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Reactive, Refractory, and Precious Metals

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Reactive, Refractory, and Precious Metals & Alloys This depicts a braze weld without the use of carbon blocks. Above are listed general precautionary measures to be ... – PowerPoint PPT presentation

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Title: Reactive, Refractory, and Precious Metals


1
Reactive, Refractory, and Precious Metals Alloys
2
Resistance Welding
  • Learning Activities
  • View Slides
  • Read Notes,
  • Listen to lecture
  • Do on-line workbook
  • Lesson Objectives
  • When you finish this lesson you will understand

Keywords
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AWS Welding Handbook
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Komuro, Welding of Zirconium Alloys, Welding
International Vol 8, 1994
7
  • Zirconium
  • Similar to Ti but 50 higher density
  • Rt-1600F hcp Alpha gt1600F bcc Beta
  • Visible oxide at 400F loose scale at gt 800F
  • Pure Zr UTS 60ksi YS 40ksi Elong 18
  • Corrosion resistance in mineral and organic
    acids, sea water
  • Uses
  • Petrochemical
  • Food Processing
  • Nuclear Industry (Lower neutron absorption than
    SS, higher than other refractory alloys)

8
Zirconium Alloys
Alpha Stabilizers Aluminum, Beryllium, Cadmium,
Hafnium (usually present), Carbon, Oxygen,
Nitrogen, Tin
Beta Stabilizers Cobalt, Niobium, Copper,
Hydrogen, Iron, Manganese, Molybdenum, Nickel,
Silver, Tantalum, Titanium, Tungsten, Vanadium
Low Solubility, Intermetallic Compounds Carbon,
Silicon, Phosphorous
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  • Zirconium Alloys have been
  • Spot Welded
  • Seam Welded
  • Flash Welded
  • Upset Butt Welded
  • Electromagnetic Force Butt Weld
  • High Frequency Welded

Surface Cleaning Recommended
  • Surface Cleaning - Mechanical or Chemical
    HF-HNO3
  • To lower surface resistance to below 50 microhms
  • To keep Zirconium Oxide out of weld metal -
    embrittlement
  • Handle with gloves
  • Store in low-humidity less than 48 hours
  • Higher resistivity for Alloys than steel lower
    current

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Electromagnetic Force Butt Weld
Nuclear Fuel Rod Assembly
Komuro, Welding of Zirconium Alloys, Welding
International Vol 8, 1994
14
The GTA Welds Have Been Replaced by Resistance
Butt Weld
Weld Current 20-24 kA Weld Time 1/60 sec
Komuro, Welding of Zirconium Alloys, Welding
International Vol 8, 1994
15
Tube
End Plug
Post Weld Flash Removal is done
Komuro, Welding of Zirconium Alloys, Welding
International Vol 8, 1994
16
Dissimilar Metals
Weld Zr Alloys only to itself or other reactive
refractory metals (Titanium, Niobium, Tantalum,
Hafnium) When welded to Iron or Copper,
extremely brittle intermetallics are formed.
17
Cu
Fe
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  • Hafnium
  • Bright, ductile metal similar to zirconium
  • RT-3200F hcp gt3200F bcc
  • Density 2 times zirconium
  • Better corrosion resistance than zirconium in
    water, steam, molten alkali metals
  • Reacts slowly in air above 750F to form oxides
  • Reacts above 1650F to form nitrides
  • Reacts rapidly above 1290F to form hydrides
  • Uses
  • Nuclear applications making use of its strong
    neutron absorption
  • control rods
  • nuclear containers

20
Hafnium is subject to severe embrittlement by
relatively small amounts of contamination by
nitrogen, oxygen, carbon, or hydrogen. Welding
usually done in a vacuum. Generally not suited
for resistance welding.
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  • Beryllium
  • hcp limited ductility at RT
  • Density 70 that of Aluminum
  • Cast or Powder metallurgy
  • Inherent refractory oxide films
  • Used
  • Aerospace Structures
  • Instrument platforms
  • Nuclear - low neutron cross section

Beryllium and its compounds in the form of dust,
fumes and vapors are toxic and a serious health
hazard. Because of the chance of expulsion,
resistance welding processes are not considered
for this material.
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AWS Welding Handbook
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  • Tantalum
  • bcc to MP, good ductility at all temps
  • Heavy, twice density of steel
  • Good corrosion resistance for most chemicals
  • Oxidizes gt 570F
  • Attacked by hydrofluoric, phosphoric, sulfuric
    acid gt300F
  • Reacts with chlorine and fluorine gases and
    C,H,N at elevated temps
  • UTS30-50 ksi YS24-32ksi Elong 20-30
  • Used
  • Chemical handling
  • Electrical capacitors
  • High Temperature Furnace Components

28
Tantalum Material Production
  • Power Metallurgy
  • Resistance Welding Not Recommended because
    porosity in weld will be excessive
  • Vacuum Arc Melting Electron Beam Melting
  • Suitable for Resistance Welding

Welding Handbook, AWS
29
Tantalum Spot Seam Welding
  • Alloying with Copper Electrodes Electrode
    Sticking is a Problem
  • Weld Under Liquid (exclusion of Air, Cooling)
  • a. Water
  • b. Carbon Tetrachloride (old practice - Health
    Problems)
  • Weld Times not to exceed 10 cycles
  • Rapid Oxidation is a Problem
  • Weld using inert gas or hydrogen

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  • Niobium
  • bcc with no allotropic transformation
  • Tensile Strength gt 25 ksi YS gt 15 ksi
  • Interstitials (O,N,H,C) effect mechanical
    properties
  • Oxidizes rapidly at gt 750F
  • Absorbs Hydrogen 500-1750F
  • Reacts with carbon, sulfur and halogens at
    elevated Temp
  • Excellent Corrosion Resistance in Aqueous
    solutions because of tenacious oxide formation

32
  • Niobium Alloys
  • Alloy with Tantalum, Tungsten, Molybdenum,
    Hafnium, Titanium, Zirconium
  • Produced into sheets, plates etc.

