28 Matching Results

Search Results

Advanced search parameters have been applied.

in creator/contributor: "Alexander, K. B."

open access

The effect of aging at 343/degree/C on type 308 stainless steel welds

Three nominally 25-mm (1-in) thick shielded metal-arc welds were prepared from 304L base plate with 308 filler material, to obtain three different ferrite levels (4, 8, and 12 %). Portions of these welds were then aged at 343/degree/C for 3000, 10000, and 20000 hours. Charpy V-notch and tensile specimens were taken from the welds. The tensile results were similar for all the specimens and showed little effect of aging on either the yield or ultimate tensile strengths. The Charpy impact properti… more

Date: January 1, 1989

Creator: Alexander, D. J.; Alexander, K. B. & Nanstad, R. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of reactive elements on the segregation behavior and microstructure of {alpha}-Al{sub 2}O{sub 3} scales on {beta}-NiAl

In order to improve oxidation resistance, small amounts of oxygen- active or ``reactive`` elements (RE) such as Y, Zr, Hf, Ce are added to chromia- and alumina-forming high-temperature alloys. As an alternative to a system where the RE-ion supply is self-limiting (Y-implant), it was desired to study effect of RE source-removal on microstructure and grain boundary segregation levels. {beta}-NiAl doped with 0.23 wt% Zr was oxidized in oxygen at 1500 C for 50 h. Upon cooling, the scale spalled int… more

Date: June 1, 1994

Creator: Alexander, K. B. & Pint, B. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Mechanically reliable scales and coatings

As the first stage in examining the mechanical reliability of protective surface oxides, the behavior of alumina scales formed on iron-aluminum alloys during high-temperature cyclic oxidation was characterized in terms of damage and spallation tendencies. Scales were thermally grown on specimens of three iron-aluminum composition using a series of exposures to air at 1000{degrees}C. Gravimetric data and microscopy revealed substantially better integrity and adhesion of the scales grown on an al… more

Date: July 1, 1995

Creator: Tortorelli, P.F. & Alexander, K.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Practical factors affecting the quantification of elemental concentrations in beam-sensitive ceramics by EFTEM

In order to obtain high spatial resolution microchemical data from beam-sensitive materials, alternative techniques which avoid the use of fine probes, such as energy-filtered imaging techniques must be used. Robust quantification procedures are currently under development. The quantification procedure which yields images whose intensities are proportional to the elemental concentrations has already been determined. The net core-loss intensity images, S{sub i}, can be corrected for diffraction … more

Date: April 1, 1997

Creator: Rice, P.M. & Alexander, K.B.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Effect of whisker surface treatments and processing conditions on the SiC/Al sub 2 O sub 3 interface

Various electron microscopy techniques have been used to evaluate the microstructural and interfacial characteristics of silicon carbide whisker-reinforced alumina composites. The effects of subjecting whiskers to oxidizing and reducing treatments prior to composite fabrication were examined. Whisker/matrix interfaces in which carbon coatings were applied to whiskers prior to specimen fabrication were also examined. Physical and thermodynamic arguments can be used to explain why it is difficult… more

Date: January 1, 1990

Creator: Alexander, K.B.; Angelini, P. & Becher, P.F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The microstructure and mechanical reliability of alumina scales and coatings

Alumina scales on iron-aluminides (Fe{sub 3}Al-based) and NiCrAl- based alloys were characterized in order to develop the knowledge to control the oxidation performance of alloys by controlling the microstructure and microchemistry of their scales. Plasma-deposited amorphous alumina coatings on iron-aluminides were used to study phase transformations, transport processes in the scales, and S segregation to the scale/metal interface. It was found that during heat treatment in absence of oxidatio… more

Date: September 1, 1997

Creator: Alexander, K.B.; Pruessner, K. & Tortorelli, P.F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Fabrication and properties of alumina matrix composites containing nickel aluminide reinforcements

