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Low-temperature fabrication of transparent silicon nitride

Description: Feasibility of producing nano-phase Si{sub 3}N{sub 4} with improved properties, and ultrafine-grained nano-phase transparent Si{sub 3}N{sub 4} by working with amorphous nano-size powders without the use of sintering aids was investigated. The approach uses cryogenic compaction of nano-size particles under liquid nitrogen followed by pressureless sintering.
Date: May 31, 1994
Creator: Chen, Wei; Malghan, S. G.; Danforth, S. C. & Pechenik, A.
Partner: UNT Libraries Government Documents Department

Modeling of thermal stresses in welds

Description: The transient stress distribution in a Sigmajig test specimen resulting from mechanical and thermal loading was calculated for a Type 316 stainless steel specimen using finite element analysis. The study attempted to resolve the relationship between the dynamic stress distribution, particularly near the trailing edge of the pool, and the observed cracking behavior in the test specimen. The initiation and propagation of the crack during welding was visually monitored using a stroboscopic vision system. The numerical results were used to understand the initiation and propagation of hot-cracks during controlled welding of a specimen subjected to external restraint.
Date: December 31, 1993
Creator: Zacharia, T. & Aramayo, G. A.
Partner: UNT Libraries Government Documents Department

Removal of wax and stickies from OCC by flotation. Progress report No. 3, July 1--September 30, 1998

Description: In this quarter we completed low consistency laboratory pulping trials. Pulping results were analyzed in terms of defibering index or yield and the concentration of free wax. The objective of these trials is to identify pulping conditions that will give higher yield and higher concentration of free wax. The yields from low consistency pulping trials ranged from 90 to 99% based on 6-cut laboratory screen rejects. In general, high temperatures (140-150{degrees}F) and high pH (9.5-10) conditions resulted in higher yield and the generation of free wax. Factors such as rotor speed and the gap (between the rotor and grate) were not significant in affecting defibering. Generally, the turbidities of filtrates from wax-contaminated pulps increased with increase in temperature and/or pH. The filtrate turbidity indicated the relative concentration of finely dispersed wax that could be removed from pulp dewatered on a 30 {micro}m filter paper. Preliminary experiments were conducted to study flotation conditions necessary for effective removal of wax from pulp. Factors which are important for effective flotation include flotation time, volume of air, surfactant concentration and type, and low temperature. Future plans include additional flotation trials to better optimize conditions. Other contaminant types include pressure sensitive adhesives and hot melts will also be examined. This will be followed by pilot plant and mill trials.
Date: November 1, 1998
Creator: Dosh, M. R.; Dyer, J.; Heise, O. & Cao, B.
Partner: UNT Libraries Government Documents Department

Annual report for Ion Replacement Program

Description: Ion replacement electrorefining is an innovative electrochemical approach to purifying and separating metals. This approach overcomes the shortcomings of conventional electrorefining and has the potential for processing a wider range of metals and metal halide salts. Salt waste is also minimized with this approach. The key element of ion replacement electrorefining is the ion replacement electrode. This electrode allows a decoupling of the electrotransport process into two separate steps, anodic dissolution and cathodic deposition. Three key accomplishments described in this report that demonstrate the feasibility of ion replacement electrorefining are: (1) we have identified a suitable sodium/{beta}{double_prime}-alumina/molten salt electrolyte system that functions reproducibly at 723 K, (2) we have oxidized and deposited dysprosium, lanthanum, uranium, and titanium by using a sodium ion replacement electrode. In several experiments, an actual separation of dysprosium and lanthanum was observed, and (3) we have identified a metal alloy, Li{sub x}Sb, as an alternative ion replacement electrode. The next stage in the program is the design, construction, and testing of a laboratory-scale electrorefiner. Follow-on development with funding from industrial and federal sponsors is being pursued.
Date: July 1, 1993
Creator: Tomczuk, Z.; Willit, J. L. & Fischer, A. K.
Partner: UNT Libraries Government Documents Department

Calculations of material removal, removal rate, and Preston coefficient in continuous lapping/polishing machines

