Role of length scale and temperature in indentation induced creep behavior of polymer derived Si–C–O ceramics

This investigation presents nanoindentation and microindentation creep analyses on polymer derived Si–C–O ceramic coatings at temperatures ranging from room temperature to 500 °C. The properties of focus include elastic modulus, hardness, creep exponent, and creep strain rate. Analyses show that at the nanoscopic length scale the deformation mechanism is dominated by dislocation climb and diffusion. With increase in length scale to microscale the thermal activation volume increases by approximately 10 times. The increase in free volume leads to the deformation mechanism switching to volumetric densification and dislocation pile up. An important physical effect analyzed is the effect of increase in temperature on the observed deformation mechanism. At the nanoscale, with increase in temperature, both hardness and elastic moduli show an increase. At the microscale, however, hardness reduces with increase in temperature. The indentation size effect is observed at both scales. However, at the nanoscale the indentation size is linked with strain hardening. At the microscale, a strain softening behavior is observed.

Research highlights▶ For the first time indentation creep analyses at temperatures ∼500 °C performed. ▶ For the first time polymer derived SiCO composites analyzed. ▶ Analyses also include effect of change in testing length scale (nano and micro). ▶ Change in nano to micro scale causes 10 times change in thermal activation volume. ▶ Observed strain hardening at nano and strain softening at micro scale are explained.