|Coating Temperature (South Africa)||450°C/480°C/520°C||Hardening temp of steel. max 1020°C.|
|Chemical Composition||TiN, TiAlN, TiCN, CrN,etc||Mainly VC, other compounds possible|
|Micro Hardness||TiN 2300 Hv, TiAlN 3300 Hv, TiCN 2800 Hv, CrN 2300 Hv||3200-3800 Hv|
|Adhesive nature to work materials||Low to Very Low||Very Low|
|Thickness||2 – 4 µm||4 – 6 µm (high impact), 8- 10 µm (form tools)|
|Adhesion to base material||Good, dependent on cleanliness and etch||Best, diffusion bonded|
|Base Material||Best on HSS, 8% CW steels and carbide.||Best on cold work steels and high Co carbide|
|Distortion/size change||Very low to none||Medium to low|
|Sensitivity to cleanliness||Very sensitive to surface condition, oxides and other contaminants.||Low sensitivity to oil, rust, paint etc.|
|Resistance to heat||TiN ~ 450°C , TiAlN ~ 900°C||500°C (oxidizing environment)|
|Prior Nitriding||White layer can affect adhesion negatively but also provides better support for PVD layer||VN and VCN may formed and this has poor tribological properties.|
|Coating restrictions||Masked from coating where jigging materials are present. Shadowing can occur. Cannot coat some geometries such as deep holes.||Coating develops on all surfaces apart from direct contact areas with jigging areas. Masking not practical.|
|Coatable Size||normal max: Ø135 x 400 mm, large part coating available on request.||Coatable volume typically Ø450 x 600.|
|Very thin, long items||Little to no problem||Higher distortion risk|
|Cutting Edges||Good an all edges||Best on cutting edges of > 45° and greater. Acute angles can be a problem.|
|Stripping||Chemical striping, non-aggressive, blasting for low tolerance parts.||Electro-chemical stripping or abrasive blast|
|Costing||Typically based on volume consumed||Typically based on weight|
*For any properties not covered above relating to your application , please consult your TD coating specialist.
Which Coating is better?
Since there are distinct characteristics that separate the two technologies, there are applications where one coating technology has an absolute advantage over its competitor.
Example 1: A flat ejector 2mm thick x 150 mm long, made of HSS would be excluded from TD due to high distortion risk and non-optimum base material suitability. This application would clearly be the domain of PVD, or other medium temperature processes.
Example 2: A tube swaging tool 150 mm in length with an ø40 ID reduces the OD of a tube through a forming operation. Tool is made of 1.2379, vacuum hardened and tempered at 200°C. PVD being a line of sight process will not easily coat inside the ID and secondly the tool has been tempered below the PVD application temperature of 450 °C, thus PVD adhesion will be compromised and dimensional changes can be expected. TD would form evenly both inside the tool ID and the OD, and be tempered at 200°C after coating to maintain hardness and dimensions.
There are however overlap applications where either of the coating technologies would add benefit and a choice between the two would need to be made. This would naturally put the two coating technologies in competition, however choosing the best coating for the particular application usually boils down to two main criteria.
Bond strength and thickness
Due to the diffusion process, the TD coating has much higher bond strength than that of PVD and is therefore more suitable for very high surface load applications such as pressing of stainless steel and very thick gauge sheet and deep draws. Conversely for low load applications, where more coating translates to longer wear life, TD has an advantage.
Precision however is the forte of PVD coating and due to its lower temperature application, it is the best when tight tolerances are critical, and need to be maintained once the steels have been heat treated correctly.
If neither of these are primary concerns then experience in the particular application, or a trial may be necessary to determine the best value to the customer.
Cost always tends to play a role, but only if the life extension is limited. The longer a coating extends a tools useful life, the greater the leverage effect of the coating.