Description: Lapping and polishing machines usually do not have deterministic model to pre-determine removal rate and total material to be removed. The removal process is mainly affected by relative motion between the lap and the substrates, by load applied, and by mechano-chemical characteristics of the substrate material, as well as the abrasive and lap materials. Therefore, frequent measurements of the removal is necessary. This paper, written for optical technicians, includes formulas to calculate material removal from mass loss and removal rate from mass loss during operation. Establishing the removal rate helps by reducing the frequency of intermediate thickness measurements. The paper also includes the calculation of Preston coefficient, which is a measure of lapping process efficiency.
Date: October 18, 1993
Creator: Hed, P. P.
Partner: UNT Libraries Government Documents Department

Tool compensation using statistical process control on complex milling operations

Description: In today`s competitive manufacturing environment, many companies increasingly rely on numerical control (NC) mills to produce products at a reasonable cost. Typically, this is done by producing as many features as possible at each machining operation to minimize the total number of shop hours invested per part. Consequently, the number of cutting tools involved in one operation can become quite large since NC mills have the capacity to use in excess of 100 cutting tools. As the number of cutting tools increases, the difficulty of applying optimum tool compensation grows exponentially, quickly overwhelming machine operators and engineers. A systematic method of managing tool compensation is required. The name statistical process control (SPC) suggests a technique in which statistics are used to stabilize and control a machining operation. Feedback and control theory, the study of the stabilization of electronic and mechanical systems, states that control can be established by way of a feedback network. If these concepts were combined, SPC would stabilize and control manufacturing operations through the incorporation of statistically processed feedback. In its simplest application, SPC has been used as a tool to analyze inspection data. In its most mature application, SPC can be the link that applies process feedback. The approach involves: (1) identifying the significant process variables adjusted by the operator; (2) developing mathematical relationships that convert strategic part measurements into variable adjustments; and (3) implementing SPC charts that record required adjustment to each variable.
Date: March 1, 1994
Creator: Reilly, J. M.
Partner: UNT Libraries Government Documents Department

The effect of process parameters on the thermal conditions during moving mold ESR

Description: Several experimental melts were conducted using a moving mold electroslag remelting furnace. The conditions of electrode immersion depth, slag cap thickness, and melt current were varied. Mold wall temperatures and slag pool temperatures were measured and the heat flux through the mold wall was calculated. The relationships between varying ESR melt parameters and the resultant thermal conditions were examined. The thermal profile of the mold, the heat transfer to the mold coolant total and fractional, and the formation of a slag skin were studied.
Date: September 1, 1994
Creator: Heilman, J. E. & Damkroger, B. K.
Partner: UNT Libraries Government Documents Department

Application of a dimensionless parameter model for Laser Beam Welding

Description: A new dimensionless parameter model for continuous wave laser welding that relates the size of the weld to the energy absorbed by the part is described. The model has been experimentally validated previously through calorimetric determinations of the net heat input and metallographic measurements of the weld size. It will be shown that both the melting efficiency and energy transfer efficiency for LBW are quite variable and need to be considered when selecting processing conditions. Specific applications will be detailed in order to observe the simplicity and value of the model in laser weld process development. It will be shown that by using certain dimensionless parameters one can determine the energy transfer efficiency and thereby correctly select processing conditions that more fully utilize the available laser output power. In applications where minimizing heat input to the surrounding weldment is paramount, the dimensionless parameters can be used to select conditions that maximize melting efficiency.
Date: September 1, 1994
Creator: Fuerschbach, P. W.
Partner: UNT Libraries Government Documents Department

