Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2000-08-14
2001-11-06
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S097200, C501S097300
Reexamination Certificate
active
06313054
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silicon nitride sintered body used for wear-resistant parts such as cutting inserts, bearings, and balls; a method for manufacturing the silicon nitride sintered body; and a cutting insert formed of the silicon nitride sintered body.
2. Background Art
Conventionally, silicon nitride sintered bodies predominantly containing silicon nitride and having an excellent strength have been used for cutting inserts, wear-resistant parts, etc.
In recent years, for the case where silicon nitride is used for cutting inserts, there has been proposed a technique of decreasing the amount of a sintering aid (an oxide) which is added to the essential component, in order to enhance wear resistance of the sintered body (See PCT Kohyo Publication 8-503664 or U.S. Pat. No. 5,525,134). As disclosed therein, a sintered body contains at least about 85 volume percent (vol. %) silicon nitride and less than 5 vol. % intergranular phase. The ceramic has greater than 0.2 weight percent (wgt. %) magnesia, greater than 0.2 wgt. % yttria wherein the sum of magnesia and yttria is less than 5 wgt. %. The ceramic also includes between 1.3 wgt. % to 2.2 wgt. % oxygen.
However, with the conventional cutting insert, there is a drawback that an extreme decrease in the amount of the sintering aid to be added renders sinterability lower than expected and decreases wear resistance and chipping resistance of the sintered body.
SUMMARY OF THE INVENTION
The present invention was made in view of the foregoing, and an object of the present invention is to provide a silicon nitride sintered body having properties such as excellent wear resistance and a method for manufacturing the same. The present invention also provides a cutting insert formed of the sintered body.
According to a first aspect of the present invention, there is provided a polycrystalline sintered body comprising predominantly &bgr;-Si
3
N
4
, i.e. between about 95 to about 97% by volume, wherein the oxygen content is 1.2-1.5 wt. %.
The silicon nitride sintered body of the first aspect of this invention has a dense texture, high hardness, and excellent wear resistance and chipping resistance.
According to a second aspect of the present invention, there is provided a method for manufacturing the above-described silicon nitride sintered body including the following steps: adding an organic binder to a composition containing silicon nitride as an essential component and exhibiting a theoretical oxygen content of 2.0-2.3 wt. %; forming a shaped or pressed body therefrom; heating to remove the binder (e.g., forming a calcined body); introducing an oxygen-containing gas so as to control the carbon content to 0.10-0.60 wt. % (e.g., cooling the calcined body); and sintering the resultant compact in a nitrogen atmosphere to control the oxygen content to 1.2-1.5 wt. % (e.g., primary and secondary sintering steps).
In the method of manufacturing the sintered body of this invention, when primary sintering is performed under pressurization, decomposition of silicon nitride is prevented. Thus, high-temperature sintering is realized. Moreover, pores are effectively closed by the high-temperature sintering at, for example, subsequent secondary sintering through HIP.
According to a third aspect of the present invention, there is provided a cutting insert formed of the silicon nitride sintered body of the first aspect.
The cutting insert of the third aspect of this invention has a dense texture, high hardness, and excellent wear resistance and chipping resistance.
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patent: 5264294 (1993-11-01), Noel et al.
patent: 5264297 (1993-11-01), Jindal et al.
patent: 5370716 (1994-12-01), Mehrotra et al.
patent: 5382273 (1995-01-01), Mehrotra et al.
patent: 5525134 (1996-06-01), Mehrotra et al.
patent: 5635431 (1997-06-01), Ikeda et al.
patent: 6232252 (2001-05-01), Kim et al.
patent: 4-201003 (1992-07-01), None
patent: 4-357174 (1992-12-01), None
patent: 8-503664 (1996-04-01), None
patent: 94/16023 (1994-07-01), None
Dougherty & Troxell
Group Karl
NGK Spark Plug Co. Ltd.
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