Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

The atomic structures of the Al2Au precipitate phase in aluminium (#93)

Laure Bourgeois 1 2 , Zezhong Zhang 1 , Jiehua Li 3 , Nikhil Medhekar 1
  1. Department of Materials Science and Engineering, Monash University, Clayton, Victoria, Australia
  2. Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria, Australia
  3. Institute of Casting Research, Montanuniversität Leoben, Leoben, Austria

The intermetallic compound Al2Au, also known as purple gold, has elicited much interest due to its unusual optical properties [1]. The precipitation of this compound in Al alloys, however, for example in interconnects of integrated circuits, can be a serious problem (the so-called Purple Plague [2-3]). Al2Au precipitates (or the η phase) are also interesting owing to their similar crystal structure and precipitation behaviour compared with the intermediate Al2Cu (θ′) phase in high-strength Al-Cu alloys [4]. Recently the θ′ phase has been found to exhibit unexpected and complex interfacial structures [5,6], and the question naturally arises as to whether the η phase also exhibits such structures.

Using high-resolution scanning transmission electron microscopy (STEM), we determine the bulk and interfacial structures of η precipitates in a binary Al-Au alloy. We show that, contrary to the θ′ phase, it does not display complex interfacial structures. Our observations also reveal the existence of an intermediate phase with a tetragonal distortion of the cubic structure of the η phase. The results deduced from the STEM imaging are in excellent agreement with first-principles and elasticity theory calculations [7].

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  7. L. Bourgeois, Z. Zhang, J. Li, N.V. Medhekar, to be submitted.