Weld pool phenomena

Description: During welding, the composition, structure and properties of the welded structure are affected by the interaction of the heat source with the metal. The interaction affects the fluid flow, heat transfer and mass transfer in the weld pool, and the solidification behavior of the weld metal. In recent years, there has been a growing recognition of the importance of the weld pool transport processes and the solid state transformation reactions in determining the composition, structure and properties of the welded structure. The relation between the weld pool transport processes and the composition and structure is reviewed. Recent applications of various solidification theories to welding are examined to understand the special problems of weld metal solidification. The discussion is focussed on the important problems and issues related to weld pool transport phenomena and solidification. Resolution of these problems would be an important step towards a science based control of composition, structure and properties of the weld metal.
Date: September 1, 1994
Creator: David, S. A.; Vitek, J. M.; Zacharia, T. & DebRoy, T.
Partner: UNT Libraries Government Documents Department

Bench-scale synthesis of nanoscale materials

Description: A novel flow-through hydrothermal method used to synthesize nanoscale powders is introduced by Pacific Northwest Laboratory. The process, Rapid Thermal Decomposition of precursors in Solution (RTDS), combines high-pressure and high-temperature conditions to rapidly form nanoscale particles. The RTDS process was demonstrated on a laboratory scale and scaled up to accommodate production rates attractive to industry. The process is able to produce a wide variety of metal oxides and oxyhydroxides. The powders are characterized by scanning and transmission electron microscopic methods, surface-area measurements, and x-ray diffraction. Typical crystallite sizes are less than 20 nanometers, with BET surface areas ranging from 100 to 400 m{sup 2}/g. A description of the RTDS process is presented along with powder characterization results. In addition, data on the sintering of nanoscale ZrO{sub 2} produced by RTDS are included.
Date: December 1, 1993
Creator: Buehler, M. F.; Darab, J. G.; Matson, D. W. & Linehan, J. C.
Partner: UNT Libraries Government Documents Department

Characterization and processing of sintered products from Nano-crystalline powders generated by the RTDS method

Description: Large quantities of nano-crystalline zirconium oxide/oxyhydroxide and nickel-chromium oxide/oxyhydroxide particles agglomerated and sieved into +320/{minus}200 mesh powders have been produced using the rapid thermal decomposition of solutes (RTDS) method. Green compacts (approximately 40% theoretical density) prepared by cold-pressing the RTDS powders at pressures of 140-280-MPa were heated to form dense (86--91% theoretical density) ZrO{sub 2} or Ni{sub 50}Cr{sub 50}components. Dimensional changes in the compacts during heating were used to extract information about the sintering kinetics in these systems. At 800C, grain-boundary diffusion coupled with some surface diffusion are the dominant mechanisms contributing toward the observed densification in the ZrO{sub 2} system. The mechanism-independent activation energy for densification was determined to be 81-kJ/mol for the ZrO{sub 2} system and 56-kj/mol for the NiCr system.
Date: August 1, 1993
Creator: Darab, J. G.; Buehler, M. F.; Linehan, J. C. & Matson, D. W.
Partner: UNT Libraries Government Documents Department

Consolidation of Zircaloy-4 End Crops by Induction Melting

Description: The Oak Ridge Y-12 Plant is investigating the use of induction melting as a method of consolidating Zircaloy-4, a zirconium alloy used in the fabrication of submarine nuclear reactor cores. Knolls Atomic Power Laboratory (KAPL) furnished about 4000 lb of typical core material, also known as hardware, for use in evaluating induction melting as a method of consolidation. Three ingots were produced by the induction melting of hardware in a graphite crucible that was protected by a laminated coating specifically developed for this application. This report includes a description of both the equipment and the crucible coating materials used for this project, a discussion of results, and a production assessment of using this technique for full-scale consolidation.
Date: January 25, 1994
Creator: Bird, E. L.
Partner: UNT Libraries Government Documents Department

