fabrication and properties of hot explosive consolidated ni-al composites

Laszlo J. KecskesEPNM-2010June 8, 2010

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-2010Bechichi, MontenegroJune 7-11, 2010


L.J. KecskesWeapons and Materials Research Directorate

US Army Research LaboratoryAberdeen Proving Ground, MD, USA

A.B. Peikrishvili, M.V. Tsikalauri, E.Sh. Chagelishvili, B.A. Godibadze

Institute of Mining and TechnologyAcademy of Sciences of Georgia

Tbilisi, GEORGIA

Zhiliang Pan, Weihua Lin, and Qiuming WeiUniversity of North Carolina, Charlotte, North Carolina, USA

EPNM-2010Bechichi, Montenegro

June 7-11, 2010


Motivation

Nickel Aluminides

Consolidation Method

Experimental Results

Prognosis - Conclusions

Outline


Explosive Consolidation

Materials with metastable structures cannot be manufacturedwith conventional techniques

Variants of alternative methods such as Hot ExplosiveCompaction (HEC) are being tried

Advantages of HEC are: short processing times, high pressures,and high temperatures

Tunability of material’s reactivity is of interest


Nickel – Aluminum

Five intermetallicsAl3Ni Tm= 850°C;Al3Ni2 Tm= 1,130°C;AlNi Tm= 1,640°C;Al3Ni5 Tm= 700°C;

AlNi3 Tm= 1,380°C.

Nickel Aluminides are used in high temperature, high strength, and high toughness applications

Equilibrium Phase Relations

M.F. Singleton et al, Binary Phase Diagrams, 1990.

Al3NiAl3Ni2

AlNi

Al3Ni5

AlNi3


Motivation

Exo


Hot Explosive Compaction

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:requires less energy and time than LPS or HIP; cracking,

poor particle-particle bonding

Typically, hot explosive compaction is a two-step process; though variations exist


Compaction Apparatus


2

6

5

11

8

4

93

7

Heating Apparatus

New Furnace

Close-Up View of Explosive Schematic


Explosive

Chemical Content

Detonation Velocity

m/s

Density

g/cm3

Heat of Explosion kcal/kg

Igdanit(ANFO)

NH4NO3+5-6%Diesel Fuel

2200-2800 1.1

Granulit (AC-4)

NH4NO3+4.2%Diesel Fuel+

4%Al2600-3200 1.1-1.3 1080

Explosive Types

Up to 10GPa pressure


Al-Ni Precursors

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: 1-2 μm Ni thickness: 7 μm

Precursor Al powder is coated with elemental Ni using a hydrometallurgical technique


External Appearance

Mach Stem


Internal Appearance

Lateral Cracks


Vibro-Densification


Experimental DataSet

ID Numbe

r

Ni : Al

RatioType

Temperature°C

Notes

#1 50-50 Blend 600#11 80-20 Blend 300

#12 50-50 Blend 300Partial

Reaction

#21 50-50 Clad 850Partial

Reaction#211 50-50 Clad 300#212 50-50 Clad 600


Reaction#221 80-20 Clad 300


Reaction


Al, Ni only; little or no intermetallics

X-ray Results

#211: 50-50; 300°C


X-ray Results

Anomalous, incomplete formation of intermetallics

#12-C: 50-50; 300°C


Microstructure Results - Blends

Edge Center

#12: 50-50; 300°C


Microstructure Results - Clads

Edge Center

#22: 80-20; 850°C


Second batch of specimens; still mostly unreacted Al and Ni

Further Microstructure Results


#1: 50-50; 600°C

Mechanical Results - Blends

Strain hardening and strain-rate hardening


#12: 50-50; 300°C

Mechanical Results - Blends

Strain hardening and strain-rate hardening


#211: 50-50; 300°C

Mechanical Results - Clads

Lesser strain hardening and strain-rate hardening


#22: 80-20; 850°C

Mechanical Results - Clads

Definite strain softening and little strain-rate hardening


#1: 50-50; 600°C

#211: 50-50; 300°C

#22: 80-20; 850°C

#222: 80-20; 600°C

Dyn

QS

Making Sense of the Results


Loading Direction

Definite shear during failure; insufficient to shear initiate an exothermic reaction in uniaxial loading…

Making Sense of the Results


Prognosis

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

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 Ni:Al 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’)

The premise of shear initiating an exothermic reaction is unlikely in Ni-Al specimens made by hot explosive compaction

Future Plans


Prior Work


Prior WorkPhase Chemistry: 22Ni-78Al

1000

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100000

20 30 40 50 60 70 80 90 100 110 120

2Theta

Inte

nsi

ty

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20 30 40 50 60 70 80 90 100 110 120

2Theta

Inte

nsi

ty

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2Theta

Inte

nsi

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AlAlAl Al

AlAlAl

NiNi

Ni NiAlNi

Precursor powder shows both Al and Ni peaks; Al:Ni peak ratio of 5:2 is consistent with composition

Regardless of temperature, the precursor reacts to form at least two Al-Ni’s. The peaks correspond to hexagonal Al3Ni2 and orthorhomic Al3Ni

300°C

400°C


300°C 400°C 500°C

Grain Morphology:two phase structure is verifiedwell-dispersed, equiaxed polyhedral Al3Ni2

grains surrounded by the second, Al3Ni grain-boundary phase.

Prior WorkPhase Morphology: 22Ni-78Al


1000

10000

100000

20 30 40 50 60 70 80 90 100 110 120

2Theta

Inte

nsi

ty

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10000

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20 30 40 50 60 70 80 90 100 110 120

2Theta

Inte

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Inte

nsi

ty

Al

Al

Al AlAlAl

Al

Ni

Ni

Ni Ni

Al

Ni

600°C

900°C

Precursor powder shows both Al and Ni peaks; Al:Ni peak ratio of 1:3 is consistent with composition

Up to 600°C:• composition of the precursors remain unchanged;

Above 600°C:• Al and Ni precursors react to form Al-Ni’s. The phases correspond to Al3Ni5 and AlNi3

Prior WorkPhase Chemistry: 61Ni-39Al


20°C 400°C 600°C

Grain Morphology:Below 600°C:• Two-phase structure; well-dispersed, polyhedral Al grains surrounded by theNi grain-boundary phase

Above 600°C:• Multi-phase structure with composition gradient and heterogeneous dispersion

800°C 1,000°C

Prior WorkPhase Morphology: 61Ni-39Al


800°C

Ni

AlNi3

Al3Ni5

Ni

Al3Ni5

AlNi3

AlNi3 Notes:

Backscattered electron micrograph reveals:

• multi-phase structure with heterogeneous dispersion• shrinkage cracks within Ni phase• stepwise composition gradient

Prior WorkPhase Morphology Detail: 61Ni-39Al


MechanismsThermodynamic 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

MechanismsKinetic Considerations

22Ni-78Al

61Ni-39Al

Ni Al

Ni Ni-Al Al

vs.

fabrication and properties of hot explosive consolidated ni-al composites

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