The turbine wheel lives in hell. Exhaust gas temperatures routinely hit 900°C (1650°F) in gas engines and can spike to 1050°C in high-output applications, while the wheel spins at 150,000–250,000 RPM. The material choice isn't about strength alone — it's about creep resistance: the tendency of metals to slowly deform under sustained load at high temperature, even below their yield strength.

Inconel 713C is the workhorse. A nickel-chromium superalloy with aluminum, titanium, and molybdenum, it's cast into turbine wheels using investment casting (lost wax). It holds up to about 950°C continuous and is what you'll find in 90% of OEM turbos — your Garrett GT2860, BorgWarner EFR series, Mitsubishi TD05, all use Inconel 713C or close cousins like 718 or 738.

MarM-247 steps up for serious applications. Developed by Martin Marietta, it adds tungsten, tantalum, and hafnium to push continuous operating temperature to 1050°C. You'll see it in diesel truck turbos that run hot continuously (think Cummins ISX, Detroit DD15) and in motorsport applications like WRC and F1-era turbos. It costs roughly 2–3× Inconel 713C per kilogram of finished wheel.

Titanium Aluminide (TiAl, gamma-TiAl) is the modern frontier. It's intermetallic — neither pure metal nor traditional alloy — with a density of 3.9 g/cm³ versus Inconel's 8.0 g/cm³. Half the mass. That's the killer feature: a TiAl turbine wheel has roughly half the rotational inertia, slashing turbo lag dramatically. Honeywell pioneered it for the 2014 Corvette ZR1 successor and it's now in BMW M-series and select Mercedes-AMG turbos. The downside: TiAl is brittle below 600°C, harder to machine, and roughly 5× the cost of Inconel.

Rule of thumb for spool-up improvement: Turbine wheel inertia scales with the fourth power of diameter and linearly with density. Halving density via TiAl gives the same spool improvement as shrinking an Inconel wheel by about 16% in diameter — but without losing top-end flow.

Real-world example: The Porsche 911 Turbo S (992) uses TiAl turbine wheels. Compared to the previous-gen Inconel wheels, peak boost arrives roughly 500 RPM earlier with no reduction in wheel size or top-end power. That's why the car feels naturally aspirated off-boost — the wheels barely have any inertia to overcome.

Failure mode to know: thermal fatigue cracking at blade roots. Repeated heat cycling (hot lap, cooldown, hot lap) eventually grows cracks at the highest-stress fillet. Inconel tolerates this better than TiAl, which is why race teams running TiAl wheels replace them on a strict service interval rather than condition.