On the development and investigation of quaternary Pt-based superalloys with Ni additions

Abstract

The objective of this work is to mimic the microstructure and strengthening mechanisms of Ni-based superalloys in a new group of high-temperature alloys based on the system Pt-Al. The elements Cr and Ni were chosen as further alloying components. Having a face-centered cubic (fcc) crystal structure with an L1 2 -ordered and coherently embedded phase, these new alloys should increase creep and corrosion resistance beyond Ni-based superalloys. After arc melting and heat treatment, the alloys were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the aged condition, the alloy composition 13 at. pct Al, 3 at. pct Cr, 7 at. pct Ni, and balance Pt showed the most promising microstructure with cubical precipitates, 30 pct precipitate volume fraction, and a lattice misfit of about Ϫ0.1 pct at room temperature.

Platinum-Based Alloys and Coatings: Materials for the Future?

“…Compressive proof stress results indicated better properties for Pt 74.5 :Hf 17 :Rh 8.5 (at.%) than the initial ternary alloys , but the oxidation resistance was much poorer. From these beginnings, two series of Pt-based alloys were developed: Pt-Al-Cr-Ru (Douglas et al, 2009;Cornish et al, 2009b) and Pt-Al-Cr-Ni (Hüller et al, 2005;Wenderoth et al, 2005Wenderoth et al, & 2007Rudnik et al, 2008;Völkl et al, 2005Völkl et al, & 2009. Both used the advantageous properties of aluminium (with the added benefit of chromium) for forming the ~Pt 3 Al precipitates and protective alumina films.…”

“…The former used ruthenium as a solid solution strengthener, whereas the latter alloys used nickel, and avoided ruthenium because of concerns over possible room temperature formation of RuO 4 , a volatile, toxic oxide (Eagleson, 1993). The Pt-Al-Cr-Ni alloys were subjected to more rigorous mechanical testing by the researchers in Germany (Hüller et al, 2005;Wenderoth et al, 2005Wenderoth et al, & 2007Rudnik et al, 2008;Völkl et al, 2005Völkl et al, & 2009. Further work was done by researchers in South Africa on the addition of alloying elements other than ruthenium to reduce the platinum content and thereby both the expense and the mass (Shongwe et al, 2009;.…”

“…Alloying additions to Pt-Al have already decreased the slope of the solvus and produced more precipitates. In Pt-Al-Cr-Ni alloys, Wenderoth et al (2005) attained over 30 vol. % precipitates, thereby deducing that the solvus had to be less vertical than in the Pt-Al binary system.…”

“…Surprisingly, the melting temperature was increased by Ni additions. The work was not continued because of the disappointingly low hardness results (Glaner & Cornish, 2003), although other research has been more encouraging (Vorberg et al, 2004Hüller et al, 2005;Völkl, et al, 2005;Wenderoth et al, 2005Wenderoth et al, & 2006.…”

“…Currently, there are three major ranges of Pt-based alloys which have been developed. One is based on Pt-Al-Cr-Ni (Hüller et al, 2005;Wenderoth et al, 2005Wenderoth et al, & 2007Rudnik et al, 2008;Völkl et al, 2005Völkl et al, & 2009, and two are based on Pt-Al-Cr-Ru (Cornish et al, 2009a;2009b;Douglas et al, 2009). Of the latter range, one is more malleable but less resistant to extreme chemical environments, whereas the other has greater chemical resistance, but is more difficult to form.…”