Sinter-forging of nanocrystalline zirconia: II, simulation

A quantitative computer simulation of densification, pore-size evolution, a nd grain growth during sinter-forging has been developed and applied to the sinter-forging of nanocrystalline yttria (30 mol%)-stabilized zirconia (3Y -TZP) at 1050 degrees and 1100 degrees C, Densification is simulated as a s uperposition of stress-assisted and plastic-strain-controlled pore-shrinkag e mechanisms. Grain growth is simulated as a pore-controlled process during intermediate-stage densification and as a combination of normal (static) g rain growth and dynamic grain growth during final-stage densification, The densification portion of the model offers very good agreement with the expe riment under a wide variety of imposed forging conditions, despite the abse nce of adjustable variables. Grain-growth predictions qualitatively illustr ate a key feature in the sinter-forging of 3Y-TZP: i.e,, the minimization o f grain size, as a function of density, under forging conditions that promo te high strain rates. This particular effect seems to be due to the quick e limination of large pores by plastic strain while small pores (which shrink by diffusion) are still available to control grain growth.