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G.S. Rohrer: Research Interests





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Complexion Transitions at Grain Boundaries and Interfaces

It has been know for many years that grain boundary composition affects grain boundary energy and mobility. Nevertheless, it had generally been assumed that the properties of grain boundaries changed continuously with temperature and composition. Over the last several years, a body of evidence has been published demonstrating that grain boundaries can undergo discontinuous changes in structure and composition and that these transitions can be associated with transitions in mobility and energy. These grain boundary states are referred to as complexions (Dillon et al., 2007). The initial studies (Dillon and Harmer, 2007a, Dillon and Harmer, 2007b) focused on alumina with controlled impurity concentrations. High-resolution microscopy was used to demonstrate that boundaries could be clean, could have a single adsorbed monolayer of solute, an adsorbed bilayer of solute, multilayer adsorption, or thin intergranular wetting films of constant thickness. While some of these boundary structures had been observed previously, the discovery that different interface states could co-exist and that transformations could occur as a function of temperature was a breakthrough in understanding interface structure and microstructure development in alumina.

More recent work has demonstrated that such interface states can also occur in metals (Luo et al., 2011), semiconductors (Ma et al., 2012), and at metal-ceramic interfaces (Baram et al., 2011), indicating that the phenomenon is wide-spread. It has also been shown that transitions from one complexion to another can be accompanied by a reduction in energy (Dillon et al., 2010), suggesting that bulk phase diagrams can be modified to include equilibrium interface phases, or complexions (Baram et al., 2011). It is also possible to imagine that time-temperature-transformation diagrams could be developed for complexions. However, at the present time, relatively little is understood about complexions and it is not possible to make any predictions about their occurrence. For example, in what cases will segregating solute be partitioned into an interface complexion instead of a second solid phase? How do transitions in the interface structure and composition nucleate? Under what conditions can nucleation be suppressed? If these and other questions were answered, it would be possible to modify bulk phase diagrams to indicate transitions in boundary structure and composition that are some times associated with transitions in boundary properties. This would be a valuable tool in controlling microstructural development and materials properties (Harmer, 2011). Our group is actively seeking the answers to these questions.


The co-existence of multiple complexions in Nd-doped alumina can lead to a bi-modal grain size distribution if the mobilities of the complexions differ significantly. The boundaries in the SEM micrograph (a) are colored to differentiate high mobility boundaries (green) from low mobility boundaries (red). Thermal groove measurements of the grain boundary energies, colored in the same way (b), indicate that he high mobility complexion has a lower energy. The two complexions also have different grain boundary orientation distributions (c, d). HRTEM shows that the low mobility boundary has a monolayer of segregated Nd and the high mobility grain boundary has a bilayer of segregated Nd (e, f).

References
Baram, M., Chatain, D. & Kaplan, W. D. 2011. Nanometer-thick equilibrium films: The interface between thermodynamics and atomistics. Science, 332, 206-209.
Dillon, S. J. & Harmer, M. P. 2007a. Direct observation of multilayer adsorption on alumina grain boundaries. Journal of the American Ceramic Society, 90, 996-998.
Dillon, S. J. & Harmer, M. P. 2007b. Multiple grain boundary transitions in ceramics: A case study of alumina. Acta Materialia, 55, 5247-5254.
Dillon, S. J., Harmer, M. P. & Rohrer, G. S. 2010. The relative energies of normally and abnormally growing grain boundaries in alumina displaying different complexions. Journal of the American Ceramic Society, 93, 1796-1802.
Dillon, S. J., Tang, M., Carter, W. C. & Harmer, M. P. 2007. Complexion: A new concept for kinetic engineering in materials science. Acta Materialia, 55, 6208-6218.
Harmer, M. P. 2011. The phase behavior of interfaces. Science, 332, 182-183.
Luo, J., Cheng, H. K., Asl, K. M., Kiely, C. J. & Harmer, M. P. 2011. The role of a bilayer interfacial phase on liquid metal embrittlement. Science, 333, 1730-1733.
Ma, S., Meshinchi Asl, K., Tansarawiput, C., Cantwell, P. R., Qi, M., Harmer, M. P. & Luo, J. 2012. A grain boundary phase transition in Si-Au. Scripta Materialia, 66, 203-206.

