3-D Modeling of Forced-Flow Thermal-Gradient CVI for Ceramic Composite Fabrication

1989 ◽  
Vol 168 ◽  
Author(s):  
Thomas L. Starr ◽  
Arlynn W. Smith
Keyword(s):  
Thermal Gradient ◽  
National Laboratory ◽  
Ceramic Composites ◽  
Chemical Vapor Infiltration ◽  
Forced Flow ◽  
Process Conditions ◽  
Uniform Density ◽  
Oak Ridge ◽  
Matrix Deposition ◽  
Wide Range

AbstractForced-flow thermal-gradient chemical vapor infiltration (FCVI) has demonstrated excellent potential for fabrication of high strength, high toughness ceramic composites. Extension of this process to large and complex shapes is facilitated by use of a computer model to optimize process conditions and hardware for rapid, uniform infiltration.A 3-D model has been developed using a “finite volume” formulation. A steady-state solution for heat conduction and Darcy's law permeation produces temperature and gas flow distributions within the fiber preform. These are used to generated matrix deposition rates within each volume element. By “marching” through time, a complete simulation of the densification process can be obtained.The model is demonstrated for a FCVI system with cylindrical symmetry and compared to experimental results obtained at the Oak Ridge National Laboratory. The model results suggest a self-optimizing feature of the force flow/thermal gradient CVI process that produces uniform density in the final composite over a range of infiltration conditions. This matches experimental observation where good uniformity has been achieved over a wide range of gas flows, pressure and temperature.

scholarly journals Octane Index Applicability over the Pressure-Temperature Domain

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 607
Author(s):  
Tommy R. Powell ◽  
James P. Szybist ◽  
Flavio Dal Forno Chuahy ◽  
Scott J. Curran ◽  
John Mengwasser ◽  
...  
Keyword(s):  
High Efficiency ◽  
National Laboratory ◽  
Operating Conditions ◽  
Dominant Factor ◽  
Compression Ignition ◽  
Oak Ridge ◽  
Operating Modes ◽  
Wide Range ◽  
Thermodynamic Conditions ◽  
Si Engines

Modern boosted spark-ignition (SI) engines and emerging advanced compression ignition (ACI) engines operate under conditions that deviate substantially from the conditions of conventional autoignition metrics, namely the research and motor octane numbers (RON and MON). The octane index (OI) is an emerging autoignition metric based on RON and MON which was developed to better describe fuel knock resistance over a broader range of engine conditions. Prior research at Oak Ridge National Laboratory (ORNL) identified that OI performs reasonably well under stoichiometric boosted conditions, but inconsistencies exist in the ability of OI to predict autoignition behavior under ACI strategies. Instead, the autoignition behavior under ACI operation was found to correlate more closely to fuel composition, suggesting fuel chemistry differences that are insensitive to the conditions of the RON and MON tests may become the dominant factor under these high efficiency operating conditions. This investigation builds on earlier work to study autoignition behavior over six pressure-temperature (PT) trajectories that correspond to a wide range of operating conditions, including boosted SI operation, partial fuel stratification (PFS), and spark-assisted compression ignition (SACI). A total of 12 different fuels were investigated, including the Co-Optima core fuels and five fuels that represent refinery-relevant blending streams. It was found that, for the ACI operating modes investigated here, the low temperature reactions dominate reactivity, similar to boosted SI operating conditions because their PT trajectories lay close to the RON trajectory. Additionally, the OI metric was found to adequately predict autoignition resistance over the PT domain, for the ACI conditions investigated here, and for fuels from different chemical families. This finding is in contrast with the prior study using a different type of ACI operation with different thermodynamic conditions, specifically a significantly higher temperature at the start of compression, illustrating that fuel response depends highly on the ACI strategy being used.

Advanced Research and Technology Development Fossil Energy Materials Program

1988 ◽  
Vol 110 (4) ◽  
pp. 670-676
Author(s):  
R. R. Judkins ◽  
R. A. Bradley
Keyword(s):  
Technology Development ◽  
National Laboratory ◽  
Development Program ◽  
Ceramic Composites ◽  
Department Of Energy ◽  
Energy Materials ◽  
Alloy Development ◽  
Fossil Energy ◽  
Oak Ridge ◽  
Research Activities

The Advanced Research and Technology Development (AR&TD) Fossil Energy Materials Program is a multifaceted materials research and development program sponsored by the Office of Fossil Energy of the U.S. Department of Energy. The program is administered by the Office of Technical Coordination. In 1979, the Office of Fossil Energy assigned responsibilities for this program to the DOE Oak Ridge Operations Office (ORO) as the lead field office and Oak Ridge National Laboratory (ORNL) as the lead national laboratory. Technical activities on the program are divided into three research thrust areas: structural ceramic composites, alloy development and mechanical properties, and corrosion and erosion of alloys. In addition, assessments and technology transfer are included in a fourth thrust area. This paper provides information on the structure of the program and summarizes some of the major research activities.