Welding Handbook, AWS
33
Niobium Spot Projection Welding Problems
  • Electrode Sticking
  • AWS recommends using Projection or diffusion
    welding process
  • Cooling with liquid nitrogen might help
  • Contamination
  • Inert shielding from atmosphere

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Molybdenum Tungsten
  • bcc Structure
  • Ductile to brittle transition temp near or above
    RT (welds will have little or no ductility)
  • low solubility for O, N,C
  • Grain Boundary Films of oxides, nitrides,
    carbides
  • Welding performed in high purity inert
    atmosphere or vacuum
  • Sensitive to stress concentrations and rate of
    loading
  • Additions of Rhenium greatly improves ductility
    Mo 40-50Re, W 20-30Re
  • W-25Re commercially available but tendency to
    solidification crack because of sigma phase

36
Molybdenum Tungsten Resistance Weld
  • Not generally resistance welded
  • Exception is thermocouple wires (generally
    capacitor discharge)
  • Exception is Tungsten for lamp filaments

37
Tungsten Powder Compact Filament Welded to Nickel
Coated Steel Wire (Resistance Butt or Resistance
Spot)
Butt Welded
Nickel Coated Steel Wire
W Power Compact W BaTiO3 TiO2
Spot Welded
Mehrotra, V, et al Multiple Layer composite
Electrodes for discharge Lamps US Patent
5,847,498 Dec 8, 1998 see also Patents
6037714, Mar 14, 2000 5847497Dec 8, 1998
38
Resistance Weld on Metal-Halide Lamp
Niobium Pin With lip (19) Thermal Expansion
Similar to Ceramic
Halide Resistant Mo or W Wire
W Electrode With Coil Wire
(W-Nb W-W) Resistance Welds
Huettinger, R Juengst, S, Metal-Halide Lamp
with Specific Lead Through Structure, US Patent
6,075,314 Jun 13, 2000
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Rhenium
  • hcp crystal structure - different from other
    refractory alloys
  • Highest modulus of all metals
  • No ductile to brittle transition
  • Low thermal conductivity (1/2 of Mo 1/3 of W)
  • High resistivity (3-4 times Mo W)
  • Superior tensile and creep properties
  • Resistant to surface oxidation oxides that form
    have good conductivity
  • However, embrittled by GB penetration of
    liquid-phase oxides
  • Does not form a carbide (I.e. low intra-granular
    embrittlement)
  • Available in sheet, strip, wire, tubing

AWS Indicates that Rhenium can be resistance
welded but no procedural data could be found
41
Electro - Brazing of Reactive and Refractory
Alloys
42
General Comment For Refractory Alloys
Electro-alloy


Ni Sheet
Caution (see below)
43
Braze Weld w/o Carbon Block
Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
44
General Comments
  • For Tungsten 1.) avoid brazing alloys with
    excessive nickel to prevent recrystalization
    in base metal due to high brazing temperatures
    2.) avoid
    contact with graphite to prevent carbide
    formation
  • For Molybdenum 1.) prevent oxidation by using
    protective coatings
    2.) prevent
    contamination by interstitials 3.) prevent
    recrystalization by careful alloy
    selection 4.) use barrier layer (e.g.
    chromium) to avoid diffusion-induced
    embrittlement by intermetallic compound
    formation
  • For Tantalum 1.) remove all reactive gases
    (O2, CO etc) Columbium 2.) electroplate with
    copper or nickel to prevent oxidation

Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
45
Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
46
Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
47
Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
48
Messler, RW, Joining of Advanced
MaterialsButterworth-Heinemann, 1993
49
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51
Gold
  • Bright yellow, malleable fcc
  • Resistance to oxidation
  • Good Electrical and Thermal Conductivity
  • Alloyed with Copper silver for jewelry
  • Alloyed with zinc, nickel, palladium, platinum
    for commercial

Resistance welding usually done on a small bench
type spot welder
52
Silver
  • Malleable fcc
  • Resistance to oxidation
  • Good Electrical and Thermal Conductivity
  • Passive chemically (except S which tarnish)
  • Dissolved Oxygen in liquid causes porosity
  • Alloyed with Copper
  • It is difficult to weld because of low
    electrical resistance
  • Projection welds for contacts to relays
  • Projections on silver to increase current
    density
  • Welded to Phosphor-bronze, copper-nickel,
    beryllium-copper, brass

53
Resistance Welding of Precious Metal Contact Tips
Application
Supply Wire (platinum, gold, iridium, osmium,
palladium, rhodium, rhenium, ruthenium, tungsten)
Resistance Weld (34 pounds, 8ms upslope, 1100
amps-16ms weld, 8 ms down slope)
Cut
2nd Weld and Coin (1410 amps, 400 pounds)
Tribble, D, Application of Precious Metal to
Spark Plug Electrode US Patent 6,132,277 Oct.
17, 2000
54
Cochlear Electrode Array
Shape Memory Rod
Silicon Rubber Body
Electrodes
Resistance Weld Wires
Platinum Electrode Strips Spot Welded to Steel
Acid Etch Steel Plate Away
Kuzma, J Cochlear Electrode Array With
Positioning Stylet US Patent 6,119,044 Sept
12, 2000
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