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Title: Joining of Tungsten Armor Using Functional Gradients

Abstract

The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

Authors:
Publication Date:
Research Org.:
Plasma Processes, Inc.
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
896793
Report Number(s):
DE-FG02-96ER82257
TRN: US1002170
DOE Contract Number:
FG02-96ER82257
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 42 ENGINEERING; ARCHITECTURE; ARMOR; BONDING; COPPER; COPPER ALLOYS; FABRICATION; FUNCTIONALS; HEAT FLUX; HEAT SINKS; PLASMA; SIMULATION; STRESSES; TESTING; THERMAL EXPANSION; THICKNESS; TUNGSTEN

Citation Formats

John Scott O'Dell. Joining of Tungsten Armor Using Functional Gradients. United States: N. p., 2006. Web. doi:10.2172/896793.
John Scott O'Dell. Joining of Tungsten Armor Using Functional Gradients. United States. doi:10.2172/896793.
John Scott O'Dell. Sun . "Joining of Tungsten Armor Using Functional Gradients". United States. doi:10.2172/896793. https://www.osti.gov/servlets/purl/896793.
@article{osti_896793,
title = {Joining of Tungsten Armor Using Functional Gradients},
author = {John Scott O'Dell},
abstractNote = {The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.},
doi = {10.2172/896793},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 2006},
month = {Sun Dec 31 00:00:00 EST 2006}
}

Technical Report:

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  • The objective of this program has been to develop and enhance the ductility of tungsten-based materials at high strain rates through the control of microstructural parameters such as grain size, distribution of phases, and texture. The technical basis for this objective is the close relationship between fine-structure and extended plasticity in metals and ceramics. To obtain a fine and equiaxed grain structure in tungsten-based materials, a number of processing routes have been evaluated under this program. Based upon a critical evaluation available processing schemes, four methods were selected to produce materials for detailed study. These processing methods included arc castingmore » and thermomechanical processing of tungsten-based binary alloys, chemical vapor deposition, liquid phase sintering and consolidation of ultrafine powder.« less
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  • A unique approach to crack-free joining of heterogeneous ceramics is demonstrated by the use of sialon polytypoids as Functionally Graded Materials (FGM) as defined by the phase diagram in the system, Si3N4-Al2O3. Polytypoids in the Al2O3-Si3N4 system offer a path to compatibility for heterogeneous ceramics. This paper describes successful hot press sintering of multilayered FGM's with 20 layers of thickness 500 mm each. Transmission Electron Microscopy was used to identify the polytypoids at the interfaces of different areas of the joint. It has been found that the 15R polytypoid was formed in the Al2O3-contained layers and the 12H polytypoid wasmore » formed in the Si3N4-contained layers.« less
  • A unique approach to crack-free joining of heterogeneous ceramics is demonstrated by the use of sialon polytypoids as Functionally Graded Materials (FGM) as defined by the phase diagram in the system, Si 3N 4-Al 2O 3. Polytypoids in the Al 2O 3-Si 3N 4 system offer a path to compatibility for such heterogeneous ceramics. The first part of the dissertation describes successful hot press sintering of multilayered FGM's with 20 layers of thickness 500 mm each. Transmission Electron Microscopy was used to identify the polytypoids at the interfaces of different areas of the joint. It has been found that themore » 15R polytypoid was formed in the Al 2O 3-contained layers and the 12H polytypoid was formed in the Si 3N 4-contained layers. The second part of the dissertation discusses the mechanical properties of these polytypoidally joined Si 3N 4-Al 2O 3. The thermal stresses of this FGM junction were analyzed using a finite element analysis program (FEAP) taking into account both coefficient of thermal expansion (CTE) and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layers. Scaling was considered, showing that the graded transition layer should constitute about 75 percent or more of the total sample thickness to reach a minimal residual stress. Oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were minimally or not deflected at the sialon layers, implying strong interfaces. Finally, flexural testing was conducted at room temperature and at high temperature. The average strength at room temperature was found to be 581 MPa and the average strength at high temperature (1200 °C) was found to be 262 MPa. Scanning electron microscope observation of fracture surfaces at a different loading rates indicated that the strength loss at higher temperatures was consistent with a softening of glassy materials present at grain junctions.« less