The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 31, 1994
Filed:
Jun. 14, 1993
Junichiro Suzuki, Gifu, JP;
Masahide Kayukawa, Gifu, JP;
NGK Spark Plug Co., Ltd., Nagoya, JP;
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.