Journal of Alloys and Compounds 416 (2006) 80–92 Investigation of as-cast alloys in the Pt–Cr–Ru system R. S ¨ uss a,b,c,∗ , L.A. Cornish a,c , M.J. Witcomb c,d a Advanced Materials Division, Mintek, Private Bag X3015, 200 Hans Strijdom Drive, Randburg 2125, South Africa b School of Process and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa c DST/NRF Centre of Excellence for Strong Materials, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa d Electron Microscope Unit, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa Received 5 July 2005; accepted 27 July 2005 Available online 5 October 2005 Abstract Platinum-based alloys are being developed which have microstructures that are analogous to the / ′ microstructure of the nickel-based super- alloys. These Pt-based superalloys have the potential to substitute Ni-based superalloys for even higher temperature applications. The Pt–Cr–Ru system has been studied experimentally as part of this project. The alloys were studied in the as-cast condition, using scanning electron microscope (SEM) and X-ray diffraction (XRD). A solidification projection and liquidus surface were constructed. The major phases were (Ru), (Pt) and ∼CrPt, with ∼Cr 2 Ru (D8 b ), ∼Cr 3 Ru (A15) and ∼Cr 3 Pt (A15) being minor in extent. Both the tetragonal (L1 0 ) and cubic (A1) forms of ∼CrPt were observed. Two invariant reactions were identified in the Pt–Cr–Ru system. © 2005 Elsevier B.V. All rights reserved. Keywords: Casting; Scanning electron microscopy; Microstructure; Phase diagram 1. Introduction Platinum alloys are being developed and characterised which have microstructures that are analogous to the / ′ microstruc- ture of the nickel-based superalloys [1–4]. With their higher melting points and good corrosion resistance, these Pt-based superalloys could potentially substitute Ni-based superalloys for high-temperature components in turbine engines. As well as optimising physical properties of the alloys, the aim of the project is to simultaneously compile a thermodynamic database for the selected alloy components. The most promis- ing overall properties to date have been for a quaternary alloy Pt 84 :Al 11 :Ru 2 :Cr 3 , and although there will be other alloying additions, for example, Co, the quaternary will be the basis of the thermodynamic database using the Thermo-Calc TM software. The information required to undertake the computer assessments is either gleaned from literature, or when not available, under- taken within the project. Experimental work has already been completed on Al–Cr–Ru [5–7], Pt–Al–Ru [8,9] and Pt–Cr–Ru [10–12], while work is being done on the Pt–Al–Cr system [13]. ∗ Corresponding author. E-mail address: rainers@mintek.co.za (R. S ¨ uss). This paper summarises results obtained from experimental work on Pt–Cr–Ru alloys. 2. Previous work 2.1. Chromium–platinum The Cr–Pt binary phase diagram given in Massalski [14] is drawn from Venkatraman and Neumann [15] who assessed the earlier work of M¨ uller [16] and Waterstrat [17] on the Pt–Cr system. The phase diagram is dominated by broad homogeneity range of the (Pt) terminal solid solution from ∼29 to 100 at.% Pt at 1530 ◦ C [17]. Both M ¨ uller and Waterstrat indicated a max- imum melting point of (Pt) at ∼80 at.% Pt. The composition and temperature of the two eutectics have been determined by Waterstrat. He also reported a syntectic decomposition of Cr 3 Pt, i.e. the presence of a liquid miscibility gap, which Venkatraman and Neumann believed to be unlikely [15], following Raub and Mahler instead who showed that Cr 3 Pt melts congruently [18]. The presence of two ordered intermediate phases, Cr 3 Pt and CrPt 3 , has been firmly established. Cr 3 Pt has the ordered cubic A15-type structure, occurring at a slightly off-stoichiometric composition of ∼20 at.% Pt. CrPt 3 has the fcc L1 2 (AuCu 3 ) structure, and exists below ∼1130 ◦ C. Ordering occurs over a 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.07.070