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Research on microwave joining of SiC. Final report

Description: Work on microwave joining of sintered SiC has showed that small samples could be jointed using Si interlayer (applied as pressed powder); SEM showed a smooth, homogeneous interlayer 50 {mu}m wide. Objective of this contract is to optimize these joints. Results showed that the interlayer could be reduced to 10-20 {mu}m using an oil-based slurry made from Si powder, and to less than 5 {mu}m by plasma spraying Si on one of the SiC surfaces. Direct joints were made in reaction bonded SiC, using the residual Si. Excellent joints with good mechanical properties were obtained in both small specimens and in small scale tube assemblies like in heat exchanger and radiant burner tubes. In situ reaction synthesis from powders to produce a SiC-TiC-SiC joint was demonstrated, as well feasibility of producing SiC from microwave-assisted decomposition of polymer precursors. Finally, new applicator designs, including a compound adjustable iris and a mitered bend single mode cavity, were demonstrated to provide improved heating of larger and longer specimens. This work provides the foundation for scaleup of microwave joining to SiC components for industrial applications.
Date: June 30, 1993
Partner: UNT Libraries Government Documents Department

Investigation into the joining of MoSi{sub 2} to 316L stainless steel

Description: Partial transient liquid phase joining and low temperature brazing were applied in joining MoSi{sub 2} to 316L ss. Exploratory studies were carried out on various interlayer materials. Mechanical, physical, and chemical compatibilities between various interlayers, brazing material, and substrate materials were investigated. Effect of thermal expansion mismatch between various components of the joint on the overall joint integrity was also studied. Preliminary findings are outlined.
Date: October 1, 1996
Creator: Vaidya, R.U.; Bartlett, A.H.; Conzone, S.D. & Butt, D.P.
Partner: UNT Libraries Government Documents Department

Solid-state joining of ultrahigh carbon steels

Description: A joining study of these steels was initiated to determine the feasibility of using ultrahigh carbon steels in structural applications. The high carbon content (1.5 wt%) in these steels and the desire to maintain the superplastic microstructure limit the use of conventional arc-welding processes. We chose two solid-state joining processes: diffusion bonding and inertia friction welding. Preliminary results show that sound bonds can be obtained with tensile properties nearly equal to those of the base metal. Of three UHC steels bonded by both inertia-friction welding and diffusion- bonding processes, the one with the lowest aluminum content had the best overall properties. Diffusion bonding with a nickel interlayer showed the most promising results for the UHC steel containing 1.6 wt% aluminum. The properties of inertia-friction-welded steels can be improved by a post-weld heat treatment.
Date: April 22, 1993
Creator: Sunwoo, A.J.
Partner: UNT Libraries Government Documents Department

Task 6.3/6.7.4 - Engineering Performance of Advanced Structural Materials

Description: Future energy systems will be required to fire low-grade fuels and meet higher energy conversion efficiencies than today's systems. The steam cycle used at present is-limited to a maximum temperature of 550C, because above that the stainless steel tubes deform and corrode excessively. However, to boost efficiency significantly, much higher working fluid temperatures are required. Although high-temperature alloys will suffice for the construction of these components in the near term, the greatest efficiency increases can only be reached with the use of advanced structural ceramics
Date: November 16, 1998
Creator: Hurley, John P. & Kay, John P.
Partner: UNT Libraries Government Documents Department

Joining NZP ceramics. Final report

Description: Objective was to assess techniques for joining NZP ceramics, a new family of ceramic materials that have low coefficient of thermal expansion, low thermal conductivity, and excellent thermal-shock resistance. Initially, the authors evaluated laser-beam welding over volatile fluxing agents (ferric oxide, copper oxide, boric acid, and boron nitride). They also examined other laser, arc-welding, brazing, and cold joining techniques. The NZP materials were capable of sustaining the thermal stresses associated with these joining processes without substantial cracking. Of the volatile fluxes, only the copper oxide promoted weld fusion. Efforts to accomplish fusion by laser-beam welding over copper, titanium, stainless steel, yttrium barium copper oxide, fused silica glass, and mullite/alumina were unsuccessful. Gas-tungsten arc welding accompanied by porosity, irregularities, and cracking was achieved on copper sheet sandwiched between NZP tiles. Attempts at conventional oxy-acetylene welding and torch brazing were unproductive. Silica-based oxide mixtures and copper oxide-based materials show potential for development into filler materials for furnace brazing, and phosphate-based cements show promise as a means of cold joining.
Date: September 26, 1995
Creator: Nicklas, K.D.; Richey, M.W.; Holcombe, C.E. Jr. & Santella, M.L.
Partner: UNT Libraries Government Documents Department

