Investigation of the Pt-Al-Cr system as part of the development of the Pt-Al-Cr-Ru thermodynamic database
Date
2008-09-03T11:52:13Z
Authors
Suss, Rainer
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Abstract
The ternary Pt-Al-Cr system was investigated as part of the continued development of a
thermodynamic database for the Pt-Al-Cr-Ru system. Scanning electron microscopy with
energy dispersive X-ray spectroscopy and X-ray diffraction analyses were used to obtain
phase equilibria data. The alloys were studied in the as-cast condition, as well as after
annealing at 600°C and 1000°C respectively. A solidification projection was constructed and
a liquidus surface derived. Isothermal sections at 600°C and 1000°C were also determined. It
was concluded that all phase regions were identified correctly since the results were selfconsistent.
Three ternary phases were found and 19 ternary invariant reactions identified.
A thermodynamic database was developed for the Pt-Al-Cr system using Thermo-Calc. Phase
relations could be reasonably accurately predicted between 600°C and 1000°C, and even up
to temperatures close to the melting point. However, the match between the calculated and
experimental diagrams could be improved. As with the Pt-Cr-Ru system, problems with the
constituting binary systems seemed to be the major cause for problems encountered in the
modelling. Only once the Al-Pt and especially the Cr-Pt and Cr-Ru binary phase diagrams are
confirmed more rigorously, the calculated ternary phase diagrams could be worked on with
more confidence.
More than half of the alloys investigated had hardnesses in excess of 600 HV10 regardless of
their state of heat treatment. Based on the examination of hardness indentations, alloys in the
Pt-Al-Cr system were also often brittle due to the presence of hard intermetallic compounds.
Alloys containing ~Pt3Al showed better behaviour with regard to toughness which was
encouraging for the Pt-based alloys that are being developed by Mintek.
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Keywords
Nickel alloys
Heat resistant alloys
Gas turbines