M. Nawa et al., MICROSTRUCTURE AND MECHANICAL-BEHAVIOR OF 3Y-TZP MO NANOCOMPOSITES POSSESSING A NOVEL INTERPENETRATED INTRAGRANULAR MICROSTRUCTURE/, Journal of Materials Science, 31(11), 1996, pp. 2849-2858
Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol %
molybdenum (Mo) composites were fabricated by hot-pressing a mixture o
f Y-TZP powder containing 3 mol % yttria (Y2O3) and a fine Mo powder i
n vacuum. This composite system possessed a novel microstructural feat
ure composed of an interpenetrated intragranular nanostructure, in whi
ch either nanometer sized Mo particles or equivalent sized zirconia (Z
rO2) particles located within the ZrO2 grains or Mo grains, respective
ly. The strength and toughness were both greatly enhanced with increas
ing Mo content for the 3Y-TZP/Mo composites thus breaking through the
strength-toughness tradeoff relation in transformation toughened ZrO2
and its composite materials. They exhibited a maximum strength of 2100
MPa and a toughness of 11.4 MPa . m(1/2) for the composite containing
70 vol % Mo. These simultaneous improvements in strength and toughnes
s were determined to be the result of a decrease in flaw size associat
ed with the interpenetrated intragranular nanostructure, and a stress
shielding effect created in the crack tip by the elongated Mo polycrys
tals bridging the crack tip in addition to the stress induced phase tr
ansformation.