Nano-Impact Testing for Thermal Barrier Coating Erosion Characterization

By AZoM.com Staff Writers

Table of Content

Introduction
Nano-Impact Testing Experiment
Conclusion
About Micro Materials

Introduction

Micro Materials' nanomechanical testing instrument, the NanoTest, has been used lately in a collaborative study published in the journal Surface and Coatings Technology in which Micro Materials partnered with Birmingham University (UK), Cranfield University (UK) and Southeast University (China).

This study evaluated the role of changing coating microstructure and mechanical properties due to thermal aging at 1100-1500°C on the repetitive impact and erosion behaviour of 150µm thick thermal barrier coatings (TBCs) for aero-engines.

Nano-Impact Testing Experiment

The key to this experiment was the multiple impact mode using a unique patented nano-impact module for the NanoTest, which provided dynamic information not available from conventional nanoindentation testing. The nano-impact technique provides a quick and efficient way to study dynamic properties of coatings, and can be used to assess toughness and fatigue induced fracture resistance.

Figure 1. Nano-impact data showing the effect of thermal aging on a thermal barrier coating

The microstructure and the mechanical properties of the thermal barrier coating (TBC) are altered by thermal aging and there is a clear need to develop a rapid laboratory test method that can assess such changes. Nano-impact offers a dynamic measurement tool and in this study it has been used to assess erosion resistance.

In this application it is superior to traditional nanoindentation as the dynamic strain rates are much higher. When compared bulk erosion testing it offers the potential advantage of testing on the scale of the individual columns in the TBC, hence measuring individual column and column cluster properties. It is shown that thermal aging resulted in increased dynamic hardness and dynamic stiffness of the TBC.

Nano-impact testing showed the increased wear rate very clearly under these conditions and this correlated well with the measured bulk erosion rate. As a repetitive dynamic test producing damage on the correct length scale, the nano-impact test was highly effective in simulating the erosion mechanism and may be used as a rapid screening test to evaluate the erosion resistance. Nanoindentation alone will not be able to predict this.

The rapid impact test shows the reduction in coating performance after thermal treatment, consistent with the results of the erosion tests. Professor John Nicholls from Cranfield University summarises the study that a clear correlation was found between the erosion performance of the TBC and its behavior in the nano-impact test.

This correlation can be attributed to the dynamic character of nano-impact producing deformation with a similar contact footprint to that produced in erosion tests.

Conclusion

Nanomechanical characterization that involves two complementary nano-scale testing techniques, quasi-static nanoindentation and the dynamic nano-impact test, is an important tool to understand how the microstructural changes caused by thermal aging affect the erosion behavior of EB-PVD TBCs.

In future such laboratory impact tests could be used as a screening tool for erosion performance in newly developed TBC compositions.

About Micro Materials

Micro Materials was formed in 1988 with the aim of becoming the world leader in development, manufacture and marketing of nanomechanical testing instruments for research and quality assurance. Our products have evolved through many stages from the original design based on a prototype at the University of Lancaster, UK, into the current, fully-automated, highly versatile instruments.

At Micro Materials, our highly specialised scientists and engineers take particular pride in their ability to solve complex problems related to specific customer needs and applications.

This responsive and flexible approach has earned us an enviable reputation for strong customer relations and for products designed to satisfy our customers' requirements.

Our pioneering approach has led to two recent world-firsts - we have developed:

  • The first commercial nanoscale impact tester, for erosive wear, toughness and contact fatigue.
  • The first commercial high temperature nanoindentation stage, capable of reaching temperatures over 500°C

This information has been sourced, reviewed and adapted from materials provided by Micro Materials.

For more information on this source, please visit Micro Materials.

 

Date Added: Nov 14, 2013 | Updated: Nov 14, 2013
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