On Extracting Mechanical Properties from Nanoindentation at Temperatures up to 1000$^{\circ}$C

TL;DR

This study demonstrates the use of nanoindentation to measure the mechanical properties of turbine coating materials at temperatures up to 1000°C, revealing temperature-dependent softening and creep behavior.

Contribution

It introduces high-temperature nanoindentation for alloyed bond coats, enabling property measurement near turbine operating temperatures, which was previously challenging.

Findings

Hardness remains constant up to 400°C then softens

Creep exponents align with literature above 700°C

Nanoindentation effectively characterizes high-temperature behavior

Abstract

Alloyed MCrAlY bond coats, where M is usually cobalt and/or nickel, are essential parts of modern turbine blades, imparting environmental resistance while mediating thermal expansivity differences. Nanoindentation allows the determination of their properties without the complexities of traditional mechanical tests, but was not previously possible near turbine operating temperatures. Here, we determine the hardness and modulus of CMSX-4 and an Amdry-386 bond coat by nanoindentation up to 1000$^{\circ}$C. Both materials exhibit a constant hardness until 400$^{\circ}$C followed by considerable softening, which in CMSX-4 is attributed to the multiple slip systems operating underneath a Berkovich indenter. The creep behaviour has been investigated via the nanoindentation hold segments. Above 700$^{\circ}$C, the observed creep exponents match the temperature-dependence of literature values in CMSX-4. In Amdry-386, nanoindentation produces creep exponents very close to literature data, implying high-temperature nanoindentation may be powerful in characterising these coatings and providing inputs for material, model and process optimisations.