Recent publications on this topic from our group

• S.A. Bojarski, M.P. Harmer, and G.S. Rohrer, "Influence of Grain Boundary Energy on the Nucleation of Complexion Transitions," Scripta Materialia, (2014), accepted for publication.
PDF file available

• S.A. Bojarski, M. Stuer, Z. Zhao, P. Bowen, G.S. Rohrer, "Influence of Y and La Additions on Grain Growth and the Grain Boundary Character Distribution of Alumina," Journal of the American Ceramic Society, 97 (2014) 622-630.
DOI: 10.1111/jace.12669
PDF file available

• P.R. Cantwell, M. Tang, S.J. Dillon, J. Luo, G.S. Rohrer, M.P. Harmer, "Grain Boundary Complexions," Acta Materialia, 62 (2014) 1-48.
DOI: 10.1016/j.actamat.2013.07.037
PDF file available

• S.A. Bojarski, S. Ma, W. Lenthe, M.P. Harmer, and G.S. Rohrer, "Changes in the grain boundary character and energy distributions resulting from a complexion transition in Ca-doped Yttria," Metallurgical and Materials Transactions A 43A (2012) 3532-3538.
PDF file available

• S.J. Dillon, M.P. Harmer, and G.S. Rohrer, "Influence of interface energies on solute partitioning mechanisms in doped aluminas," Acta Materialia, 58 (2010) 5097-5108.
PDF file available

• S. J. Dillon, M. P. Harmer, and G. S. Rohrer, "The Relative Energies of Normal and Abnormal Grain Boundaries Displaying Different Complexions," Journal of the American Ceramic Society, 93 (2010) 1796-1802.
PDF file available

• S. J. Dillon, H. Miller, M. P. Harmer, and G. S. Rohrer, "Grain Boundary Plane Distributions in Aluminas Evolving by Normal and Abnormal Grain Growth and Displaying Different Complexions," International Journal of Materials Research, 101 (2010) 50-56.
PDF file available


Photochemical Properties of Ceramic Surfaces

Particulate semiconductors can be used as relatively inexpensive catalysts to photochemically split water and produced hydrogen (Osterloh, 2008). This reaction has been the subject of extensive research for two primary reasons. The first is that hydrogen is a high energy density fuel whose combustion does not produce greenhouse gases. The second is that if sunlight can be used as the source of photons, then the production and combustion of hydrogen would provide a sustainable energy cycle. However, the efficiency of the reaction is too low for the practical synthesis of hydrogen by this route. The main factors that reduce efficiency are related to the small size of the catalyst particles, which are typically less than 100 nm in diameter. The confinement of both the photoexcited electrons and holes and the oxidation/reduction reactions to such a small volume leads to enhanced recombination of photogenerated electron-hole pairs within the particle and the back reaction of intermediate species on the surface of the particle (Kudo and Miseki, 2009). While one might think a simple solution is to use larger particles, the surface area reduction associated with larger particles leads to reduced reaction rates that quickly offsets any gains that arise from reduced recombination. Considering this situation, it was hypothesized that if particles could be electrically polarized, then the oppositely charged photogenerated charge carriers would be transported in opposite directions. Because of this charge carrier separation, recombination would be less likely. Furthermore, if the oxidation and reduction half reactions occur at different spatial locations, then the rate of the back reaction would be reduced.

Our research has focussed on testing this hypothesis, which is illustrated schematically in the figure below. The research relies on the use of ferroelectric materials to provide a source of polarization (b). However, the ferroelectrics of interest are not stable when illuminated in aqueous solutions. Therefore, to create a practical catalyst, the ferroelectric must be used in a composite structure with a protective titania layer (c). Using TiO2 films supported by BaTiO3, it has been demonstrated that oxidation and reduction reactions can be spatially separated (Burbure et al., 2010) and that for some hierarchically structured catalysts, the rate of the water photolysis reaction can be increased.(Li et al., 2012)
Schematic illustration catalyst particles to illustrate the main hypothesis of the research. (a) A conventional titania photocatalyst particle with a diameter of less than 100 nm. Pt is added to promote hydrogen formation, but spatial confinement promotes recombination. (b) It is hypothesized that if the particle were a polarized ferroelectric, the reduction and oxidation reactions would be promoted at opposite poles of the crystal. (c) A thin titania coating protects the ferroelectric from degradation by photo-corrosion.



More recent research has concentrated on TiO2 films supported by BiFeO3, a visible light absorbing ferroelectric (see Figure below). It has been found that the visible light photochemical reactivity of TiO2 can be enhanced by the BiFeO3 support. This is attributed to electron-hole separation in the space charge region of the supporting ferroelectric that reduces recombination and makes more charge carriers available to participate in the reaction.

(a) Out-of-plane PFM phase image a BiFeO3 grain surface with a (001) orientation. Dark contrast in the image corresponds to regions with a positive polarization and bright regions correspond to areas with a negative polarization. (b) Topographic AFM image of the same area of the sample after the photochemical reduction of Ag. The light contrast corresponds to the areas that reduced silver.

