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Thermophysical Properties of Heat Resistant Shielding Material

Description: This project was aimed at determining thermal conductivity, specific heat and thermal expansion of a heat resistant shielding material for neutron absorption applications. These data are critical in predicting the structural integrity of the shielding under thermal cycling and mechanical load. The measurements of thermal conductivity and specific heat were conducted in air at five different temperatures (-31 F, 73.4 F, 140 F, 212 F and 302 F). The transient plane source (TPS) method was used in the tests. Thermal expansion tests were conducted using push rod dilatometry over the continuous range from -40 F (-40 C) to 302 F (150 C).
Date: December 15, 2004
Creator: Porter, W.D.
Partner: UNT Libraries Government Documents Department

Environmental microcracking of [NZP] type ceramics

Description: NZP ceramics (sodium zirconium phosphate and its crystal structure analogs) have very low thermal expansion through a large temperature range. Some compositions, with a high degree of thermal expansion anisotropy, are prone to microcracking upon cooling to room temperature. The onset of microcracking is a function of sintering temperature and hence grain size. Subsequent thermal cycling affects the thermal expansion behavior of highly anisotropic compositions due to microcrack healing. Recently it has been determined that this microcracking behavior can be delayed or enhanced by controlling the atmosphere in which the ceramic is heated and cooled. The effects of various atmospheres on the thermal expansion of isotropic and anisotropic [NZP] compositions are presented.
Date: December 31, 1994
Creator: Jackson, T.B. & Porter, W.D.
Partner: UNT Libraries Government Documents Department

Oxidation and degradation of a plasma-sprayed thermal barrier coating system

Description: The isothermal oxidation behavior of thermal barrier coating (TBC) specimens consisting of single-crystal superalloy substrates, vacuum plasma-sprayed Ni-22Cr-10Al-1Y bond coatings and air plasma-sprayed 7.5 wt.% yttria stabilized zirconia top coatings was evaluated by thermogravimetric analysis at 1150{degrees}C for up to 200 hours. Coating durability was assessed by furnace cycling at 1150{degrees}C. Coatings and reaction products were identified by x-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy.
Date: April 1, 1996
Creator: Haynes, J.A.; Ferber, M.K. & Porter, W.D.
Partner: UNT Libraries Government Documents Department

Thermal transport properties of grey cast irons

Description: Thermal diffusivity and thermal conductivity of grey cast iron have been measured as a function of graphite flake morphology, chemical composition, and position in a finished brake rotor. Cast iron samples used for this investigation were cut from ``step block`` castings designed to produce iron with different graphite flake morphologies resulting from different cooling rates. Samples were also machined from prototype alloys and from production brake rotors representing a variation in foundry practice. Thermal diffusivity was measured at room and elevated temperatures via the flash technique. Heat capacity of selected samples was measured with differential scanning calorimetry, and these results were used to calculate the thermal conductivity. Microstructure of the various cast iron samples was quantified by standard metallography and image analysis, and the chemical compositions were determined by optical emission spectroscopy.
Date: October 1, 1996
Creator: Hecht, R.L.; Dinwiddie, R.B.; Porter, W.D. & Wang, Hsin
Partner: UNT Libraries Government Documents Department

Isothermal and cyclic oxidation of an air plasma-sprayed thermal barrier coating system

Description: Thermogravimetric methods for evaluating bond coat oxidation in plasma-sprayed thermal barrier coating (TBC) systems were assessed by high-temperature testing of TBC systems with air plasma-sprayed (APS) Ni-22Cr-10Al-1Y bond coatings and yttria-stabilized zirconia top coatings. High-mass thermogravimetric analysis (at 1150{sup degrees}C) was used to measure bond coat oxidation kinetics. Furnace cycling was used to evaluate APS TBC durability. This paper describes the experimental methods and relative oxidation kinetics of the various specimen types. Characterization of the APS TBCs and their reaction products is discussed.
Date: August 1, 1996
Creator: Haynes, J.A.; Ferber, M.K.; Porter, W.D. & Rigney, E.D.
Partner: UNT Libraries Government Documents Department

The effect of thermal aging on the thermal conductivity of plasma sprayed and EB-PVD thermal barrier coatings

Description: Thermal barrier coatings (TBCs) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBCs is of primary importance. Electron beam-physical vapor deposition (EV-PVD) and air plasma spraying (APS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The density of the APS coatings was controlled by varying the spray parameters. The low density APS yttria-partially stabilized zirconia (yttria-PSZ) coatings yielded a thermal conductivity that is lower than both the high density APS coatings and the EB-PVD coatings. The thermal aging of both fully and partially stabilized zirconia are compared. The thermal conductivity of the coatings permanently increases upon exposure to high temperatures. These increases are attributed to microstructural changes within the coatings. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the EB-PVD coatings are less susceptible to thermal aging effects, results suggest that they typically have a higher thermal conductivity than APS coatings before thermal aging. The increases in thermal conductivity due to thermal aging for plasma sprayed partially stabilized zirconia have been found to be less than for plasma sprayed fully stabilized zirconia coatings.
Date: May 1, 1996
Creator: Dinwiddie, R.B.; Beecher, S.C.; Porter, W.D. & Nagaraj, B.A.
Partner: UNT Libraries Government Documents Department

The effects of thermal cycling on the physical and mechanical properties of [NZP] ceramics

