This is the same as the similarly named achievement from the original 360 version.
Here is the original solution from o DEEVIUS o.
This is a story progression Achievement and cannot be missed, yet I felt it necessary to help anyone who may get stuck on the specifics for whatever reasons.
*For these Shards you will need to have your Mask activated and they appear on your local map and radar as a Gold Shards symbol.
ASHLANDS (2 of 7)
THE DRY ROADS (3 of 7)
CROSSROADS (4 of 7)
DROWNED PASS (5 of 7)
BROKEN STAIR (6 of 7)
THE CHOKING GROUNDS (7 of 7)
When you have all the Shards you can make your way to the Anvil's Ford to see Ulthane. There's a cutscene and Ulthane will re-forge the Armageddon Blade for you, the achievement will pop after the cutscene.
*Note this will replace Chaoseater but will be fully levelled so if you have your Scythe/Harvester and Gauntlet fully upgraded you'll get the Battle Hardened achievement regardless.