Joining of Ion Transport Membranes Using a Novel Transient Liquid Phase Process

Description: The feasibility of a novel transient liquid phase (TLP) joining method has been demonstrated in joining La{sub 0.9}Ca{sub 0.1}FeO{sub 3} materials. Metal oxide powders were processed to form the TLP compositions which were used in the joining process. The method has been successful in producing joint interfaces that effectively disappear, as they are the same material and have the same properties as the joined parts. The feasibility of the method has been demonstrated for a single system, but many systems where the method can potentially be applied have been identified.
Date: August 30, 2006
Creator: Butt, Darryl P.
Partner: UNT Libraries Government Documents Department

Pressure Resistance Welding of High Temperature Metallic Materials

Description: Pressure Resistance Welding (PRW) is a solid state joining process used for various high temperature metallic materials (Oxide dispersion strengthened alloys of MA957, MA754; martensitic alloy HT-9, tungsten etc.) for advanced nuclear reactor applications. A new PRW machine has been installed at the Center for Advanced Energy Studies (CAES) in Idaho Falls for conducting joining research for nuclear applications. The key emphasis has been on understanding processing-microstructure-property relationships. Initial studies have shown that sound joints can be made between dissimilar materials such as MA957 alloy cladding tubes and HT-9 end plugs, and MA754 and HT-9 coupons. Limited burst testing of MA957/HT-9 joints carried out at various pressures up to 400oC has shown encouraging results in that the joint regions do not develop any cracking. Similar joint strength observations have also been made by performing simple bend tests. Detailed microstructural studies using SEM/EBSD tools and fatigue crack growth studies of MA754/HT-9 joints are ongoing.
Date: October 1, 2010
Creator: Jerred, N.; Zirker, L.; Charit, I.; Cole, J.; Frary, M.; Butt, D. et al.
Partner: UNT Libraries Government Documents Department

Fast Tree: Computing Large Minimum-Evolution Trees with Profiles instead of a Distance Matrix

Description: Gene families are growing rapidly, but standard methods for inferring phylogenies do not scale to alignments with over 10,000 sequences. We present FastTree, a method for constructing large phylogenies and for estimating their reliability. Instead of storing a distance matrix, FastTree stores sequence profiles of internal nodes in the tree. FastTree uses these profiles to implement neighbor-joining and uses heuristics to quickly identify candidate joins. FastTree then uses nearest-neighbor interchanges to reduce the length of the tree. For an alignment with N sequences, L sites, and a different characters, a distance matrix requires O(N^2) space and O(N^2 L) time, but FastTree requires just O( NLa + N sqrt(N) ) memory and O( N sqrt(N) log(N) L a ) time. To estimate the tree's reliability, FastTree uses local bootstrapping, which gives another 100-fold speedup over a distance matrix. For example, FastTree computed a tree and support values for 158,022 distinct 16S ribosomal RNAs in 17 hours and 2.4 gigabytes of memory. Just computing pairwise Jukes-Cantor distances and storing them, without inferring a tree or bootstrapping, would require 17 hours and 50 gigabytes of memory. In simulations, FastTree was slightly more accurate than neighbor joining, BIONJ, or FastME; on genuine alignments, FastTree's topologies had higher likelihoods. FastTree is available at http://microbesonline.org/fasttree.
Date: July 31, 2009
Creator: N. Price, Morgan; S. Dehal, Paramvir & P. Arkin, Adam
Partner: UNT Libraries Government Documents Department

Contamination and solid state welds.

