Hard Material Coatings

Hard materials only function efficiently as protection against abrasion if coating thickness, composition and surface hardness are right. Test instruments from FISCHER use a variety of procedures such as X-ray fluorescence or nanoindentation, for example to determine the exact properties of TiN and other hard metal or carbide coatings.

Hard coatings

Application notes

Determining the mechanical properties of hard coatings used on machining and milling tools

Hard coatings are used for many industrial purposes. Especially for machining and milling, the tools used are made with hard-coated cutting materials. Depending on the application area, specialised coating solutions have been developed to enhance abrasion resistance and, therefore, durability. Controlling the quality of these coatings according to distinct material properties such as micro-hardness is a tough challenge for most measurement technologies.

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.

Fig.1: Depth dependent Martens hardness of a 1µm thick TiN coating. Starting at one-tenth of the layer thickness the measurement results are influenced by the base material (Bückle rule).

The standard deviation reflects the degree of surface roughness on the coating. But despite the roughness, the repeat measurements make it possible to characterise the coating’s hardness exactly. Between the easy sample preparation and its intuitive handling, the FISCHERSCOPE® HM2000 ensures quick and efficient micro-hardness testing on such hard, thin industrial coatings.

For the exact determination of essential wear resistance properties, such as hardness or ductility, of the hard coatings on machining and milling tools like drill bits or inserts, the easy-to-use FISCHERSCOPE® HM2000 is the right instrument. For further information or sample measurements, please contact your local FISCHER representative.

Analysing cemented carbide alloys used for making cutting tools

Milling cutters and drill bits are used for processing various materials. Depending on their intended application, they are made from different cemented carbide alloys. In order to determine the quality of the source material, manufacturers of such tools must verify the exact material composition of the hard metal alloy – which requires very precise analysis during the incoming goods inspection.

The cemented carbides most often employed industrially are made by sintering grains of tungsten carbide with a metallic binder, frequently cobalt. Tiny amounts of titanium, tantalum, chromium and/or vanadium carbides are also used; depending on the final composition, these additives significantly influence the material properties – and thus the performance – of the finished material.

Carbides are divided into different ISO classifications based on the industrial application they are best suited for. The “P” class carbides, for example, contain a relatively high proportion of titanium and tantalum carbide (TiC and TaC) and are used for the processing of long-chipping materials such as steel or cast steel. Hard metals of the “K” group contain little to no TiC or TaC; they are preferred for machining short-chipping materials like cast iron, non-ferrous metals, hardened steel, wood or plastic. In addition to the conventional tungsten-carbide-based hard metals, there are those that contain only titanium carbide and titanium nitride as hard materials; these are characterised by very high hardness and wear resistance.

Extensive industrial application has established the non-destructive X-ray fluorescence (XRF) method as superior to chemical analysis for precisely analysing the composition of the respective hard metals. With XRF, the alloy components can be measured quickly and accurately, even at concentrations as low as ~0.1%. Therefore, devices with semiconductor detectors such as the FISCHERSCOPE® X-RAY XDAL® are ideal for clearly delimiting the elements contained in the alloy.

Fig.1: Analysis of two samples in comparison to pure tungsten: yellow = pure W, blue = 1.2 % TaC (sample 1) and green = 9.8% TaC (sample 2)

   

WC

Co

TiC

TaC

NbC

Cr3C2

VC

Ni

Mo

sample 1

X

92.48

5.99

-0.41

1.16

0.60

-0.10

0.13

0.17

-0.02

s

0.28

0.14

0.29

0.13

0.03

0.09

0.20

0.05

0.01

sample 2

X

69.19

8.17

10.17

9.77

2.51

-0.11

0.14

0.18

-0.02

s

0.53

0.07

0.48

0.41

0.05

0.11

0.24

0.04

0.01

Tab.1: Results (in %) of measuring the spectra of both samples above

For analysing samples that consist of not only pure elements but also chemical compounds (e.g. carbides), the WinFTM® software provides a ‘components mode’. This makes it possible to measure a number of components, such as WC or TiC and TaC, just like any other element and display them in the results with a measured value for the entire component: no further conversion necessary.

The FISCHERSCOPE® X-RAY XDAL® is perfectly suited for precise alloy analysis of cemented carbides. Employed in the inspection of incoming goods, it enables determination of the composition of hard metals and facilitates rapid and accurate material identification. For more information please contact your local FISCHER representative.

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Windsor/United States

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