Synthesis of bulk reactive Ni-Al composites using high pressure torsion

Self-propagating exothermic reactions, for instance in the nickel-aluminum (Ni-Al) system, have been widely studied to create high performance intermetallic compounds or for in-situ welding. Their easy ignition once the phase spacing is reduced below the micron scale, makes top-down methods like high-energy ball milling, ideal to fabricate such reactive nanostructures. A major drawback of ball milling is the need of a sintering step to form bulk pieces of the reactive material. However, this is not possible, as the targeted reactions would already proceed. Therefore, we investigate the ability of high pressure torsion as an alternative process, capable to produce bulk nanocomposites from powder mixtures. Severe straining of powder mixtures with a composition of 50 wt% Ni and 50 wt% Al enables fabrication of self-reactive bulk samples with microstructures similar to those obtained from ball milling or magnetron sputtering. Samples deformed at ambient temperature are highly reactive and can be ignited significantly below the Al melting point, finally predominantly consisting of Al3Ni2 and Al3Ni, independent of the applied strain. Although the reaction proceeds first at the edge of the disk, the strain gradient present in the disks does not prevent reaction of the whole sample. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

High pressure torsion is investigated as an alternative process to produce bulk nanocomposites with high reactivity, similar to those obtained from ball milling or magnetron sputtering. Samples deformed at ambient temperature can be ignited significantly below the Al melting point, consisting predominantly of Al3Ni2 and Al3Ni, independent of the applied strain. The reaction, although initiated at the edge of the disk, is not prevented by the strain gradient present in the disks.