Microstructural observations of high temperature creep processes in hardmetals

ABSTRACT

High-temperature properties of hardmetals are critical to their use in many applications but a challenge to measure accurately. Creep behaviour is not well understood so this work has studied uniaxial tensile testing of small simple geometry samples to look at how modifications to the microstructure can affect creep behaviour at temperatures between 800 and 900°C. In particular, a carbon-ladder series with high, medium and low carbon contents in the 10wt-%Co binder has been investigated. Significant differences between the stress–strain curves of the different carbon contents have been observed, but the underlying microstructural mechanisms appear to be similar in detailed large area examination of samples after failure. Penetration of Co along WC-WC boundaries with ‘precipitation’ of discrete islands is seen as well as the formation of continuous thin lamellae while void formation tends to occur at WC-Co boundaries. EBSD mapping suggests Co penetration varies as a function of WC-WC misorientation.

KEYWORDS:

• Hardmetals
• creep
• microstructure
• WC-Co
• carbon-ladder
• miniaturised testing

Acknowledgements

Funding by Hilti, Sandvik and Ceratizit and from the National Measurement System of the UK Government Department for Business, Energy and Industrial Strategy is gratefully acknowledged. Members of the British Hardmetals Research Group are thanked for the provision of samples.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Department for Business, Energy and Industrial Strategy [NMS].