Dry Sliding of Ductile Metals (2003-)

As a postdoctoral researcher with Prof. David Rigney, I tried to understand interfacial processes that lead to the formation of nanocrystalline, mechanically-mixed tribomaterial during sliding, particularly at high velocities. The formation of tribomaterial has important implications on the transient friction and wear response of the tribopair. To answer these issues, we did Molecular Dynamics (MD) simulations of sliding in amorphous and crystalline systems. We discovered that tribomaterial is formed mainly due to fluid-like plastic flow at the sliding interface, with features strongly reminiscent of “vorticity”. This behavior has been observed in both crystalline and amorphous systems.

I also attempted to model velocity, strain-rate and strain gradients that develop adjacent to the sliding surface based on fluid flow principles. We developed analytical models for determining the high velocity friction. We are currently tring to verify these models by characterization of near-surface deformation structures using Transmission Electron Microscopy. We believe that MD simulations can also aid in the understanding of the fundamental friction-related processes, particularly at high velocities.  This research is a collaboration between Ohio State and Los Alamos National Labs, where they have built a new Rotating Barrel Gas Gun (RBGG) that enables the dynamic measurement of high sliding velocity (1-10 m/s), and in addition could help probe the synergistic effect of high velocity impact.

I was involved in the building of an intermediate speed pin-on-disc tribometer with capabilities for testing in air, nitrogen and high vacuum and for rapid data acquisition. The samples tested with this equipment at Ohio State are being characterized presently.

Modeling Microtwinning in Ni-based disc alloys (2003- )

Electron microscopy has confirmed that high temperature creep (over a given window of stress and temperature) in some Ni-based disc alloys is dominated by a microtwinning mechanism - something not usually expected under creep conditions. I worked with Prof. Mike Mills, to understand microtwinning in Ni-based disc alloys under creep conditions. As part of this work, wesimulated various defects such as superlattice stacking faults and twins and calculated their energies using EAM potentials. We employed Monte Carlo methods to probe the reordering that occurs during microtwinning in these alloys. We also developed a simple creep model based on such reordering.

Understanding Creep Behavior and Microstructural Stability of g-TiAl alloys (1997- )

For my PhD, I worked with Prof. Mike Mills to understand creep deformation, and microstructural and alloying effects in gamma titanium aluminide alloys which have potential high temperature structural applications. To this effect, we carried out high temperature constant strain-rate and creep testing of these alloys in different microstructures. Deformation microstructures were characterized using techniques including TEM. We subsequently developed a physically-based dislocation-level creep model based on the jogged-screw mechanism and which is substantiated by microstructural observations. We also did dynamic simulation of jogged-screw dislocation motion based a line-tension model. This model was subsequently modified to not only account for microstructure (Equiaxed Vs. Fully lamellar), but also adapted for other materials systems including titanium and a-Zr alloys. Extensive studies, utilizing conventional TEM tools were carried out to investigate the thermal stability in -TiAl alloys, particularly in the fully lamellar microstructure.