Description: Since sensitivity to contamination is one of the verities of solid state joining, there is a need for assessing contamination of the part(s) to be joined, preferably nondestructively while it can be remedied. As the surfaces that are joined in pinch welds are inaccessible and thus provide a greater challenge, most of the discussion is of the search for the origin and effect of contamination on pinch welding and ways to detect and mitigate it. An example of contamination and the investigation and remediation of such a system is presented. Suggestions are made for techniques for nondestructive evaluation of contamination of surfaces for other solid state welds as well as for pinch welds. Surfaces that have good visual access are amenable to inspection by diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. Although other techniques are useful for specific classes of contaminants (such as hydrocarbons), DRIFT can be used most classes of contaminants. Surfaces such as the interior of open tubes or stems that are to be pinch welded can be inspected using infrared reflection spectroscopy. It must be demonstrated whether or not this tool can detect graphite based contamination, which has been seen in stems. For tubes with one closed end, the technique that should be investigated is emission infrared spectroscopy.
Date: May 1, 2007
Creator: Mills, Bernice E.
Partner: UNT Libraries Government Documents Department

Research on microwave joining of SiC

Description: Results: identification of optimum joining temperature range for reaction bonded Si carbide at 1420-1500 C; demonstration that specimens joined within this range have fracture roughness greater than as-received material; and demonstration of ability to use SiC formed in situ from the decomposition of polycarbosilane as a joining aid for sintered Si carbide. In the latter case, the interlayer material was also shown to fill any pores in the joining specimens near the interlayer. Together with the demonstration of leaktight joints between tube sections of reaction bonded and sintered SiC under the previous contract, these results provide the foundation for scaleup to joining of the larger and longer tubes needed for radiant burner and heat exchanger tube assemblies. The formation of SiC in situ is important because maintaining roundness of these large tubes is a technical challenge for the tube manufacturer, so that formation of a leaktight joint may require some degree of gap filling.
Date: July 31, 1995
Creator: Silberglitt, R.
Partner: UNT Libraries Government Documents Department

Indentation and oxidation studies on silicon nitride joints

Description: Si nitride ceramics have been joined with a Y oxide-SiO{sub 2} interlayer. A 1:2 molar ratio of Y{sub 2}O{sub 3} to SiO{sub 2} was chosen to obtain the desired Y{sub 2}Si{sub 2}O{sub 7} stoichiometry, which should give the interlayer better oxidation resistance compared to other interlayer materials. Mechanical characterization of the joints performed by indentation shows it to have good room temperature strength.
Date: May 1, 1996
Creator: Gopal, M.; De Jonghe, L.C. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Areal array jetting device for ball grid arrays

Description: Package designs for microelectronics devices have moved from through-hole to surface mount technology in order to increase the printed wiring board real estate available by utilizing both sides of the board. The traditional geometry for surface mount devices is peripheral arrays where the leads are on the edges of the device. As the technology drives towards high input/output (I/O) count (increasing number of leads) and smaller packages with finer pitch (less distance between peripheral leads), limitations on peripheral surface mount devices arise. A solution to the peripheral surface mount issue is to shift the leads to the area under the device. This scheme is called areal array packaging and is exemplified by the ball grid array (BGA) package. In a BGA package, the leads are on the bottom surface of the package in the form of an array of solder balls. The current practice of joining BGA packages to printed wiring boards involves a hierarchy of solder alloy compositions. A high melting temperature ball is typically used for standoff. A promising alternative to current methods is the use of jetting technology to perform monolithic solder ball attachment. This paper describes an areal array jetter that was designed and built to simultaneously jet arrays of solder balls directly onto BGA substrates.
Date: August 1, 1997
Creator: Frear, D.R.; Yost, F.G.; Schmale, D.T. & Essien, M.
Partner: UNT Libraries Government Documents Department

Task 6.3 -- Engineering performance of advanced structural materials. Semi-annual report, January 1--June 30, 1995

Description: SiC sublimes without melting at temperatures over 2,000 C. This makes SiC difficult to use in the fabrication of large structures, because pieces made from SiC cannot be joined together in the same way that metals can be welded. Therefore, the size of the monolithic ceramic structures that can be manufactured are limited by the size of the sintering furnaces (approximately 10 feet for sintered alpha silicon carbide). In order to make larger objects such as heat exchangers, many small ceramic pieces must be fused or joined. In addition, repair of the objects will require the use of field joining techniques. At present, no joining techniques for high-temperature structural ceramics are routinely available. The objective of this work at the Energy and Environmental Research Center (EERC) is to develop a patentable technique for joining large silicon based advanced ceramics in the field. The key to developing a successful technique will be the use of reactive joining compounds to lower the joining temperature but without leaving continuous channels of unreacted compounds that can weaken the joint or be conduits for corrosion at temperatures over 1,400 C. Special efforts will be made in this project to transfer the developed technologies to the materials industry via licensing agreements through the EERC Foundation.
Date: August 1, 1997
Creator: Hurley, J.P.; Kay, J.; Nowok, J.W. & Schuster, M.
Partner: UNT Libraries Government Documents Department

