Chromium Nitride (CrN)
Chromium Nitride (CrN) is a light silver-colored coating with appearance similar to metallic chrome.
Because of the combination of its properties, such as boiling temperature and thermal conductivity, metallic chromium has a weaker tendency for micro-droplet formation during arc evaporation than metals, such as titanium and to a lesser degree, zirconium.
The low density of micro-droplets in the deposited films yields a smoother surface, which is advantageous in chip formation and control during cutting, and aids material flow during forming soft, pliable materials, such as electrolytic copper, cutting some areo-space composites, or soft, low-alloy draw grade steels, such as, e.g., 1006 or 1010.
It is also useful in sliding wear applications, where un-hindered flow of the material, with low friction and without mechanical locking or impediments over the tool surface is critical. In these applications, it eliminates galling, fretting, microwelding, seizing and adhesion.
It is harder than hard chrome plating and it is also a dense, continuous coating, unlike hard chrome, which typically has an island-like morphology, with micro – cracking.
On the negative side, CrN is a softer coating than TiN, with lower abrasion resistance, and therefore in many applications it has a shorter service life than other (harder) PVD coatings. Also, it should be noted that often similarly good cutting behaviour can be achieved with TiN, K-Coat, ZrN, or TiCN, which all expected to have longer service lives if their surfaces are smoothened by, e.g., light abrasion with Crocus Cloth or slight wet blasting with a soft blasting medium which removes droplets from the as-deposited surface without substantially affecting sharp edges.
CrN has a slightly extended temperature range of application or higher temperature resistance and more corrosion protection of the substrate compared to TiN. This is though to be the result of the formation of a finely distributed Cr2O3 oxide phase, with molecular nitrogen in the interstitial positions in the lattice of the surface oxide layers at elevated temperatures which, mixing with the CrN matrix, forms a solution hardened structure. This sturcture is a good oxygen diffusion barrier, which protects the interior of the film and extends its temeprature range of applicability.
As is the case with all commonly used hard and wear resistant functional coatings, it is highly inert – will not chemically interact or corrode at low and moderate temperatures and has excellent chemical stability. It enhances the corrosion resistance of coated items, but does not perfectly encapsulate the part.
CrN is non-toxic and FDA – approved; can be used for medical surgical devices and food processing equipment.
Because of limited market demands, the lead time for CrN coating of small batches of tools or other items is considerably longer than more commonly used coatings. For more information please call us.