Mechanical Engineering Commons^™

Influence Of Crystal Structure On The Electrochemical Performance Of A-Site-Deficient Sr1-SNb0.1Co0.9O3-Δ Perovskite Cathodes, Yinlong Zhu, Ye Lin, Xuan Shen, Jaka Sunarso, Wei Zhou, Shanshan Jiang, Dong Su, Fanglin Chen, Zongping Shao

Faculty Publications

The creation of A-site cation defects within a perovskite oxide can substantially alter the structure and properties of its stoichiometric analogue. In this work, we demonstrate that by vacating 2 and 5% of Asite cations from SrNb_0.1Co_0.9O_3-δ (SNC1.00) perovskites (Sr_1-sNb_0.1Co_0.9O_3-δ,s = 0.02 and 0.05; denoted as SNC0.98 and SNC0.95, respectively), a Jahn–Teller (JT) distortion with varying extents takes place, leading to the formation of a modified crystal lattice within a the perovskite framework. Electrical conductivity, electrochemical performance, chemical compatibility and microstructure of Sr_1-sNb_0.1Co …

Probabilistic Simulation Of Solidification Microstructure Evolution During Laser-Based Metal Deposition, Jingwei Zhang, Frank W. Liou, William Seufzer, Joseph William Newkirk, Zhiqiang Fan, Heng Liu, Todd E. Sparks

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A predictive model, based on a Cellular Automaton (CA) - Finite Element (FE) method, has been developed to simulate microstructure evolution during metal solidification for a laser based additive manufacturing process. The macroscopic FE calculation was designed to update the temperature field and simulate a high cooling rate. In the microscopic CA model, heterogeneous nucleation sites, preferential growth orientation and dendritic grain growth kinetics were simulated. The CA model was able to show the entrapment of neighboring cells and the relationship between undercooling and the grain growth rate. The model predicted the dendritic grain size, structure, and morphological evolution during …

The Effect Of Isostatic Pressing On The Dielectric Properties Of Screen Printed Ba0.5Sr0.5Tio3 Thick Films, Siwei Wang, Lingling Zhang, Jiwei Zhai, Fanglin Chen

Faculty Publications

Ba_0.5Sr_0.5TiO₃ thick films with B₂O₃–Li₂O glass sintering aid were prepared by the screen printing method on Al₂O₃ substrates. A 200 MPa isostatic pressure was applied to the films before sintering. After being sintered at 950^∘C, lower porosity and denser microstructure was obtained compared with the films without isostatic pressing. The dielectric constant and dielectric loss were 238 and 0.0028, respectively. A tunability of 61.7% was obtained for the isostatic pressed films, a 27.8% enhancement compared to unpressurized films. These results suggest that isostatic pressing …

Microstructure Selection Of Sm-Co-Al Alloys To Increase Magnetization, Brian Dick

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

An ever increasing demand for higher performing magnets drives the need for new and innovative methods to achieve this goal. Sm-Co rare earth permanent magnets have a unique eutectic microstructure that, through refinement, could become a two-phase magnet which would significantly increase their energy product. The eutectic structure of Sm₈Co₉₂ is comprised of αCo rods embedded within a Sm₂Co₁₇ matrix. If the rods are small enough to encourage exchange coupling and the matrix is smaller than the single domain limit, then an efficient two-phase magnet is created.

Refining the Co rods and matrix size …

A New Method Of Synthesizing Black Birnessite Nanoparticles: From Brown To Black Birnessite With Nanostructures, Shizhi Qian, Marcos A. Cheney, Pradip K. Bhowmik, Sang W. Joo, Wensheng Hou, Joseph M. Okoh

Mechanical Engineering Faculty Research

A new method for preparing black birnessite nanoparticles is introduced. The initial synthesis process resembles the classical McKenzie method of preparing brown birnessite except for slower cooling and closing the system from the ambient air. Subsequent process, including wet-aging at 7◦C for 48 hours, overnight freezing, and lyophilization, is shown to convert the brown birnessite into black birnessite with complex nanomorphology with folded sheets and spirals. Characterization of the product is performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N2 adsorption (BET) techniques. Wet-aging and lyophilization times are shown to …

