| Effects of Pollutants and Microorganisms on the Absorption of Electrolytic Hydrogen in Iron |
MAY 97 |
23 pages |
| Authors:
H. W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
 | The objective of this research is to define the conditions under which pollutants, in particular those produced by bacteria such as the sulfide end product of the SRB, affect the amount of hydrogen absorbed by iron/steel during open circuit corrosion and under cathodic polarization conditions. At the same time we will be investigating protective measures including the development of improved inhibitors that will work under occluded conditions as exist during ... |
|
| Ductile Fracture and Failure Criteria of Structural Steels |
JUN 96 |
39 pages |
| Authors:
D. A. Koss; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Progress is reviewed for a program which examines multiaxial failure criteria and the associated mechanisms of ductile fracture in structural steels using HY100 as a model system. Failure limit diagram data are presented for the dependence of failure initiation of HY100 over a range of multiaxial tensile stresses and microstructural conditions including material heat treated to simulate heat-affected zone material in a weldment. An analysis of experimental observations suggests two ... |
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| Prediction of Hydrogen Entry and Permeation in Metals and Alloys |
JAN 96 |
60 pages |
| Authors:
Howard W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The ongoing objectives of this research project are to understand the mechanism of hydrogen entry into metals and to search for and evaluate various remedial measures to control this process and the subsequent hydrogen embrittlement. Several parallel approaches are pursued to achieve these objectives. During the last year, significant progress has been achieved on several tasks. A brief description is given below on each of these following tasks: (1) Effect ... |
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| Prediction of Hydrogen Entry and Permeation in Metals and Alloys |
FEB 95 |
45 pages |
| Authors:
Howard W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This report summarizes results of the past year on our continuing experiments directed to the problem of hydrogen entry and degradation of materials both of planar surfaces and for the more complicated recessed surface. For the planar surface the hydrogen permeation and scanning tunneling microscopy (STM) techniques were used, and for the recessed surface the study used the hydrogen permeation technique and a microscopy/electrochemical probe technique. Microstructural effects and the ... |
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| Ductile Fracture and Failure Criteria of Structural Steels |
20 JUN 94 |
13 pages |
| Authors:
D. A. Koss; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Progress is reviewed for a program which examines aspects of ductile fracture of structural steels. The research seeks to establish multiaxial failure criteria which have sufficient microstructural sensitivity to account for variations in microstructure such that fracture initiation can be predicted. The research involves both experimental and computational analysis. Progress for the period March 1, to May 31, 1994 is reviewed for (1) the initiation of a study of failure ... |
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| Microstructures and Epitaxy in Oxide Superconductor Thin Films and Devices |
01 MAR 94 |
17 pages |
| Authors:
Altaf H. Carim; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This report summarizes the work performed at the Pennsylvania State University (PSU) and the Westinghouse Science and Technology Center (WSTC) under the project entitled 'Microstructure and Epitaxy in Oxide Superconductor Thin Films and Devices', AFOSR Grant F49620-92-J-0159, under the direction ofd the principal investigator, Prof. A. H. Carim. The total period of the project was from February 1, 1992 to January 31, 1994. Results over the first year of the ... |
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| A Modeling Study of the Effect of Stress State on Void Linking During Ductile Fracture |
28 JAN 94 |
34 pages |
| Authors:
A. B. Geltmacher; D. A. Koss; P. Matic; M. G. Stout; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Specimens containing arrays of through-thickness holes are used to model aspects of void linking during ductile, microvoid fracture. Specifically, the contrasting deformation and fracture behavior of sheet specimens containing either pairs or pseudo -random arrays of equi-sized holes is examined in both uniaxial and equal-biaxial tension utilizing experiment as well as computer simulation. Our results show for this plane-stress situation that hole linking is always caused by flow localization within ... |
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| Carbon Dioxide Laser Cutting of a Carbon-Fiber-Silicon Carbide-Matrix Composite |
94 |
|
