Director of Additive Manufacturing Innovation Center
Associate Director of the Institute of Materials Science (IMS)
Director for Undergraduate Studies
Ph.D., University of Wisconsin-Madison (2003)
Department of Materials Science & Engineering
97 North Eagleville Road, Unit 3136
Storrs, CT 06269-3136
Phone: (860) 486-3155
Coordinator: ASM Annual Materials Mini-Camp, ASM International
Editor, Review Board Member: International Scholarly Research Network
Vice Chair: ASM Hartford Chapter
Member: Association of Iron and Steel Technology
Member: American Ceramic Society
Member: The Minerals and Metals Society
Member: ASM International
|Ph.D. Students||Undergraduate Students|
|Ellen Lavorato||Drew Capolupo*
|*Co-advised with Prof. Body|
Metallic glasses: thermomechanical behavior under sustained deformation
We are interested in the effect of repeated elastic deformation of metallic glasses on their thermal and thermomechanical behavior. Upon repeated deformation, local configurational changes can occur that can cause changes in the structural relaxation behavior and in mechanical properties such as compressive stress-strain behavior. Our experimental analysis is based on thermomechanical (TMA) and differential scanning calorimetry analyses. We furthermore use transmission electron microscopy to obtain insight into microstructures of partially devitrified glasses. Our model system has been amorphous Cu50Hf41.5Al8.5 glass, which we obtain in different shapes and sizes upon suction casting. Using samples with square cross-sections we were recently able to analyze the effect of casting direction, annealing treatment, and elastic loading direction on the thermomechanical behavior. To better discern between the reversible, inherent thermal expansion, and irreversible length changes due to structural relaxation or viscous effects we use temperature-modulated TMA. Among the recent key results we were able to demonstrate that the repeated elastic deformation induces a thermomechanical anisotropy. We furthermore demonstrated that the casting process entails a thermomechanical anisotropy that can be eliminated with careful annealing treatments. We currently work on analyzing the modulated TMA and DSC results within the framework of activation energy spectra.
Metallic glasses: wear behavior, driven crystallization
The literature on metallic glasses is riddled with contradictions on the wear characteristics, for example, the relation between hardness and wear volume loss. Building on our experience with devitrification of amorphous alloys, we focus on wear studies under defined experimental conditions. For amorphous Cu50Hf41.5Al8.5 glass we recently demonstrated ‘self-healing’ effects, i.e., the improvement in wear resistance with sliding due to the formation of nanocrystals during sliding. Following up on these results we currently study the role of devitrification for fracture toughness, elastic properties, hardness, and wear behavior of Cu50Hf41.5Al8.5 bulk metallic glasses.
Plastic instability in metallic multilayers during accumulative roll bonding
We use accumulative roll bonding to deform metallic multilayers to increasing strain. For most multilayer systems, plastic instability develops as multiple diffuse necking in one or more elemental layers. We are interested in the mechanisms that induce plastic instabilities and the role that the confinement of the layers between other layers has on the instabilities. To succeed in this research it is critical that the mechanical properties, notably the flow stresses, can be determined for the layers, not only for the multilayer as a composite. We use nanoindentation studies on cross-sectional samples to determine the hardness of individual layers and use the hardness information for plastic instability models to predict the onset of instabilities in individual layers. We have recently focused on Mo-Mo and Mo-Ta multilayers and work on the analysis of the nanoindentation data taking into account grain-boundaries and layer boundaries in the vicinity of the indents. With this work we can test and further develop continuum mechanics models for the plastic behavior of multiphase materials.
|2012-2013||Technology Development Engineer, Pratt & Whitney, Engineering Integrated Solutions Group, Additive Manufacturing (sabbatical)|
|2007-2012||Assistant Professor, MSE UConn|
|2008||NRL Summer Faculty Fellowship|
|2003-2005||Postdoctoral Fellow, U of Wisconson-Madison|
|2003-2005||Post Doctoral Fellow Research Center Karlsruhe, Germany (now: Karlsruhe Institute of Technology)|
|2010-2011||Materials Science and Engineering Program Teaching Award|
“Nanocrystals in metallic glasses”, InTech Publisher, open access (June 2011)
Poudyal, N. (Dept. of Phys., Univ. of Texas at Arlington, Arlington, TX, United States); Chuanbing Rong; Ying Zhang; Dapeng Wang; Kramer, M.J.; Hebert, R.J.; Liu, J.P: “Self-nanoscaling in FeCo alloys prepared via severe plastic deformation”, J. Alloys Comp., vol. 521, pp. 55-59, 2012.
D.R. Maddala, R.J. Hebert, “Effect of notch toughness and hardness on sliding wear of Cu50Hf41.5Al8.5 bulk metallic glass”, Scripta Mater., vol. 65, 630-633 (2011).
C. Rong, Y. Zhang, N. Poudyal, M.J. Kramer, I. Szlufarska, I., R.J. Hebert, J.P. Liu, J., “Self nanoscaling of the soft magnetic phase in bulk nanocomposites”, Mater. Sci. Vol. 46(18), 6065-6074 (2011).
“Metallic glasses: no disdain for disorder”, AZOM.COM Materials Thought Leader Series (online).
G. Marathe, R.J. Hebert, “Hardness measurements of accumulative roll-bonded Mo foils”, J. Mater. Sci. Vol. 45 (17), pp. 4770-4777 (Special Issue: Ultrafine-grained materials), September 2010
D. Maddala, R.J. Hebert, “Sliding wear behavior of Cu50Hf41.5Al8.5 bulk metallic glass”, Wear, Vol. 269 (7-8), pp. 572-580 (August 2010)
A. Mubarok, R.J. Hebert, “Thermomechanical behavior of Cu50Hf41.5Al8.5 bulk metallic glass after sustained elastic deformation”, Met. Mat. Trans. A, Vol. 41 (7), pp. 1658-1663, July 2010
G. Marathe, R.J. Hebert: “Hardness measurements of accumulative roll-bonded Mo foils”, J. Mater. Sci., Special issue: Ultrafine Grained Materials, in press.
Maddala, D. , Mubarok, A. , Hebert R.J. (2010) Sliding Wear Behavior of Cu50Hf41.5Al8.5 Bulk Metallic Glass, Wear, vol. 269, pp. 572-580.
Rong, C., Zhang, Y., Poudyal, N., Kramer, M.J., Szlufarska, I., Hebert, R.J., Liu, J.P. (2011) Self Nanoscaling of the Soft Magnetic Phase in Bulk Nanocomposites, J. Mater. Sci. Vol. 46(18), 6065-6074.
J. H. Perepezko, S. Imhoff, R.J. Hebert: “Nanostructure development during devitrification and deformation”, J. Alloys and Compounds, v. 495 (2010), p. 360-64.