Developing an advanced Si-bearing DS Ni-base superalloy

High Temperature Oxidation and Corrosion Properties of High Entropy Superalloys

“…By contrast, HESA-1 only contains 3.9 wt.% of Al, and it does not form continuous Al 2 O 3 , though its Al activity is the highest among the three alloys. As for HESA-2, which contains similar levels of Al and Cr compared to that of CM247LC, its high content of Ti may also attribute to its high Al activity [22], although Ti-rich oxides may form rapidly during the initial stage of oxidation. Therefore, to further improve the oxidation resistance of high entropy superalloys, future alloy design will try to limit the content of Ti in order to minimize the formation of complex oxides, and further increase the Al activity by alloy design for rapid Al 2 O 3 formation.…”

“…For the following ageing process to uniformly reprecipitate γ 1 particles, different ageing temperatures from 800 to 1100˝C with different ageing times were tested, and 1000˝C/3 h was determined to be the primary ageing condition due to preferred γ 1 volume fraction (between 50% and 70% for HESA-1 and HESA-2) and also size of γ 1 (around 300 nm for both HESAs). The secondary ageing can further adjust γ 1 morphology to be more regular, asnd it was conducted at 800˝C for 20 h. Samples of a Ni-based superalloy-CM247LC processed by the same DS casting process and standard heat treatment [21,22] were examined for comparative studies. Specimens for oxidation and hot corrosion tests were machined to a dimension of 8 mmˆ8 mmˆ3 mm by electrical discharge machining.…”

Oxidation Behaviour of Si-Bearing Co-Based Alloys

“…When temperature is higher than 1000°C, Cr 2 O 3 layer has become less protective [2,14], and the protective oxide scale has primarily been Al 2 O 3 [15]. Several literature have indicated that Si addition can promote the formation of Al 2 O 3 and improve the adhesion between Al 2 O 3 and substrate in Ni-based superalloys [16][17][18][19]. Similar concept has also been explored by Klein et al [5] on Co-based superalloys; although oxidation resistance can be improved, the formation of Al 2 O 3 does not seem to be dense and continuous in these studies.…”

In-Service Oxidation and Microstructural Evolution of a Nickel Superalloy in a Formula 1 Car Exhaust

“…However, Mo 5 Si 3 is a known thermodynamically stable species (DG f = -319 kJ/mol at 1273°C [34]), and the formation of (Nb, Mo) 5 Si 3 silicides has been observed in high Si-content Nb-based alloys [35]. Prior studies have examined the effects of Si addition on superalloy properties [36,37], but the partitioning behaviour of Si to c or c 0 phases appears to change with different alloying additions (such as Ti). Whilst the addition of Si is known to improve oxidation resistance [33,37] and mechanical properties such as thermal-mechanical fatigue [38] in single-crystal alloys, Si segregates to grain boundaries and has been known to trigger the formation of topologically closepacked (TCP) phases in polycrystalline alloys [38].…”

“…5b confirm that silicon oxides are indeed forming, even if only at levels detectable using sub-nm resolution. All of these scales are more protective than the transient oxides that would otherwise form [39], underlining the benefits to oxidation resistance [36][37][38] and the need for further dedicated studies on the effect of Si content.…”