Ductile nickel-aluminide intermetallic alloys have been successfully used to toughen ceramic materials intended for use at a wide range of temperatures. Traditional ceramic processing procedures have been used to produce a variety of microstructures. The fracture toughness increases with increasing particle aspect ratio, however, the flexural strength decreases with increasing particle size. Fracture toughnesses up to 7.6 MPa m{sup 1/2} and flexural strengths up to 550 MPa were observed in an a… more

Date: September 1, 1994

Creator: Alexander, K. B.; Lin, H. T.; Schneibel, J. H. & Becher, P. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Multivariate statistical analysis of spectrum lines from Si{sub 3}N{sub 4} grain boundaries

It is well known that the high-temperature properties of polycrystalline Si{sub 3}N{sub 4} ceramics are strongly influenced by the nanometer-scale glassy phase at the grain boundaries. The authors have recently analyzed the variation of the near-edge fine structure (ELNES) of the Si-L{sub 2,3} edges using a combination of TEM spectrum-line acquisition with an imaging filter and multivariate statistical analysis. The glassy phase at the Si{sub 3}N{sub 4} grain boundaries is easily damaged by the… more

Date: April 1, 1997

Creator: Rice, P. M.; Alexander, K. B. & Anderson, I. M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Monte Carlo simulation of spatial resolution for electron backscattered diffraction (EBSD) with application to two-phase materials

The study of texture and grain boundary misorientation in multiphase materials has been greatly benefited from the recent automation of the electron back-scattered diffraction (EBSD) technique. With this technique, each phase in a multiphase material can be individually sampled and analyzed. This is of great significance and interest in the study of thin films, inclusions and multiphase alloys. Spatial resolution, which depends on experimental conditions such as beam energy and specimen tilt, a… more

Date: October 1, 1997

Creator: Ren, S.X.; Kenik, E.A. & Alexander, K.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of aging at 343 degrees C on type 308 stainless steel weldments

The effect of long-term aging at intermediate temperatures on the mechanical properties of stainless steel welds has been studied. Three type 308 multipass shielded metal-arc welds with ferrite levels of 4, 8, and 12% were aged up to 343{degrees}C. Tensile tests showed little effect of aging on either the yield or ultimate tensile strengths, but the impact toughness was significantly degraded. The extent of the degradation increased with increasing ferrite content and increasing aging time. Exa… more

Date: January 1, 1990

Creator: Alexander, D. J.; Alexander, K. B.; Miller, M. K. & Nanstad, R. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of aging at 343{degree}C on the mechanical properties and microstructure of type 308 stainless steel weldments

The effect of long-term aging at intermediate temperatures on the mechanical properties of stainless steel welds has been studied. Three type 308 multipass shielded metal-arc welds with ferrite levels of 4, 8, and 12% were aged up to 20,000 h at 343C. Tensile tests showed little effect of aging on either the yield or ultimate tensile strengths, but the impact toughness was significantly degraded. The extent of the degradation increased with increasing ferrite content and increasing aging time. … more

Date: December 31, 1992

Creator: Alexander, D. J.; Alexander, K. B.; Miller, M. K. & Nanstad, R. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Iron aluminide-titanium carbide composites: Microstructure and mechanical properties

Composites of intermetallics and carbides (with binder contents less that 50 vol.%) are considered as potential candidates for applications requiring high wear resistance in corrosive environments. Intermetallics, especially aluminides, provide the corrosion resistance, and the high hardness of the carbide phase contributes to increased wear resistance of the composites. In this study, cost effective and simple processing techniques to obtain FeAl-TiC composites, over a wide range of binder vol… more

Date: September 1, 1996

Creator: Subramanian, R.; Schneibel, J. H. & Alexander, K. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of various oxide dispersions on the oxidation resistance of Fe{sub 3}Al