Joining SI3N4 for Advanced Turbomachinery Applications

Description: The main objective of this project was to develop reliable, low-cost techniques for joining silicon nitride (Si{sub 3}N{sub 4}) to itself and to metals. For Si{sub 3}N{sub 4} to be widely used in advanced turbomachinery applications, joining techniques must be developed that are reliable, cost-effective, and manufacturable. This project addressed those needs by developing and testing two Si{sub 3}N{sub 4} joining systems; oxynitride glass joining materials and high temperature braze alloys. Extensive measurements were also made of the mechanical properties and oxidation resistance of the braze materials. Finite element models were used to predict the magnitudes and positions of the stresses in the ceramic regions of ceramic-to-metal joints sleeve and butt joints, similar to the geometries used for stator assemblies.
Date: July 1, 2000
Partner: UNT Libraries Government Documents Department

Superplasticity and joining of zirconia-based ceramics

Description: Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C.
Date: December 10, 1999
Creator: Dominguez-Rodriguez, A.; Gutierrez-Mora, F.; Jimenez-Melendo, M.; Chaim, R. & Routbort, J. L.
Partner: UNT Libraries Government Documents Department

Task 6.3 - Engineering Performance of Advanced Structural Materials Semi-annual report, July 1- December 31, 1996.

Description: The objective of this work by the Energy {ampersand} Environmental Research Center (EERC) is to assist in the development of new materials that can be used for the construction of high-temperature components in advanced energy systems. This work will include the development of data on corrosion resistance of selected high- temperature alloys and the development of a patentable technique for joining large silicon-based advanced ceramics in the field. The key to developing a successful joining technique will be the use of reactive joining compounds to lower the joining temperature without leaving continuous channels of unreacted compounds that can weaken the joint at temperatures over 1400{degrees}C or serve as conduits for transport of corrodents. Special efforts will be made in this project to transfer the developed technologies to the materials industry via licensing agreements through the EERC Foundation.
Date: 1997
Creator: Kay, J. P.; Hurley, J. P. & Roling, T. A.
Partner: UNT Libraries Government Documents Department

Low temperature reactive bonding

Description: Disclosed is a joining technique that requires no external heat source and generates very little heat. It involves the reaction of thin multilayered films deposited on faying (closely fit or joining) surfaces to create a stable compound that functions as an intermediate or braze material in order to create a high strength bond. While high temperatures are reached in the reaction of the multilayer film, very little heat is generated because the films are very thin. It is essentially a room temperature joining process. It can be used for joining silicon wafers and integrated circuits.
Date: June 23, 1995
Creator: Makowiecki, D.M. & Bionta, R.M.
Partner: UNT Libraries Government Documents Department

Effects of processing conditions and ambient environment on the microstructure and fracture strength of copper/niobium/copper interlayer joints for alumina

Description: Partial transient liquid phase (PTLP) bonding is a technique which can be used to join ceramics with metals and is used to form niobium-based joints for alumina. The principal advantage to PTLP bonding is that it enables refractory joints to be fabricated at temperatures below those typically required by solid state diffusion bonding. A thorough review of the important parameters (chemical compatibility, thermal expansion match, sufficient wettability of the liquid phase on the solid phases) in choosing a joining material for ceramics by the PTLP method is provided. As in conventional PTLP joining, the current study uses thin (=3 (mu)m) copper layers sandwiched between the alumina (bulk) and niobium (127 (mu)m). However, unlike the case of copper/nickel/copper obium is limited. Consequently, the copper is not entirely dissolved in the process, resulting in a two phase (copper-rich and niobium-rich phases) microstructure. Different processing conditions (temperature and applied load) result in different morphologies of the copper-rich and niobium-rich phases at the interface. These different microstructures exhibit distinct strength characteristics. Extended annealing of as-processed joints can influence the strengths differently depending on the ambient partial oxygen pressure at the annealing temperature. The focus of this work is to correlate processing conditions, microstructure, and resulting joint strength. Under optimum processing conditions (1400 degrees C, 2.2 MPa), joints with strengths in excess of 200 MPa at 1200 degrees C are fabricated.
Date: December 15, 1999
Creator: Marks, Robert Alan
Partner: UNT Libraries Government Documents Department

