General Motors/Brown Collaborative Research Laboratory on Computational Materials Research
The laboratory for computational materials research at Brown University is one of several collaborative research laboratories established worldwide by General Motors to accelerate the pace of innovation in strategic technology areas. The goal of the laboratory is to develop computer simulations that predict the mechanical properties of materials used in automotive applications, and to use these simulations to help General Motors to develop materials with enhanced performance. The computations are guided and verified by experiments. The laboratory changed its focus during the past year to two areas: (i) Development of aluminum and magnesium alloys with enhanced room temperature and elevated temperature formability; and (ii) Development of battery materials with enhanced life and charge capacity.
Work on forming is focused on developing multi-scale simulation methods to predict the influence of the composition and microstructure of Aluminum and Magnesium alloys on their formability. During the past year, Curtin has completed ab-initio computations of dislocation/solute strengthening in Al-Mg alloys; and has completed systematic MD computations of dislocation core structures and Peierls stresses in Magnesium. Bower and Curtin have implemented a kinetic model of dynamic strain ageing in continuum finite element code, and have used the full atomistically calibrated constitutive equations to predict the ductility of Al alloys as a function of temperature. This success now provides a way to design alloy chemistries with improved formability. Bower and GM colleagues have shown that multi-scale simulations can predict dome height and thinning during hot blow forming of Al sheet, and are currently extending this work to Mg.
A new thrust area, focusing on battery materials, was added to the CRL in Fall 2009. The team from Brown and GM are using a combination of in-situ experimental studies, aided by atomic and continuum scale computer simulations, to study mechanisms of deformation and failure in anode materials during cyclic charging. In work completed to date, Sheldon has developed a sealed cell that enables stress evolution in thin Si and C films during intercalation to be measured using MOSS. This capability will be used to measure crack growth rates and stress cycles in simple model systems. Kim has developed a novel interferometric method to measure deformation in full-scale battery packs, which provides a way to probe transport and degradation in batteries during cyclic charging. In a parallel modeling effort, Bower has developed a preliminary finite element model of coupled deformation, viscous flow and diffusion during intercalation of anode materials. Preliminary results show good agreement between stress and voltage cycles predicted by this model and those measured by Guduru in the MRSEC seed project. Shenoy had completed preliminary computations of charge distributions, band structure and elastic constants for crystalline and amorphous Si intercalated by Li, as a function of Li concentration. Future studies will combine modeling and in-situ experiments to study the influence of microstructure on degradation in battery materials.
KIST: Korea Institute of Science and Technology; SNU: Seoul National University
Kim is the main collaborator with KIST and this collaboration is composed of two parts. One is for high performance computing on mechanics of nano and micro structures. The other is for advanced multiscale experiments on mechanics of nano and micro structures. KIST provides supercomputing capabilities with 1024 CPU for ab initio DFT and MD simulations. It provides additional 3096 CPU for vastly parallel computing as needed. KIST also furnishes fabrication facilities for surface nano and micro structures. Brown provides analytical multi-scale modeling as well as advanced characterization experiments. SNU collaborates in primarily DFT simulations and advance quantum mechanical simulations for computational design of nanostructures. For this collaboration, investigations on dynamic compressive fracture processes of single wall nanotubes in ultrasonication have been carried out with vastly parallel MD simulations. Also nano tribology of reptile skin friction has been investigated experimentally as well as analytical modeling. Currently ab initio calculations on nanostructural behavior of CIGS solar cell surface nanostructures and associated experiments are under way. For this collaboration, KIST is providing approximately $2M ($1M to Brown and $1M to SNU) for the next five years – half of through supercomputing budget and nanofabrication budget. In addition,
they send a post doc every year for this collaboration.
Sandia National Lab
Sheldon continues to work on intrinsic stress evolution includes an experimental collaboration with Dr. Sean Hearne at Sandia National Lab. This is largely based on a lithographic technique developed by Hearne; that makes it possible to electrodeposit islands with uniform size and spacing. This has allowed us to conduct in situ stress studies with systematic variations in the island size. A Brown graduate student, Sumit Soni, spent one month during the past year working on this project with Hearne at Sandia. He is currently working on a manuscript that is based on this work.
