Can a DA Librarian......

[Stibbok]

Be upgraded to have an invulnerable save? Or articifer armour?

As I cannot find the answer in the codex

[David Crossley]

Artificer armour no, Invulnerable save yes.
Things that grant varying inv saves he can take:
Terminator Armour 5++
Combat Shield 6++
Conversion Field 4++ (plus blind tests)
Displacer Field 3++ (plus scatter)
Power Field Generator 4++ (with a 3" bubble)

[Stibbok]

Thanks for that