Coatings – Overview and Comments on Properties
IVAC offers a variety of hard, inert, wear resistant and heat resistant tool coatings with low friction coefficients. The hardness improves wear resistance, which extends tool life. The low friction improves chip flow and evacuation and reduces the heat generated during sliding, thus permitting faster machining with increased productivity, and yielding a better surface finish. The chemical inertness of these coatings improves the oxidation resistance of coated tools, reduces the chemical interaction between the tool and the work material, thus contributing the reduction of friction, and reduces surface buildup.
The optimum temperature for our Physical Vapor Deposition (PVD) process depends on the specifics of the process and the material of the items to be coated. For typical high speed steel items this is somewhere between 900 ºF – 950 ºF (480 ºC – 510 ºC), and for cobalt and nickel cemented tungsten carbide, 1100 ºF – 1300 ºF (600 ºC – 700 ºC). There are some more temperature sensitive tools, such as circular saw blades under tension, which must be coated at a lower temperature.
The thickness of our coatings is in the range of 2-5 µm (or~0.0001″-0.0002″). The PVD deposition is a quazi line of site process: the uniformity of the growing films depends on the variations of the solid angle subtended to a specific surface location. The more a certain point on the surface “sees” the evaporation source, the more intense the ion bombardment at that particular point will be, and the thicker the resulting film will grow. This explains why is there a thinner coating in crevices and flutes of tools.
The formation of PVD films occurs by condensation directly from vapor phase, at comparatively low temperatures, way below the melting temperatures of their constituents, and under energetic ion bombardment conditions. This increases the propensity for metastable phase formation and virtually eliminates the likelihood that bulk properties can be extrapolated to corresponding PVD thin films. Their phases, structures, and compositions strongly depend on the specific deposition conditions.
Note that, as a consequence of the above-stated facts, the physical properties of PVD coatings are not well known, and therefore we do not quote them. While the bulk properties of materials used as hard coatings are known, those for their thin film counterparts can be very different, and are ill-defined. These depend strongly upon the interplay of factors, such as deposition conditions, substrate material, surface preparation and morphology, the presence or absence of para-surface impurities introduced into the substrate during manufacturing, temperature, humidity, and other measurement conditions.
Also, properties derived in the laboratory are typically poor predictors of actual manufacturing performance of coated tools. Consequently, applications of a particular coating to new operations must be tested and optimized under production conditions on the shop floor.