I have some troubles here to know which tense I should use: The Lord hasn't expected that those bloodthirsty weapons would corrupt them. OR
The Lord didn't expect that those bloodthirsty weapons would corrupt them.
A possibility which is much more likely than 'hasn't expected' is 'hadn't expected'.
This is used to signal a past change of expectation.
Suppose someone gives a present which is much better than what would be usual.
The delighted recipient says, 'Oh, I hadn't expected that!'
This says there had been expectation beforehand, but not of such a good gift.
Depending on context, 'hadn't' may fit your situation.