Local melting in Al embedded with TiNi powder induced by microarea self-propagating high-temperature synthesis

Abstract

Microarea self-propagating high-temperature synthesis (microSHS) was ignited by the heat of mixing generated at the boundaries between an Al matrix and TiNi particles during plastic deformation at room temperature. The temperature of the boundaries was rapidly increased by microSHS; the temperature elevation resulted in local melting of the TiNi particle and the surrounding Al matrix, because the heat of mixing was localized in the vicinity of the TiNi particle although the amount of the heat of mixing was limited. Since the amount of the local melting region induced by microSHS is restricted, not only major elements (i.e. Al, Ti and Ni) but also impurities were involved in the solidification followed by local melting. As a result, ${\mathrm{Al}}_9$FeNi nanoprecipitates, which have not been reported in SHS studies, were formed by inclusion of Fe, initially included as an impurity in raw materials. The formation mechanism of ${\mathrm{Al}}_9$FeNi nanoprecipitates is discussed based on reference to the Al–Fe–Ni ternary alloy phase diagram. It is expected that local melting induced by microSHS is a key phenomonon for amorphization during severe plastic deformation of elemental sheets.

Keywords:

• aluminum alloys
• powder metallurgy
• self-propagating high-temperature synthesis (SHS)
• local melting
• Al₉FeNi
• severe plastic deformation (SPD)

Acknowledgements

The author thanks Prof. Kato, the Hokkaido University, and Prof. Nagase, the Osaka University, for their discussion. The author also thanks Mr. Kanomata and Mr. Murakami, Institute for Materials Research, the Tohoku University, for assisting gas atomization and operating the EPMA, respectively.

Additional information

Funding

This work was supported by Grant-in-Aid for Young Scientists (B) [grant number 21760548]; Challenging Exploratory Research [grant number 24656432] from the Japan Society for the Promotion of Science (JSPS); by the Amada Foundation for Metal Work Technology. Part of this work was also supported by the Light Metal Educational Foundation Inc.