scholarly journals Shared Research Equipment at OAK Ridge National Laboratory

1998 ◽  
Vol 4 (S2) ◽  
pp. 470-471
Author(s):  
N. D. Evans ◽  
E. A. Kenik ◽  
M. K. Miller
Keyword(s):  
Semiconductor Device ◽  
National Laboratory ◽  
Atomic Scale ◽  
Fiscal Year ◽  
Probe Field ◽  
Oak Ridge ◽  
Wide Range ◽  
Oak Ridge National Laboratory ◽  
Electron Microscopes ◽  
Research Equipment

The Shared Research Equipment (SHaRE) User Facility and Program at Oak Ridge National Laboratory (ORNL) provides microanalytical facilities for studies within the materials sciences. Available instrumentation includes advanced analytical electron microscopes, atom probe field ion microscopes, and nanoindentation facilities. Through SHaRE, researchers from U.S. universities, industries, and government laboratories may collaborate with Facility scientists to perform research not possible at their home institutions. International collaborations are also possible. Most SHaRE projects seek correlations at the microscopic or atomic scale between structure and properties in a wide range of metallic, ceramic, and other structural materials. Typical research projects include studies of magnetic materials, advanced alloys, catalysts, semiconductor device materials, high Tc superconductors, and surface-modified polymers. Projects usually involve one or more external researchers visiting the SHaRE Facility for up to three weeks during the fiscal year (October 1 - September 30). Project approval is based upon the scientific excellence and relevance of proposed collaborative research.

Forced flow-thermal gradient chemical vapor infiltration (FCVI) for fabrication of carbon/ carbon

Carbon ◽  
1995 ◽  
Vol 33 (9) ◽  
pp. 1211-1215 ◽  
Author(s):  
Sundar Vaidyaraman ◽  
W.Jack Lackey ◽  
Pradeep K. Agrawal ◽  
Garth B. Freeman
Keyword(s):  
Thermal Gradient ◽  
Chemical Vapor ◽  
Chemical Vapor Infiltration ◽  
Forced Flow ◽  
Vapor Infiltration

Production function for short-rotation woody-crop Populus spp. plantations

1994 ◽  
Vol 24 (1) ◽  
pp. 180-184 ◽  
Author(s):  
David A. Lortz ◽  
David R. Betters ◽  
Lynn L. Wright
Keyword(s):  
Production Function ◽  
Cultural Practices ◽  
National Laboratory ◽  
Development Program ◽  
The United States ◽  
Oak Ridge ◽  
Short Rotation ◽  
Wide Range ◽  
Woody Crop ◽  
Populus Spp

Short-rotation woody-crop Populus spp. plantations have the potential to produce large amounts of biomass in short time periods, typically 4–8 years. A production function equation is shown to predict yields for such plantations. The equation is based, in part, on information from biomass production experiments conducted across the United States. These experimental plots are sponsored by the Biofuels Feedstock Development Program of Oak Ridge National Laboratory. The equation uses nine parameters including both cultural practices and climatic and soil site conditions as independent variables. The equation (R2 = 0.86) is accurate and applicable to a wide range of conditions.

Creep Strength and Microstructure of AL20-25+Nb Alloy Sheets and Foils for Advanced Microturbine Recuperators

2006 ◽  
Author(s):  
Philip J. Maziasz ◽  
John P. Shingledecker ◽  
Neal D. Evans ◽  
Yukinori Yamamoto ◽  
Karren L. More ◽  
...  
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
Creep Resistance ◽  
National Laboratory ◽  
Rupture Life ◽  
Cost Effective ◽  
Test Facility ◽  
Oak Ridge ◽  
Collaborative Program ◽  
Wide Range

The Oak Ridge National Laboratory (ORNL) and ATI Allegheny-Ludlum began a collaborative program in 2004 to produce a wide range of commercial sheets and foils of the new AL20-25+Nb stainless alloy, specifically designed for advanced microturbine recuperator applications. There is a need for cost-effective sheets/foils with more performance and reliability at 650–750°C than 347 stainless steel, particularly for larger 200–250 kW microturbines. Phase I of this collaborative program produced the sheets and foils needed for manufacturing brazed plated-fin (BPF) aircells, while Phase II provided foils for primary surface (PS) aircells, and modified processing to change the microstructure of sheets and foils for improved creep-resistance. Phase I sheets and foils of AL20-25+Nb have much more creep-resistance than 347 steel at 700–750°C, and foils are slightly stronger than HR120 and HR230. Preliminary results for Phase II show nearly double the creep-rupture life of sheets at 750°C/100 MPa, with the first foils tested approaching the creep resistance of alloy 625 foils. AL20-25+Nb alloy foils are also now being tested in the ORNL Recuperator Test Facility.

