Platinum alloys are being developed and characterised which have microstructures that are analogous to the g/g¢ microstructure of the nickel-based superalloys [2003Süs1]. The microstructures comprise particles of Pt3Al in a (Pt) matrix. These Pt based superalloys, with their higher melting point and good corrosion resistance, have the potential to substitute Ni-based superalloys for high-temperature components in turbine engines. The Pt-Cr-Ru system has been studied experimentally as part of this project [2002Süs, 2003Süs2]. The system was studied in the as-cast condition, and after annealing at 600°C and 1000°C. A solidification projection and a liquidus surface were constructed, together with isothermal sections at 600°C and 1000°C. The major phases are (Ru), (Pt) and ~CrPt, with ~Cr2Ru (D8b), ~Cr3Ru (A15) and ~Cr3Pt (A15) being minor. Both the tetragonal (L10) and cubic (A1) forms of ~CrPt were observed. Two invariant reactions were identified in the Pt-Cr-Ru system.
The second part of the project involves building a thermodynamic database for Pt-based alloys. Previously a preliminary CALPHAD-like assessment has been done for the Pt-Cr and Cr-Ru systems, with an extrapolation into Pt-Cr-Ru [2003Gla]. The calculations were done with the Thermo-CalcTM software. The preliminary results of the CALPHAD-like assessment were compared with the experimental results. It was found that the calculated liquidus was in good agreement, considering the limited data used. Optimisation of the Pt-Cr-Ru system is to follow, as well as the calculation of isothermal sections at 600°C and 1000°C.
The financial assistance of the South African Department of Science and Technology and the Platinum Development Initiative is acknowledged.
References:
[2002Süs] R. Süss, L.A. Cornish, L. Glaner and D.N. Compton, 15th International Congress on Electron Microscopy, 1st - 6th September 2002, Durban, South Africa.
[2003Gla] U. Glatzel and S. Prins, CALPHAD XXXII, 25-30 May 2003, Montreal, Canada.
[2003Süs1] R. Süss, L.A. Cornish, P.J. Hill and J. Hohls, Proc. Advanced Materials and Processes for gas turbines, September 22-26 2002, Copper Mountain, Colorado, USA, TMS, 301-308.
[2003Süs2] R. Süss, U. Glatzel, S. Prins and L.A. Cornish, Proc. of the 2nd International Conference of the African Materials Research Society, University of the Witwatersrand, 8–11 December 2003, Johannesburg, 141-142.