Micro Materials CORE Range: Micro-Scratch

The CORE Micro-scratch system combines a wide force range with high measurement repeatability and accurate determination of critical loads and coefficient of friction. It can perform both single pass scratch testing and multi pass wear testing.

The CORE Micro-scratch tester features are given below:

  • 30 N maximum load
  • High friction sensitivity combined with high lateral rigidity
  • Experiment protocols to place the peak stresses at the coating-substrate interface improving the sensitivity to adhesion strength compared to macro-scale scratch testing

The CORE Micro-scratch tester is fully compliant with the applicable standards for micro-scratch testing - ASTM 7187-10 and ASTM 7027-05.

Micro-scratch and wear testing

Clear failure identification in metal-doped DLC coatings on steel for automotive applications

Repetitive wear tests on monolayer AlTiN and AlCrN tool coatings on cemented carbide. In this example the 1 N wear load enables the peak stresses to be positioned at the interface between the coating and substrate, increasing the sensitivity to differences in adhesion. In a ramped load micro-scratch test the AlCrN coating has a higher critical load (5.7 N) than AlTiN (4.5 N) and it is initially more scratch resistant at 1 N. However, due to weaker adhesion the AlCrN fails rapidly over a few cycles whilst the AlTiN shows a more gradual wear.

Friction Measurement

The CORE micro-scratch has a high lateral rigidity flexure design guaranteeing that sensitive friction sensors can be used and measurements performed across the whole 30 N load range.

In this automotive application, sensitive friction measurements reveal differences in critical load on two different types of multi-layered DLC coatings on hardened steel.

Two repeat scratch tests up to 30 N on WC-Co with a 100 micron radius probe. The tests show excellent reproducibility in friction coefficient. Its variation with load is due to changing ploughing contribution as the probe scratches deeper and moves from spherical to conical-dominated geometry.

Micro-tribology – single asperity tribology

Depending on the choice of indenter radius and load, the highest stress can be positioned at the interface, or at interfaces between different layers in a multi-layer coating system, to examine any potential deficiencies in adhesion.

Multiple wear passes with the repetitive (sub-critical) constant load micro-scratch tests enables extra control over the contact pressure and the location of highest stress, and depending on the applied load, it is possible to analyze either coating wear properties or adhesion.

The micro-scale scratch test is designed as a model single asperity contact. Analyzing single asperity contact has distinct benefits compared to standard tribological tests with much larger contact sizes where the real contact occurs only at the peaks of the asperities and the actual contact pressures accountable for the observed behavior are not known.

Wear depth as a function of applied load for a 10 cycle wear test on a TiAlN coating

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