References
N. V. Burbure, P. A. Salvador, and G. S. Rohrer, "Photochemical reactivity of titania films on BaTiO3 substrates: Origin of spatial selectivity," Chemistry of Materials, 22[21] 5823-30 (2010).
A. Kudo and Y. Miseki, "Heterogeneous photocatalyst materials for water splitting," Chemical Society Reviews, 38[1] 253-78 (2009).
L. Li, G. S. Rohrer, andP. A. Salvador, "Heterostructured ceramic powders for photocatalytic hydrogen production: Nanostructured TiO2 shells surrounding microcrystalline (Ba,Sr)TiO3 cores," Journal of the American Ceramic Society, 95[4] 1414-20 (2012).
F. E. Osterloh, "Inorganic materials as catalysts for photochemical splitting of water," Chemistry of Materials, 20[1] 35-54 (2008).


Recent publications on this topic from our group

• R. Munprom, P.A. Salvador, and G.S. Rohrer, "Polar Domains at the Surface of Centrosymmetric BiVO4," Chemistry of Materials, 26 (2014) 2774-2776.
DOI: 10.1021/cm501087j
PDF file available

• L. Li, P.A. Salvador and G.S. Rohrer, "Photocatalysts with Internal Electric Fields," Nanoscale, 6 (2014) 24-42.
DOI: 10.1039/C3NR03998F
PDF file available

• L. Li, X. Liu, Y. Zhang, N.T. Nuhfer, K. Barmak, P.A. Salvador, G.S. Rohrer, "Visible-Light Photochemical Activity of Heterostructured Core-Shell Materials Composed of Selected Ternary Titanates and Ferrites Coated by TiO2," ACS Applied Materials and Interfaces, 5 (2013) 5064-5071.
DOI: 10.1021/am4008837
PDF file available

• L. Li, X. Liu, Y. Zhang, P.A. Salvador and G.S. Rohrer, "Heterostructured (Ba,Sr)TiO3/TiO2 Core/Shell Photocatalysts: Influence of Processing and Structure on Hydrogen Production," International Journal of Hydrogen Energy, 38 (2013) 6948-6959.
DOI: 10.1016/j.ijhydene.2013.03.130
PDF file available


• L. Li, Y. Zhang, A.M. Schultz, X. Liu, P.A. Salvador and G.S. Rohrer, "Visible Light Photochemical Activity of Heterostructured PbTiO3/TiO2 Core-Shell Particles," Catalysis Science & Technology 2 (2012) 1945-1952.
PDF file available

• L. Li, G.S. Rohrer, P.A. Salvador, "Heterostructured Ceramic Powders for Photocatalytic Hydrogen Production: Nanostructured TiO2 Shells surrounding Microcrystalline (Ba,Sr)TiO3 Cores," Journal of the American Ceramic Society, 95 (2012) 1414-1420.
PDF file available

• A.M. Schultz, P.A. Salvador, G.S. Rohrer, "Enhanced photochemical activity of alpha-Fe2O3 films supported on SrTiO3 substrates under visible light illumination" Chemical Communications, 48 (2012) 2012-2014.
PDF file available

• A.M. Schultz, Y. Zhang, P.A. Salvador and G.S. Rohrer, "Effect of crystal and domain orientation on the visible light photochemical reduction of Ag on BiFeO3," ACS Applied Materials and Interfaces, 3 (2011) 1562-1567.
PDF file available

• Y. Zhang, A.M. Schultz, P.A. Salvador and G.S. Rohrer, "Spatially Selective Visible-light Photocatalytic Activity of TiO2/BiFeO3 Heterostructures," Journal of Materials Chemistry, 21 (2011) 4168-4174.
PDF file available

• A. Bhardwaj, N.V. Burbure, G.S. Rohrer, "Enhanced Photochemical Reactivity at the Ferroelectric Phase Transition in Ba1-xSrxTiO3," Journal of the American Ceramic Society, 93 (2010) 4129-4134.
PDF file available

• N.V. Burbure, P.A. Salvador, G.S. Rohrer, "Photochemical Reactivity of Titania Films on BaTiO3 Substrates: Influence of Titania Phase and Orientation," Chemistry of Materials, 22 (2010) 5831-5837.
PDF file available

• N.V. Burbure, P.A. Salvador, G.S. Rohrer, "Photochemical Reactivity of Titania Films on BaTiO3 Substrates: Origin of Spatial Selectivity substrates," Chemistry of Materials, 22 (2010) 5823-5830.
PDF file available

• A. Bhardwaj, N.V. Burbure, A. Gamalski, G.S. Rohrer, "Composition Dependence of the Photochemical reduction of Ag by Ba1-xSrxTiO3," Chemistry of Materials, 22 (2010) 3527-3534
PDF file available



Combinatorial Substrate Epitaxy

Little is currently known about the crystallization preferences of films on high index surfaces. Epitaxy in thin films is usually ascribed to preferred lattice matching at low index two-dimensional interfaces; the extension of such theories to high index surfaces is difficult. To better understand the nature of crystallization of films on general surfaces, it is necessary to observe growth over the entire range of possible surface orientations. The conventional approach of growing films on large area, low index, single crystal substrates is not practical for a comprehensive study of growth on high index surfaces.