Oxide-dispersed Fe-28at.%Al-2%Cr alloys were produced by a powder metallurgy technique followed by hot extrusion. Yttria and ceria were added to the base alloy to assess the effect of these dopants on the oxidation behavior. The amount of dopant was varied from 0.05-0.5 at.% Y in a series of Y{sub 2}O{sub 3}-dispersed alloys. isothermal and cyclic oxidation testing was conducted at temperatures from 800{degrees} to 1300{degrees}C. A CeO{sub 2} addition was detrimental to the oxidation behavior.… more

Date: October 1, 1996

Creator: Pint, B. A.; Alexander, K. B. & Tortorelli, P. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Processing and properties of FeAl-bonded composites

Iron aluminides are thermodynamically compatible with a wide range of ceramics such as carbides, borides, oxides, and nitrides, which makes them suitable as the matrix in composites or cermets containing fine ceramic particulates. For ceramic contents varying from 30 to 60 vol.%, composites of Fe-40 at. % Al with WC, TiC, TiB{sub 2}, and ZrB{sub 2} were fabricated by conventional liquid phase sintering of powder mixtures. For ceramic contents from 70 to 85 vol.%, pressureless melt infiltration … more

Date: December 31, 1996

Creator: Schneibel, J.H.; Subramanian, R.; Alexander, K.B. & Becher, P.F.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Grain boundary segregation of cation dopants in {alpha}-Al{sub 2}O{sub 3} scales

A Fe-20at.%Cr-10%Al matrix was dispersed with a wide range of different oxides in order to study the effect of oxygen-active dopants on the high-temperature growth and adhesion of {alpha}-Al{sub 2}O{sub 3} scales. Effect of these various cation dopants on the alumina scale microstructure was correlated with dopant ion segregation to the {alpha}-Al{sub 2}O{sub 3} grain boundaries using analytical electron microscopy. Elements such as Mn and V showed little effect on the oxide scale and were not … more

Date: December 1996

Creator: Pint, B. A. & Alexander, K. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The Effect of Platinum on the Growth and Adhesion of alpha-Al{sub 2}O{sub 3} Scales

Cast PtAl and NiPtAl alloys were used as model materials to study the effect of Pt on the oxidation behavior of aluminide bond coats. The addition of Pt improves alpha-Al{sub 2}O{sub 3} scale adhesion in cyclic testing at 1150{degrees}C and 1200{degrees}C. However, in comparison with aluminides which contain reactive elements (e.g. Zr and Hf), the beneficial effect of Pt was not as great. SEM and TEM analysis of the oxides indicated little effect of the Pt on scale microstructure. Using TEM/EDS… more

Date: December 1997

Creator: Dickey, E. C.; Pint, B. A.; Alexander, K. B. & Wright, I. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The MBE growth and optical quality of BaTiO{sub 3} and SrTiO{sub 3} thin films on MgO

High quality epitaxial BaTiO{sub 3} and SrTiO{sub 3} have been grown on MgO; stabilized at a one unit cell height; and grown to film thicknesses of 0.5--0.7 {mu}m. These relatively thick films remain adherent when thermally cycled between growth temperatures and room temperature, are crack free with high optical quality, and have both in-plane and out-of-plane X-ray rocking curves of 0.3--0.5{degree}. These films have been grown using molecular beam epitaxy (MBE) methods starting with the TiO{s… more

Date: May 1, 1994

Creator: McKee, R. A.; Specht, E. D.; Alexander, K. B. & Walker, F. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Transformation behavior in Al{sub 2}O{sub 3}-ZrO{sub 2} ceramic composites

Neutron powder diffraction was used to investigate the tetragonal to monoclinic transformation of ZrO{sub 2} in a A1{sub 2}O{sub 3}-ZrO{sub 2} ceramic composite containing 40 vol % tetragonal ZrO{sub 2}. The neutron diffraction data were analyzed using the Rietveld refinement technique, which allowed to determine the extent of the transformation as a function of temperature. The onset transformation temperature determined for this sample was 130 K. Below this temperature, the fraction of the mo… more

Date: August 15, 1994

Creator: Wang, X. L.; Fernandez-Baca, J. A.; Hubbard, C. R.; Alexander, K. B. & Becher, P. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Improving the Oxidation Resistance in Advanced Single Crystal Nickel-Based Superalloys for Turbine Applications