Microwave-assisted pyrolysis of SiC and its application to joining

Description: Microwave energy has been used to pyrolyze silicon carbide from commercially available polycarbosilane precursor. The pyrolysis was performed on SiC surfaces having various surface treatments, to identify conditions which improve the wetting and adherence. Grinding and etching of the surfaces in hydrofluoric (HF) acid promotes the bonding of precursor derived ceramic to the SiC ceramic. Finally, the polycarbosilane precursor mixed with fine silicon carbide powder was used as the interlayer material to join silicon carbide specimens.
Date: July 1995
Creator: Ahmad, I.; Silberglitt, R. & Shan, T. A.
Partner: UNT Libraries Government Documents Department

Needs and Membership in Terrorist Organizations

Description: One key to reducing terrorism may be to understand why individuals join terror groups, and to find ways to meet their needs through alternatives to discourage membership in terrorist organizations. The study introduces the hierarchy of needs framework to capture all previous pieces of explanations on why individuals join terror groups under one big umbrella, in order to see the big picture. It does not do a meta-analysis, but rather tests the framework. This study is designed to find out what perceived needs commonly motivate individuals to join terror groups in general and specific terror groups in particular. The research uses Turkey's terrorism experience as a case study which is supported with data from real terrorist in Turkey. Findings of the descriptive analyses show that majority joined a terror group due to social and affiliative needs. The remaining analyses (bivariate, cross-tabulation and binary logistic regression) show that confitents who perceived esteem and recognition were more likely to become members of other/leftist terror groups, and that rightist terror group members in Turkey tend to have higher education. Education mainly affects a confitent's perception of two needs: social and affiliation and self-actualization. Other demographic variables (age group, region of birth, marital status) die not yield any significant relation with membership in terror groups.
Date: December 2009
Creator: Ekici, Siddik
Partner: UNT Libraries

Development of automated welding process for field fabrication of thick walled pressure vessels. Fourth quarter technical progress report for period ending September 30, 1979

Description: Progress in developing an automated welding process for the field fabrication of thick walled pressure vessels is reported. Plans for the demonstration facility, for nondestructive testing, and for the procurement of materials are discussed. (LCL)
Date: January 1, 1979
Partner: UNT Libraries Government Documents Department

Kinetics of Reactive Wetting

Description: The importance of interfacial processes in materials joining has a long history. A significant amount of work has suggested that processes collateral to wetting can affect the extent of wetting and moderate or retard wetting rate. Even very small additions of a constituent, known to react with the substrate, cause pronounced improvement in wetting and are exploited in braze alloys, especially those used for joining to ceramics. The wide diversity of processes, such as diffusion, chemical reaction, and fluxing, and their possible combinations suggest that various rate laws should be expected for wetting kinetics depending on the controlling processes. These rate laws are expected to differ crucially from the standard fluid controlled wetting models found in the literature. Voitovitch et al. and Mortensen et al. have shown data that suggests diffusion control for some systems and reaction control for others. They also presented a model of wetting kinetics controlled by the diffusion of a constituent contained by the wetting fluid. In the following a model will be constructed for the wetting kinetics of a small droplet of metal containing a constituent that diffuses to the wetting line and chemically reacts with a flat, smooth substrate. The model is similar to that of Voitovitch et al. and Mortensen et al. but incorporates chemical reaction kinetics such that the result contains both diffusion and reaction kinetics. The model is constructed in the circular cylinder coordinate system, satisfies the diffusion equation under conditions of slow flow, and considers diffusion and reaction at the wetting line to be processes in series. This is done by solving the diffusion equation with proper initial and boundary conditions, computing the diffusive flux at the wetting line and equating this to both the convective flux and reaction flux. This procedure is similar to equating the current flowing in ...
Date: September 9, 1999
Partner: UNT Libraries Government Documents Department