Fabrication and Properties of Hot Explosive Consolidated Ni-Al Composites

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Fabrication and Properties of Hot Explosive
Consolidated Ni-Al Composites
L. Kecskes, A. Peikrishvili, E. Chagelishvili, M.
Tsiklauri, B. Godibadze, Z. Pan, W. Lin, and Q.
Wei EPNM-2010 Bechichi, Montenegro June 7-11,
2010
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L.J. Kecskes Weapons and Materials Research
Directorate US Army Research Laboratory Aberdeen
Proving Ground, MD, USA A.B. Peikrishvili, M.V.
Tsikalauri, E.Sh. Chagelishvili, B.A.
Godibadze Institute of Mining and
Technology Academy of Sciences of
Georgia Tbilisi, GEORGIA Zhiliang Pan, Weihua
Lin, and Qiuming Wei University of North
Carolina, Charlotte, North Carolina,
USA EPNM-2010 Bechichi, Montenegro June 7-11,
2010
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Outline
Motivation Nickel Aluminides Consolidation
Method Experimental Results Prognosis -
Conclusions
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Explosive Consolidation
Materials with metastable structures cannot be
manufactured with conventional techniques Variant
s of alternative methods such as Hot
Explosive Compaction (HEC) are being
tried Advantages of HEC are short processing
times, high pressures, and high
temperatures Tunability of materials reactivity
is of interest
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Nickel Aluminum
Nickel Aluminides are used in high temperature,
high strength, and high toughness applications
Equilibrium Phase Relations
Five intermetallics Al3Ni Tm
850C Al3Ni2 Tm 1,130C AlNi Tm 1,640C Al3N
i5 Tm 700C AlNi3 Tm 1,380C.
AlNi
AlNi3
Al3Ni2
Al3Ni
Al3Ni5
M.F. Singleton et al, Binary Phase Diagrams, 1990.
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Motivation
Exo
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Hot Explosive Compaction
Typically, hot explosive compaction is a two-step
process though variations exist
Step 1 sample heated to desired temperature by
an electric current for about 60-120
seconds Step 2 once temperature is uniform,
the ampoule is consolidated by the detonation of
an explosive charge Advantages/Disadvantages re
quires less energy and time than LPS or HIP
cracking, poor particle-particle bonding
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Compaction Apparatus
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Heating Apparatus
Close-Up View of Explosive Schematic
New Furnace
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Explosive Types
Explosive Chemical Content Detonation Velocity m/s Density g/cm3 Heat of Explosion kcal/kg
Igdanit (ANFO) NH4NO3 5-6Diesel Fuel 2200-2800 1.1
Granulit (AC-4) NH4NO3 4.2Diesel Fuel 4Al 2600-3200 1.1-1.3 1080
Up to 10GPa pressure
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Al-Ni Precursors
Precursor Al powder is coated with elemental Ni
using a hydrometallurgical technique
Thin Ni Layer
Thick Ni Layer
Good adhesion of the coating layer to the base
particles No evidence of impurities, compounds,
or intermetallics
Ni thickness 7 µm
Ni thickness 1-2 µm
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External Appearance
Mach Stem
13
Internal Appearance
Lateral Cracks
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Vibro-Densification
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Experimental DataSet
ID Number Ni Al Ratio Type Temperature C Notes
1 50-50 Blend 600
11 80-20 Blend 300
12 50-50 Blend 300 Partial Reaction
21 50-50 Clad 850 Partial Reaction
211 50-50 Clad 300
212 50-50 Clad 600
22 80-20 Clad 850 Partial Reaction
221 80-20 Clad 300
222 80-20 Clad 600 Partial Reaction

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X-ray Results
Al, Ni only little or no intermetallics
211 50-50 300C
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X-ray Results
Anomalous, incomplete formation of intermetallics
12-C 50-50 300C
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Microstructure Results - Blends
12 50-50 300C
Edge
Center




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Microstructure Results - Clads
22 80-20 850C
Edge
Center


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Further Microstructure Results

