In Captain America: The Winter Soldier, we can see that Bucky's metal arm can exert a force when needed. We can see and hear that in Cap and Bucky's fight scene.
And as far as I know, Bucky's metal arm can also discharge some EMP.
(This was taken from Wikipedia )
That can disable Iron Man for short amount of time. So is there any MCU explanation why Bucky's arm lost this kind of skill or power?