Wrexham, United Kingdom
Wrexham, United Kingdom

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Chen J.,Nanjing Southeast University | Chen J.,University of Birmingham | Beake B.D.,Micro Materials | Wellman R.G.,Cranfield University | And 2 more authors.
Surface and Coatings Technology | Year: 2012

Nanomechanical testing (nano-impact and nanoindentation mapping) has been carried out on the top surfaces of as-received and aged 8wt.% yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) produced by electron-beam physical vapour deposition (EB-PVD). The correlation between the nanomechanical test results and the previously reported erosion resistance of the TBCs has been investigated. The experimental results revealed that aged TBCs on zirconia for 24h at 1500°C or on alumina for 100h at 1100°C resulted in large increases in their hardness (H), modulus (E), H/E and H 3/E 2 ratios but their erosion resistance was reduced. Nano-impact tests showed a dramatic decrease in impact resistance following the ageing of these TBCs, which is consistent with the erosion results. The strong correlation between the nano-impact and erosion resistances has confirmed the premise that rapid laboratory impact tests must produce deformation with similar contact footprint to that produced in the erosion tests. © 2012 Elsevier B.V.

Chen J.,University of Birmingham | Bell G.A.,University of Birmingham | Beake B.D.,Micro Materials | Dong H.,University of Birmingham
Tribology Letters | Year: 2011

Previous studies on low temperature tribological investigations were limited to macro-scale studies because of the lack of suitable instrumentation. This limitation has been overcome using a newly developed low temperature nanoscratch tester capable of characterizing the scratch resistance of coatings down to-30 °C. The scratch resistance and mechanical properties of a functionally graded a-C:H(Ti)/ TiCN/TiN/Ti coating have been investigated for temperatures ranging from 25 to-30 °C. It has been found that the a-C:H(Ti)/TiCN/TiN/Ti coating failed at high loads by cracking and spallation during the room-temperature scratch tests. Fractography suggests that these failures originate from or close to the interface between the top a-C:H(Ti) and the TiCN layers. Decreasing the test temperature from 25 to 0 °C resulted in increased values in H, H/Er and H3/Er 2, consistent with improved crack- and wear resistances, with further smaller improvements being achieved on further decreasing the temperature to-30 °C. © Springer Science+Business Media, LLC 2011.

Beake B.D.,Micro Materials | Bell G.A.,University of Birmingham | Goodes S.R.,Micro Materials | Pickford N.J.,Micro Materials | Smith J.F.,Micro Materials
Surface Engineering | Year: 2010

The development and implementation of a wide range of innovative nanomechanical test techniques to solve tribological problems in surface engineered systems are described in this review. By combining results with several different nanomechanical techniques, predictive design rules based on the elastic and plastic deformation energies involved in contact are proposed to optimise mechanical properties in the various contact situations that occur for different applications. Results are presented with the NanoTest platform for applications in biomedical devices, surface engineering of lightweight alloys, wear resistance of physical vapour deposition and chemical vapour deposition coatings as well as fracture fatigue resistance of diamond-like carbon coatings. Surface engineering to increase the ratio of hardness to elastic modulus (H/E) can be beneficial in a range of applications but care should be taken that, first, it be done without introducing too large intrinsic stress or stress discontinuities in mechanical contact loading, second, the severity of the contact results in high stresses and there is a requirement for some plasticity in contact to avoid fracture. © 2010 Maney Publishing.

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