A modified model for the sintering of tungsten with nickel additions

Gessinger, Gernot H.; Fischmeister, H. F.

doi:10.1016/0022-5088(72)90025-2

Cited by 69 publications

(27 citation statements)

References 8 publications

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“…No model accounts for this complexity. A similar treatment by Gessinger et al [127,128] assumed the liquid layer wets the grain boundary with a small dihedral angle, giving essentially the same sintering shrinkage as Kingery. Solid-state diffusion by grain boundary diffusion in the grain contact is another densification mechanism.…”

Section: Densificationmentioning

confidence: 94%

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Review: liquid phase sintering

2009

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Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Section: Densificationmentioning

confidence: 94%

“…39c [127,128]. The contact zone enlarges to change the grain shape with simultaneous shrinkage of the grains.…”

Section: Densificationmentioning

confidence: 99%

Review: liquid phase sintering

2009

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“…The Zr2Cu composition chosen for the present work is particularly attractive as this compound melts congruently at only 1025°C (i.e., more than 800°C lower than pure Zr) [20,22]. Furthermore, the Gibbs free energy change of reaction (1) for the case where {Zr} is present in molten Zr2Cu remains strongly negative at modest temperatures (e.g., AGn",(1200°C) = -136.8 kJ/mole) [21,23]. The residual liquid copper generated upon removal of the zirconium from the Zr2Cu liquid by reaction (1) can not form stable compounds with ZrC or W. Copper also has minimal effect on the melting point of tungsten (a decrease of only about 8°C) [24].…”

Section: Resultsmentioning

confidence: 99%

“…The starting W and WC powders' '^ possessed purities of >99.9% and particle sizes of <12 jim and <10 |im, respectively. For some of the W-rich preforms, 5-10 wt% of Ni powder^(=3.0 urn, 99.9% purity) was added as a sintering aid [23]. After blending with 5-10 wt% of an aqueous poly vinyl alcohol solution^, the mixtures were pressed into bars (0.25 cm X 1.1 cm X 1.1 cm) and disks (1.3 cm dia., X 3.5 mm thick) at peak stresses of 34-48 MPa.…”

Section: Methodsmentioning

confidence: 99%

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Fabrication of Dense, Near Net-Shaped W/ZrC Composites by the PRIMA-DCP Process

Sandhage¹

2004

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the i gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments ret " . j o of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE ^DD-yW SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)USAF/AFRL AFOSR 801 N. Randolph Street ArlingVA 22203 SPONSOR/MONITOR'S ACRONYM(S) AFOSR SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTDistribution Statement A. Approved for public release; distribution is unlimited. The fundamental conversion mechanism for the following net liquid/solid displacement reaction has been examined: (Zr) + WC(s)=ZrC(s)+W(s) (1) where (Zr) refers to zirconium dissolved within a Zr-Cu melt. Such mechanistic knowledge is needed in order to be able to predict die time required, under various processing conditions, for full conversion of porous WC performs into dense ZrC/W composites (e.g., for rocket nozzle applications) by die DCP method. For this fundamental study, dense wafer of WC were prepared by hot isostatic pressing at 1850oC. The wafers were then unmersed in a vertical orientation in a Zr-Cu melt at temperatures in die range of 1150-1400oC for times up to 24 hours. After such exposure, the polished WC surfaces were found to be coated with two reaction product layers. A layer of tungsten was observed to be in direct contact with the WC. A second, external layer of ZrC separated die W layer from die melt. The diicknesses of die W and ZrC layers were found to: i) increase at a parabolic rate with time, ii) be independent of the relative vertical position on the WC surface, and iii) increase Objective: This project has been focused on developing a better understanding of the fundamental kinetic mechanism(s) (i.e., rate-limiting step(s), kinetic rate law(s)) of the DCP (Displacive Compensation of Porosity) process for fabricating ZrCAV composites. Approach and Key Results:The fundamental conversion mechanism for the following net liquid/solid displacement reaction has been examined:where (Zr) refers to zirconium dissolved within a Zr-Cu melt. Such mechanistic knowledge is needed in order to be able to predict the time required, under various processing conditions, for full conversion of porous WC preforms into dense ZrCAV composites (e.g., for rocket nozzle applications) by the DCP method. For this fundamental study, dense wafers of WC were prepared by hot isostatic pressing at 1850°C. The wafers were then...

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Refractory Metals and Their Alloys

Pink

Eck

2006

Materials Science and Technology

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A modified model for the sintering of tungsten with nickel additions

Cited by 69 publications

References 8 publications

Review: liquid phase sintering

Review: liquid phase sintering

Fabrication of Dense, Near Net-Shaped W/ZrC Composites by the PRIMA-DCP Process

Refractory Metals and Their Alloys

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