Zirconium Nitride (ZrN)
Zirconium (Zr) is a silvery, hard, brittle metal with high melting temperature (1852 ºC) and very high boiling temperature (4377 ºC). The high boiling point weakens the propensity for droplet formation during “un-steered” arc evaporation. Therefore, the condensate thin films of zirconium and its chemical compounds, such as zirconium nitride (ZrN), tend to be smoother than those of less refractory metals or metalloids.
It should be noted that there are many additional factors which influence droplet emission, such as the velocity of movement of cathode spots, thermal conductivity, effectiveness of cooling (which influences the average emission surface temperature), deposition system configuration, and residual coverage of the surface by oxides, nitrides, or carbides. This last factor is defined by the ratio of the chemical reaction rates of the cathode material with reactive gases present over the surface versus the pure cathode metal and reacted surface film removal rate (“surface poisoning”).
The melting temperature of ZrN in bulk form is 2980 ºC, only slightly higher than that of TiN, which is 2930 ºC, and its bulk hardness is ~1500 HV, lower than that of bulk TiN (~2000 HV). As a case to the point of unpredictability or uncertainty in predictions of thin film properties from the properties of their bulk counterparts, the hardness of PVD deposited ZrN films tend to be higher that that of TiN films.
For reasons alluded to above, the arc evaporated zirconium nitride (ZrN) films are typically smoother than, e.g., titanium nitride films deposited on tool surfaces under similar conditions, and have a higher oxidation resistance.
ZrN is a slightly more expensive coating than TiN or TiCrN, but this difference is often offset and justified by its higher cutting performance, especially in finishing operations. We recommend it in applications where superior lubricity is required. The most common application is aluminum machining, though wood working and machining of copper are amongst the applications in which it has shown high performance.
There are reports from end-users of excellent finishing performance of ZrN coated, lightly honed high speed steel and carbide tools with small edge radii in abrasive work materials, such as hyper-eutectic automotive grade aluminum.
Zirconium nitride is a comparatively seldom-used coating; therefore, the lead time for small batches of items is considerably longer than other, more widely used coatings. Please call us for information about lead times before submitting an order for ZrN coating.