Hydrogen Embrittlement
Hydrogen embrittlement is a unique form of material degradation. It is caused by the accumulation of atomic hydrogen within a material, eventually leading to catastrophic failure and irreparable damage. It affects a wide range of materials and many structural components, and is a major safety hazard in many industries. Understanding the mechanisms and causes of hydrogen embrittlement is essential for controlling and mitigating its effects.
Hydrogen embrittlement is one of the most enigmatic materials science phenomena. It occurs when hydrogen atoms are absorbed into the grain boundaries of a metal, leading to grain boundary sliding and dislocations. This can cause the metal to become brittle and prone to cracking, even under relatively low stress levels. The effects of hydrogen embrittlement are most prevalent in high-strength and high-hardness steels and alloys, but it can also occur in other metals and alloys.
Hydrogen embrittlement is also known as hydrogen induced cracking, or HIC. It is distinct from corrosion and other forms of materials degradation. Corrosion occurs on the surface of the material, while hydrogen embrittlement occurs within the material itself. The mechanism is fairly simple, but the effects are complex and varied.
Hydrogen embrittlement is caused by the absorption of atomic hydrogen into the grain boundaries of a material. This is typically caused by an imbalance of the hydrogen concentration on either side of the grain boundary. This can be caused by a number of external factors, such as water vapor, liquids, electrochemical reactions, and high pressure hydrogen gas. It is important to note that the hydrogen does not need to diffuse into the material to cause hydrogen embrittlement; it simply needs to be present on one side of the grain boundary, creating a concentration gradient.
Once the atomic hydrogen has been absorbed into the grain boundaries, it contributes to the degradation of the material by causing the grain boundaries to become more brittle and prone to cracking. This is known as hydrogen cracking. The effect of this is known as hydrogen assisted cracking. In some cases, the hydrogen can even cause the material to become ductile and lose its strength.
Hydrogen embrittlement can occur in a wide range of materials, including steels, aluminum alloys, titanium alloys, and plastic materials. It is most prevalent in high-strength, high-hardness steels and alloys, as they are more susceptible to hydrogen embrittlement compared to low-strength materials. It is also important to note that any material can become brittle and prone to cracking due to hydrogen embrittlement, regardless of its composition.
The effects of hydrogen embrittlement can be minimized by controlling the amount of hydrogen present in the environment. This can be achieved by proper design and construction of components, using suitable materials and coatings, controlling the processing temperatures, controlling the environment around components, and using inert gas shielding. For example, components should be stored in an environment without water vapor and/or hydrogen gas, and components should be pre-heated prior to welding in order to prevent hydrogen from entering into the material.
In conclusion, hydrogen embrittlement is a unique form of material degradation caused by the absorption of atomic hydrogen into grain boundaries. It affects a wide range of materials and is a major safety hazard in many industries. Understanding the mechanisms and causes of hydrogen embrittlement is essential for controlling and mitigating its effects.
