Claims
- 1. A unitary silicon nitride comprising ceramic formed from about 4% to about 12% by weight Y.sub.2 O.sub.3 and the remainder consisting of Si.sub.3 N.sub.4 and a minor amount of SiO.sub.2, wherein the Y.sub.2 O.sub.3 /SiO.sub.2 weight ratio is at least about 1.6 and which has intergranular crystalline secondary phases consisting essentially of YSiO.sub.2 N, Y.sub.10 Si.sub.7 N.sub.4 O.sub.23 and Y.sub.2 Si.sub.2 O.sub.7, with the YSiO.sub.2 N phase comprising at least 25% by volume of said secondary phases.
- 2. A unitary silicon nitride comprising ceramic in accordance with claim 1, wherein said ceramic exhibits a thermal shock parameter at 1200.degree. C. of at least ##EQU4##
- 3. A ceramic in accordance with claim 1 which has been formed into a cutting tool.
- 4. A ceramic in accordance with claim 1, wherein said Y.sub.2 SiO.sub.7 is essentially the only oxide in said secondary phases.
RELATED APPLICATIONS
This is a division of application Ser. No. 232,754 filed Feb. 9, 1981, which is a continuation-in-part of U.S. Ser. No. 911,256, filed May 31, 1978 by the same inventors as the present application, now abandoned.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4102698 |
Lange et al. |
Jul 1978 |
|
Divisions (1)
|
Number |
Date |
Country |
Parent |
232754 |
Feb 1981 |
|
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
911256 |
May 1978 |
|