This scene is so powerful. Tony's on the verge of tears. Steve gives up his shield without a second thought to save Bucky. Bucky is without his arm. There's so much symbolism here:

Without his arm, Bucky is no longer the Winter Soldier.
By giving up his shield, Steve quits being Captain America.
Tony's arc reactor and suit is destroyed, leaving the broken man who was always hidden beneath now exposed.

This isn't a scene with superheroes; it's now just three men shattered by their experiences.