Titanium Alloyed With Boron, Seshacharyulu Tamirisakandala, Daniel B. Miracle, Raghavan Srinivasan, Jay S. Gunasekera

Mechanical and Materials Engineering Faculty Publications

Small additions of boron to conventional titanium alloys have been found to produce significant changes to the microstructures and associated properties. Grain refinement and improved strength and stiffness are first-order effects, which lead to possibilities for developing novel and affordable processing methodologies and to enhance performance over conventional titanium alloys. In this article, we introduce this new class of titanium alloys and describe unique formability benefits achieved via engineering microstructures.

Evaluation Of Mechanical Properties And Microstructure For Laser Deposition Process And Welding Process, Yaxin Bao, Jianzhong Ruan, Todd E. Sparks, Jambunathan Anand, Joseph William Newkirk, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Laser Aided Manufacturing Process (LAMP) can be applied to repair steel die/molds which are currently repaired using traditional welding process in industry. In order to fully understand the advantages of laser deposition repair process over traditional welded-repair process, the mechanical properties such as tensile strength and hardness of H13 tool steel samples produced by these two processes were investigated. The microstructure and fracture surface of the samples were analyzed using optical microscope and SEM (Scanning Electron Microscope). Moreover, depositions on substrates with different shapes were studied to evaluate the performance of LAMP on damaged parts with complicated geometric shape.

Recovery Of The Grain Boundary Character Distribution Through Oblique Double-Sectioning, Brent L. Adams, David T. Fullwood, E. R. Homer

Faculty Publications

This work was supported primarily by the MRSEC program of the National Science Foundation under DMR-0079996. A method for the retrieval of the complete grain boundary character distribution by oblique double-sectioning is proposed. The method, which is similar to the recovery of the orientation distribution from sets of incomplete pole-figures, is efficient and provides many advantages as compared to calibrated serial sectioning. As compared to standard stereological approaches, the new methodology retains the advantage of direct measurement of the grain boundary inclination parameters. Solutions to the fundamental equation of oblique double-sectioning are provided in the Fourier space, and some specifics …

Two-Dimensional Grain Boundary Percolation In Alloy 304 Stainless Steel, Brent L. Adams, John A. Basinger, David T. Fullwood, E. R. Homer

Faculty Publications

This work was supported by the MRSEC program of the National Science Foundation under Award Number DMR-0079996. An experimentally-obtained percolation threshold for high-angle random grain boundary networks in alloy 304 stainless steel is compared to thresholds predicted by percolation theory. A discrepancy occurs in the two values (0.46 experimental and 0.65 theoretical). Possible reasons for the discrepancy are explored. The grain boundary network appears to be composed of two distinct sub-networks, with the 'outer' network acting as the dominant contributor to the percolating paths.

New Stereology For The Recovery Of Grain-Boundary Plane Distributions In The Crystal Frame, Brent L. Adams, Ryan J. Larsen

Faculty Publications

One of the authors (RJL) is grateful to the Office of Naval Research for fellowship support. BLA acknowledges the support of the NSF through the Materials Research Science and Engineering Center, Carnegie Mellon University (Grant No. DMR-0079996). A new experimental method is given for recovering the probability-distribution function Sv(ns/g). The function Sv(na/g) is the grain-boundary area per unit volume as a function of grain-boundary plane orientation (na), given a lattice misorientation (g) between the adjoining grains. The grain-boundary normal (na) is expressed in the crystal frame in which the misorientation g originates. The proposed method recovers the three-dimensional Sv(na/g) function …

Microstructures By Design: Linear Problems In Elastic-Plastic Design, Brent L. Adams, B. Henrie, M. Lyon

