Soroush, nice pic of the turbocharger.
Understand in our FGT application the temperatures depicted in that picture would not occur for a very long duration, and in a mile run would only achieve Tmax at the end of a run. And a run at "Mullet speeds" only takes about 27 seconds. (I guesstimated approx 130 MPH average for the mile, 0 at start and 225 thru the traps).
At turbocharger Tmax and maximum rotational speed, the turbine stresses are quite high and the material Ultimate Tensile Strength (UTS) properties diminished due to temp (inversely proportional). Think about what might happen if the turbine disc bursts at that condition which I am relatively certain would be an "uncontained" event. Disc failures are always catastrophic in any application because they contain so much kinetic energy (which is usually not appreciated by the user). Just hope your turbo designer allowed for speed margin above his assumed design point when you push the envelope...
On a lighter note, turbine discs CAN be designed to operate at these elevated temperatures if the designer knows of these conditions during the design phase. Below is a picture of an engine which operates continuously (i.e. for HOURS) at the indicated metal translucent temperatures. And a disc failure in this engine would lead to loss of the aircraft.