When hydrogen is introduced or infused into metals, they can start to become brittle in a process that is called hydrogen embrittlement. The extent to which embrittlement occurs depends on the structure of the metal and the amount of hydrogen that has been absorbed by the material.
This Royal Society Publishing journal article offers an interesting and in-depth discussion amongst a number of knowledgeable individuals on hydrogen embrittlement that you may wish to explore further. But let’s start by running through when it can occur and whether there are steps that can be taken to prevent it.
When does hydrogen embrittlement occur?
Typically, hydrogen can only enter metals as ions or atoms. However, when the temperature rises above 150 degrees Celsius, gaseous hydrogen molecules start to separate into atoms and can be absorbed. This means that higher rates of hydrogen absorption are seen when metals are in a molten state, so welding and casting operations are particularly prone to hydrogen embrittlement.
Additionally, processes like electroplating, corrosion and cathodic protection are known to produce hydrogen ions, which means that these processes also provide opportunities for hydrogen to combine with metal components.
What happens when hydrogen embrittlement occurs?
Hydrogen embrittlement can start to cause severe issues when cracking occurs, which can happen during fabrication and when stresses are placed on the metal. This issue has several different names, depending upon the scenario in which it occurs.
For example, cold or delayed cracking typically refers to cracks that appear when welded metal starts to cool. Hydrogen-induced cracking (HIC) is often used to refer to the cracking that can occur when hydrogen is absorbed into steel vessels and pipelines during their service.
Preventing hydrogen embrittlement with thermal plasma spray
Hydrogen embrittlement can be prevented by minimising contact between hydrogen and metals. One method of doing this is to apply a thermal plasma spray. This technique can be employed with a number of metals including copper alloy, steel, aluminium and titanium.
Thermal plasma sprays can be applied to a range of different products, including piston caps, exhausts, turbine blades, cranes, and gear cones.