The Fundamentals of Nitriding and Plasma-Nitriding

Terminology

According to DIN EN 10052 nitriding is a thermochemical treatment of metallic materials to increase the nitrogen content in the workpiece's surface

 

Deterioration and wear mechanisms

The burden of surface layers can be characterized strongly simplified by three deterioration mechanisms:

  • corrosion - physical or chemical reaction of the work piece with its surrounding
  • wear (abrasive, adhesive) - loss of material due to mechanical stress of the work piece
  • fatigue - failure of the work piece by crack initiation due to intermittent load or alternating stress

 

Deterioration mechanisms rarely occur by themselves, most likely they involve complex interactions. Thus, the overview above only functions as a guideline. With regard to the particular kind of stresses involved there are also the following claims for specific characteristics and endurance of the load on the part or structure.

Abrasion:

To avoid abrasion, high hardness in combination with sufficient ductility is needed, for example hard phases within a strengthening matrix.

Adhesion:

The reduction of the adhesion requires weak adhesive bond forces, obtainable by dissimilar barrier layers (especially by avoiding metallic tribological pairing). Hard materials are perfect for this kind of stress, because of the low deformation in the contact area.

Corrosion:

The corrosion resistance can be increased by applying an inert coating.

Fatigue:

The fatigue can be reduced by elimination of stress concentration caused by microstructure and generation of internal compressive stress in the case .

Thermal fatigue:

For stress through thermal fatigue the actions taken against fatigue, for example, the generation of internal compressive stresses has to be stable at the operating temperature of the work piece.