Collaborative Research: Exploring Chemical Effects in Surface Plasticity to Enhance Material Removal Processes for Refractory Metals

About This Grant

This research will advance the state-of-the-art of industrial material removal processes for high-temperature refractory metals through a recently uncovered chemical effect (local embrittlement) in surface plasticity, referred to as Organic Monolayer Embrittlement (OME), arising from nanoscale organic films. It is well known that high-strength metal alloys, e.g., hard steels, are difficult to machine. What is much less well recognized is that relatively soft, refractory metals like tantalum and niobium are equally challenging to cut, grind and comminute, with high forces and surface quality problems, earning them the moniker "gummy." The gummy behavior is due to the high malleability of these metals, with non-homogeneous deformation and intense energy dissipation. This award supports research that seeks to solve the gumminess challenge via scientific understanding of the nanoscale OME phenomenon and its implementation in manufacturing processes. The research project will test the hypothesis that if the gumminess can be eliminated by local embrittlement, using benign organic media that induce a surface stress in the metal, then material removal will occur by fracture, with low forces/energy, improved surface quality and increased productivity. A suite of high-performance chemomechanical manufacturing processes should emerge, advancing refractory metal applications in areas including aerospace, hypersonics, nuclear energy and electronics. Complementing the research is an education program involving undergraduate researchers in creating a video gallery of plastic flow and fracture phenomena for manufacturing, and scientific collaborations with companies and universities. The research combining high-speed in situ observations of deformation, chemistry/material interactions and surface science will explain how nanoscale organic films influence (a) large-strain deformation and material removal in refractory metals via surface stress and (b) forces, deformation, and fracture, which are all manifest at the macroscale. A fully instrumented plane-strain cutting system will impose controlled large-strain deformation typical of material removal processes. The basis of the chemical effect in plasticity will be established by (a) integrating surface molecular probes and high-resolution in situ imaging of deformation, with ex situ materials characterization, (b) multiscale modeling of materials behavior and chemical effects in plasticity/fracture, and (c) characterizing media effects on process attributes such as forces, energy, and workpiece surface quality (finish, metallurgy). The study will investigate model material systems, including tantalum and nickel alloys, selected for their deformation response and technological interest. The findings will impact areas such as manufacturing, wear, and environmentally assisted cracking, wherein interactive effects of chemistry, plasticity and fracture often play a key role. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.