A fatigue crack had initiated in weld metal on the inner surface of the socket.

After propagating through the weld metal during a large number of flights, the fatigue crack entered the socket's parent metal.

For these you can buy 'coronets' of welded metal to push in around the crown to hold the heavy-headed stems comfortably, but not rigidly upright.

In general the finished weld metal should have mechanical properties similar to those of the base material with no defects such as discontinuities, entrained contaminants or porosity within the weld.

Ultrasonics can also be used to weld metals, but are typically limited to small welds of thin, malleable metals, e.g. aluminum, copper, nickel.