In this research, we have developed a new high-throughput technique we refer to as "combinatorial substrate epitaxy" (CSE) to determine phase and orientation relationships between a substrate and deposited film for all possible orientations. In the CSE approach, films are deposited on hundreds of substrates with different, known orientations in a single experiment and then characterized by electron backscatter diffraction (EBSD). An example is illustrated in the Figure below. Our initial studies of oxide heterostructures indicate that epitaxy in these systems are driven by the alignment of close packed planes and directions in three dimensions.


(a) An orientation map of the BiFeO3 substrate. The colors show the orientations of the grains with respect to the surface normal, according to the key in the inset. (b) An orientation map of the TiO2 film, in the same area as (a). The surface normal orientations of anatase and rutile are shown by the color key in the inset. The grains in (a) and (b) marked with the same symbols (A, B, C, and D) are substrate/film pairs. (c) A phase map of the TiO2 film grown on BiFeO3 substrate, in the same are as (b). Red indicates anatase and green indicates rutile. In all of the maps, black indicates areas with a confidence index less than 0.1.


Recent publications on this topic from our group

• A.M. Schultz, Y. Zhu, S.A. Bojarski, G.S. Rohrer, P.A. Salvador, "Eutaxial growth of hematite Fe2O3 films on perovskite SrTiO3 polycrystalline substrates," Thin Solid Films, 548 (2013) 220-224.
DOI: 10.1016/j.tsf.2013.09.073
PDF file available

• S. Havelia, S. Wang, K.R. Balasubramaniam, A.M. Schultz, G.S. Rohrer, P.A. Salvador, "Combinatorial substrate epitaxy: a new approach to growth of complex metastable compounds," CrystEngComm 15 (2013) 5434-5441.
DOI: 10.1039/C3CE40469B
PDF file available

• Y. Zhang, A.M. Schultz, L. Li, H. Chien, P.A. Salvador, and G.S. Rohrer, "Combinatorial Substrate Epitaxy: A high throughput method for determining phase and orientation relationships and its application to BiFeO3/TiO2 heterostructures," Acta Materialia 60 (2012) 6486-6493
PDF file available

• N.V. Burbure, P.A. Salvador, G.S. Rohrer, "Orientation and phase relationships between titania films and polycrystalline BaTiO3 substrates as determined by electron backscatter diffraction mapping," Journal of the American Ceramic Society, 93 (2010) 2530-2533.
PDF file available



Three Dimensional Materials Science

In the past decade, there has been a rapid expansion in capabilities for three-dimensional microstructure studies that have made it possible to study ceramic structures across a wide range of length scales. For example, the recent development of laser assisted, three-dimensional atom probe microscopy (3DAP) has made it possible to make three-dimensional, near-atomic resolution images of reasonable volumes of a wide range of materials, including alumina (Marquis, 2010). In fact, the capabilities for three-dimensional imaging by TEM (Batenburg, 2009), Dual Beam, Focused Ion Beam SEM (Dillon, 2009), X-ray tomography (Morales-Rodriguez, 2009), and diffraction contrast X-ray microscopy (Syha, 2012) have all made significant strides in capabilities (Robertson, 2011).

Our group is focused on coupling Dual Beam, Focused Ion Beam SEM with electron backscatter diffraction (EBSD) mapping to make three dimensional orientation maps. Our goal is the measure the crystallographic distribution of the types of interfaces and grain boundaries that occur in polycrystalline materials. These data are extracted from three dimensional maps, such as the ones shown below.


(a) A three-dimensional orientation map of yttria (Y2O3) based on 43 parallel EBSD maps. (b) A three-dimensional orientation map of 8% yttria (Y2O3) stabilized zirconia (ZrO2).

