xpensive wrote:Is anyone using Titanium for the xhaust, would that work temperature-wise?
No, it would not. Titanium is really only an option up to temperatures around 600 degC, after that it does not offer the properties you desire. Corrosion would for instance be a major problem where your nice titanium exhaust would end up as white powder.
For high temperature applications it's properties like creep resistance, thermal cycle fatigue, hot corrision restistance, scaling temperature and high temperature strength that matters.
xpensive wrote:I understand that turbo-impellers are often made from cheramics, but does anyone know what material those glowing housings are?
The impeller (another name for the compressor wheel) is commonly cast aluminum. High boost versions can use higher strength aluminum alloys such as 2618 machined from forging or titanium (both cast and machined). Compressor housing can be aluminum, magnesium or cast iron.
Center housing is generally heat resistant cast iron such as GG25. Racing turbochargers can use thinwall castings and titanium as the material.
Turbine shaft is carbon steel electron beam welded to the turbine (it has a hollow section at the turbine for low heat conduction). The turbine is usually Inconel 713LC or similar nickel based superalloys. Modern turbochargers having a higher temperature resistance (1050 degC) are usually Mar-M 247 a directionally solidified nickel based superalloy (with high cobalt and tungsten content).
Silicon nitride (ceramic) turbines are very rare, even in racing applications.
For the turbine housing there are several options. Up to roughly 700 degC grey iron can be used. Up to 900 degC nodular iron, Ni-resist, Si-Mo alloyed iron are possebilities. Above 900 degC heat resistant casting steel and stainless casting steel such as HK30 are options. Garrett racing turbochargers usually use thinwall HK30 castings.
