WE know the original full-size bell is made from a very expensive niobium alloy, for heat resistance. But I notice that the new bell hardly glows at all - just very faintly at the extreme outer edge. The film cooling provided by the turbopump exhaust protects it completely.
So, I am wondering - are they still using that expensive niobium for the stubby nozzle? From what I can see of the bell, they could use simple mild steel and be perfectly OK.
I can’t imagine them using something expensive if they don’t have to, considering they are already sacrificing isp to save a few Bob.
What are regular raptor bells made from? I’d say if they could use common material they would
The regular raptor bells (and the regular Merlin bells, which we are discussing here) are made from a copper-rich alloy, for high thermal conductivity. They are fully regeneratively cooled by the engine’s fuel (kero or methane). The extensions are radiatively cooled, with the base section film cooled by bleeding the cooler turbopump exhaust in a ring around the base of the extension/lip or the nozzle.