O'Hara, John

Development of strong, oxidation and corrosion resistant nickel-based superalloys: critical review of challenges, progress and prospects

“…It must be mentioned that, though Re contributes significantly to the TCP precipitation, the latest generations of superalloys contain up to 70% by volume of the γ ′ phase, and consequently, the γ matrix is supersaturated with the solid-solution strengthening refractory elements, thus potentially creating an unstable microstructure. It should be mentioned that Ruthenium (Ru) initially discovered as a strengthening element by the GE Aviation researchers [25,26] decrease the tendency of TCP formation to be discussed later. The improved stability provided by Ru has been utilised to develop the fifthand sixth-generations of SX alloys by the Japan National Institute of Material Science (NIMS) researchers [29,30] where the Cr content has been increased modestly to 4.2 wt%.…”

“…Ruthenium effect: During the development of a third-generation SX alloy, Rene' N6, the GE group [25,26] discovered a highly significant beneficial effect of ruthenium on the high temperature rupturestrength attributed to reduction in the occurrence of TCP phases (Table 2). An arbitrator TCP severity scale, N Z , based on microstructural observations of TCP, was used during the initial screening of a large number of Ru-containing alloys: alloys with Nz of 3 and higher were rejected.…”

“…The presence of the brittle TCP phases has been shown to be highly detrimental to the stress rupture strength [25,26]. A prudent selection for screening the types and amounts of alloying elements mandates that the TCP phases be minimised as much as possible while trying to obtain higher creep and rupture strengths.…”