Seminar Speaker: Dr. Bharat Gwalani, PNNL

Speaker Dr. Bharat Gwalani, PNNL Title “Deformation-Induced Modification of Phase Transformation Pathways in Metallic Systems”    

Abstract

Deformation-induced microstructural modification is utilized by several high strain processing methods such as rolling, friction-stir-based processing, welding, or additive manufacturing. Consistent distribution of high density of crystallographic defects allows heterogeneous nucleation sites for nano-scale precipitation of intermetallic phases and often results in high-performing nanostructured alloys. The state of high defect density in the material also makes them highly susceptible to reactive gases, such as oxygen, present in the atmosphere. Atomic-scale studies on understanding deformation-induced defect formation and diffusion, especially in the presence of oxygen, are limited to deformation strains < 1 where material vulnerability to the environment is minimal due to lower defect density.

Investigation of fundamental mechanisms related to phase stability/transformations, and oxidation of metals and alloys under high strain deformation, has been the core of my research in the past few years. This seminar will present insights into  (a) the influence of high strain deformation in modifying transformation pathways; (b) adding the compositional complexity to the microstructural template to tailor the physical property; (c) integrating in situ and ex situ experimental characterization tools such as environmental transmission electron microscopy and atom probe tomography, and synchrotron X-ray diffraction and involving combinatorial approaches based on rapid prototyping, at multiple lengths and time scales to understand the effect defect density, thermal activation and environment on microstructural changes.

The experimentally observed variations in the transformation pathway have been rationalized via the competition between the thermodynamic driving force and activation barrier for second-phase nucleation, coupled with the kinetics of the process. The microstructural variations that result from these dramatically different phase transformation pathways lead to exceptional mechanical properties that can be varied over a large range.

Biography

 

Appointments

2022- present                                      Materials Scientist-III, Pacific Northwest National Laboratory

2020-2021                                             Materials Scientist-II, Pacific Northwest National Laboratory

2019-2020                                      Post-Doctoral Researcher, Pacific Northwest National Laboratory

2017-2019                                          Post-Doctoral Researcher, University of North Texas, Denton

2013-2017                                     Graduate Research Assistant, University of North Texas, Denton

2011-2013       Junior Manager, Steel Authority of India Limited (SAIL), Bokaro Steel Plant, India

2010-2011                                      Associate Manager, Jindal Stainless Limited (JSL), Hisar, India