Arya Chatterjee

A state of the art, custom-built direct-metal deposition (DMD)-based additive manufacturing (AM) system at the University of Michigan was used to manufacture 50Cu–50Fe alloy with tailored properties for use in high strain/deformation environments. Subsequently, we performed preliminary high-pressure compression experiments to investigate the structural stability and deformation of this material. Our work shows that the alpha (BCC) phase of Fe is stable up to ~16 GPa before reversibly transforming to HCP, which is at least a few GPa higher than pure bulk Fe material. Furthermore, we observed evidence of a transition of Cu nano-precipitates in Fe from the well-known FCC structure to a metastable BCC phase, which has only been predicted via density functional calculations. Finally, the metastable FCC Fe nano-precipitates within the Cu grains show a modulated nano-twinned structure induced by high-pressure deformation. The results from this work demonstrate the opportunity in AM application for tailored functional materials and extreme stress/deformation applications.

Bicontinuous, nanocomposite thin film morphologies depend largely on the deposition conditions applied during physical vapor deposition. With the introduction of high-power impulse magnetron sputtering (HiPIMS), the range of potential morphologies achieved during deposition has been increased. In this work, we compare the deposition outcomes between traditional direct-current magnetron sputtering (DCMS) and HiPIMS for a thin film co-deposit of Cu and Fe. Modular control of the columnarity, porosity, and roughness was achieved by varying the Cu and Fe metal ion currents during deposition. The directionality of the nanostructured phase-separated morphology was also controlled as the ion current increased. At zero ion current for both Cu and Fe sputtered species during DCMS, the film exhibited lateral concentration modulations of Cu and Fe. The directionality of the Cu- and Fe-rich phases shifted to vertical concentration modulations at low ion currents of IFe=1A and ICu=0.1A and to lateral concentration modulations at relatively moderate ion currents of IFe=5A and ICu=2A. At high ion currents of IFe=18A and ICu=2A, a more randomized phase domain structure was observed on the nanoscale. This structural shift is rationalized using an interdiffusion model. The role of different kinds of phase-separated morphologies, achieved during DCMS deposition, on the mechanical properties has also been studied. Results indicated an increase in hardness, indentation modulus, and flow strength values with the increase in indentation strain rates. Bicontinuous Cu–Fe nanocomposites are found to be stronger than multilayer Cu–Fe samples.