References
Batenburg, K. J., Bals, S., Sijbers, J., Kubel, C., Midgley, P. A., Hernandez, J. C., Kaiser, U., Encina, E. R., Coronado, E. A. & Van Tendeloo, G. 2009. 3D imaging of nanomaterials by discrete tomography. Ultramicroscopy, 109, 730-740
Dillon, S. J. & Rohrer, G. S. 2009. Characterization of the grain-boundary character and energy distributions of yttria using automated serial sectioning and EBSD in the FIB. Journal of the American Ceramic Society, 92, 1580-1585.
Marquis, E. A., Yahya, N. A., Larson, D. J., Miller, M. K. & Todd, R. I. 2010. Probing the improbable: Imaging C atoms in alumina. Materials Today, 13, 34-36.
Morales-Rodriguez, A., Reynaud, P., Fantozzi, G., Adrien, J. & Maire, E. 2009. Porosity analysis of long-fiber-reinforced ceramic matrix composites using x-ray tomography. Scripta Materialia, 60, 388-390.
Robertson, I. M, et al., 2011. Towards an integrated materials characterization toolbox. Journal of Materials Research, 26, 1341-1383.
Syha, M., Rheinheimer, W., Baurer, M., Lauridsen, E. M., Ludwig, W., Weygand, D. & Gumbsch, P. 2012. Three-dimensional grain structure of sintered bulk strontium titanate from x-ray diffraction contrast tomography. Scripta Materialia, 66, 1-4.


Recent publications on this topic from our group

• H. Beladi, N.T. Nuhfer, and G.S. Rohrer, "The Five Parameter Grain Boundary Character and Energy Distributions of a Fully Austenitic High Manganese Steel Using Three Dimensional Data,"Acta Materialia, 70 (2014) 281-289.
DOI: 10.1016/j.actamat.2014.02.038
PDF file available

• S.-B. Lee, G.S. Rohrer and A.D. Rollett, "Three-dimensional digital approximations of grain boundary networks in polycrystals," Modelling Simul. Mater. Sci. Eng., 22 (2014) 025017 (21 pp).
DOI: 10.1088/0965-0393/22/2/025017
PDF file available

• P.G. Kotula, G.S. Rohrer and M.P. Marsh, "Focused ion beam and scanning electron microscopy for 3D materials characterization," MRS Bulletin, 39 (2014) 361-365.
DOI: 10.1557/mrs.2014.55
PDF file available

• H. Beladi and G.S. Rohrer, "The Relative Grain Boundary Area and Energy Distributions in a Ferritic Steel Determined from Three Dimensional Electron Backscatter Diffraction Maps," Acta Materialia 61 (2013) 1404-1412.
DOI: 10.1016/j.actamat.2012.11.017
PDF file available

• S.-B. Lee, T.S. Key, Z. Liang, R.E. Garcia, S. Wang, X. Tricoche, G.S. Rohrer, Y. Saito, C. Ito, T. Tani, "Microstructure design of lead-free piezoelectric ceramics," Journal of the European Ceramic Society 33 (2013) 313-326.
DOI: 10.1016/j.jeurceramsoc.2012.08.015
PDF file available

• S.J. Dillon, L. Helmick, H.M. Miller, L. Wilson, R. Gemman, R.V. Petrova, K. Barmak, G.S. Rohrer, P.A. Salvador, "The Orientation Distributions of Lines, Surfaces, and Interfaces around Three-Phase Boundaries in Solid Oxide Fuel Cell Cathodes," Journal of the American Ceramic Society, 94 (2011) 4045-4051.
PDF file available

• L. Helmick, S. Dillon, K. Gerdes, R. Gemmen, G.S. Rohrer, S. Seetharaman, P.A. Salvador, "Crystallographic characteristics of grain boundaries in dense yttria-stabilized zirconia," International Journal of Applied Ceramic Technology, 8 (2011) 1218-1228.
PDF file available

• G.S. Rohrer, "Measuring and Interpreting the Structure of Grain Boundary Networks," Journal of the American Ceramic Society, 94 (2011) 633-646.
PDF file available

• A. Khorashadizadeh, D. Raabe, S. Zaefferer, G.S. Rohrer, A.D. Rollett, M. Winning, "Five-parameter grain boundary analysis by 3D EBSD of an ultra fine grained CuZr alloy processed by equal channel angular pressing," Advanced Engineering Materials, 13 (2011) 237-244.
PDF file available

• G.S. Rohrer, J. Li, S. Lee, A.D. Rollett, M. Groeber, M.D. Uchic, "Deriving the grain boundary character distribution and relative grain boundary energies from three dimensional EBSD data," Materials Science and Technology, 26 (2010) 661-669.
PDF file available

• J. Li, S.J. Dillon and G.S. Rohrer, "Relative Grain Boundary Area and Energy Distributions in Nickel," Acta Materialia, 57 (2009) 4304-4311.
PDF file available

• S.J. Dillon and G.S. Rohrer, "Characterization of the Grain Boundary Character and Energy Distributions of Yttria using Automated Serial Sectioning and EBSD in the FIB," Journal of the American Ceramic Society, 92 (2009) 1580-1585.
PDF file available

