Recent improvements in nanomechanical test techniques to encompass a greater range of test temperatures (to 750 deg C) and strain rates (up to 10-3 – 10-4 s^-1) have opened up the exciting possibility of obtaining design rules for coating properties to provide improved durability under the tribologically extreme conditions of dry machining of hard-to-cut materials at high speed.Nano-impact testing is an advanced nanomechanical test technique which can simulate the interrupted contact (and cyclic loading) conditions occurring in severe contact applications and evaluate the fatigue fracture resistance of materials such as coated components. Nano-impact enables fast repetitive nanoindentation and has been developed to test coating properties at high strain rates and to investigate surface fatigue and fracture due to repetitive contact with the aim of using results to optimise materials properties for improved durability. In contrast to conventional impact testing at the macro-scale, nano-impact testing offers distinct potential advantages for testing thin coatings, in throughput, automation, surface sensitivity. In this case study, the nanomechanical properties relevant to the contact/wear situation, such as (1) hot hardness, (2) H/E at temperature (3) fatigue fracture resistance are evaluated for different coatings and their relative importance in different contact situations has been determined Excellent correlationsare observed with actual performance testing. The rapid, automated, laboratory nano-impact tests correlate well with the longer, more laborious and expensive tests of (1) cutting tool life,ranking coating performance in terms of tool life in end milling and simulatingthe evolution of the tool wear (2) coating wear in high performance engine applications 1-4. The principles and applications of the nano-impact technique are reviewed in this presentation.
Mike completed a degree in Physics at the University of Nottingham, and went on to complete a PhD in high temperature nanoindentation focusing on the characterisation of the mechnical properties and creep behaviour of power station structural materials at their operating temperatures.
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