The alloy on the oxygen side pump in the Raptor engine is a work of magic and or art. An oxygen rich turbopump runs so hot it was thought impossible to create because the turbine would fail before the burn was over. SpaceX had to invent the alloy before the first Raptor full duration fire. That's a very low level, never done before, breakthrough required just to get to the real hard stuff.
edit: if you watch gas generator tests on youtube the gas coming out is dark because it's very fuel rich which keeps it cool (in a relative sense)
> SpaceX had to invent the alloy before the first Raptor full duration fire. That's a very low level, never done before, breakthrough required just to get to the real hard stuff.
Russians had oxydizer-rich gas generators in large engines since e.g. early 1960-s (see Proton 1st stage engines). Oxygen-rich gas generators are at least since mid-1980-s (RD-170). So not exactly never done before.
Russians sold RD-180 with technology to reproduce them in USA. It was just too expensive to make them in America, so eventually Energomash got all orders to make them for Atlases. And now Falcons are pretty good too, so less need in RD-180 - Orbital still buys RD-181, single chamber engine though. And Raptors could be in use soon. And BE-4 from Blue Origin hopefully will power new ULA Vulcan rockets soon too... and that oxygen-resisting metallurgy is likely used at least in some of them (RD-181 for sure).
edit: if you watch gas generator tests on youtube the gas coming out is dark because it's very fuel rich which keeps it cool (in a relative sense)