| Authors:
Mladen F. Trubelja; Sriram Ramanathan; Michael F. Modest; Vladimir S. Stubican; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
 | CO2 laser scribing and cutting were studied on a carbon-fiber-silicon carbide-matrix (C/SiC) composite containing 45 vol% fibers. The scribing and cutting were performed using laser powers between 750 and 1500 W, and specimen translation velocities between 0.5 and 4 cm/s. The results were compared to predicted values obtained by solving the quasi-steady-state heat conduction equation in three dimensions for a moving body. Good agreement between theory and experiment was found. ... |
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| Fracture Behavior of CVD SiC-Coated Graphite: II, Conditions for the Onset of Multiple Cracking |
94 |
|
| Authors:
Thomas R. Watkins; David J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Crack arrest and multiple cracking can be observed during the fracture of coated substrates even in the absence of coating delamination. Clearly, it would be useful to understand the mechanics and material parameters that control this process. The conditions for the arrest of the initial crack were modeled using an approximate stress intensity factor approach, and it was determined there is a critical coating thickness, below which the multiple cracking ... |
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| Oxide Matrix Composite by Directional Oxidation of a Commercial Aluminum-Magnesium Alloy |
94 |
|
| Authors:
Tarasankar DebRoy; Amitaa Bandopadhyay; Rustum Roy; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Oxidation rates of a commercial Al-Mg alloy, Al-5083, were investigated to understand the synthesis of an oxide-based composite. In some experiments, the oxide layer was grown with several platinum wires embedded in the matrix to facilitate transport of electrons. The oxidation rate was not controlled by the rate of transport of the electrons and positive holes through the ceramic oxide layer. In the initial phase of the composite growth, an ... |
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| Fabrication of Continuous-Fiber-Reinforced Polycrystalline Oxide Composites via Molten Salt Infiltration |
94 |
|
| Authors:
Yeong-Shyung Chou; C. Eric Ramberg; John R. Hellmann; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| A novel molten nitrate salt infiltration technique was developed for the fabrication of continuous-fiber-reinforced polycrystalline-alumina-matrix composites containing a high volume fraction (47%) of small-diameter fibers (Du Pont PRD 166 alumina/zirconia; 20 micrometer diameter). A single infiltration resulted in sufficient matrix yield to permit densification of the resulting composites to >93% of theoretical density with excellent microstructural uniformity. Hot-pressed composites fabricated in this manner exhibited Young's modulus of 270 GPa, flexural ... |
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| Investigation of Strut Crack Formation in Open Cell Alumina Ceramics |
94 |
|
| Authors:
David D. Brown; David J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| An investigation was made into the source of strut cracking during the fabrication process of open cell ceramics that are produced by coating a polymeric foam. Several sources for the stress that produces these cracks were considered, viz., differential drying, thermal expansion mismatch between the polymer and the green ceramic coating, and the gas pressure produced by pyrolysis of the organic skeleton. Thermogravimetric analysis of the polymeric foam was used ... |
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| Fabrication of Oriented SiC-Whisker-Reinforced Mullite Matrix Composites by Tape Casting. |
1994 |
|
| Authors:
Mianxue Wu; Gary L. Messing; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Dense SiC-whisker-reinforced mullite composites with up to 50 vol% whiskers can be obtained by tape casting and hot pressing. The tape casting process results in high degrees of SiC whisker orientation as determined visually and by X-ray diffraction. The ability to achieve dense composites with as much as 50 vol% whiskers is attributed to the higher percolation threshold of aligned whiskers. The factors affecting the degree of whisker orientation during ... |
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| Processing and Mechanical Properties of a Silicon Carbide Platelet/Alumina Matrix Composite. |
1994 |
|
| Authors:
Y. S. Chou; D. J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This paper presents an integrated study of the processing and mechanical properties of a SiC platelet/alumina composites. The major goal was to investigate the potential application of plate-like particles in toughening ceramic matrices. In the processing part of the study, the microstructures were found to possess preferred platelet orientation, with the platelets tending to lie parallel to each other after hot-pressing. In the mechanical property part of the study, Young's ... |
