Nitride coatings for environmental barriers: the key microscopic mechanisms and momentous applications of first-principles calculations

Protective nitride coatings are widely used in various industrial fields due to their exceptional mechanical, structural, and chemical stabilities under various harsh environments. Many nitride coatings have the inherent barrier function against the attack of environmental agents, making them splendid materials for, e.g., hydrogen permeation barriers, high-temperature-environment barriers, and tribocorrosion coatings. However, the long-term contact with aggressive environments may still result in the degradation of these coatings, where many processes occuring on various atomistic microstructures (e.g., surfaces, vacancies, grain boundaries, and coating/substrate interfaces) usually play the key roles. Here, we make a timely review on the microscopic mechanisms associated with the interactions between various microstructural entities and environmental agents, for which the first-principles calculations will be powerful in quantitatively revealing the essential interatomic bondings and thermodynamic/kinetic trends therein. Many successful application cases and possible future directions of first-principles calculations for these three kinds of nitride coatings are discussed here, which can shed much light on more optimization ways towards superior and durable nitride coatings through precise chemical tuning and structural design in the future.