In Empire Strikes Back Vader very clearly says that he "Plans to Rule the Galaxy and defeat the emperor" and asks Luke to Join him.

Luke resists but plays it off against Vader in the throne room that he would join him but not on the dark side. So it was really a trap that was set for the emperor and not so much about Luke Facing Vader.

Vader became practically a half good guy at the end of Empire Strikes Back.

The only conflict was joining the darkside but Luke manages to Bring Vader to his senses. Although the emperors hopes were resting in Luke destroying Vader.