Titansteel Bar

Titansteel Bars are used as the main ingredient for almost all of the level 80 Blacksmithing epics, as well as some Engineering epics; including the Mechano-Hog / Mekgineer's Chopper.

Source
This item can be crafted using Mining (450); taught by Grand Master Mining trainers for.

Until patch 3.3.3, Titansteel Bar had a 20 hour cooldown.

Acquisition
A great place to acquire all the materials is in Wintergrasp. Elementals that often drop the crystallized elements of all varieties can be found there. If your faction controls the fortress, Revenants that drop the crystallized materials more reliably also appear. Circling the area with Find Minerals on should eventually yield enough titanium ore.

If one has access to a highly trained alchemist, the much easier to acquire saronite can be transmuted into titanium (without a cooldown).

The downside of searching in Wintergrasp is that if your faction is highly outnumbered, it can prove difficult to live long enough to mine these nodes.

Enchanting

 * Enchant Weapon - Blade Ward