• S.J. Dillon and G.S. Rohrer, "Three-Dimensional FIB-OIM of Ceramic Materials," in Applications of Texture Analysis, A.D. Rollett, Editor, (Ceram. Trans., 201, J. Wiley & Sons, Hoboken, NJ, 2009) 117-124.
PDF file available



Interface Energy Anisotropy and Its Effect on Microstructure

The anisotropy of the grain boundary energy has been recognized since at least the time of Smith (Smith, 1948). The energy anisotropy arises because different grain boundaries have different microscopic structures. In this research, macroscopically observable crystallographic parameters are used to classify boundaries with different microscopic structures. To classify the boundaries, five independent parameters must be specified. Three describe the misorientation of the crystal lattice and two describe the orientation of the grain boundary plane. The implication of having five independent parameters is that the number of different grain boundary types is large. (Rohrer et al., 2004) If the five dimensional domain of grain boundary types is discretized in 10 degree intervals, then there are roughly 6000 different grain boundaries for a material with cubic symmetry. The number of distinct boundaries increases rapidly for finer discretizations and for crystals with reduced symmetry.

It is possible to evaluate the full anisotropy of the grain boundary energy using the Herring (Herring, 1951) equation and the method of Moraweic. (Moraweic, 2000) To do this, one needs to examine triple junctions involving all different types of grain boundaries. Because the necessary number of junctions is in the range of 10,000 to 100,000, it was not feasible to conduct such measurements using manual techniques. However, the development of automated electron backscatter diffraction orientation mapping in the scanning electron microscope has made it possible to characterize the crystallography of 10,000 to 100,000 triple junctions in a reasonable amount of time. When coupled with serial sectioning, it is possible to determine the complete geometry for triple lines involving all boundary types and determine the anisotropy of the energy. Our research is aim at measuring grain boundary energies and understanding their role in microstructure evolution.


The relative areas of grain boundary planes and relative grain boundary energies for four materials, as a function of grain boundary plane orientation, without consideration of misorientation. In all four materials, there is an approximate inverse relation between the GBPD and the GBED. (a) Y2O3, (b) Ni, (c) YSZ, and (d) SrTiO3.

References
C Herring (1951) in Kingston WE (ed) The Physics of Powder Metallurgy, McGraw-Hill, New York.
A Morawiec (2000) Acta Mater. 48: 3525.
GS Rohrer et al, (2004) Z. Metallk. 95: 197.
CS Smith (1948) Trans. AIMME 175: 15.


Recent publications on this topic from our group

Recent publications on this topic from our group

• S. Ratanaphan, Y. Yoon, and G.S. Rohrer, "The Five Parameter Grain Boundary Character Distribution of Polycrystalline Silicon,"Journal of Materials Science 49 (2014) 4938-4945.
DOI: 10.1007/s10853-014-8195-2
PDF file available

• H. Beladi, G.S. Rohrer, A.D. Rollett, V. Tari and P.D. Hodgson, "The Distribution of Intervariant Crystallographic Planes in a Lath Martensite Using Five Macroscopic Parameters," Acta Materialia, 63 (2014) 86-98.
DOI: 10.1016/j.actamat.2013.10.010
PDF file available

• X. Liu, D. Choi, H. Beladi, N.T. Nuhfer, G.S. Rohrer, and K. Barmak, "The five parameter grain boundary character distribution of nanocrystalline tungsten," Scripta Materialia 69 (2013) 413-416.
DOI: 10.1016/j.scriptamat.2013.05.046
PDF file available

• H. Beladi and G.S. Rohrer, "The Distribution of Grain Boundary Planes in IF Steel," Metallurgical and Materials Transactions A 44A (2013) 115-124.
DOI: 10.1007/s11661-012-1393-0
PDF file available

• A.D. Darbal, K.J. Ganesh, X. Liu, S.-B. Lee, J. Ledonne, T. Sun, B. Yao, A.P. Warren, G.S. Rohrer, A.D. Rollett, P.J. Ferreira, K.R. Coffey, and K. Barmak, "Grain Boundary Character Distribution of Nanocrystalline Cu Thin Films Using Stereological Analysis of Transmission Electron Microscope Orientation Maps," Microsc. Microanal. 19 (2013) 111-119.
DOI: 10.1017/S1431927612014055
PDF file available

• K.J. Ganesh, A.D. Darbal, S. Rajasekhara, G.S. Rohrer, K. Barmak and P.J. Ferreira, "Effect of downscaling nano-copper interconnects on the microstructure revealed by high resolution TEM-orientation-mapping," Nanotechnology, 23 (2012) 135702 (7pp)
DOI: 10.1088/0957-4484/23/13/135702
PDF file available

