Investigation of as-cast alloys in the Pt–Cr–Ru system

Abstract

Platinum-based alloys are being developed which have microstructures that are analogous to the ␥/␥ microstructure of the nickel-based superalloys. 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.

Investigation of isothermal sections at 1000 and 600°C in the Pt–Cr–Ru system

“…3). The interdendritic phase had become more rounded on annealing, compared to the as-cast condition [8].…”

“…During annealing, the dendrite outlines of alloy Pt 6 :Cr 56 : Ru 38 became less defined compared to the as-cast condition [8], and there was precipitation in the (Ru) dendrites (Fig. 2).…”

“…18), it was assumed that this alloy was not at equilibrium and that the remainder of the white phase (∼CrPt) would disappear on further annealing. Its proportion had already substantially decreased compared to the as-cast condition [8]. 14 The more complicated microstructure of the as-cast Alloy Pt 14 :Cr 72 :Ru 14 [8] simplified significantly to that of a mostly single phase ∼Cr 3 Pt alloy, with isolated spots of small white L1 0 ∼CrPt observed, as well as black regions of porosity.…”

“…Its proportion had already substantially decreased compared to the as-cast condition [8]. 14 The more complicated microstructure of the as-cast Alloy Pt 14 :Cr 72 :Ru 14 [8] simplified significantly to that of a mostly single phase ∼Cr 3 Pt alloy, with isolated spots of small white L1 0 ∼CrPt observed, as well as black regions of porosity. The white ∼CrPt would probably disappear on further annealing, as deduced from the plot of compositions.…”

“…Expermounted and ground to 1200 grit on SiC paper. After examination of the as-cast microstructures [8], one half of the samples were annealed at 600 • C, and the other half at 1000 • C, for 1000 h (the maximum time interval allowed due to furnace availability constraints). The samples were annealed in air and subsequently quenched in water.…”