Faculty Publications

Materials microstructure is considered to be a design variable in the methodology called microstructure sensitive design (MSD). Based upon existing homogenization relations, relating the first-order representation of microstructure (the local state distribution function) to elastic and yield properties, the paper describes the construction of properties closures. These establish the theoretically-possible combinations of properties achievable by the set of all possible microstructures, which is called the microstructure hull. Exemplary homogenization relations are shown to be, typically, hypersurfaces (often hyperplanes) in the Fourier space in which the microstructure hull resides. All points lying on (or to one side of) the hypersurface, that …

Microstructure Design Of A Two Phase Composite Using Two-Point Correlation Functions, Brent L. Adams, H. Garmestani, G. Saheli

Faculty Publications

This work has been funded under the AFOSR Grant no. F49620-03-1-0011 and Army Research Lab contract no. DAAD17-02-P-0398 and DAAD 19-01-1-0742. Two-point distribution functions are used here as to introduce "Microstructure Sensitive Design" in two-phase composites. Statistical distribution functions are commonly used for the representation of microstructures and also for homogenization of materials properties. The use of two-point statistics allows the composite designer to include the morphology and distribution in addition to the properties of the individual phases and components. Statistical continuum mechanics is used to make a direct link between the microstructure and properties (elastic and plastic) in terms …

A Texture Evolution Model In Cubic-Orthotropic Polycrystalline System, Brent L. Adams, H. Garmestani, D. S. Li

Faculty Publications

This work has been funded under the AFOSR Grant # F49620-03-1-0011 and Army Research Lab Contract # DAAD17-02-P-0398 and DAAD 19-01-1-0742. B.L. Adams acknowledges support of Army Research Office, Proposal No. 42566-MS. The authors express their sincere gratitude to Professor Surya Kalidindi, for helpful suggestions and correspondence for the derivation of the processing path functions. A new methodology based on a conservation principle in the orientation space is developed to simulate the texture evolution in a cubic-orthotropic polycrystalline system. A least squares error method was used to improve the accuracy of the simulation results obtained from the texture evolution function. …

Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi

Faculty Publications

Support of the Army Research Office is greatly appreciated. Mechanical design can be conducted in a framework where consideration of microstructure as a continuous design variable is facilitated by the use of a Fourier space. Selection of the mechanical framework for the problem (e.g., mechanical constitutive model and homogenization relations) dictates the dimensionality of the pertinent microstructure representation. Microstructure is comprised of basic elements that belong to the local state space. Local state includes crystallographic phase and orientation, and other parameters such as composition. The local state space is transformed into an isomorphic set in Fourier space. The universe of …

Extracting The Relative Grain Boundary Free Energy And Mobility Functions From The Geometry Of Microstructures, Brent L. Adams, D. Kinderlehrer, W. W. Mullins, Anthony D. Rollett, Shlomo Ta'asan

Faculty Publications

This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-9632556. This paper describes a method for extracting, from measurements of a polycrystal, the relative excess free energy and the relative mobility of the grain boundaries as functions of the crystallographic type (five degrees of freedom) and relevant thermodynamic variables. The method requires the simultaneous measurement of both the geometry and the crystallography of a large number of grain boundary intersections; the crystallographic information may be obtained from orientation imaging microscopy (OIM). For simplicity, the intersections will be assumed to be triple junctions …

Chemcial Vapor Deposition Precursor Chemistry. 5. The Photolytic Laser Deposition Of Aluminum Thin Films By Chemical Vapor Deposition, John A. Glass, Seong-Don Hwang, Saswati Datta, Brian W. Robertson, James T. Spencer

Department of Mechanical and Materials Engineering: Faculty Publications

Thin films of very high purity aluminum were formed from the laser photolysis of trimethylamine alane (TMAA) using both ultraviolet (pulsed nitrogen) and visible (argon ion) laser irradiation on a variety of substrates including gold. Si (111), GaAs (110) and Teflon (PTFE). At thicknesses of up to 1 μm, nearly linear growth rates of 377 Ås^-1 and 112 Ås^-1 were observed. The formation of volatile species formed during the deposition of aluminum from TMAA was investigated by quadrupole mass spectrometry (QMS) of the reactant gas stream. The highest intensity post-deposition mass fragments were observed at m/z 58, …