(605f) Dynamic Processing of Electrodeposited Graded Density Alloys

Driven by an interest in dynamic high-pressure research, we are developing methods to create thick (mm) electrodeposited alloys with graded composition/density. The use of graded density alloy impactors allows access to varied acoustic impedance profiles and ranges of imparted velocities using gas gun instruments which are accessible and wide spread. These dynamic compression experiments present an unparalleled opportunity to access unique thermodynamic pathways including sequential combinations of shock, quasi-isentropic compression, constant pressure, and controlled release regions within a single experiment.

In this work, we are designing dynamic electrodeposition processes to fabricate graded compositional/density alloy structures to correlate grain structure and dynamic properties. An initial constraint in these experiments is complete solid solubility between components, limiting fully dense material combinations to Ag-Au, Co-Re, Mg-Mn, and Al-In as examples. Both the development of aqueous and non-aqueous electrolytes and the associated pulse electrodeposition parameters will be discussed.

Specifically, gold is of interest as a model system in high pressure and dynamic research because of its high compressibility and inert character, especially as purity, defects, and grain structure can be carefully controlled. Further, gold has complete solid solubility with silver and similar deposition chemistries, presenting a model system to investigate the fabrication of graded density alloys.

However, initial experiments have demonstrated limited control over the compositional gradient. Instead dynamic processing approaches, such as temperature ramps and varying applied current densities (peak current, pulse on/off times), have been investigated. Notably, these dynamic processing approaches impact the relative nucleation and growth rates of each component during electrodeposition. As the grain structure of the deposit can influence dynamic compression properties, we have as been investigating how deposition parameters control the structure.

We present a comprehensive study of electroplated films with compositional gradients and varied microstructures up to thicknesses of several millimeters for gold and silver. To broaden the potential for high-pressure research, similar techniques can be applied to any material that can be electrodeposited, and we will show some initial exploratory work for graded compositions varying from aluminum to rhenium.