Abstract A method is disclosed comprising placing in a hot pressing environment a controlled mixture of a first powder of Si 3 N 4 containing a controlled amount of SiO 2 (with or without a limited amount of milling media) with a second powder consisting essentially of Y 2 O 3 , hot pressing the controlled mixture, and cooling the resultant unitary object. A novel silicon nitride comprising a unitary object is disclosed which can be shaped to form a novel cutting tool useful for machining metal such as cast iron. The object has selected crystalline phases formed beta Si 3 N 4 and beta prime Si 3 N 4 and has intergranular crystalline secondary phases consisting essentially of YSiO 2 N, Y 10 Si 17 N 4 O 23 and Y 2 Si 2 O 7 with the YSiO 2 N phase representing at least a 25% volume fraction of the secondary phases and comprising essentially all of the yittria-silicon oxide.
A unitary silicon nitride comprising ceramic formed from about 4% to about 12% by weight Y 2 O 3 and the remainder consisting of Si 3 N 4 and a minor amount of SiO 2 , wherein the Y 2 O 3 /SiO 2 weight ratio is at least about 1.6 and which has intergranular crystalline secondary phases consisting essentially of YSiO 2 N, Y 10 Si 7 N 4 O 23 and Y 2 Si 2 O 7 , with the YSiO 2 N phase comprising at least 25% by volume of said secondary phases.
Claim 2
Dependent Claim
96 words
A unitary silicon nitride comprising ceramic formed from about 4% to about 12% by weight Y 2 O 3 and the remainder consisting of Si 3 N 4 and a minor amount of SiO 2 , wherein the Y 2 O 3 /SiO 2 weight ratio is at least about 1.6 and which has intergranular crystalline secondary phases consisting essentially of YSiO 2 N, Y 10 Si 7 N 4 O 23 and Y 2 Si 2 O 7 , with the YSiO 2 N phase comprising at least 25% by volume of said secondary phases.
Claim 3
Dependent Claim
26 words
A unitary silicon nitride comprising ceramic in accordance with claim 1, wherein said ceramic exhibits a thermal shock parameter at 1200° C. of at least ##EQU4##
Claim 4
Dependent Claim
15 words
A ceramic in accordance with claim 1 which has been formed into a cutting tool.
Claim 5
Dependent Claim
22 words
A ceramic in accordance with claim 1, wherein said Y 2 SiO 7 is essentially the only oxide in said secondary phases.