What materials are used to make the high temperature-high pressure bearing parts in a jet engine? I'm asking about the combustion chamber, combustors, nozzle and diffuzers (as in ramjets) rather than turbomachinery. Could cast aluminium or cast steel do the job for a low thrust small model engine?
Short answer: No. Unfortunately the yield strength of typical aluminum alloys drops off after about 300° F and long term exposure to high temperatures dramatically affects their creep and fatigue lives. Typical aviation gas turbine hot sections run between 1700°-2600° F and rotate at angular speeds as high as 40,000 RPM, making Aluminum totally unsuitable for this role. Most hot section components eg cumbustors, stator buckets, rotor buckets, etc. are manufactured from exotic nickel-cobalt superalloys and employ novel single crystal casting techniques as well as passages to bleed compressor air as a boundary layer over them to protect them from that kind of intense heat.
Aluminum has a melting point of 660 C.
Really depends on what "low thrust small model engine" refers to. But if it burns kerosene or jet fuel, probably not for the combustion chamber.