High Temperature Plastic Deformation Of Superplastic 3Y-TZP

The high temperature plastic deformation behavior, concurrent grain growth and cavitation, densification of the presintered body during deformation and superplastic diffusion bonding of superplastic 3 mol% Y₂O₃-stabilized tetragonal zirconia polycrystals (3Y-TZP) have been systematically studied by both constant crosshead speed and constant load tests in compression in air as well as electronic microscopy analysis.The results illustrate that 3Y-TZP exhibited high ductility at temperatures over 1250°C. Plastic flow stress increased with the increase of strain rate and grain size and the decrease of temperature. Strain-hardening occurred during testing due to the increase of strain rate with strain and dynamic grain growth. The dynamic grain growth showed slightly anisotropic with a contribution to strain less than 5%. The flow stress decreased with the decrease of density.This research reveals that the measured value of stress exponent, activation energy and inverse grain size exponent for very fine-grained (0.30 and 0.53 μm) 3Y-TZP varied with strain rate or stress. The stress exponent and activation energy decreased from about 5 to about 2 and from about 720 to about 470 kJ/mol, respectively, with the increase of strain rate from about 10^-6 to about 10^-3 s^-1. The inverse grain size exponent was measured to be 2 and 3.3 at medium (10^-510^-4 s^-1) and high (10^-410^-3 s^-1) strain rates. This phenomenon can be satisfactorily explained with the model of grain boundary sliding with a threshold stress. Based on this model a "intrinsic" stress exponent of 2, a "intrinsic" activation energy of 406 kJ/mol and a "intrinsic" inverse grain size exponent of 3.3 were deduced. The grains remained equiaxed and only limited dislocations were observed in the deformed...