several things happen when you run (overspeed) an engine above its design operating speed >110% redline RPM
The weakest disk will probably grow in size and rub the blade tips and loosen itself on its shaft
The compressors will likely run into their surge line and barf enough to prevent additional speed increases
Both the compressor and Turbine rotors will likely run into an unintended blade-disk coupled frequency and break either the disk or the blades
An unloaded turbine will likely runaway to 150-175% speed and start shedding blades or worse, the disk itself.