IBM / Brookhaven National Lab
Chason continued collaborations with IBM and BNL to study growth of semiconductor layers on the large area single crystal metal foils that they are producing in their lab. The technique for creating these foils was initiated in the MRSEC. Chason spent a week at BNL as a user at the Center for Functional Nanomaterials to study the growth of Si layers on Ni(100) foils. Characterization of the metal foils with the STM showed that they had large areas that were nearly flat and other regions with pyramidal mounds. The in situ STM in Peter Sutter’s lab was used to study the initial stages of growth; XPS was used to follow the phase formation as the Si reacted with the Ni to form silicides. Most of the week was devoted to learning how to clean the samples for good epitaxy. IBM also attempted to grow Si on Ni(100) foils produced by Chason’s group.
Jim Hannon and Ruud Tromp of IBM have been collaborating with Shenoy on modeling the growth of graphene on SiC and on transition metals. Shenoy has been carrying out density functional calculations to model the structure of graphene -substrate interface in these systems. Peter Sutter of Brookhaven National Lab has been working with Shenoy on photocatalysis on TiO2 surfaces. Shenoy has simulated STM images of water clusters to understand the transition states and reaction pathways for water splitting on TiO2.
Advanced Photon Source
Chason has collaborated with the Oak Ridge group at the APS synchrotron to study the growth of tin whiskers. We used their unique microdiffraction instrument to measure the orientation and strain in Sn grains with submicron resolution as the layer reacts with Cu in real time. We simultaneously measured the fluorescence from the Cu and Sn layers to monitor the intermetallic growth and the change in Sn layer morphology. The resulting maps are enabling us to correlate the whisker growth with the strain and the grain structure in the underlying layer.
Nanoelectronics Research Initiative
Beresford presented Brown’s NRI project overview at the NSF / NRI Annual Review in Gaithersburg, MD, Oct. 27, 2009. This event was attended by representatives of all NRI research centers, as well as agency personnel. The NRI Liaison Team visit to the Brown MRSEC was completed on Jan. 15, 2010. Led by Luigi Colombo of Texas Instruments, the team also included Zoran Krivokapic (GlobalFoundries), Albert Davydov (NIST), Jim Hannon (IBM, for C.Y. Sung), and attending remotely via the Web, Steven Kramer (Micron) and Ajey Jacob (Intel).
New and Emerging Industrial Partnerships
Medtronic Corp (Minneapolis, MN): A collaborative research program with Medtronic is in the final stages of creation. Three thrust areas have been identified for research: high strength steels, engineered surfaces for biofunctionality, and mechanics of battery materials, each aligning with an MRSEC IRG or SEED area. Faculty leads are expected to be Sheldon, Guduru, Kumar, and Webster, with Chason, Gao, Kim, Bower, Franck, and Curtin also participating. Funding for year one is imminent, and a long-term partnership is planned.
Arcelor-Mittal Steel (East Chicago, IN): A collaborative project on sheet steels is also in the final stages of formalization with Arcelor-Mittal. In year one, they will support Kumar’s research and plan to expand to include a parallel materials modeling with Bower and/or Curtin effort in the future.
Simulia (Providence, RI): Interactions with Simulia, owners of the ABAQUS FEM technology developed by former Brown Mechanics PhDs, are beginning in earnest. Areas of mutual interest have been identified, further technical visits are planned, a three-way collaboration with Boeing is being explored, and plans for graduate student summer interns at ABAQUS are being made. Faculty involved to date are: Curtin, Bower, Gao, and Shenoy.
Schlumberger (Cambridge, MA): Dr. John Ullo, a technology leader at Schlumberger, visited Brown in March, 2010 for a full day of discussion on Mechanics and Materials expertise at Brown emphasizing the MRSEC, and research concepts and needs at Schlumberger. Brown faculty will visit Schlumberger in April or May 2010 to engage more scientists.