Pellets of advanced fuels with compositions MC1-xNx (x = 0, 0.2, 0.5, and 1.0 and M = U0.8Puo.2) have been deformed under axial compression in the temperature ranges from 293 to 1573 K and from 1673 to 1873 K in two deformation modes:

  1. barrel-type deformation due to constrained end faces of the pellets
  2. cylindrical deformation due to lubricated end faces of the pellets.
The absolute values of the flow stresses and of the work hardening coefficients at 8% deformation were perceptibly higher for the cylindrical deformation mode than for barrel-type deformation, whereas the temperature coefficients of flow stress and work hardening are hardly affected by the deformation modes. Structural analysis of the deformed pellets by ceramography and transmission electron microscopy shows contributions from crack formation and true crystal plasticity to the total deformation. Until now, relatively little attention has been paid to crack formation as an active deformation mechanism in advanced fuels. The tendency for crack formation seems to increase with increasing nitrogen content in the fuels, but metallic impurities and the amount of second phases such as M2C3 (in carbon-rich carbonitrides) and MO2 (in MN) may mask this effect completely.