Fourteen Pt-Al-Nb alloys were made by arc melting and studied in both the as-cast condition and after annealing at 1000 °C for 1000 h, using scanning electron microscopy with energy dispersive x-ray analysis, and x-ray diffraction. A modified electro-etching method was used to etch as-cast alloys which gave much clearer microstructures, by helping to remove the Al oxide scale on the surface. One ternary phase was found, Nb47.8Pt50.3Al1.9 (at.%). A solidification projection, liquidus projection surface and 1000 °C isothermal section were derived. The extensions into the ternary on solidification were: ~Nb2Pt: ~ 20 at.% Al; ~NbPt2: ~ 5 at.% Al; βNbPt3: ~ 4 at.% Al; ~PtAl: ~ 2 at.% Nb; ~Pt5Al3: ~ 5 at.% Nb; ~Pt3Al: ~ 10 at.% Nb; and β: ~ 30 at.% Nb. Ten invariant reactions were found on the liquidus surface. The samples were annealed at 1000 °C for 1000 h under air, and while some alloys showed phases with little reduction in extension, some alloys had oxidised to form (Pt) and the oxides of aluminium and niobium.
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The authors would like to acknowledge Dr Clive Oliphant, NIMISA for earlier SEM analyses, Mr Shadrack Moqabulane for assistance with metallography, and Mr Brayner Ndivhuwo Nelwalani for helping with SEM analysis. The authors thank the University of the Witwatersrand and the Advanced Materials Division, Mintek for access to research facilities. The Department of Science and Innovation (formerly the Department of Science and Technology) and National Research Foundation are thanked for financial support.
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This invited article is part of a special tribute issue of the Journal of Phase Equilibria and Diffusion dedicated to the memory of Günter Effenberg. The special issue was organized by Andrew Watson, Coventry University, Coventry, United Kingdom. Svitlana Iljenko, MSI, Materials Science International Services GmbH, Stuttgart, Germany and Rainer Schmid-Fetzer, Clausthal University of Technology, Clausthal-Zellerfield, Germany.
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Ndlovu, G.F., Ukabhai, K.D., Nape, K.T. et al. Study of Pt-Al-Nb Alloys Above 45 at.% Pt. J. Phase Equilib. Diffus. 41, 391–417 (2020). https://doi.org/10.1007/s11669-020-00798-1
- experimental phase equilibria
- liquidus surface
- phase diagram
- ternary phase diagram