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| Residual Stress-Induced Spontaneous Microcracking in Alpha-SiC Platelet Al2O3 Composites. |
1994 |
|
| Authors:
Y. S. Chou; D. J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The micromechanical stresses associated with hexagonal (6H) alpha-SiC platelets within a fine-grained alumina matrix were calculated using an Eshelby approach. The stresses within and around the interface of SiC platelets were determined. Both stresses were found to be strongly dependent on the morphology and the volume fraction of the SiC particles. The morphology effect, however, tended to be limited at aspect ratios >= 10. Owing to anisotropy in the thermal ... |
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| The Time Dependent High Temperature Mechanical Behavior of Polycrystalline Alpha-SiC Fibers. |
1994 |
|
| Authors:
K. L. Rugg; L. A. Giannuzzi; R. E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| A preliminary investigation of the time dependent high temperature (>1200 c) tensile properties of polycrystalline alpha sic fibers have been assessed utilizing dynamic and static fatigue measurements in conjunction with creep experiments. from these initial results we cannot confirm the existence of a threshold stress intensity for crack growth as has been proposed for monolithic sintered alpha sic. the fibers exhibit primary creep to strains less than 1 %. the ... |
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| Prediction of Hydrogen Entry and Permeation in Metals and Alloys |
30 SEP 93 |
15 pages |
| Authors:
H. W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This Grant focused on the investigation of the factors which affect hydrogen entry and permeation into metals/alloys that by themselves or in combination with other materials are used under conditions for which hydrogen embrittlement and cracking are a major concern. Factors that affect H entry include a broad range of metallurgical, environmental and interface properties such as adsorption, surface segregation, surface films and recesses in the surface. Research during this ... |
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| FI-STM Investigation of Atomic Hydrogen Adsorption on the Si(100)2x1 Surface |
APR 93 |
27 pages |
| Authors:
Xiangdong Wang; T. Hashizume; H. Lu; H. W. Pickering; T. Sakurai; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| A field ion-scanning tunneling microscopy study on hydrogen chemisorption on the Si(100)2x1 surface is presented. At low coverages, hydrogen atoms reside singly on top of the dimerised Si atoms, and are imaged brightly. The hydrogen chemisorption induces the buckling of dimers, indicating the strong bonding between Si and H atoms. With increasing coverage, both the 2x1 monohydride and 1x1 dihydride phases were formed. The former is imaged dark compared with ... |
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| Mechanisms of Fracture and Creep of Structural Alloys |
29 MAR 93 |
37 pages |
| Authors:
D. A. Koss; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Progress is reviewed for a research which focuses on two aspects which limit the performance of structural alloys. First, in a study generic to a wide range of materials, we are determining the mechanisms, as well as local failure criteria, by which voids grow, interact and link during ductile fracture due to damage accumulation. Secondly, in a study focused specifically at high strength titanium alloys, we are examining the deformation ... |
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| The Temperature Dependence of the Deformation and Oxidation Behavior of an Age-Hardenable Beta + Alpha-Two Titanium Alloy |
05 MAR 93 |
16 pages |
| Authors:
D. M. Goto; L. S. Quattrocchi; D. A. Koss; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The beta Ti alloy Ti-23Nb-11Al (at %) is unique in that it is age hardenable due to the formation of lath-like alpha 2-phase precipitates based on Ti3Al. Furthermore age-hardening occurs at temperatures significantly higher than most conventional beta Ti alloys. This suggests the possibility of the elevated temperature usage of alpha 2-strengthened beta Ti alloys such as Ti- 23Nb-11Al. The study examines the compressive deformation behavior of the Ti- 23Nb-11Al ... |
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| Interface Chemistry in Ceramic Matrix Composites |
MAR 93 |
29 pages |
| Authors:
Carlo G. Pantano; Karl Spear; Greg Bibbo; Jim Walck; Anant Singh; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| There are many possible effects of interface reactions in fiber or whisker reinforced glass or glass ceramic matrix composites. In most cases, interface reactions must be minimized because they can lead to degradation of fiber or whisker strength, destruction of interphase coatings, and modification of the interface adhesion. Nevertheless, there are systems where interface reactions are beneficial. The best example of this is in the NiCALON reinforced glass-ceramic composites where ... |
