Fabrication and Properties of Hot Explosive Consolidated Ni-Al Composites

1. 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

2. 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

3. Outline Motivation Nickel Aluminides Consolidation Method Experimental Results Prognosis - Conclusions

4. Explosive Consolidation Materials with metastable structures cannot be manufactured with conventional techniques Variants 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 material’s reactivity is of interest

5. Nickel – Aluminum Nickel Aluminides are used in high temperature, high strength, and high toughness applications Equilibrium Phase Relations Five intermetallics Al3Ni Tm= 850°C; Al3Ni2 Tm= 1,130°C; AlNi Tm= 1,640°C; Al3Ni5 Tm= 700°C; AlNi3 Tm= 1,380°C. AlNi AlNi3 Al3Ni2 Al3Ni Al3Ni5 M.F. Singleton et al, Binary Phase Diagrams, 1990.

6. Motivation Exo

7. 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: requires less energy and time than LPS or HIP; cracking, poor particle-particle bonding

8. Compaction Apparatus

9. 7 4 11 5 2 6 9 8 3 Heating Apparatus Close-Up View of Explosive Schematic New Furnace

10. Explosive Types Up to 10GPa pressure

11. 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

12. External Appearance Mach Stem

13. Internal Appearance Lateral Cracks

14. Vibro-Densification

15. Experimental DataSet

16. X-ray Results Al, Ni only; little or no intermetallics #211: 50-50; 300°C

17. X-ray Results Anomalous, incomplete formation of intermetallics #12-C: 50-50; 300°C

18. Microstructure Results - Blends #12: 50-50; 300°C Edge Center

19. Microstructure Results - Clads #22: 80-20; 850°C Edge Center

20. Further Microstructure Results Second batch of specimens; still mostly unreacted Al and Ni

21. Mechanical Results - Blends Strain hardening and strain-rate hardening #1: 50-50; 600°C

22. Mechanical Results - Blends Strain hardening and strain-rate hardening #12: 50-50; 300°C

23. Mechanical Results - Clads Lesser strain hardening and strain-rate hardening #211: 50-50; 300°C

24. Mechanical Results - Clads Definite strain softening and little strain-rate hardening #22: 80-20; 850°C

25. Making Sense of the Results #1: 50-50; 600°C #211: 50-50; 300°C #22: 80-20; 850°C #222: 80-20; 600°C Dyn QS

26. Making Sense of the Results Definite shear during failure; insufficient to shear initiate an exothermic reaction in uniaxial loading… Loading Direction

27. 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

28. 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 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’)

29. Prior Work

30. Prior Work Phase Chemistry: 22Ni-78Al Al Al Ni Al Al Ni Ni Al Al Ni Ni Al Al 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

31. Prior Work Phase Morphology: 22Ni-78Al 300°C 400°C 500°C Grain Morphology: two phase structure is verified well-dispersed, equiaxed polyhedral Al3Ni2grains surrounded by the second, Al3Ni grain-boundary phase.

32. Prior Work Phase Chemistry: 61Ni-39Al Ni Al Ni Ni Ni Ni Al • 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 Al Al Al Al Al Al 600°C 900°C

33. Prior Work Phase Morphology: 61Ni-39Al 20°C 400°C 600°C • Grain Morphology: • Below 600°C: • Two-phase structure; well-dispersed, polyhedral Al grains surrounded by the • Ni grain-boundary phase • Above 600°C: • Multi-phase structure with composition gradient and heterogeneous dispersion 800°C 1,000°C

34. Prior Work Phase Morphology Detail: 61Ni-39Al 800°C 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

35. Mechanisms Thermodynamic Considerations

36. Ni Al Ni Ni-Al Al 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