Typically, machining tools like drill bits and indexable inserts are protected against abrasion by hard coatings, since the hardness and viscosity of the cutting edge are defined by the coating, not the softer substrate. But coatings applied by physical or chemical vapour deposition (PVD or CVD) such as titanium nitride (TiN) are often only a few micrometres thick, making it very difficult to determine their material properties via classic hardness measurement methods. However, the instrumented indentation test (“micro-hardness testing”) enables accurate measurement even on very thin coatings (requiring very shallow indenter penetration depths) while still preventing any influence of the substrate on the readings. The FISCHERSCOPE® HM2000 operates according to this measurement principle, accurately determining not only the Martens hardness (HM) of the layer but also other parameters, such as elastic deformation.
The instrument’s integrated microscope allows exact positioning even on small shapes. Since the coating process generates a rough surface, it is recommended to repeat the measurements several times in order to yield a meaningful average value; the HM2000’s precise positioning stages make it straightforward to program and automatically reproduce these measurements. Typical results for hardness determination of the TiN coating on a drill bit are shown in Figure 1.