The main application of surface engineering is to build a solid coating on a rough material surface to improve wear resistance. Nitriding is a surface hardening mechanism that involves diffusing nitrogen through a product's surface to create a hard case. As a consequence of the nitriding method, there are very little distortions and excellent power. Gas nitriding, liquid nitriding, and plasma (ion) nitriding are some of the nitriding methods. Surface hardness, wear resistance, and fatigue resistance are all improved by nitriding. The case structure of a nitrided metal, which includes diffusion and compound zones, is determined by the shape and concentration of alloying components, as well as the time-temperature application of a given nitriding procedure. The alloy content has little effect on the micro-hardness of the compound region, while nitride-forming elements decide the micro-hardness of the diffusion zone. The form and concentration of alloying elements affect the diffusion zone (X); the case depth (Y) rises with temperature and decreases with alloy concentration.
Nitriding is a thermochemical process in which a nitrogen-carrying medium, such as gaseous ammonia, cyanide-containing salts, or ionized nitrogen gas, diffuses nitrogen across the surface of a metal or alloy (plasma), at an appropriate temperature, typically in the range (450-600)°C, for several hours to create dense layers of (5-10) μm. Nitrogen forms hard nitrides on the alloy's surface, which causes the hardening effect. Typically, the reinforcement occurs as a result of the production of strong substances (nitrides). Because of its light weight and high strength, aluminum is beginning to overtake cast iron in engine production. This would result in an engine with a high power-to-weight ratio. Aluminum has a poor toughness and wear resistance, which is a concern. Owing to the reciprocating action of the piston within the engine during use, the cylinder wall begins to wear down, resulting in engine blow-by. By creating an aluminum nitride sheet, nitriding is one of the processes for improving such properties. This coating is very strong and resistant to wear. Nitriding an aluminum surface is challenging due to a thin oxide coating on the surface that prevents nitrogen from dispersing through the aluminum substrate, rendering the process sluggish. After nitriding, the color of the aluminum surface can shift from silver to dark gray or glossy black due to the forming of an aluminum nitride coating on the surface. Aluminum nitride has a great hardness of (1400) HV, as well as high thermal conductivity and electrical resistance. It has a hexagonal crystal structure and is covalently bonded, so breaking it took a ton of energy.

Lect. Dr. Marwan Abbas Madhloom