Hydrogen embrittlement weakens metals by making them brittle and prone to cracking due to hydrogen infiltration. It can occur during manufacturing processes or as a byproduct of corrosive reactions. The trapped hydrogen creates internal pressure, leading to cracks and stress points. Some metals are more susceptible than others, and firing the metal within an hour after electroplating can prevent embrittlement.
Hydrogen embrittlement is a technical term that refers to a compromise in the tensile strength of a metal or molded alloy due to a gaseous or atomic hydrogen infiltration. In short, the hydrogen molecules that occupy the metal react in a way that makes the material brittle and prone to cracking. Obviously, hydrogen embrittlement presents significant problems in terms of being able to rely on the structural integrity of bridges, skyscrapers, airplanes, ships, etc. In fact, this natural phenomenon leads to a condition known as catastrophic failure by fracture and is the direct cause of many mechanical disasters that have occurred on land, as well as in the air and at sea.
The process begins with exposure to hydrogen, which can occur while a metal undergoes certain manufacturing processes, such as electroplating. Successful plating relies on preparing the metal with an acid bath before it can accept layers of chromium. The electricity used during the “pickling” and plating process initiates a reaction called hydrolysis in which water molecules are broken down into positively charged hydrogen ions and negatively charged hydroxide anions.
Hydrogen is also a byproduct of corrosive reactions, such as rust. The decomposition of hydrogen can also be triggered by the same measures taken to prevent it, if applied improperly. For example, hydrogen embrittlement can sometimes be attributed to cathodic protection, which is intended to increase the corrosion resistance of the coated metal by modifying the hydrogen-vulnerable components of the material. This is achieved by introducing a counter current to cause the “sacrifice” of metal anodes which possess a lower corrosion potential than the metal itself. In effect, the material becomes polarised.
Once hydrogen is present, however, individual atoms begin to disperse throughout the metal and accumulate in small spaces in its microstructure, where they then cluster together to form hydrogen molecules. The absorbed hydrogen, now trapped, begins to look for an escape route. It does this by creating internal pressure, which allows hydrogen to emerge in bubbles that ultimately crack the metal’s surface. To counteract this process, the metal must be fired within an hour or less after electroplating to allow trapped hydrogen to escape the plating layers without creating cracks or stress points.
Although hydrogen can invade most metals, some metals and alloys are known to be more susceptible to hydrogen embrittlement, especially magnetic steel, titanium and nickel. Conversely, copper, aluminum and stainless steel are the least affected. However, steel and oxygen-containing copper can become vulnerable to embrittlement when exposed to hydrogen under high heat or pressure. Respectively, these materials suffer from hydrogen attack or steam embrittlement generated by reactions between hydrated molecules and oxides of carbon or copper.
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