Silicon nitride base sintered body

Details Silicon nitride base sintered body Silicon nitride base sintered body

1993-06-14

1994-05-31

Turner, A. A.

Stock material or miscellaneous articles

Composite

Of silicon containing

428698, 428697, 428699, 428701, 428704, 501 96, 501 97, 501 98, 501126, 501154, C04B 3558

Patent

active

053168569

ABSTRACT:
A sintered body of silicon nitride base solidly formed of interior and surface portions wherein the rate of decrease of the content Si or Si.sub.3 N.sub.4 and Sialon grains in the surface portion, with respect to that in the interior portion, is not less than 20% by weight or 30-100 vol %, respectively. The grain boundary phase of the surface portion is glassy, or crystallized partly or entirely. Crystallized boundary phase comprises Si.sub.3 N.sub.4 -Y.sub.2 O.sub.3 base compounds Si.sub.3 N.sub.4 -nY.sub.2 O.sub.3 -mX (n=1-5, X=SiO.sub.2, Al.sub.2 O.sub.3, m=0-4) such as mellilite, J phase (mohlerite), K phase (wollastonite), H phase (apatite), or A phase (Si.sub.3 N.sub.4.5Y.sub.2 O.sub.3.Al.sub.2 O.sub.3). Sintering aids of Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, AlN, MgO, CaO, Y.sub.2 O.sub.3 and/or rare earth oxides form boundary phases. The sintered body may comprise 30% by weight or less of compounds (oxide, carbide or nitride) of subgroups IVa, Va and VIa of the International Periodic Table as third dispersed component.
This sintered body with the modified surface portion exhibits the intrinsic property of the interior portion and the property of the surface portion resulting in high wear resistance and toughness useful as cutting tools.

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