Here, you can see an example of heavy wear and polishing damage caused to a turbine shaft and wheel by a lack of oil, either due to a poor supply, or low oil pressure.
The increased friction caused by a lack of oil lubrication has caused significant wear on the shaft. In turn, this has allowed excessive movement of the rotor, pushing it far beyond its tolerances. The excessive movement has then caused the turbine wheel profile to rub against the housing, damaging the wheels, and preventing the turbocharger from working efficiently.
In cases like this, where there is significant wearing damage to both the turbine shaft and wheel, the unit will need to be completely replaced.
To protect your turbo from this kind of damage, always ensure that your oil levels are topped up to ensure that your turbocharger gets the lubrication it needs to work properly.