Predictive Theories for Guiding Materials Design (16/12/22)

Speaker and Affliation:

Dr. Shankha Nag
PostDoctoral Researcher, Material Modeling Division,
Institute for Materials Science, Technical University Darmstadt, Germany.

About the Speaker:

Dr. Shankha Nag earned his Bachelor degree in Metallurgical and Materials Engineering from National Institute of Technology Durgapur (India) in 2013 and his Master degree in Materials Engineering from Indian Institute of Science Bangalore in 2015. After graduation, Dr. Nag pursued his doctoral study at the Swiss Federal Institute of Technology Lausanne (EPFL) in the Laboratory for Multiscale Mechanics Modeling, supervised by Prof. William Curtin. At EPFL, Dr. Nag developed new methods for accurate atomistic-continuum coupling of random alloys. As part of his dissertation, he also developed a generalized solute-strengthening theory applicable to single-phase homogeneous alloys, where he considered the effect of chemical short-range order and solute-solute interactions across the slip plane. Dr. Nag obtained his doctorate degree from EPFL in November 2020, for successful completion of dissertation entitled “Concurrent multiscale modeling and theory of solute-strengthening for dilute and complex concentrated alloys”. Starting January 2021, Dr. Nag has been working as a postdoctoral researcher at Technical University in Darmstadt (Germany) in the Material Modeling Division, headed by Prof. Karsten Albe. As a part of his postdoctoral research, he has studied the deformation mechanisms in nanocrystalline high-entropy entropy alloys with low/negative stacking fault energy. He has also worked independently on developing a theory for nucleation of slip mediated planar defects. Dr. Nag’s research aims at the fundamental, multi-scale understanding (atomistic and continuum) of plasticity and phase transitions in metallic alloys, in order to develop predictive theories that can be used to guide materials design in uncharted regions of the material properties space.

When?

16^th December, 2022 (Friday), 03:30 PM (India Standard Time)

Venue

KPA Auditorium, Department of Materials Engineering

Abstract

Materials modeling using atomistic simulations (like molecular dynamics or MonteCarlo) has supplemented experiments in understanding key mechanisms behind macroscopic material behavior. However, the many degrees of freedom associated with these simulations coupled with practical limitations in simulation length and time scales, make it difficult to correlate complex physical phenomena like dislocation nucleation and glide to basic material parameters like elastic constants, stacking fault energy, etc. across different material systems. However, this goal can be realized with predictive theories which model underlying mechanisms in terms of basic material parameters and aid in efficiently combing through the vast space of material properties in search for new materials with enhanced performance. In this presentation, I will discuss theories, free of adjustable parameters, that address the long-standing problems of (1) solute-strengthening by pinning of dislocation segments in metallic alloys during glide [1, 2], and (2) homogeneous and heterogeneous dislocation nucleation. The solute-strengthening theory has been applied to dilute as well as complex concentrated alloys (CCAs) with remarkable success in predicting experimentally obtained yield strengths. In keeping with the recent surging interest in strengthening of alloys with short-range order (SRO), the strengthening theory has been extended to include the effects of SRO [3]. This generalized solutestrengthening theory is state of the art which is applicable to any macroscopically homogeneous and single-phase alloy, and the theory takes inputs that can be measured or computed. On the other hand, the theory for dislocation nucleation finds the minimum stress required to nucleate stable dislocation loop at rates below 0.01s −1 at different temperatures. The theory is applicable to deformation of metals and alloys with nanocrystalline microstructure and shear coupled grain boundary migration mediated by the nucleation and propagation of grain boundary disconnections.

REFERENCES

[1] S. Nag, W. A. Curtin, Effect of Solute-Solute Interactions on Strengthening of Random Alloys from Dilute to High Entropy Alloys, Acta Materialia 200, 659–673 (2020)
[2] S. Nag, C. Varvenne, W. A. Curtin, Solute-strengthening in elastically anisotropic fcc alloys, Modelling Simul. Mater. Sci. Eng. 28, 025007 (2020)
[3] S. Nag, W. A. Curtin, Solute-strengthening in alloys with short-range order (Submitted)