Deptartment of Metallurgical Engineering and Materials Science
12 PM, Friday, May 19th, 2017
1070 Bainer Hall
Abstract: Despite ceramic nanocomposites possessing improved mechanical/tribological properties compared to corresponding monoliths and composites having coarser microstructure, processing challenges associated with handling/dispersion of nanosized particles/fibers and requirements of advanced sintering techniques (usually with inert/reducing atmosphere) have severely hindered their commercial take-up . Additionally, nanocomposites developed via physical mixing of starting powders and reinforcing fibers, followed by sintering, lead to the presence of deleterious/coarse second phase fibers/particles, primarily at the matrix grain boundaries (with the grain interiors nearly completely devoid of the reinforcements); thus resulting in considerably suppressed improvements in the various properties . This is especially the case for carbon nanotube (CNT) reinforced bulk polycrystalline ceramics, leading to the unsatisfactory improvements (sometimes even degradation) in the properties. Against these backdrops, recent developments of bulk polycrystalline ‘ceramic alloys’, via facile solid-state precipitation route (in air), resulting in achieving ‘near-ideal’ microstructures characterized by uniformly dispersed nanosized inter/intragranular coherent second phase particles, will be presented. The ‘age hardened/toughened’ ‘ceramic alloys’ (based on bulk polycrystalline MgO, to start with) possessed nanosized second phase precipitate particles, uniformly distributed within the matrix grains and at the grain boundaries. Interestingly, the intragranular second phase particles were coherent with the MgO matrix . Development of such microstructural features for two-phase bulk ceramics (i.e., uniformly distributed second phase particles, nanosized intergranular particles and coherent particles) are not possible via the usual powder metallurgical routes. The mechanical and tribological properties were not inferior to MgO-based ceramic nanocomposites, rendering them viable alternatives to the otherwise difficult to process ceramic nanocomposites [3,4]. Following this, successful developments of multi-walled carbon nanotube (MWCNT) reinforced bulk polycrystalline Al2O3, with the reinforcing MWCNTs present uniformly within the sintered matrix grains (i.e., intragranular reinforcements), as achieved for the first time using an innovative wet-chemical synthesis based processing route (sans ball-milling) will be discussed . The route comprised of direct addition of well-dispersed MWCNTs to matrix sol, followed by rapid gelation (in few minutes) and sintering (which also included the step for formation of polycrystalline α-Al2O3). Such microstructure-type, not only led to improvements in the fracture properties, but to significant improvements in the wear resistance (decrease in wear-rate by even >95%); as possibly never achieved before.
Biography: Amartya Mukhopadhyay is presently Associate Professor at the Department of Metallurgical Engineering and Materials Science, IIT Bombay. He earned his Doctoral in Materials Research from the University of Oxford, UK, in December, 2009. He had obtained his Master’s by research in Materials and Metallurgical Engineering from the Indian Institute of Technology (IIT), Kanpur, India in September, 2006. Prior to that he did his undergraduate work in Metallurgical Engineering at the Regional Engineering College (presently, National Institute of Technology; NIT), Durgapur, India (1999-2003) and had also subsequently worked for one year (2003 – 2004), as a graduate engineer trainee at ESSAR steel plant, Hazira, India. Following his PhD he did his Post-doctoral Research at Brown University, USA for a couple of years. His major research interests include materials for electrochemical energy storage (i.e., Li/Na/K-ion batteries; including solid-state batteries) and advanced structural ceramics/nanocomposites/‘ceramic-alloys’. To date, Amartya has authored/co-authored 40 research papers in peer-reviewed International Journals, contributed three chapters for books published by internationally recognized publishers and has 3 patents.