Size effect and time-dependent nanohardness of ZrO2-based ceramics

A modified setup and a method of dynamic indentation with a triangular symm etric force pulse of controllable amplitude and duration are employed for a nalyzing the time-dependent elastic properties of ZrO2-based ceramics in a contact time range of 20 ms-4 s. It is shown that the duration of the loadi ng-unloading cycle considerably affects the dynamic hardness: the variation of the contact time from 20 ms to 4 s leads to a 20% change in the dynamic hardness for P-max = 25 mN. The variation of the hardness sensitivity m to the strain rate upon a transition from the initial stage of indenter intru sion to the next stages from m(1) = 1.56 to m(2) = 0.49 may point to the di fference in the mechanisms of mass transfer of a material under an indenter at these stages. (C) 2001 MAIK "Nauka/Interperiodica".