Nitrided White Layer – Formation, Function, Usefulness, Variations and Challenges. How is this helping Electric Vehicle Engineering?

Gas Nitriding (and Ferritic Nitrocarburizing) has seen tremendous growth. Today, growth continues to accelerate as more uses are being found, especially in electric vehicles (EV). One of the reasons for its growth has been due to controllability of protection layers consistent with the needs of the vehicle component engineer. Steels are still the metal of choice for many applications and the nitrided layer of a steel is well-known for its Tribological features (some would say even more than three) which include wear resistance, lubricity, and friction. But corrosion resistance has become a mainstay of white layer formation and the presence (or lack thereof) of white layer plays an important role in steels and alloys of steels. White layer (known as compound zone) consists of two iron nitrides known as Epsilon (Fe_2-3[N,C] and Gamma Prime (Fe₄N). As well, the Epsilon layer can contain varying amounts of iron carbides and/or iron carbonitrides. This paper will focus mainly on the how’s and why’s of white layer: how to form and craft it; and how to minimize it, if required. Just as importantly, some applications of how the EV component engineers have found uses for this important steel treatment are discussed, including brake rotors.