Influence of chromium on microstructure and etching behaviour of new Ni–Fe–Al based alloy

Abstract

In the present study, the influence of chromium on the microstructure and etching behaviour of the polycrystalline alloy Ni–13Fe–8Al–4Ti (at-%) has been examined. The alloy was recently designed for nanomembrane fabrication, but although it showed the necessary γ/γ′ microstructure with cubic, well aligned γ′ precipitates, it proved to be unsuitable for nanomembrane fabrication as the γ matrix was dissolved during chemical etching. To obtain the passivation of the γ matrix, chromium has been added in further modifications containing 1, 2, 3 and 4 at-% chromium. Moreover, the influence of heat treatment and the different cooling rates of heat treatment in air/vacuum have been investigated. For chemical phase extraction, the application of the chemical etchants MoO₃ acid and ‘G’ etchant has been examined, the formability was characterised by Vickers hardness testing. The main purpose of the present study, namely the passivation of the γ matrix, could be achieved by the addition of 4 at-% chromium and etching with ‘G’ etchant.

Keywords:

• Nickel alloys
• Nanoporous membranes
• γ/γ′ microstructure
• Ni–Fe–Al alloys
• Chromium
• Passivation
• Etching behaviour
• Lattice misfit

Acknowledgements

The authors gratefully thank the German Research Foundation (DFG) for financial support of the presented work within the project ‘Development of metallic nanomembranes based on Ni–Fe–Al alloys’ (project no. RO 2045/27-1/2).