Hafnia-silicon carbide nanocomposites II: Measurements of the residual stress

In this follow up article we report on the residual stresses induced by the phase transition in hafnia grains, in two-phase nanocomposites made with 30 vol% silicon carbide, after cooling down to room temperature from the processing temperature of 1800 °C. The residual stress, lying in the range of 300-500 MPa can be reduced to 50 MPa by annealing at 1400 °C, which has the effect of raising the average fracture strength from 660 MPa to 850 MPa. The residual stress is ascribed to the phase transformation in hafnia from the tetragonal to the monoclinic phase at 1700 °C.