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| A New Index for the Crevice Corrosion Resistance of Materials |
FEB 93 |
21 pages |
| Authors:
Yuan Xu; Howard W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Recent studies have revealed the crucial role played by the macro corrosion cell (potential coupling between the inside and outside of a cavity) in crevice and pitting corrosion. It was found that acidification and the existence of chloride ions in the local cell are not the sole and necessary conditions for localized corrosion to occur, and that their accelerating effects on crevice corrosion and pit growth can be explained within ... |
|
| Development of Predictive Reaction Models of Soot Formation |
26 JAN 93 |
18 pages |
| Authors:
Michael Frenklach; Hai Wang; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| During the second twelve-month period of the project, progress has been made in the following areas: (1) The computational study of sooting limits in laminar premixed flames was completed. It was found that the critical equivalence ratios for soot appearance, both the absolute values and temperature dependencies, can be predicted fairly close to the experimental observations. Sensitivity and reaction path analyses were performed to examine the factors responsible for the ... |
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| Prediction of Hydrogen Entry and Permeation in Metals and Alloys |
JAN 93 |
49 pages |
| Authors:
Howard W. Pickering; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This report summarizes results of the past year on our continuing experiments directed to the problem of hydrogen entry and degradation of materials both of planar surfaces and for the more complicated recessed surface. For the planar surface the hydrogen permeation and scanning tunneling microscopy (STM) techniques are being used, and for the recessed surface the study uses the hydrogen permeation technique and a microscopy/electrochemical probe technique. In-situ scanning tunneling ... |
|
| Microstructural Development in the Coarse-Grained, Heat-Affected Zone in Titanium-Vanadium Microalloyed HSLA Steels |
93 |
|
| Authors:
R. Varughese; A. W. Pense; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The development of the microstructure in the coarse-grained, heat- affected zone (CGHAZ) of two medium-strength Ti-V microalloyed steels was examined. Single-pass welding of 19mm-thick plates at 5.5kJ/mm resulted in a smaller austenite grain size and a correspondingly narrower CGHAZ in the low-Ti, high-V steel than in the high-Ti, low-V steel. The observed effect is correlated to the differing stability of microalloy precipitates, TiN/TiCN in the high-Ti, low-V steel and TiVN/TiVCN ... |
|
| Advanced Structural Ceramics: Recent Developments and Reliability Issues |
93 |
|
| Authors:
Richard E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The status of Advanced Structural Ceramics is reviewed with emphasis on new developments in mechanical reliability and fabrication which are required to assure widespread application of these materials. New processes for high temperature processing of ceramics and ceramic composites, are described with emphasis on immediate applications of these technologies. Recent developments in toughened ceramics which include in situ or self-reinforced silicon nitride, nanoparticle composites, and continuous fiber reinforcement are emphasized. ... |
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| Threshold Stress Intensity for Crack Growth in Silicon Carbide Ceramics |
93 |
|
| Authors:
Bulent O. Yavuz; Richard E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Measurements of threshold stress intensities for crack growth, K(sub th), of three polycrystalline SiC materials were attempted using interrupted static fatigue tests at 1200-1400 C. Weibull statistics were used to calculate conservative K(sub th) values from test results. The K(sub th) of a chemically vapor deposited beta-SiC could not be determined, as a result of its wide variations in strength. The K(sub th) > 3.3, 2.2, and 1.7 MPa sq ... |
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| Silicon Carbide Platelet/Alumina Composites: II, Mechanical Properties |
93 |
|
| Authors:
Yeong-Shyung Chou; David J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The mechanical properties, i.e., Young's modulus, fracture toughness, and flexural strength, of SiC-platelet/Al2O3 composites with two different platelet sizes were studied. Both Young's modulus and the fracture toughness of composites using small platelets (12 microns) increased with increasing SiC volume fraction. Maximum values for toughness and Young's modulus of 7.1 MPa sq rt m and 421 GPa were obtained for composites containing 30 vol% platelets. Composites fabricated using larger platelets ... |
|
| Adsorption as a Method of Doping 3-mol%-Yttria-Stabilized Zirconia Powder With Copper Oxide |
93 |
|
| Authors:
