What phenomenon occurs if titanium is drilled at too high a speed, causing it to melt and re-harden?

When titanium is drilled at excessively high speeds, the friction generated can lead to a significant increase in temperature, causing the titanium to melt. This melting occurs due to the thermal properties of titanium, which has a relatively low thermal conductivity. As a result, the heat doesn't dissipate quickly enough, leading to localized melting around the drill bit. Once the drilling is halted or the speed is reduced, the molten titanium can cool and re-harden, resulting in a surface condition known as galling.

Galling is a type of material failure characterized by the adhesion between sliding surfaces, and in this case, it is exacerbated by the thermal and mechanical stresses involved in the drilling process. This phenomenon is particularly pronounced in titanium due to its ductility and the tendency for its softer, molten state to adhere to the drill bit or tooling. Understanding this behavior is crucial for aerospace assembly mechanics, as improper drilling techniques can compromise the integrity of titanium components used in aircraft structures.