• H.J. Ryu, D.B. Fortner, G.S. Rohrer, and M.R. Bockstaller, "Measuring Relative Grain-Boundary Energies in Block-Copolymer Microstructures," Physical Review Letters, 108 (2012) 107801.
DOI: 10.1103/PhysRevLett.108.107801
PDF file available

• G.S. Rohrer, "Grain Boundary Energy Anisotropy: A Review," Journal of the Materials Science, 46 (2011) 5881-5895.
PDF file available

• E.A. Holm, G.S. Rohrer, S,M. Foiles, A.D. Rollett, H.M. Miller, D.L. Olmsted, "Validating computed grain boundary energies in FCC metals using the grain boundary character distribution," Acta Materialia, 59 (2011) 5250-5256.
PDF file available

• G.S. Rohrer, E.A. Holm, A.D. Rollett, S.M. Foiles, J. Li, D.L. Olmsted, "Comparing calculated and measured grain boundary energies in nickel," Acta Materialia, 58 (2010) 5063-5069.
PDF file available

• J. Gruber, G.S. Rohrer, A.D. Rollett, "Misorientation texture development during grain growth. Part II: Theory," Acta Materialia, 58 (2010) 14-19.
PDF file available

• J. Gruber, H.M. Miller, T.D. Hoffmann, G.S. Rohrer, A.D. Rollett, "Misorientation texture development during grain growth. Part I: Simulation and experiment," Acta Materialia, 57 (2009) 6102-6112.
PDF file available

• J. Li, S.J. Dillon and G.S. Rohrer, "Relative Grain Boundary Area and Energy Distributions in Nickel," Acta Materialia, 57 (2009) 4304-4311.
PDF file available

• S.J. Dillon and G.S. Rohrer, "Characterization of the Grain Boundary Character and Energy Distributions of Yttria using Automated Serial Sectioning and EBSD in the FIB," Journal of the American Ceramic Society, 92 (2009) 1580-1585.
PDF file available

• S.J. Dillon and G.S. Rohrer, "Mechanism for the Development of Anisotropic Grain Boundary Character Distributions during Normal Grain Growth," Acta Materialia, 57 (2009) 1-7.
PDF file available

• D.M. Saylor, A. Morawiec, and G.S. Rohrer, "The Relative Free Energies of Grain boundaries in Magnesia as a Function of Five Macroscopic Parameters," Acta Mater., 51 (2003) 3675-86.
PDF file available



Structure-Property relationships for Hard Materials

Cemented carbides (or sintered carbides) are common hard materials which have outstanding mechanical properties that make them commercially useful in machining, mining, metal cutting, metal forming, construction, wear parts, and other applications. Like many other engineering materials, the mechanical properties of cemented carbides are influenced by their microstructures.

The purpose of this work is to understand how the microstructural characteristics of WC-Co composites and CVD coatings on these materials (usually consisting of alpha-Al2O3 and TiCxN1-x, as in the examples shown in the Figure) affect their responses to mechanical and/or thermal loads. Among the microstructural parameters that are considered are texture, contiguity, angularity, aspect ratio, and grain size distribution. The work is divided in two parts: the quantitative and comprehensive assessment of microstructural characteristics, and the simulation of the microstructure's response to loads. Simulations of real and hypothetical microstructures allow the independent variation of particular microstructural characteristics (the contiguity, angularity, aspect ratio, or grain size distribution) while keeping the others as constant as possible, so that each parameter's influence on the strength could be independently determined. More detailed information can be found in the publications below.


Inverse pole figure maps for the alpha-Al2O3 (upper) and TiCxN1-x (middle) and WC/Co substrate (bottom). Different colors indicate different grain orientations.


• X. Yuan, G.S. Rohrer, X. Song, H. Chien, J. Li, "Modeling the Interface Area Aspect Ratio of Carbide Grains in WC-Co Composites," International Journal of Refractory Metals and Hard Materials, 44 (2014) 7-11.
DOI: 10.1016/j.ijrmhm.2014.01.004
PDF file available

• X. Yuan, X. Song, H. Chien, J. Li, G.S. Rohrer, "Effect of Densification Mechanism on the Sigma-2 Grain Boundary Plane Distribution in WC-Co Composites," Materials Letters 92 (2013) 86-89.
DOI: 10.1016/j.matlet.2012.10.074
PDF file available

• H. Chien, C. Diaz-Jimenez G.S. Rohrer, Z. Ban, P. Prichard, and Y. Liu, "The influence of residual thermal stresses on the mechanical properties of multilayer alpha-Al2O3/TiCxN1-x coatings on WC/Co cutting tools," Surface and Coating Technology 215 (2013) 119-126.
DOI: 10.1016/j.surfcoat.2012.07.088
PDF file available