Z-Contrast Imaging of Grain Boundaries in Semiconductors

1996 ◽  
Vol 54 ◽  
pp. 332-333
Author(s):  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Grain Boundaries ◽  
Chemical Potential ◽  
National Laboratory ◽  
Atomic Scale ◽  
Structural Defects ◽  
Specimen Thickness ◽  
Contrast Imaging ◽  
Oak Ridge ◽  
Wide Range ◽  
Annular Detector

Interest in grain boundaries in semiconductors is linked to the application of polycrystalline semiconductors as photovoltaic and interconnect materials. In real devices such as solar cells and MOS structures as well as future devices such as flat-panel displays, the intergranular regions of the polycrystalline solid have a significant effect on the flow of electronic current. These grain boundary barriers exist because the chemical potential of the boundary atoms are shifted from the bulk value by the change in local symmetry. The chemical potential is also changed by impurities, other structural defects, and other phases in the boundary. The lack of knowledge on the atomic structure of grain boundaries is, at present, the greatest barrier to advancements in the understanding of the electrical properties of these defects.The advances of the last few years have provided the tools with which to probe these interfaces at the true atomic scale. One such tool is the high-resolution scanning transmission electron microscope installed at Oak Ridge National Laboratory (VG Microscopes HB603) that can form a 1.27Å electron probe. Images are formed by scanning the probe across a thin sample and using an annular detector to collect electrons scattered to high angles. Because the annular detector collects electrons scattered over a wide range of angles, phase correlations and dynamical diffraction effects are averaged by this annular integration. Thus, an image with incoherent characteristics is produced and retained to relatively large specimen thickness.

Advances in Modeling of the Chemical Vapor Infiltration Process

1991 ◽  
Vol 250 ◽  
Author(s):  
Thomas L. Starr
Keyword(s):  
Chemical Vapor ◽  
Ceramic Matrix Composites ◽  
Ceramic Composites ◽  
Chemical Vapor Infiltration ◽  
Forced Flow ◽  
Material Transport ◽  
Process Technology ◽  
Infiltration Process ◽  
Design And Manufacture ◽  
Vapor Infiltration

AbstractThe technology of chemical vapor infiltration (CVI) has progressed dramatically over the past twenty-five years and stands now as the leading process for fabrication of high temperature structures using ceramic matrix composites. Modeling techniques also have advanced from extensions of catalyst theory to full 3-D finite element code with provision for temperature and pressure gradients. These modeling efforts offer insight into critical factors in the CVI process, suggest opportunities for further advances in process technology and provide a tool for integrating the design and manufacture of advanced components.Early modeling identified the competition between reaction and diffusion in the CVI process and the resulting trade-off between densification rate and uniformity. Modeling of forced flow/thermal gradient CVI showed how the evolution of material transport properties provides a self-optimizing feature to this process variation.“What-if” exercises with CVI models point toward potential improvements from tailoring of the precursor chemistry and development of special preform architectures.As a link between component design and manufacture, CVI modeling can accelerate successful application of ceramic composites to advanced aerospace and energy components.

Developing New Cast Austenitic Stainless Steels With Improved High-Temperature Creep Resistance

2007 ◽  
Author(s):  
Philip J. Maziasz ◽  
John P. Shingledecker ◽  
Neal D. Evans ◽  
Michael J. Pollard
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Creep Strength ◽  
Stainless Steels ◽  
Creep Resistance ◽  
National Laboratory ◽  
Austenitic Stainless Steels ◽  
Alloy Development ◽  
Oak Ridge ◽  
Wide Range

Oak Ridge National Laboratory (ORNL) and Caterpillar have recently developed a new cast austenitic stainless steel, CF8C-Plus, for a wide range of high-temperature applications, including diesel exhaust components and turbine casings. The creep-rupture life of the new CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless steel, and the creep-strength is about double. Another variant, CF8C-Plus Cu/W has been developed with even more creep strength at 750–850°C. The creep-strength of these new cast austenitic stainless steels is close to that of Ni-based superalloys like 617. CF8C-Plus steel was developed in about 1.5 years using an “engineered microstructure” alloy development approach, which produces creep resistance based on formation of stable nano-carbides (NbC) and prevention of deleterious intermetallics (sigma, Laves). CF8C-Plus steel won a 2003 R&D 100 Award, and to date, over 32,000 lb have been produced in various commercial component trials. The current commercialization status of the alloy is summarized.

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