Lyman,
I only mention the IP shaft because
you think it move rearward, somehow separating from the coupling in the compressor section.
It did not!
Your quotes:
Yet with a shaft transiting aft, the friction can create instant molten metal, whilst the shaft retains integrity
And,
I still suggest that the slowing of the IPC demonstrates the axial migration of the IShaft aft ward into the "stationery parts of the engine" (AD). Integrity of the shaft is required until disintegration of the I Turbine, IMO.
The IP disc is a smooth bore disc. It fits snuggly around the end of the IP shaft and is held in place by a series of bolts through bolt holes in the power drive arm. If you review the photos in the ATSB reports, the initial failure occurred at the circumferential bolt holes releasing the disc to overspeed. From a design point of view, it is never good to have bolt holes in the area they are in because of the fact bolt holes are built in stress risers. So this was the weakest point once the disc overheated due to the oil fire.
At some point in time, seconds after the power drive arm failure, the disc, still containing the turbine blades, moved rearward, contacting the inner band leading edge of the LPT stage 1 nozzle ring. There was no IP blade to LP nozzle contact to slow the accelerated disc. At this point in time, the disc was highly accelerated, near burst and had stretched so that the "pine tree" features of the disc were enlarged, the turbine blades were now loose. The contact with the LPT nozzle created the metal splatter and then the disc burst. The turbine blades may have come out of the several disc fractured sections in two directions, radially and rearward as the disc departed the engine.
I agree with
barit1, this is a classic disc burst, have seen it happen in a test cell, not a pretty sight.