Description: The [NZP] ceramics, sodium zirconium phosphate and its crystal structure analogs, are noted for their very low thermal expansion characteristics. What has not been widely studied is the effect of thermal cycling on physical and mechanical properties. Two [NZP] compositional series were selected (Ba{sub 1+x}Zr{sub 4}P{sub 6{minus}2x}Si{sub 2x}O{sub 24} and Ca{sub 1{minus}x}Sr{sub x}Zr{sub 4}P{sub 6}O{sub 24}) that exhibit varying bulk thermal expansion from positive to negative and varying degrees of thermal expansion anisotropy. The effect of thermal cycling, to 1,250 C, on the bulk thermal expansion and flexural strength of these ceramics is discussed in relationship to changes in density, thermal expansion anisotropy and microstructure.
Date: December 31, 1994
Creator: Jackson, T.B.; Limaye, S.Y. & Porter, W.D.
Partner: UNT Libraries Government Documents Department

Application of the metal compression forming process for the production of an aluminum alloy component

Description: Metal Compression Forming (MCF) is a variant of the squeeze casting process, in which molten metal is allowed to solidify under pressure in order to close porosity and form a sound part. MCF applies pressure on the entire mold face, thereby directing pressure on all regions of the casting. It also enhances the solidification rate of the metal, promoting a very fine grain structure which results in improved properties. Consequently, the process is capable of producing parts with properties close to that of forgings, while retaining the near net shape, complex geometry, and relatively low cost of the casting process.
Date: January 1, 1997
Creator: Viswanathan, S.; Porter, W.D.; Ren, W. & Purgert, R.M.
Partner: UNT Libraries Government Documents Department

Production of A357 motor mount bracket by the metal compression forming process

Description: The use of aluminum alloy castings for safety critical structural components such as engine mount brackets, steering knuckles, and control arms, offers significant opportunities for achieving weight reduction in automobiles, since they are typically about half the weight of the steel, cast iron, or ductile iron component that they replace. Metal Compression Forming (MCF) is a variant of the squeeze casting process, in which molten metal is allowed to solidify under pressure in order to close porosity and form a sound part. However, the MCF process applies pressure on the entire mold face, thereby directing pressure on all regions of the casting and producing a uniformly sound part. The process is capable of producing parts with properties close to those of forgings, while retaining the near net shape, complexity in geometry, and relatively low cost of the casting process. The paper describes the casting process development involved in the production of an aluminum A357 alloy motor mount bracket, including the use of a filling and solidification model to design the gating and determine process parameters. Tensile properties of the component are presented and correlated with those of forged components. Limited fatigue properties obtained by fully reversed strain controlled testing are also presented.
Date: September 1, 1997
Creator: Viswanathan, S.; Brinkman, C.R.; Porter, W.D. & Purgert, R.M.
Partner: UNT Libraries Government Documents Department

Metal Compression Forming of aluminum alloys and metal matrix composites

Description: Metal Compression Forming (MCF) is a variant of the squeeze casting process, in which molten metal is allowed to solidify under pressure in order to close porosity and form a sound part. However, the MCF process applies pressure on the entire mold face, thereby directing pressure on all regions of the casting and producing a uniformly sound part. The process is capable of producing parts with properties close to those of forgings, while retaining the near net shape, complexity in geometry, and relatively low cost of the casting process.
Date: February 1, 2000
Creator: Viswanathan, S.; Ren, W.; Porter, W.D.; Brinkman, C.R.; Sabau, A.S. & Purgert, R.M.
Partner: UNT Libraries Government Documents Department

Development of sol-gel derived coating for NICALON{sup TM}/SiC composites

Description: Mullite and aluminum titanate precursor polymeric sols were developed for applying as coatings on Nicalon{trademark} fabrics and tows. A Nicalon{trademark}/SiC composite with a mullite interface was fabricated. The mullite precursor interface coatings were applied by a vacuum infiltration method and the SiC matrix was deposited by a forced flow chemical vapor infiltration process. Thin, uniform mullite interface coatings were obtained. However, the Nicalon{trademark}/SiC composite exhibited brittle fracture. Mullite and alumina-titania coatings were applied on Nicalon{trademark} tows and the effect of heat treatment at 1000{degrees}C in air is discussed.
Date: May 1, 1996
Creator: Shanmugham, S.; Liaw, P.K.; Stinton, D.P.; Besmann, T.M.; More, K.L.; Bleier, A. et al.
Partner: UNT Libraries Government Documents Department

Microstructural Characterization of Water-Rich Boehmite (AlO(OH)): TEM Correlation of Apparently Divergent XRD and TGA Results

Description: An understanding of the solid-phase thermodynamics and aqueous speciation of aluminum is critical to our ability to understand and predict processes in a wide variety of geologic and industrial settings. Boehmite (AIO(OH)) is an important phase in the system Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O that has been the subject of a number of structural and thermodynamic studies since its initial synthesis [l] and discovery in nature [2]. Unfortunately, it has long been recognized that thermogravimetric analysis (TGA) of both synthetic and natural boehmite samples (that appear well crystallized by powder XRD methods) yields significant excess water - typically losing 16-16.5 wt. % on heating as compared with a nominal expected weight loss of 15.0 wt. % [3,4]. The boehmite used in our experiments was synthesized hydrothermally from acid-washed gibbsite (Al(OH)<suv>3</sub>) at 200°C. Powder XRD and SEM examination showed no evidence of the presence a contaminant phase. The TGA patterns do not suggest that this is due to adsorbed water, so a structural source is likely. We therefore undertook to examine this material by TEM to clarify this phenomenon.
Date: August 1999
Creator: Allard, L. F.; Anovitz, L. M.; Benezeth, P.; Coffey, D. W.; Palmer, D. A.; Porter, W. D. et al.
Partner: UNT Libraries Government Documents Department