Wear-resistant coating

During recent years there has been a progressive increase in the use of wear-resistant coatings. Titanium nitride
is the best known of the coatings: thanks to its high degree of hardness and a very low friction coefficient, it enables
a considerable reduction in abrasive wear, which is the main cause of a reduction in the efficiency of machine tools.
New coatings have also been developed to resolve specific problems, to such a point that high-speed, dry machining is possible.
The fields of application of the tools are constantly expanding with constant improvements in the die-sating or extrusion of aluminium, injection of plastics, drawing or shearing, as well as in the automotive and food industry.
The advantages may be seen in the longer service life of the coated piece, reduction in maintenance requirements and machine stoppages, and increased productivity.
Coating techniques are so detailed and difficult to explain that this is best left to the experts in this particular sector; a description is merely given of some of their experiences and the most commonly used systems

PVD TECHNIQUE

The PVD technique (Physical Vapour Deposition) is carried out at low temperatures, guarantees an excellent finish and applies various types of coatings, including self-lubricating ones, as well as the possible multi-layer combinations.
Inconvenients: it is not effective when there is limited space for circulation of the vapours, since the formation of gases does not allow a good penetration.

CVD PROCESS

The CVD process (Chemical Vapour Deposition) provides coatings with better characteristics, both in terms of thickness and adhesion. The performance is also better, especially when the material coated is used in cold deformation processes. The trickiest problem consists in the deposition temperature of approx. 1050 °C, which sometimes does not allow the deformations to be contained within the tolerances set by the designer.
Inconvenients: coatings with different materials are not possible e.g. TiANl, the thickness at the edge of the coatings tends to be rounded, toxic metallic chlorides are used.

PACVD

The PACVD process (Plasma Assisted Chemical Vapour Deposition) has a greater resistance to abrasion than the PVD process and does not have the disadvantages of the the CVD method. Due to the size of the plants it is possible to coat very large pieces. The finish is similar to that of the PVD. The performance has been seen to be better than that of the PVD technique when used with drawing.
Inconvenients: limited suitability in the presence of small holes and channels.