Nitridation

Nitridation is a thermochemical surface treatment in which nitrogen atoms are introduced into a material to form nitride phases, typically in the near-surface diffusion zone. The process is used to modify surface properties such as hardness, wear resistance, fatigue strength, and sometimes oxidation resistance without significantly altering the core material.

Nitridation can be performed by several methods. Gas nitriding uses nitrogen-containing gases, often ammonia, or nitrogen/hydrogen mixtures, at temperatures around 500–550 °C for steels to form iron nitrides. Plasma or ion nitriding uses plasma-activated nitrogen species, enabling diffusion at similar or lower temperatures and allowing more precise control of case depth and microstructure. Salt bath nitriding employs molten nitriding salts at controlled temperatures, offering rapid diffusion in some alloys. Chemical vapor nitridation and related vapor-phase techniques use nitrogen-containing precursors to form nitride layers, suitable for specialized materials and shapes.

Common outcomes include the formation of hard nitride layers on metals, notably iron nitrides such as Fe3N and Fe4N, as well as coatings of TiN, CrN, or AlN when applied to various substrates. In ceramics and semiconductor contexts, nitridation can lead to stable nitrides such as silicon nitride (Si3N4), titanium nitride (TiN), and aluminum nitride (AlN), which contribute high hardness, thermal stability, and electrical properties.

Considerations for nitridation include diffusion depth, temperature, gas composition, and treatment time, which determine nitride phase, layer thickness, and residual stresses. Potential drawbacks include distortion, altered toughness, and environmental or safety concerns related to reactive nitrogen species and processing media.