Hot Forging of Spherical Particles with Nanocrystalline Microstructures
An alternate method for fabricating ceramics with fine‐ or nano‐ scale microstructures is presented. Powder consisting of 2–25 μm diameter spherical particles (average 16 μm) obtained by plasma melting of spray‐dried powder and quenching into
water, were hot pressed and hot forged. Three different compositions were studied: eutectic alumina‐zirconia, the eutectic composition with 1%Y2O3, and the eutectic composition
with borosilicate glass. As‐quenched particles (Al2O3–(1%Y2O3)ZrO2)
contained both amorphous material and 50–80 nm crystallites. Microstructural development of the Al2O3–(1%Y2O3)
ZrO2 was followed from room temperature up to hot pressing/hot forging temperatures. When fully dense after forging at 1350°C, the microstructure contained ZrO2 phases <100 nm
in diameter embedded in the Al2O3 matrix. Al2O3 grains had an irregular morphology
and were on the scale of ~1 μm diameter. A higher order structure designated as cells, containing a few of these grains, were enclosed by boundaries decorated with ZrO2 particles.