msepostdoc-list Final Exam Seminar Friday, December 3, 2021, 3:30 PM at ARMS 1103

[Morgan, Yuan-Yu Karen]

Please consider attending this seminar:
MATERIALS ENGINEERING
SEMINAR
"EXPLORING THE TUNABILITY OF MARTENSITIC TRANSFORMATION IN SHAPE MEMORY ALLOYS VIA COHERENT SECOND PHASE"
By
Shivam Tripathi
Purdue MSE Ph.D. Final Exam

Advisors: Professor Alejandro Strachan and Professor Michael Titus

ABSTRACT

Shape memory alloys (SMAs) belong to an important class of active materials. Beyond shape memory, these alloys exhibit super-elasticity and pseudo-plasticity, all originating from a reversible phase transformation from a high-temperature austenitic phase to a low temperature martensitic phase. Their unique thermo-mechanical properties make these SMAS desirable for a wide range of applications in automobiles, robotics, aerospace, construction, and medicine. Only a fraction of the known metallic alloys exhibits martensitic transformations, and a relatively small subset exhibits shape memory. Given this limited pool of SMAs, tunability of this martensitic transformation and, hence, thermo-mechanical properties is a way to move forward for effectively designing the next-generation SMAs for specific applications. The modification in composition has always been at the heart of designing new SMAs for future applications. However, a relatively recent discovery of incorporating a second non-transforming phase in base martensitic materials to tune martensitic transformation to achieve unprecedented thermo-mechanical properties has shown great promise.

The objective of this work is to utilize the second phase to provide design guidelines for next-generation SMAs and to understand the detailed physics behind the experimentally observed unprecedented thermo-mechanical properties in SMAs as a result of the incorporation of coherent second phases. We first investigate Mg-Sc shape memory alloys that are attractive for a wide range of applications due to their low density. Unfortunately, the use of these alloys is hindered by a low martensitic transformation temperature (173 K). We observe from first-principles calculations that epitaxial strains arising from appropriate substrate or coherent second phase selection increase the martensitic transformation and operational temperature to room temperature. Next, we develop a novel approach to induce martensitic transformation in composite systems of two non-transforming materials. While we demonstrate this approach for the technologically relevant ultra-lightweight Mg/MgLi superlattices, however, our approach is general and will open a wide material space for the discovery and design of next-generation SMAs.

Finally, to bridge the gap between computationally studied single-crystalline materials and experimentally studied polycrystalline systems, we characterize the role of nanoscale precipitates on temperature- and stress-induced martensitic phase transformation in nanocrystalline Ni63Al37 SMAs using multi-million-atoms molecular dynamics simulations. Simulations provide the understanding of underlying atomistic mechanisms of experimentally observed unprecedented thermo-mechanical properties and the guidelines to design low-fatigue ultra-fine grain shape memory alloys. As a result of the exploration of novel thermomechanical properties in SMAs via coherent second phases, we also published a software package to discover coherent precipitates within a base multi-component system by coupling high-throughput equilibrium thermodynamics calculations with strain-based lattice matching.



Date: Friday, December 3, 2021

Time: 3:30 P.M.
Place: ARMS 1103


Yuan-Yu Karen Morgan,Ph.D.
Academic Advisor-Graduate Program
School of Materials Engineering
Neil Armstrong Hall of Engineering, Room 2217
765-494-4103
ymorgan at purdue.edu<mailto:ymorgan at purdue.edu>

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