Hydrogen Embrittlement is a process whereby metals become brittle and fracture as a result of the introduction and diffusion of hydrogen into the material.
Also known as hydrogen induced cracking, embrittlement is often caused by the introduction of hydrogen during forming, coating, cleaning, finishing and plating processes. This often called internal embrittlement. External embrittlement can also occur as a result of environment exposure to soils and chemicals (including water), corrosion, cathodic protection and from hydrogen created through coating corrosion.
Three factors are needed for a metal to be susceptible to hydrogen damage, these are the presence and diffusion of hydrogen atoms, the use of a susceptible material, and stress. Stress corrosion cracking occurs when hydrogen is introduced into the metal and sufficient tensile stress is applied, this stress factor is called the threshold stress or Ki_SCC.
Not all metals are vulnerable to hydrogen embrittlement as it affects hydride-forming metals such as niobium, tantalum, titanium, vanadium and zirconium. The most vulnerable metals are high strength steels and titanium and aluminium alloys. However, when it does occur, hydrogen embrittlement can cause reduced ductility and a lessening of load-bearing capacity, which can lead to hydrogen induced cracking and brittle failures below the yield stress of the susceptible materials themselves.