Abstract
This article reports the solid state synthesis and high-speed superplastic forging of the fully dense nanocrystalline ZrO2-20mol%Al2O3 product via the thermal-mechanical testing combined with the pulse discharging and d.c. heating. The full-density cylindric specimen with the height, 9.8 mm can be obtained by the consolidation of the amorphous ZrO2-20mol%Al2O3 powder compact at the relatively low temperature of 1331 K, when the pressure of 160 MPa is applied. For bulk nanocrystalline ZrO2-20mol%Al2O3 with a grain size (d) of 11 nm for tetragonal ZrO2 as deduced from X-ray diffraction, we find that the sample can be plastically forged up to the compressibility of 43 % during heating in a range of testing temperature from 1175 to 1377 K without macroscopic fracturing. The strain rate of nearly uniaxial plastic deformation at the early stage of forging shows an extremely high level of 2⋅10-2 s-1 at 1358 K under an initial uniaxial stress (σ) of 100 MPa, and is characterized by an activation energy (Q) of 457 kJmol-1 according to the usual constitutive law of ε=Aσ1/m(1/d)P exp (-Q/kT) for superplastic flow.
