Plasma Nitriding, also referred to as ion nitriding, is a thermochemical treatment that improves the wear, corrosion resistance and fatigue properties of the product being nitrided. The process was developed in the early 1930’s as an alternative to the gas nitriding. It involves diffusion of nitrogen atoms into the metal surface in presence of a plasma environment. The plasma nitriding apparatus consists of a vacuum chamber which is connected to anode and a cathode, where the parts are placed.
A nitriding atmosphere, consisting of a mixture of nitrogen and hydrogen gasses, is established at pressures that may vary from 1 to 10 mbar. The voltage applied between anode and cathode typically lies in the range of 300 to 800 volts. The applied potential ionises the gas mixture. The plasma generated by the ionization, envelops the surface of the workpiece with a blue-violet glow. The charged positive (nitrogen) ions are accelerated and hit the negatively charged workpieces with a relatively high level of kinetic energy. A large proportion of this (up to 90%) is then transferred to heat energy and thereby heats the workpiece to its required nitriding temperature.