Feasibility of ceramic joining with high energy electron beams

Description: Joining structural ceramics is possible using high melting point metals such as Mo and Pt that are heated with a high energy electron beam, with the potential for producing joints with high temperature capability. A 10 MeV electron beam can penetrate through 1 cm of ceramic, offering the possibility of buried interface joining. Because of transient heating and the lower heat capacity of the metal relative to the ceramic, a pulsed high power beam has the potential for melting the metal without decomposing or melting the adjacent ceramic. The authors have demonstrated the feasibility of the process with a series of 10 MeV, 1 kW electron beam experiments. Shear strengths up to 28 NTa have been measured for Si{sub 3}N{sub 4}-Mo-Si{sub 3}N{sub 4}. These modest strengths are due to beam non-uniformity and the limited area of bonding. The bonding mechanism appears to be a thin silicide reaction layer. Si{sub 3}N{sub 4}-Si{sub 3}N{sub 4} joints with no metal layer were also produced, apparently bonded an yttrium apatite grain boundary phase.
Date: January 1, 1995
Creator: Turman, B. N.; Glass, S. J.; Halbleib, J. A.; Helmich, D. R.; Loehman, R. E. & Clifford, J. R.
Partner: UNT Libraries Government Documents Department

Nucleation and Growth of Cubic Boron Nitride Films Produced by Ion-Assisted Pulsed Laser Deposition

Description: We are studying the boron nitride system using a pulsed excimer laser to ablate from hexagonal BN (cBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25--800C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N{sub 2} source gases to produce BN films with a high percentage of sp{sup 3}-bonded cBN. In order to optimize growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp{sup 3}-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30--40 mn. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm{sup {minus}1} and the position decreases with growth time to a constant value of 1085 cm{sup {minus}1}. Since in bulk cBN this IR mode appears at 1065 cm{sup {minus}1}, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.
Date: December 31, 1993
Creator: Friedmann, T. A.; Medlin, D. L.; Mirkarimi, P. B.; McCarty, K. F.; Klaus, E. J.; Boehme, D. R. et al.
Partner: UNT Libraries Government Documents Department

Identification of nitriding mechanisms in high purity reaction bonded silicon nitride

Description: The rapid, low-temperature nitriding results from surface effects on the Si particles beginning with loss of chemisorbed H and sequential formation of thin amorphous Si nitride layers. Rapid complete conversion to Si{sub 3}N{sub 4} during the fast reaction can be inhibited when either too few or too many nuclei form on Si particels. Optimally, {approximately} 10 Si{sub 3}N{sub 4} nuclei form per Si particles under rapid, complete nitridation conditions. Nitridation during the slow reaction period appears to progress by both continued reaction of nonpreferred Si{sub 3}N{sub 4} growth interfaces and direct nitridation of the remaining Si/vapor interfaces.
Date: March 1, 1993
Creator: Haggerty, J. S.
Partner: UNT Libraries Government Documents Department

Tensile strength of dried gelcast green bodies

Description: Ceramic green bodies were prepared by three different techniques, dry pressing, slip casting, and gelcasting. The tensile strength of the green bodies was measured using a diametral compression test. It was found that the gelcast samples were from 2 to 20 times stronger than the conventionally formed green bodies. SEM examination of the gelcast samples revealed a homogeneous, brittle fracture surface indicating a very uniform distribution of the binder and excellent dispersion of the ceramic powder.
Date: April 1, 1994
Creator: Nunn, S. D.; Omatete, O. O.; Walls, C. A. & Barker, D. L.
Partner: UNT Libraries Government Documents Department

Bibliography of the technical literature of the Materials Joining Group, 1951--1991

Description: This document contains a listing of the written scientific information originating in the Materials Joining (formerly the Welding and Brazing Group), Metals and Ceramics Division, Oak Ridge National Laboratory during 1951 through June 1991. This registry of documents is as much as possible, in the order of issue date.
Date: December 1, 1991
Creator: David, S. A.; Goodwin, G. M. & Gardner, K.
Partner: UNT Libraries Government Documents Department

A transient FGM interlayer based approach to joining ceramics

Description: In most cases, functionally gradient materials have been designed to produce a desirable property gradient in a material or in a joint region. In this paper, the concept of a transient gradient structure is introduced. The function of the intentional property discontinuities in these multilayer interlayers is to facilitate processing of assemblies and materials combinations that would be difficult to process using conventional bonding approaches. Specifically, the methods make use of a thin or partial layer of a low melting point transient liquid phase to facilitate bonding via brazing, yet produce refractory joints. Several mechanisms for consuming the transient liquid former are outlined, and examples of interlayer designs that exploit these mechanisms are presented. Specific results from experiments joining alumina to alumina via Cu/Pt/Cu, Cu/Ni/Cu, Cu/Nb/Cu and Sn/Nb/Sn interlayers are presented.
Date: January 1, 1993
Creator: Glaeser, A. M.; Shalz, M. L.; Dalgleish, B. J. & Tomsia, A. P.
Partner: UNT Libraries Government Documents Department

