Creep of a thermally stable nanocrystalline nickel tungsten alloy as measured by high temperature nanoindentation

https://doi.org/10.1016/j.msea.2020.139309Get rights and content
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Abstract

The creep behavior of pure nanocrystalline (nc) fcc metals has not been studied above 200 °C because the nanoscale grains tend to grow at temperatures moderately above ambient. In this work, we study the creep of nanocrystalline Ni–W (nc Ni–W) up to 450 °C, near its thermal stability limit. A nanoindenter with the capability to heat both the specimen and the indenter tip addresses the issue of heat flow and provides more accurate test temperatures when compared to heating only the specimen. Creep experiments are performed on a nc Ni–W film (grain size ~15 nm) at 300, 350, 400 and 450 °C using the constant load and hold (CLH) method combined with the constant stiffness measurement (CSM) technique in which the peak load is maintained at a constant level. No grain growth occurs even at the highest temperature and highest stress. We conduct an analysis that accounts for the effect of the oscillating loads used in this combined CLH-CSM technique on creep. We find that nc Ni–W exhibits negligible creep at 300 °C, and that at 350 °C, creep in nc Ni–W is three orders of magnitude smaller than creep in pure nc Ni at 100 °C. The creep response of nc Ni–W differs significantly from that predicted by the standard Coble creep model and is attributed to the dislocation–grain boundary interaction.

Keywords

Nanoindentation
Creep
High temperature
Nickel–tungsten alloy
Thermally stable

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