Guest lecture by Dr. Rajaprakash Ramachandramoorthy | Additive metal micromanufacturing and extreme in situ micromechanical characterization

Speaker: Dr. Rajaprakash Ramachandramoorthy
Group Leader – Nanomechanical instrumentation and extreme nanomechanics (XNano) | Group Leader – Additive micromanufacturing (AMMicro)
Max Planck Institute for Sustainable Materials GmbH (previously Max-Planck-Institut für Eisenforschung GmbH), Max-Planck-Straße 1, 40237 Düsseldorf, Germany

Abstract: Relentless pursuit of miniaturization means microscale and nanoscale materials have become ubiquitous functional elements in a variety of applications. Yet, microscale manufacturing largely relies upon thin film technology and focused ion beam-based milling to fabricate 2-2.5D architectures, which puts severe limitations on the material, geometric and phase freedoms. Further, after almost two decades of intense micro and nano-mechanics research, the majority of experimental work is still conducted at quasi-static speeds, owing to the lack of testing platforms with stringent requirements needed for small-scale testing at high strain rates. In this talk, I will present viable solutions to these typical bottlenecks in small-scale manufacturing and mechanical metrology.

Specifically, I will introduce a localized electrodeposition in liquid (LEL) method to address the lack of small-scale 3D additive metal manufacturing technologies. In addition, a piezo-based in situ micromechanical testing setup capable of conducting high strain rate micro-to-meso compressions upto 1000/s and high constant strain rate nanoindentations upto 100000/s inside the scanning electron microscope (SEM) will be presented. Subsequently, I will present two case studies on copper microlattices and liquid filled copper microcylinders. Beginning with the microstructural analysis of the copper microlattices using TKD, a systematic study will be presented on the unique rate- (upto 100/s) and cryogenic temperature dependent deformation behavior of copper microlattices. The copper microlattice deformation would be explained via deformation mechanisms of the base copper identified using copper micropillars tested at similar extreme conditions.

Further, a second case study on a new method to encapsulate picolitre liquids in metal microarchitectures using the LEL process will be shown. Structural cross-sections obtained using focused ion beam milling at cryogenic conditions will be used as a means to confirm the presence of liquids inside these microscale vessels. I will then present the impact of the encapsulated liquids on the rate-dependent micromechanical properties of copper microcylinders at room temperature and cryogenic conditions. It will be shown that the internal pressure exerted by the liquid supplements the yield and flow stress of the microcylinders especially at cryogenic conditions, where a water-to-ice transformation occurs – exploitable for 4D printing as microscale temperature sensors in the future. Finally, a unique application of liquid filled copper microcylinders as nanoreactors will be showcased by heating them above the boiling point of water.

Short bio: Raj was born in Virudhunagar, India. He received his Bachelor's degree in Aerospace Engineering from both the University of Glasgow (Scotland, UK) and the University of Illinois Urbana Champaign (USA). He then moved to McGill University (Montreal, Canada) to earn his Master’s degree in mechanical engineering, where he worked on laser transmission welding of thermoplastic composites using laser refraction. He then earned his PhD in Theoretical and Applied Mechanics at Northwestern University (USA) on the topic of deformation and failure in metallic nanowires under stress-relaxation, cyclic and high strain rate loading conditions. Further, in 2017, he joined Empa – Swiss federal laboratories for materials science and technology (Switzerland) as a Marie-Curie postdoctoral fellow to research high strain rate testing of microscale materials at extreme temperatures and templated electrodeposition based micromanufacturing. In 2020, he joined Max-Planck-Institut für Eisenforschung (Germany) as Group Leader of Nanomechanical instrumentation and extreme nanomechanics group (XNano), which focuses on developing in situ testing platforms and the necessary protocols/methods to conduct nano-to-meso scale mechanical testing under extreme strain rates/temperatures and LEL-based 3D printing of metallic micro/nano architectures.