Solid-state resistance upset welding: A process with unique advantages for advanced materials

Description: Solid-state resistance upset welding is suitable for joining many alloys that are difficult to weld using fusion processes. Since no melting takes place, the weld metal retains many of the characteristics of the base metal. Resulting welds have a hot worked structure, and thereby have higher strength than fusion welds in the same mate. Since the material being joined is not melted, compositional gradients are not introduced, second phase materials are minimally disrupted, and minor alloying elements, do not affect weldability. Solid-state upset welding has been adapted for fabrication of structures considered very large compared to typical resistance welding applications. The process has been used for closure of capsules, small vessels, and large containers. Welding emphasis has been on 304L stainless steel, the material for current applications. Other materials have, however, received enough attention to have demonstrated capability for joining alloys that are not readily weldable using fusion welding methods. A variety of other stainless steels (including A-286), superalloys (including TD nickel), refractory metals (including tungsten), and aluminum alloys (including 2024) have been successfully upset welded.
Date: December 31, 1993
Creator: Kanne, W. R. Jr.
Partner: UNT Libraries Government Documents Department

A model for the biaxial post-yield behavior of extruded powder aluminum at elevated temperature

Description: A model has been developed which describes the post-yield behavior of extruded powder aluminum tested biaxially in tension and torsion at elevated temperature. Plots of shear stress versus shear strain for the powder aluminum loaded in simple torsion show that the shear stress increases linearly to the yield point, then remains relatively constant in a pure plastic type of behavior. For the tension-torsion tests, there is an initial linear region up to the yield point followed by a fairly linear decrease in shear stress. A similar linear decrease in axial stress with increasing axial strain is observed in uniaxial tension tests. The model for post-yield behavior of extruded powder aluminum gives a quantified description of the macroscopic material behavior in terms of changes in the laminar powder aluminum structure.
Date: December 31, 1990
Creator: Woods, T. O.; Berghaus, D. G. & Peacock, H. B.
Partner: UNT Libraries Government Documents Department

Machining and grinding: High rate deformation in practice

Description: Machining and grinding are well-established material-working operations involving highly non-uniform deformation and failure processes. A typical machining operation is characterized by uncertain boundary conditions (e.g.,surface interactions), three-dimensional stress states, large strains, high strain rates, non-uniform temperatures, highly localized deformations, and failure by both nominally ductile and brittle mechanisms. While machining and grinding are thought to be dominated by empiricism, even a cursory inspection leads one to the conclusion that this results more from necessity arising out of the complicated and highly interdisciplinary nature of the processes than from the lack thereof. With these conditions in mind, the purpose of this paper is to outline the current understanding of strain rate effects in metals.
Date: April 1, 1993
Creator: Follansbee, P. S.
Partner: UNT Libraries Government Documents Department

X-ray absorption study of pulsed laser deposited boron nitride films

Description: B and N K-edge x-ray absorption spectroscopy measurements have been performed on three BN thin films grown on Si substrates using ion- assisted pulsed laser deposition. Comparison of the films` spectra to those of several single-phase BN powder standards shows that the films consist primarily of sp{sup 2} bonds. Other features in the films`s spectra suggest the presence of secondary phases, possibly cubic or rhombohedral BN. Films grown at higher deposition rates and higher ion-beam voltages are found to be more disordered, in agreement with previous work.
Date: February 2, 1994
Creator: Chaiken, A.; Terminello, L. J.; Wong, J.; Doll, G. L. & Sato, T.
Partner: UNT Libraries Government Documents Department