• H. Chien, M.C. Gao, H.M. Miller, G.S. Rohrer, Z. Ban, P. Prichard, Y. Liu, "Microtexture and Hardness of CVD Deposited alpha-Al2O3 and TiCxN1-x Coatings," International Journal of Refractory Metals and Hard Materials, 27 (2009) 458-464.
PDF file available

• H. Chien, Z. Ban, P. Prichard, Y. Liu, G.S. Rohrer, "Influence of Microstructure on Residual Thermal Stresses in TiCxN1-x and alpha-Al2O3 Coatings on WC-Co Tool Inserts," Proceedings of the 17th Plansee Seminar 2009 (Editors: L.S. Sigl, P. Rodhammer, H. Wildner, Plansee Group, Austria) Vol. 2, HM 42/1-11.
PDF file available

• C.-S. Kim, T.R. Massa, G.S. Rohrer, "Interface character distributions in WC-Co composites," J. Am. Ceram. Soc., 91 (2007) 996-1001.
PDF file available

• C.-S. Kim, T.R. Massa, G.S. Rohrer, "Modeling the Influence of Orientation Texture on the Strength of WC-Co Composites," J. Am. Ceram. Soc. 90 (2007) 199-204.
PDF file available

• C.-S. Kim, T.R. Massa, G.S. Rohrer, "Modeling the Relationship between Microstructural Features and the Strength of WC-Co Composites," International Journal of Refractory Metals and Hard Materials, 24 (2006) 89-100.
PDF file available

• C.-S. Kim and G.S. Rohrer, "Geometric and Crystallographic Characterization of WC Surfaces and Grain Boundaries in WC-Co Composites," Interface Science, 12 (2004) 19-27.
PDF file available





Current projects



Madeleine Kelly: The temperature dependence of grain boundary complexion transitions and their effect on the grain boundary character and energy distributions

Xiaoting Zhong: Measuring Grain Boundary Properties with 3D Microstructure Data

Ajay Pisat: Controlling Charges on Oxide Surfaces for Enhanced Photochemical Reactivity


Past Doctoral Dissertations

Yisi Zhu, Effect of the Surface and Interface Electric Potential on the Photochemical Reactivity of Transition Metal Oxides

James Glickstein, Computational Investigations of Photocatalytic Surfaces exhibiting Spatially Selective Reactivity

William Frazier, A Potts Model Investigation of Complexion Transitions and Abnormal Grain Growth

Hang-Ah Park, TiO2-Carbon Nanotube Hybrids for High Efficiency Photocatalysts

Brian Lin, Investigating annealing twin formation mechanisms in face-centered cubic nickel

Ratiporn Munprom, Effects of crystal orientation and ferroelastic domain structure on the photochemical reactivity of BiVO4 and related compounds

Stephanie Bojarski, The Effects of Grain Boundary Character and Energy on Complexion Transitions in Ceramics

Sutatch Ratanaphan, Grain Boundary Character Distributions in Isostructural Materials

Yiling Zhang, Visible-light photochemical activity of TiO2/BiFeO3 heterostructures

Andy Shultz, The growth and photochemical activity of hematite films on perovskite substrates

Li Li, Photocatalytic Activity of Heterostructured Powders: Nanostructured TiO2 Shells surrounding Microcrystalline Cores

Debashis Kar, Correlating grain boundary properties to distributions during anisotropic grain growth - an interface field study in two and three dimensions

Harry Chien, The effects of microstructure and thermal stresses on the hardness of CVD Deposited alpha-Al2O3 and TiCxN(1-x) Coatings

Lisa Chan, Synthetic Three-Dimensional Voxel-Based Microstructures that Contain Annealing Twins

Nina Burbure, Influence of Ferroelectric Substrates on the Photochemical Reactivity of TiO2 Thin Films

Abhilasha Bhardwaj, The Composition Dependence of the Photochemical Reactivity of Barium Strontium Titanates

Herb Miller, Influences of Processing and Composition on the Grain Boundary Character Distribution

Jason Gruber, Interface Texture Development During Grain Growth

Tomoko Sano, Interface Anisotropy and its Effect on Microstructural Evolution During Coarsening

Chang-Soo Kim, Microstructural-Mechanical Property Relationships in WC-Co composites

Jennifer Giocondi, Effect of Dipolar Fields, Surface Termination, and Surface Orientation on Photochemical Reactions on Transition Metal Oxides

David Saylor, The Character Dependence of Interfacial Energies in Magnesia

Jennifer Lowekamp, The Anisotropy of the Surface Energy and Photochemical Activity of Rutile

Richard Smith, The Structural Evolution of the MoO3(010) Surface during Reduction and Oxidation Reactions.

Weier Lu, STM Image Contrast Interpretation and its Role in Determining the Structure of Transition Metal Surfaces.


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