John R. Seidensticker; Merrilea J. Mayo; K. Osseo-Asare; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The adsorption behavior of Cu(2+) on 3-mol%-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder was studied. There is a window of pH values (10 < pH < 11) where adsorption may be used as a method of doping 3Y-TZP with Cu(2+). The maximum mole percent of the CuO additions is determined by the specific surface area of the 3Y-TZP powder; a powder with a specific surface area of 16.1 (sq m)/g is ... |
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| Determination of Young's Modulus in Chemically Vapor-Deposited SiC coatings |
93 |
|
| Authors:
Thomas R. Watkins; David J. Green; Earle R. Ryba; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Young's modulus of CVD and SiC coatings was measured in situ (on the substrate) using strain gage/flexure and dynamic resonance techniques. The average Young's moduli of CVD SiC from these techniques were 446 and 415 GPa, respectively, and were considered to be in good agreement. The determination of a representative coating thickness and cross section is critical in order to accurately estimate Young's modulus of coatings. |
|
| Silicon Carbide Platelet/Alumina Composites: III, Toughening Mechanisms |
93 |
|
| Authors:
Yeong-Shyung Chou; David J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| This is the last part of a series of papers on the processing and fracture behavior of SiC-platelet/Al2O3 composites. The objective of this paper was to identify the mechanisms involved in the toughening process. A hot- pressed composite with a SiC volume fraction of 0.3 was chosen as the model system for study. Based on microstructural observations, crack deflection and grain bridging were both identified as possible toughening mechanisms and ... |
|
| Reactivity of Alumina Toward Phosphoric Acid |
93 |
|
| Authors:
James V. Bothe Jr.; Paul W. Brown; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Reaction between alumina and 33.3 wt% orthophosphoric acid was investigated by monitoring the heat liberated under isothermal conditions at temperatures from 25 to 90 C. In a separate set of experiments, the H3PO4 concentration was varied from 0 to 50 wt%, at 25 C. Reactivities of five alumina (three anhydrous and two hydrated) differing in particle size, surface area, and crystallinity were studied. Relationships between the properties of the aluminas ... |
|
| Microstructure and Viscosity of Hot Pressed Silicon Oxycarbide Glasses |
93 |
|
| Authors:
Michael Hammond; Else Breval; Carlo G. Pantano; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The microstructural evolution of silicon oxycarbide glasses has been studied as a function of hot pressing temperature up to 1650 C. The silicon oxycarbide glasses were synthesized using a sol/gel process. Due to the metastable nature of the oxycarbide glass precursor, the temperature and pressure used to process these materials was expected to influence their final microstructure and properties. The materials were characterized by chemical analysis, X-ray diffraction, TEM and ... |
|
| Slow Crack Growth in Sapphire Fibers at 800 Degrees to 1500 Degrees C |
93 |
|
| Authors:
Stephen A. Newcomb; Richard E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Sapphire fibers with (near) c-axis orientation were tested in tension over a range of strain rates (0.00001 to 0.5/min) at elevated temperatures (800 to 1500 C). The strength of the fibers was dependent on the strain rate. Slow crack growth was confirmed as the degradation process by direct inspection of the fracture surfaces and estimation of fracture stresses from measured flaw sizes. The slow crack growth parameter, N, decreased with ... |
|
| Fracture Behavior of Chemically-Vapor-Deposited SiC-Coated Graphite: I, Experimental Results |
93 |
|
| Authors:
Thomas R. Watkins; David J. Green; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| CVD SiC coatings on polycrystalline graphite substrates exhibited a crack arrest/multiple cracking phenomenon when fractured in four-point flexure. This fracture behavior appeared to be controlled by the magnitude of the coating thickness. When the coating thickness was less than 50 microns, crack arrest and multiple cracking were observed in the tensile coating surface before catastrophic failure of the composite. In order to understand the fracture behavior of the layered composites, ... |
|
| The Formation and Oxidation of BC3, A New Graphitelike Material |
93 |
|
| Authors:
D. L. Fecko; L. E. Jones; P. A. Thrower; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| A study was performed to investigate improved oxidation resistance in a graphitic material containing high concentrations of substitutional boron. The method of producing such samples was the chemical vapor deposition (CVD) reaction between boron trichloride and benzene at temperatures near 973 K. This reaction is known to produce a novel material containing about 25% boron, and having the chemical formula BC3. The material was produced and examined for chemical composition, ... |
