Observation of a minimum reaction initiation threshold in ball-milled Ni+Al under high-rate mechanical loading

Herbold, Eric B.; Thadhani, Naresh N.; Jordan, Jennifer L.

doi:10.1063/1.3549822

Cited by 26 publications

(21 citation statements)

References 20 publications

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“…5 It was observed that material milled for 35% of the critical milling time (t cr ) had lower impact ignition thresholds than material milled for 65% t cr , where the t cr is the time at which reaction of the Ni/Al material would take place during milling if the milling is not arrested first. It was stated that this behavior is a result of competing effects of increased reactivity and increased strain hardening as the duration of milling increases.…”

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confidence: 99%

“…[1][2][3] Numerous experimental and theoretical studies have been published on impact behavior and shock compression of metal-based reactive powder mixtures with metals such as Al, Ni, Si, Ti, W, Nb, and more. [1][2][3][4][5] Yet the fundamental mechanisms that govern the initiation and front propagation are not well understood. For example, their energy release characteristics depend on the mode of initiation, and reaction propagation, in a currently unpredictable way.…”

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confidence: 99%

“…It was stated that this behavior is a result of competing effects of increased reactivity and increased strain hardening as the duration of milling increases. 5 This work, however, only investigated two milling durations and did not investigate combustion behavior upon reaction and therefore further work is required.…”

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confidence: 99%

“…4,5,10 Increasing the ignition sensitivities through MA occurs by changes in morphology, ductility, and hardness through cold working. This is achieved by high energy collisions between the particles and milling media.…”

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confidence: 99%

“…It has been shown that the intermixing of these materials on an intimate scale causes the observed increase in thermal and impact sensitivity due to smaller diffusion distances. 5,[10][11][12][13][14] However, the role and extent to which the modified microstructure properties have on compaction, ignition, and subsequent reaction propagation of impacted reactive powders has yet to be fully investigated and quantified.…”

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confidence: 99%

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The role of microstructure refinement on the impact ignition and combustion behavior of mechanically activated Ni/Al reactive composites

Mason

Groven

Son

2013

Journal of Applied Physics

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Metal-based reactive composites have great potential as energetic materials due to their high energy densities and potential uses as structural energetic materials and enhanced blast materials however these materials can be difficult to ignite with typical particle size ranges. Recent work has shown that mechanical activation of reactive powders increases their ignition sensitivity, yet it is not fully understood how the role of microstructure refinement due to the duration of mechanical activation will influence the impact ignition and combustion behavior of these materials. In this work, impact ignition and combustion behavior of compacted mechanically activated Ni/Al reactive powder were studied using a modified Asay shear impact experiment where properties such as the impact ignition threshold, ignition delay time, and combustion velocity were identified as a function of milling time. It was found that the mechanical impact ignition threshold decreases from an impact energy of greater than 500 J to an impact energy of $50 J as the dry milling time increases. The largest jump in sensitivity was between the dry milling times of 25% of critical reaction milling time (t cr ) (4.25 min) and 50% t cr (8.5 min) corresponding to the time at which nanolaminate structures begin to form during the mechanical activation process. Differential scanning calorimetry analysis indicates that this jump in the sensitivity to thermal and mechanical impact is dictated by the formation of nanolaminate structures, which reduce the temperature needed to begin the dissolution of nickel into aluminum. It was shown that a milling time of 50%-75% t cr may be near optimal when taking into account both the increased ignition sensitivity of mechanical activated Ni/Al and potential loss in reaction energy for longer milling times. Ignition delays due to the formation of hotspots ranged from 1.2 to 6.5 ms and were observed to be in the same range for all milling times considered less than t cr . Combustion velocities ranged from 20-23 cm/s for thermally ignited samples and from 25-31 cm/s for impacted samples at an impact energy of 200-250 J.

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confidence: 99%