They protect the smallest components in watch mechanisms, lend scratch-resistance to spectacle glass and prevent abrasion on tools: vapor-deposited coatings such as PVD or CVD are true all-rounders. With measurement devices from FISCHER you can test all of the properties of high-performance surfaces without influence from the substrate material, whether the coatings consist of TiN, TiCN or oxidized materials such as SiO2.
Determining coating thickness on PVD-coated tools
High-precision industrial saws, drills and dies used for the cutting, punching and forming of steel, hard metal or aluminium parts are subject to extreme wear and tear. To increase the service life of these often very expensive tools, they are coated with a hard material coating via a PVD (physical vapour deposition) process. The thickness of the PVD layer determines the durability and therefore the life expectancy of the tool. Tool and die makers must therefore guarantee a minimum coating thickness, requiring high-precision control measurement technology.
PVD coatings are physically spattered onto workpiece surfaces in a vacuum furnace. For this purpose, the tools are carefully stacked in a chamber which is then evacuated and heated. Next, the entire setup is bombarded with ions (such as titanium or chromium). With the addition of gases such as nitrogen layers like TiN, CrN, TiCN, etc., are thus evenly deposited onto the tools. Sophisticated workpiece holders within the furnace guarantee that the layers are deposited as evenly as possible over the tools’ entire surface.
Fig.1: PVD-coated tool
Specific process parameters such as vacuum, temperature, ion beam intensity and duration determine the layer deposition process and result in the required thickness. As with all types of coatings, the PVD process must also be closely monitored and the thickness of the PVD-deposited layer measured. Alongside standard destructive testing methods, the non-destructive X-ray fluorescence method (XRF) has found broad acceptance for this purpose. The FISCHERSCOPE® X-RAY XDLM, with its robust design concept, is optimised for these requirements as it combines the high-intensity beam of a micro-focus tube with a small Aperture and large detector window. The salient advantages of this device are:
· Non-destructive measurements, no damage to valuable workpieces
· Fast measurement times
· Smallest measurement spots: 100 µm
The instrument’s specialisation for this purpose means that layer thickness can be accurately measured on even the finest cutting edges of very high-end tools. Furthermore, using the same instrument, it is possible to determine the base tools’ precise metallic composition – e.g. to determine Cobalt leaching when an old coating is chemically removed before a new coating is applied.
TiN-coating on HSS tools
Single measurement readings
Average (10 measurements)
Coefficient f Variation
Tab.1: Example for a TiN coating on HSS tool steel, measured with 10 s measurement time, collimator 0.1 mm on FISCHERSCOPE X-RAY XDLM
To determine the thickness of hard coatings on tools and for quality monitoring of the PVD coating process, the FISCHERSCOPE® X-RAY XDLM is the optimal measurement system. For more information, please contact your local FISCHER representative.
Hardness measurement of nano coatings on spectacle lenses
Whether used for eye protection or vision correction, spectacles with lenses made of plastic are preferred over glass for their considerably lower weight and better fracture strength. In order to provide the required life-long quality of such lenses a specific scratch-resistance is necessary.
Nowadays, spectacle lenses made of plastic are commonly provided with an anti-scratch, dirt-repellent and anti-reflective surface. They are vacuum coated using a physical vapour deposition (PVD) method with up to 10 protective layers, each only a few nanometres thick, which together ensure very high scratch-resistance. Hardness and scratch-resistance of these coatings are directly related: therefore, determining the hardness is a suitable method for quantifying the quality of these protective coatings.
To avoid commingling the hardness results of the coatings with those of the base materials while measuring, the test load must be absolutely minimal, as low as a few micronewtons: The indenter may only penetrate up to one tenth of the overall coating depth in order to correctly determine its hardness without being influenced by the properties of the substrate (Bückle’s-Rule).
Fig. 1: Hardness measurement of protective coatings of lenses (Martens hardness). Sample P4 has a significantly lower hardness and was identified as far less scratch-resistant (samples courtesy of Rodenstock)
Another important measuring parameter is the elastic/plastic deformation ratio of the coating material. The coatings must have a very high elastic component to prevent separation from the base material upon deformation. Therefore, multilayer coating systems are used that gradually adjust the modulus of elasticity from the base material to the top coating. These systems also have much higher adhesive bond strengths compared to single-layer coatings.
To secure the functionality of these protective coatings it is important to find the right balance between hardness and elastic behaviour.
The PICODENTOR® HM500 is ideal for measuring the hardness and elastic properties of these complex, nano-thin multi-coatings, which requires a measuring system capable of load generation as low as a few micronewtons and highly accurate depth measurement in the picometre range – exactly the designed operating range of the PICODENTOR®. The hardness can then be calculated from the measured load/depth curves. For further info contact your local FISCHER partner.
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Fischer Instrumentation (GB) Ltd
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