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| Towards and Understanding of the Reaction Sequences in Brazed Joints: Investigation of the Ti-Cu-O Ternary at 945 Degrees C. |
1993 |
|
| Authors:
G. P. Kelkar; A. H. Carim; K. E. Spear; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The joining of ceramics using active metal braze alloys is an attractive technique and has been used for a variety of material systems. The braze alloys usually contain an active element such as Ti which can reduce the ceramic and form a strong bond across the interface. Microstructural characterizations of brazed interfaces have been widely reported, though reasons for the formation of reaction products and their sequence is not clear ... |
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| TEM Investigation of Microwave Joined Si-SiC/Al/Si-SiC and Alpha SiC/Al/Alpha-SiC. |
1993 |
|
| Authors:
S. Arunajatesan; A. H. Carim; T. Y. Yiin; V. K. Varadan; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) have been used to examine the SiC/Al interfaces in microwave joined Si-SiC/Al/Si-SiC and alpha-SiC/Al/alpha-SiC. Both the SiC/Al interfaces display intimate contact between the ceramic and metal and are free of porosity. EPMA of the alpha-SiC/Al/alpha-SiC joints reveals that no Al has diffused into the bulk alpha-SiC, unlike the reported diffusion of Al in Si-SiC/Al/Si-SiC. The TEM investigations show that while the ... |
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| Thermochemical Modeling of Interface Reactions in Glass Matrix Composites. |
1993 |
|
| Authors:
Carlo G. Pantano; Karl E. Spear; Gang Qi; Douglas M. Beall; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| The reinforcement of glasses and glass-ceramics with continuous ceramic fibers is one of the most active areas of composites research and development. Although the majority of these studies has been limited to the use of NiCALON, many more glass matrix compositions have been investigated. It is now quite clear that even minor changes in the glass matrix composition can influence the chemistry, microstructure and mechanical properties of the fiber/matrix interfaces. ... |
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| High Temperature Strength and Creep Behavior of Carborundum Alpha Silicon Carbide Fibers. |
1993 |
|
| Authors:
Lucille A. Giannuzzi; Kevin L. Rugg; Richard E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Preliminary results on the high temperature strength and creep properties of the Carborundum polycrystalline sintered alpha-SiC fiber show that the fiber fails by slow crack growth at 1400 C. In addition, a threshold stress intensity below which no slow crack growth occurs is estimated. Preliminary creep testing yields a stress exponent = 1.86 +/- 0.50, and an apparent creep activation energy = 274 +/- 12 kJ/mole. |
|
| Microstructural Influences on the Creep Behavior of CVD Silicon Carbide Monofilaments. |
1993 |
|
| Authors:
C. A. Lewinsohn; C. E. Bakis; R. E. Tressler; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Textron SCS-6 silicon carbide (SiC) monofilaments made by the chemical vapor deposition (CVD) technique are currently under consideration for high-temperature composite materials. The microstructure of this monofilament is heterogeneous, with at least five concentric cylinders of distinct compositions commonly recognized. Most prominent among these layers are a 37 micron diameter graphite coated carbon core, a 136 micron diameter SiC sheath of graded microstructure, and a 3 micron thick silicon-containing carbon-rich ... |
|
| Superplasticity of Nanostructured Ceramics. |
1993 |
|
| Authors:
M. J. Mayo; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| To date, compressive superplasticity has been observed in several studies on nanocrystalline ceramics. Despite initial reports of room temperature superplasticity, the current results show that elevated temperatures are required for this phenomenon to take place. In addition, the nanocrystalline ceramics appear to obey the well-established phenomenological law for superplastic deformation, with strain rate sensitivities and grain size exponents similar to those observed in submicron and larger-grained ceramics. The major advantage ... |
|
| Sinter-Forging of Chemically Precipitated Nanocrystalline TiO2. |
1993 |
|
| Authors:
D. C. Hague; M. J. Mayo; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
|
| Two mechanisms appear to occur during the sinter-forging of nanocrystalline titania. The first mechanism occurs at stresses below 25 MPa where the densification kinetics are shown to be independent of the stress. However, at higher stresses, the densification kinetics are greatly enhanced by a plastic flow mechanism. The nucleation rate of rutile during the concurrent anatase-to-rutile phase transformation is shown to be enhanced by compressive stresses; however, the overall transformation ... |
|
