Is a wire worn out by a current that flows through it? How long does a cupper wire last with or without a current? Do the current electrons loosen the atoms in the metallic bonding so there is a kind of wear of the wire? Or does it not have any effect on the lifetime of a wire whether there is a current or not?
 A: Yes, a wire is worn out when a current flows through it for a long enough time at sufficient density. The phenomenon is called electromigration which is a very practical reliability problem leading to the failure of metallic (Cu) circuit connections in computer chips. Electromigration is a material transport due to (among other mechanisms) the momentum transfer from conduction electrons to diffusing metal ions. It can lead to the mechanical interruption of circuit connections in integrated circuits. Extensive research work is done to understand and minimize this failure effect.
A: No the current does not loosen the metallic bonds. The random thermal velocity of the free electrons in the wire without current is about 1600 km/s. The drift velocity of the electrons when current flows is typically less than 0.1mm/s, which is superimposed on the random motion. So the current has no effect on the structure of the metal which the random motion of electrons does not have.  
Current does have an effect in incandescent light bulbs where the metal gets white-hot and either reacts with the surrounding gas or (in the case of bulbs containing an inert gas like argon) it is gradually vaporized. This causes the cross-section of the wire to decrease, which increases the density of the current and further increases temperature, causing an increased rate of vaporization. Such bulbs last about 1000 hours of use.
