Randomised impact

Micro Materials have extended the repetitive impact technique to allow a programmed number of impacts to be distributed within a specified region of the sample in order to directly study how damage from one impact affects subsequent damage, therefore providing a more realistic analogue for simulating the ‘random’ nature of erosive wear.

How it works:

A programmed number of random impact sites are set within a specified region X-Y (shown by the dotted area in the figure below) centred around a point marked by the asterisk.  Circles mark each impact location and show that overlap with previous impacts varies.  Different distributions can be programmed, for example Gaussian, rectangular etc.

The full range of impact parameters (load, acceleration distance, indenter geometry) can be modified as necessary, and the test technique is compatible with the full range of environmental capability of the NanoTest (high and low temperature, liquid, controlled humidity).

 

Tests on BK7 and fused silica

500 mN applied load impacts using a 25 µm end-radius diamond conical probe were performed in a rectangular distribution over a 500 µm x 500 µm area.

Optical microscopy clearly shows greater damage on the BK7 sample.  This correlates with greater erosion rate reported in literature.

EB-PVD Thermal barrier coating systems

To increase fuel efficiency of gas turbine engines and reduce CO2 emissions, engines need to operate at higher temperatures.  Thermal barrier coatings (TBSc) can effectively protect superalloy turbine blades but can be susceptible to erosion damage which limits the maximum operating temperature.  More erosion resistant TBCs are needed to achieve higher operating temperatures.  The new randomised impact test is being used to characterise the performance of these coating systems.

As an example, the novel thermal barrier coating gadolinium zirconate (GZO) was subjected to randomised impact tests using a 25 µm end-radius diamond probe.

 

GZO – 500 impacts at 500 mN rectangular distribution over 1 mm x  1 mm

Summary

Micro Materials have developed a novel randomised impact technique to simulate erosive wear on the nano and micro-scale.

The technique is particularly well suited for studying damage mechanism on thermal barrier coatings and exhibits good correlation to erosion tests, both in terms of damage mechanism and wear rate.  The randomised impact test can be extended further by changing load/test probe geometry/test temperature/angle etc, enabling complete characterisation of erosive wear of materials at the relevant in-service conditions.

Watch the seminar presented by Prof Ben Beake, Micro Materials Ltd’s Director of Material Research, covering all aspects of the randomised impact test technique on You Tube by clicking here:

 

Acknowledgements

We would like to thank Prof John Nicholls, Dr Luis Isern and Dr Christine Chalk (all Cranfield University) and Prof Mark Gee and Dr Hannah Zhang (both at NPL) for all their help with this work.

Contact us:

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Ellice Way, Wrexham, LL13 7YL,UK
Tel: +44(0) 1978 261615
E-mail:  info@micromaterials.co.uk
www.micromaterials.co.uk