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AssigneeSumitomo Electric Industries, Ltd.
InventorsTakehisa Yamamoto, Takao Nishioka, Kenji Matsunuma, Akira Yamakawa, Masaya Miyake
Estimating the term…
The present invention relates to a silicon nitride sintered body [wherein the composition of Si.sub.3 N.sub.4 -first aid (Y.sub.2 O.sub.3 +MgO)-second aid (at least one of Al.sub.2 O.sub.3 and AlN)] falls within a range defined by lines joining points A, B, C and D in FIG. 1, the crystal phase of the sintered body contains both .alpha.-Si.sub.3 N.sub.4 and .beta.'-sialon, and the relative density is 98% or more. This sintered body is produced by subjecting a green compact of the above-described source to primary sintering in a nitrogen gas atmosphere at 1300.degree. to 1700.degree. C. so that the relative density reaches 96% or more, and the precipitation ratio of the .alpha.-Si.sub.3 N.sub.4 crystal phases to the .beta.'-sialon crystal phase in the sintered body is in the range of from 40:60 to 80:20; and then subjecting the primary sintered body to secondary sintering in a nitrogen gas atmosphere at 1300.degree. to 1700.degree. C. so that the relative density reaches 98% or more. The sintered body has superior strength properties, especially at ordinary temperatures, and can be produced with a high productivity in a high yield at a low cost.
A silicon nitride sintered body consisting of a composition falling within a range surrounded by the lines joining the points A, B, C and D in the ternary composition diagram of Si.sub.3 N.sub.4 -first aid-second aid shown in FIG. 1, the first aid consisting of a combination of two oxides of Y.sub.2 O.sub.3 and MgO, the second aid consisting of one or both of Al.sub.2 O.sub.3 and AlN wherein the addition composition ratio of Si.sub.3 N.sub.4 to the first aid is in the range of from 85:15 to 99:1 percent by mole and the addition composition ratio of Si.sub.3 N.sub.4 to the second aid is in the range of from 90:10 to 99:1 percent by mole, said sintered body comprising crystal phases containing both an .alpha.-Si.sub.3 N.sub.4 crystal phase and a .beta.'-sailon crystal phase, the relative density of the sintered body being 98% or more, the precipitation ratio of the .alpha.-Si.sub.3 N.sub.4 crystal phase to the .beta.'-sialon crystal phase in the sintered body being more than 0 but not more than 30 in terms of the peak intensity in X-ray diffraction.
Dependencies are inferred from the claim text.