Nope, to take a weapon to its highest upgrade level you require a titanate slab. Titanite Slabs are available only in a small amount in the world of Dark Souls 3. Once you acquire all the Titanite Slabs in Dark Souls 3 and use them, you will have to start a new playthrough or have a partner willing to drop you a titanite slab in order to upgrade more weapons to their highest level.