| Mechanical Properties of a Laser-Cut Alumina-Matrix-Silicon-Carbide Whisker Composite. |
1993 |
|
| Authors:
Mladen F. Trubelja; Vladimir S. Stubican; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| Flexure strength and fracture toughness of a laser-cut Al2O3-30 vol% SiC composite were measured by the four-point bending and the indentation methods, respectively, and compared to the values obtained from the diamond cut material. For the laser-cut composite, the flexure strength was 402 +/- 31 MPa (approximately 30% lower for the diamond-cut), whereas the fracture toughness was 6.4 +/- 0.4 MPa sq rt m (approximately 12% lower). The strength and ... |
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| Structure-Property Relationships in High Permittivity Ceramics. |
1993 |
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| Authors:
R. E. Newnham; S. Trolier-McKinstry; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| High dielectric constant ceramics are widely used today in electronic circuitry. In this paper, the mechanisms responsible for the high permittivity in ceramics capacitors are addressed and related to the temperature dependence of the permittivity and its modification. In addition, the structure-property relations controlling important corollary properties such as the dielectric loss, the electrical resistivity, and degradation in capacitors are also reviewed. Finally, the microstructure and crystal chemistry of some ... |
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| Towards an Understanding of the Reaction Sequences in Brazed Joints: Investigation of the Ti-Cu-O Ternary at 945 Degrees C. |
1993 |
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| Authors:
G. P. Kelkar; A. H. Carim; K. E. Spear; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| The joining of ceramics using active metal braze aloys is an attractive technique and has been used for a variety of material systems. the braze alloys usually contain an active element such as ti which can reduce the ceramic and form a strong bond across the interface. microstructural characterizations of brazed interfaces have been widley reported, though reasons for the formation of reaction products and their sequence is not clear ... |
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| Transport Phenomena in the Scale-Up of Hot Filament-Assisted Chemical Vapor Deposition of Diamond. |
1993 |
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| Authors:
K. Tankala; T. Debroy; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| Heat transfer and fluid flow in a diamond deposition reactor were examined to identify parameters important to reactor design and scale-up. Physical and mathematical modeling of hot filament-assisted diamond deposition reactors indicated that both ordinary and thermal diffusion are equally important in the transport of nutrient species to the substrate surface. The atomic hydrogen concentration field in the reactor is established mainly by diffusive mixing of the atomic hydrogen with ... |
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| On the Oxidation Resistance of C/C Composites Obtained by Liquid-Phase Impregnation/Carbonization of Different Carbon Cloths. |
1993 |
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| Authors:
J. Rodriguez-Mirasol; P. A. THROWER; L. R. Radovic; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| Two commercial carbons (an activated carbon cloth and a rayon-derived carbon cloth) having vastly different properties were used as substrates for the preparation of low- and high-temperature carbon/carbon composites by the liquid-phase impregnation/carboniza- tion technique with two different pitches and one resin system as matrix precursors. The percentage of matrix in the composites was dependent on the surface area of the carbon cloth substrate. The oxidation behavior of the composites ... |
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| Nanocomposites: Retrospect and Prospect. |
1993 |
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| Authors:
Rustum Roy; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| Advanced Thermally Stable Coal-Derived Jet Fuels Compositional Factors Affecting Thermal Degradation of Jet Fuels |
DEC 92 |
177 pages |
| Authors:
C. Song; S. Eser; H. H. Schobert; P. G. Hatcher; M. M. Coleman; PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MATERIALS SCIENCE AND ENGINEE RING
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| This project focuses on the compositional factors affecting high temperature thermal stability of coal-derived and petroleum-based jet fuels in pyrolytic regime. Thermal stability refers to the resistance of fuel to chemical decomposition at high temperatures to cause the solid deposition and liquid depletion. There are four broad objectives in this project, and the research work is divided into four tasks. The first task clarifies the chemistry of fuel degradation and ... |
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