Postdoctoral Scholar, Purdue University
Presented: December 3 and 4, 2020
“Nanoscale 4D Microstructural Characterization of Corrosion in High Performance Light Metal Alloys using Correlative Microscopy”
AA 7XXX alloys are used extensively in aircraft and naval structures due to their excellent strength to weight ratio. These alloys are often exposed to harsh corrosive environments and mechanical stresses that can compromise their reliability in service. Furthermore, they are comprised of constituent particles of different chemical compositions that determine their performance. Of interest in this study are nanoscale precipitates that are designed to improve the mechanical performance of AA 7XXX alloys.
Precipitate location, size, and composition also play a pivotal role in determining the initiation and propagation of corrosion damage in these alloys. Visualizing the effect of precipitates on a local as well as global length scale can be challenging due to the small length scales involved. In this study, x-ray nanotomography using Transmission X-ray microscopy (TXM) has been employed to non-destructively study localized corrosion in AA 7075 exposed to 3.5 wt.% NaCl solution. Four-dimensional (4D) ex situ experiments conducted on peak and highly overaged AA 7075 yielded extremely interesting insights into the complex interplay between precipitates, grain boundaries, and other second phase particles. The time dependent tomography yielded valuable information pertaining the preferred sites of intergranular corrosion initiation, and propagation at the nanoscale. Coupling this with serial sectioning EBSD provided insight into the role of grain boundary character on precipitate distribution and propensity for intergranular corrosion. The use of a correlative microscopy-based approach yielded multimodal characterization results that have provided a unique and seminal insight into corrosion mechanisms in AA 7075.
Sridhar Niverty, Ph.D., Postdoctoral Scholar, Purdue University
Sridhar Niverty is a postdoctoral scholar at the School of Materials Engineering at Purdue University. He has a doctorate in materials science and engineering from Arizona State University where he studied the effects of environmentally assisted damage in light metal alloy systems under the guidance of Professor Nikhilesh Chawla. Prior to joining Arizona State University, Sridhar spent two years as a junior manager at JSW Steels Ltd., India, where he led a team of engineers and technicians responsible for the production of a variety of grades of steel using a continuous slab caster.
Sridhar is very interested in pursuing a career in academia wherein he intends on implementing correlative microscopy-based workflows to study microstructural evolution during processing and damage evolution in-service.
He is also passionate about materials science education and teaching and is a recipient of the Outstanding Teaching Assistantship award from Arizona State University.