Final stage free sintering and sinter forging behavior of a yttria-stabilized tetragonal zirconia

Abstract

A comprehensive study was undertaken to characterize quantitatively the final stage sintering behavior of a yttria-stabilized tetragonal zirconia (YTZ) under free sintering and sinter forging conditions and to evaluate the role of deformation which occurs concurrently during sinter forging. The results indicated that the activation energies for densification were 585 ± 45 and 620 ± 70 kJ mol^-1 during free sintering and sinter forging, respectively, which were similar to the value of 650 ± 70 kJ mol^-1 observed for deformation during sinter forging. Sinter forging experiments revealed that the densification rate, ρ, was proportional to σ² where σ is the applied stress, whereas the deformation rate, ε, was proportional to σ³. Microstructural observations showed that grain growth kinetics were independent of the volume fraction of porosity. After extensive creep deformation during sinter forging, grains remained equiaxed with average linear intercept grain sizes of 180~nm. A detailed analysis of possible mechanisms revealed that densification in YTZ is controlled by the rate of grain boundary vacancy absorption. Furthermore, it was demonstrated that deformation mechanisms in porous and dense YTZ are identical.