Does the DC universe have an equivalent "unbreakable" metal? And if so, has Superman ever been shown to bend and/or break it?

Correction:  After thinking about this, I recalled that Fawcett had 3 metals, Shazamium was the one that Shazam wore as a bracelet that let him exist as a phantom and teleport to/from the Rock of Eternity.

Sivanium was Sivana's 'Living Metal' that he used to make androids of himself with. 

It was Marvelium that was "The World's Mightiest Element"; so strong that no known force in the universe could work it, except Captain Marvel.

All these are from Captain Marvel Adventures 100, 1949

Supermanium appeared first in World's Finest 41, also in 1949

I'm just the geekiest.  Once it sets, nothing can damage Adamantium.  Nothing.  Now, Element Lad could get rid of it, though!!

"Could Wonder Woman and GL together bend supermanium?"

In my opinion, either of them alone could.

  Whatever the difference in strength is between Superman and Wonder Woman, I don't think it's great enough to make a difference here.

  As to GL, what that ring can accomplish is limited only by the wearer's willpower.  Hal could probably muster enough to bend it.  A few others might, as well.  But that's the least interesting way to write a GL story.  Far better to say he can't, and then have him come up with a creative workaround.  Say he's in a Supermanium cell.  Failing to bend the bars, he might use the ring to, oh, say travel back in time to before the cage was there, or shrink himself and travel between the bars or even atoms of the prison. Or he could use the ring to pick the lock, mind-control his jailer, or turn the cell or himself invisible to trick his captors into releasing him.  Written well, there's not a whole lot GL can't do.