Second batch of specimens still mostly
unreacted Al and Ni
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Mechanical Results - Blends
Strain hardening and strain-rate hardening
1 50-50 600C
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Mechanical Results - Blends
Strain hardening and strain-rate hardening
12 50-50 300C
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Mechanical Results - Clads
Lesser strain hardening and strain-rate hardening
211 50-50 300C
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Mechanical Results - Clads
Definite strain softening and little strain-rate
hardening
22 80-20 850C
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Making Sense of the Results
1 50-50 600C
211 50-50 300C
22 80-20 850C
222 80-20 600C
Dyn
QS
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Making Sense of the Results
Definite shear during failure insufficient to
shear initiate an exothermic reaction in uniaxial
loading
Loading Direction
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Prognosis
The premise of shear initiating an exothermic
reaction is unlikely in Ni-Al specimens made by
hot explosive compaction
blended samples have better integrity and display
response corresponding to Al or Ni (less Ni
better) clad samples do not have the required
inter-particle bonding compaction temperatures
of specimens are not commensurate with expected
progress of the Al Ni reaction uniaxial
compression testing may not be the right test to
examine reaction initiation in shear
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Future Plans
The premise of shear initiating an exothermic
reaction is unlikely in Ni-Al specimens made by
hot explosive compaction
improve particle-particle surface adhesion by
changing explosive type (i.e., samples lack
dynamic strength) alternate NiAl ratios, with
lower reaction initiation threshold
energy alternative precursor microstructure may
be more conducive for friction-induced reaction
initiation (i.e., at present, extent of shear
displacement is insufficient to generate a hot
spot)
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Prior Work
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Prior Work Phase Chemistry 22Ni-78Al
Al
Al
Ni
Al
Al
Ni
Al
Al
Ni
Ni
Ni
Al
Al
Precursor powder shows both Al and Ni peaks
AlNi peak ratio of 52 is consistent with
composition Regardless of temperature, the
precursor reacts to form at least two Al-Nis.
The peaks correspond to hexagonal Al3Ni2 and
orthorhomic Al3Ni
300C
400C
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Prior Work Phase Morphology 22Ni-78Al
300C
400C
500C
Grain Morphology two phase structure is
verified well-dispersed, equiaxed polyhedral
Al3Ni2 grains surrounded by the second, Al3Ni
grain-boundary phase.
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Prior Work Phase Chemistry 61Ni-39Al
Ni
Al
Ni
Ni
Ni
Ni

Al

• Precursor powder shows both Al and Ni peaks
  AlNi peak ratio of 13 is consistent with
  composition
• Up to 600C
• composition of the precursors remain unchanged
• Above 600C
• Al and Ni precursors react to form Al-Nis.
  The phases correspond to Al3Ni5 and AlNi3

Al
Al
Al
Al
Al
Al
600C
900C
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Prior Work Phase Morphology 61Ni-39Al
20C
400C
600C

• Grain Morphology
• Below 600C
• Two-phase structure well-dispersed, polyhedral
  Al grains surrounded by the
• Ni grain-boundary phase
• Above 600C
• Multi-phase structure with composition gradient
  and heterogeneous dispersion

800C
1,000C
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Prior Work Phase Morphology Detail 61Ni-39Al
800C
AlNi3

• Notes
• Backscattered electron micrograph reveals
• multi-phase structure with heterogeneous
  dispersion
• shrinkage cracks within Ni phase
• stepwise composition gradient

Ni
Ni
Al3Ni5
AlNi3
Al3Ni5
AlNi3
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Mechanisms Thermodynamic Considerations
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Mechanisms Kinetic Considerations

• Both systems are the same at the interface
• At the threshold temperature, a Al-rich
  eutectic forms, initiating the reaction. Heat
  transferred across the product layer to unreacted
  Al and Ni advances the reaction
• Wider Ni layer in 61Ni-39Al slows the reaction
  by
• mass diffusion of Al or Ni across the
  intermetallic
• thick layer acts as a barrier to a sustained
  reaction
• more time needed for heat transfer to unreacted
  zone heat losses compound this effect

22Ni-78Al
vs.
61Ni-39Al