The focus of this project was the examination of the role of yttrium and other alloying elements on the microstructure and oxidation performance of improved single crystal nickel-based superalloys for advanced turbine applications. The microstructure and microchemistry of both base and modified alloys and their surface oxides have been measured with state-of-the-art microanalytical techniques (atom probe field ion microscopy) and then correlated with identifying the partitioning behavior of the… more

Date: July 1, 1999

Creator: Alexander, K. B.; Kenik, E. A.; Miller, M. K.; Lin, L. S. & Cetel, A. D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Interfacial Segregation in Oxide Scales on NiCrAl-Based Alloys

Previous studies addressing the segregation of reactive elements in protective oxide scales and their beneficial effect on scale adhesion have primarily concentrated on primary alumina-formers. In this study the isothermal oxidation behavior of three NiCrAl alloys, which form complex oxide scales was studied in air at 1,473 K for 100 hrs. The resulting oxide scales were characterized by scanning electron microscopy (SEM) and cross=sectional transmission electron microscopy (TEM) techniques. Seg… more

Date: April 1, 1997

Creator: Pruessner, K.; Alexander, K. B.; Pint, B. A.; Tortorelli, P. F. & Wright, I. G.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Interfacial composition analysis of silicon nitride whisker reinforced oxynitride glass systems

Scanning transmission electron microscopy combined with energy-dispersive x-ray spectroscopy and parallel-detection electron energy-loss spectroscopy was used to analyze the composition at interfaces in {beta}-Si{sub 3}N{sub 4} whisker reinforced oxynitride glass systems.

Date: June 1, 1995

Creator: Sun, E. Y.; Alexander, K. B.; Becher, P. F. & Hwang, S. L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Ceramic composites with a ductile Ni{sub 3}Al binder phase

Composites using B-doped ductile Ni{sub 3}Al alloys were produced with both non-oxide (WC, TiC) and oxide (Al{sub 2}0{sub 3}) ceramic powders. Typical powder processing techniques were used to fabricate materials with ceramic contents from 0-95 vol. %. The microstructural morphology of the composites depends primarily on the wetting behavior between the alloys and the ceramic powders. The non-oxide ceramic powders wet well and the Ni{sub 3}Al alloys form a semi-continuous intergranular phase. O… more

Date: June 1, 1995

Creator: Tiegs, T. N.; Alexander, K. B.; Plucknett, K. P.; Menchhofer, P. A.; Becher, P. F. & Waters, S. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Approaches to the design of structural ceramics incorporating whiskers and particulate phases

Advances in the technologically and commercially important areas of energy production and conversion, transportation, chemical processing, manufacturing, electronics, and communications are predicted upon the development of materials with greatly improved performance. Many of these components will be exposed to tensile stresses, and possibly quite high temperatures, which will require that the materials be designed to (1) achieve greater fracture resistance, (2) resist deformation at elevated t… more

Date: September 1, 1994

Creator: Becher, P. F.; Lin, H. T.; Hsueh, C. H.; Alexander, K. B.; Warwick, W. H. & Waters, S. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Sulfur segregation to oxide/metal interfaces: a comparison of thermally grown and plasma deposited Al{sub 2}O{sub 3}

Segregation of S to oxide/metal interfaces was studied using scanning Auger microscopy after removing the oxide film in ultrahigh vacuum. Two types of alumina films were investigated: one formed from oxidation at 1000 C on Fe-28at.%Al-5at.%Cr; the other was deposited on the same alloy via plasma synthesis, where Al was codeposited with O to form an amorphous Al2O3 film, 0.2 or 0.8 {mu}m thick. Subsequent heat treatment of the deposited film at 1000 C caused it to slowly transform to {alpha}-Al2… more

Date: September 1, 1996

Creator: Hou, P. Y.; Wang, Z.; Pruessner, K.; Alexander, K. B. & Brown, I. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department