Analyses of individual properties of coatings

Hardness

Hardness is defined as a material resistance against penetration introduced object. Different shapes of objects characterize standard material hardness – HB, HRC, HV, etc.and determine it. The course of analysis is as follows. For a certain time the load increases up to a maximum value followed by unloading and value readout, the value corresponding with the depth or the size of the trace as the case may be. The resulting hardness is learnt from those readings.

Microhardness

Microhardness analysis is used mainly for thin coatings. Its definition is the same as of the standard hardness, but the main difference lies in the maximum load size selection. Here the maximum load is in orders of tens of mN (milinewtons which correspond with grams). The reason for applying such low load forces lies in a necessity of analyzing the actual coating hardness, without an influence of the material the coating is deposited on. There are equipment suitable for hardness analyzing of thin coatings such as wear-resistant coatings, galvanic coatings, polishes, etc. Their main advantage lies in hardness analysis during the load application as well as during the unloading. The outcome is then not only the resulting value of hardness of the coating but also the shape of the loading and unloading curve. It is possible to recognize unhomogenities, macroinclusions in different depths, etc. upon the curve but among the main advantages recognition of elastic and plastic deformation belongs. Equipments of such type are practically the only widely used means of analyzing hardness the few thousandths millimeter thin coatings.


microhardnessmeter Fischerscope H100	microhardness analysis

Roughness

Roughness is a summary of surface protrusions with relatively short distances, which inevitably create during production or under its influence. In case of the PVD coating deposition the roughness is caused by the tool treatment itself as well as by the powdered material deposited on the substrate. The roughness analysis does not include random irregular protrusions such as scratches, cracks, depressions, etc. and protrusions in material quality, protrusions caused by mechanical damage, etc. To eliminate the influence of previous treatment of the tool, specially polished etalons, whose starting roughness Ra ranges between 0,01 and 0,02 μm are used for roughness analysis. Thus the resulting roughness measured is not influenced by the previously treated tool but by the deposited coating.

roughnessmeter Mitutoyo SJ 201

Adhesion

Adhesion is characterized by evaluation of adhesive forces of coatings to the tool. In our laboratory we use two methodes of adhesion evaluation.
Scratch test - A principal of progressively increasing loading force upon a Rockwell diamond point while concurrently moving the point across the analyzed coating is used for adhesion evaluation. With respect to standard adhesive forces a loading force ranging between 20 – 120 N is used. During the process acoustic emission is detected. It changes when the coating scratches off, which corresponds with a specific value in N. This critical moment (coating scratch off) is then determined as the coating adhesion. Furthermore, it is possible to carry out a final control by means of an optical microscope. Here a place of the coating scratch off is determined and the exact value of the critical load is read out.


scratch tester	analysis principal

Rockwell test - Is a routine method of adhesion measurement, which is done by Rockwell indentor. Indentation on an instrumental sample done by Rockwell point is evaluated. Empiric scale HF0 to HF8 is used for the evaluation, where HF0 to HF3 meets the adhesion requirements.


Rockwell indentor	indentation evaluation

Thickness

Callotest apparatus is used for thickness analysis. Its principal is as follows: A pivoting polished ball with applied diamond paste polishes through the deposited coating as well as a thin under-surface layer. Knowing the ball diameter and a diameter of the spherical cap measured by a microscope it is possible to use a simple calculation and thus determine the thickness of the deposited coating. To achieve the highest accuracy possible it is preferable to perform this analysis on polished etalons.


thickness analysis principal	apparatus schema

Supplementary diagnostic methods

SEM is another device and method available in daughter company PIVOT. With SEM it is possible to carry out very operational evaluation of coating surfaces, layer structure on fractures or microsections and evaluate geometry of tool edges including a way of wear etc. Scanning electron microscope TESCAN VEGA TS5130 is available in our laboratories since June 2006.


SEM - TESCAN	SEM-surface profile	SEM-end-mill detail

It is possible to carry out metallographic evaluation of samples by means of instrumentation from Struers company. We evaluate metallographic microsections of samples focusing on coating thickness and structure. Subsequently we are also able to evaluate quality of substrates, mainly cemented carbides.