Abstract
Application of a DC electric field (E = 46 V/cm) during the tensile deformation of an ultrafine-grained 2.5Y-TZP (d = 350 nm) at 1450�C resulted in a significant reduction in the flow stress ! , which reversed upon removal of the field. At strains!" 0.6 , the reduction in flow stress E "! consisted of two components: (a) a rapid initial decrease in stress ( *E "! ) due to the effect of the field on the deformation mechanism(s) and (b) a longer-time decrease in stress ( T "! ) due to Joule heating, giving E E T "! = "! + "! * . At !> 0.6 , an additional contribution ( str E "! ) occurred, which was attributed to a change in defect structure, e.g., grain growth and cavitation.
It was concluded that the rate-controlling mechanism in the present tests is grain boundary sliding accommodated by lattice diffusion of the Zr ions with a threshold stress o ! , giving an acting effective stress e o ! =! "! . It was determined for this case that * E "! contained reductions in both the ffective stress ( * e,E "! ) and in the threshold stress ( o,E "! ). Analysis of the behavior in terms of an electrochemical potential for vacancy formation showed that * e,E "! and o,E "! are related to changes in the electric field potential pertaining to the space charge at the grain boundaries. The calculated width of the space charge region acted on by the electric field was 3-5 nm in the temperature range of 1450� !1550�C .