys and UnderBump Metallizations (UBM).

Metal-silicides are important in many different areas. Nb- and Mo-based silicides are emerging as potential candidates to replace third generation Ni-based single crystal alloys (3GXs) in gas turbines. Silicides are important to use as protective coatings for refractory metals. In microelectronics devices, thin silicide layers are used as contacts and interconnections because of lower electrical resistivity. In view of intimate relationships between microstructure and properties, acquiring knowledge on phase diagram, diffusion parameters and growth kinetics of the silicide layers is of primary interest.

Cu interconnects have replaced Al interconnects in fast switching devices because of superior conductivity and electromigration resistance. In this project, study will be carried on different aspects, like interaction of diffusion barrier layer with Cu and Si, texture evolution in Cu after deposition and the effect of alloying elements on different properties. This work is in collaboration with Mr. G.V. Mahesh and Dr. Satyam Suwas.

Nb3Sn superconductor is one of the most important superconductors in applications. This is grown by bronze technique, where Nb3Sn phase forms between Nb and Cu(Sn) alloy by diffusion controlled process. Study is going on to determine growth kinetics of the phase and to determine diffusion parameters in this system. Further to shed lights on atomic mechanism of diffusion other superconductors with A15 structure, such as V3Si, Nb3Au, V3Au. In these phases, we shall determine tracer diffusion coefficients following diffusion couple technique.

Designing of new alloys with much improved properties is always required for different applications. To achieve a property balance, very frequently we need to produce alloy with different elements. In this respect, the classical diffusion multiple technique can be used as the first step to accelerate alloy-design. This technique is useful for acquiring knowledge on the variation of mechanical properties with composition, from a limited number of experiments. Different materials will be coupled at elevated temperature and annealed for certain time so that diffusion controlled reaction product layers form with varying compositions of different elements. Composition profile is measured with the help of Electron Probe MicroAnalysis (EPMA) and instrumented nanoindentation is used to evaluate hardness and elastic modulus at a submicron scale. This way one can correlate mechanical properties with the variation of composition in interdiffusion zone. Accordingly, few selected alloy compositions can be considered for further study to develop processing techniques and to study mechanical properties for the purpose of finding a suitable alloy for application. Ni-based superalloys and alloys with shape memory effect are considered in this project

These systems are important for high temperature applications. We shall concentrate our studies in these systems to determine diffusion parameters, such as, interdiffusion coefficients, intrinsic diffusion coefficients and tracer diffusion coefficients.