Date of Award

Summer 2019

Project Type

Dissertation

Program or Major

Materials Science

Degree Name

Doctor of Philosophy

First Advisor

David Lashmore

Second Advisor

James Krzanowski

Third Advisor

Carmela Amato-Wierda

Abstract

Compositionally modulated alloys and artificial superlattices are thin-layered structures where the layer thickness is on the order of a few 10s of lattice constants. These alloys have been shown to be unusually strong. Their overall thickness can be very large, in this study we have grown these to a thickness of 45 µm by 2.5 cm, in diameter, much greater than the average. We posit the reasons for this strength are that, during deformation, glissile dislocations are pinned at layer boundaries, the presence of image forces, and the formation of Lomer-Cottrell and Hirth dislocation locks. In this thesis we examine the fundamental reasons why layered alloys show such as high yield stress and compare our experimental data with our strength model using compositionally modulated copper-nickel as an example. We combine experimental synthesis with the molecular dynamics modelling using LAMMPS to compare this data with first principle modelling. LAMMPS shows dislocations pinning at alternate boundaries, consistent with literature observations. The consequences of this work bears directly on the fields of electrical contacts, sliding wear, and even enhancement of bulk materials strength. We have found that Cu-Ni compositionally modulated alloys can exhibit a hardness of over 500 Hv which corresponds to breaking stresses over 1.5 GPa. We have not observed a significant systematic modulus enhancement. We show that is it possible to produce these compositionally modulated alloys directly on copper coated silicon by electrodeposition through a mask to yield strong materials that can have consequences for new kinds of technological advances in integrated circuit processing that can be integrated into existing manufacturing methods. Because electrochemical deposition is widely used in the field of contacts, these results can have almost immediate practical application in this field. Electrodeposition is also an ambient temperature process, so interfaces can be made very compositionally sharp allowing components mounted on adjacent circuits to remain thermally undamaged. Using this process, it is possible to electrochemically place extremely strong metals anywhere on conductive substrate at essentially ambient temperature.

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