Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2001-03-14
2004-09-28
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S097200, C384S492000, C384S907100
Reexamination Certificate
active
06797660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wear resistant member made of a sintered body essentially consisting of silicon nitride and a manufacturing method thereof, in particular relates to silicon nitride wear resistant member excellent in rolling fatigue life characteristics and a manufacturing method thereof.
2. Description of the Related Art
Wear resistant member is used in a variety of fields such as for instance bearing member, various kinds of roll materials for rolling, compressor vanes, gas turbine blades, and engine components such as cam roller or the like. For such wear resistant member, so far ceramic material has been used. In particular, silicon nitride sintered bodies, being excellent in wear resistance, are broadly used in a variety of fields.
Since the silicon nitride is sintered with a great difficulty, various compounds are added as sintered additive in manufacturing a sintered body. As existing compositions of the silicon nitride sintered body, such systems as silicon nitride-rare earth oxide-aluminum oxide and silicon nitride-rare earth oxide-aluminum oxide-titanium oxide are known. In these compositions, the sintered additive such as rare earth oxides is a component that forms, during the sintering, a grain boundary phase (glassy phase) consisting of Si—R—Al—O—N compound (R: rare earth element) to densify the sintered body, resulting in higher strength.
In the silicon nitride sintered body of an existing composition also, flexural strength, fracture toughness and wear resistance and the like are improved. However, these characteristics are not sufficiently improved. In particular, in the wear resistant member such as rolling bearing member, slide characteristics such as rolling fatigue life is in strong demand to be furthermore improved.
As to raw material composition of a silicon nitride sintered body, for instance Japanese Patent Laid-open Application No. HEI 1-93470 discloses the following. That is, a ceramic mixture containing, as sintered additive, from 1 to 10% by mass of rare earth oxide, from 1 to 10% by mass of aluminum oxide and from 0.1 to 5% by mass of titanium oxide, and the rest essentially consisting of silicon nitride is molded and sintered to obtain a sintered body. In the above publication, it is also disclosed that titanium oxide is segregated, after the sintering, in a grain boundary phase as titanium nitride or the like to promote densification of the sintered body, thereby contributing in an improvement of thermal shock resistance.
However, when titanium oxide is simply added to the raw material mixture to sinter, during the sintering, titanium oxide is rapidly converted into titanium nitride to tend to cause fluctuation in particle diameters of titanium nitride particles, resulting in coarse particles of titanium nitride. The coarse titanium nitride particle in the silicon nitride sintered body may be a starting point of crack due to the difference of thermal expansion coefficients between that of silicon nitride grain. Thereby, characteristics such as strength and fracture toughness may be deteriorated.
As to an improvement of wear resistance of a silicon nitride sintered body, Japanese Patent Laid-open Application No. HEI 6-122563 discloses the following. That is, in silicon nitride matrix of an average particle diameter of 10 &mgr;m or less, a Ti compound of which ratio (aspect ratio) of a long axis to a short axis is two or more is dispersed in the range from 1 to 50% by mass to prepare ceramic composite material. Here, as the Ti compound, whiskers essentially consisting of TiN, TiC or TiCN is used.
The Ti compound (TiN whisker, for instance) of which aspect ratio is two or more in the above publication shows an effect of improving strength and toughness of the sintered body. However, when using the silicon nitride sintered body in such as bearing member, rolling fatigue life tends to deteriorate, on the contrary. That is, when Ti whisker or the like large in shape anisotropy is present on a slide surface, it becomes a thorn like projection. The projection may be a starting point of fracture or may be highly aggressive against an opponent member.
Furthermore, Japanese Patent Laid-open Application No. HEI 5-178668 discloses a silicon nitride-titanium nitride composite sintered body in which fine particles of titanium nitride are dispersed in a matrix consisting of silicon nitride and grain boundary phase. The silicon nitride-titanium nitride composite sintered body contains silicon nitride in the range of from 45 to 95% by volume and is manufactured in the following ways. First, an organic precursor of silicon nitride containing Ti element is heat-treated to prepare fine crystalline composite powder of silicon nitride and titanium nitride. Then, a sintered additive is added to the fine composite powder to mix, the mixture being sintered to obtain a composite sintered body.
In the silicon nitride-titanium nitride composite sintered body thus obtained, fine particles of titanium nitride are mainly dispersed in grains of silicon nitride. The fine particles of titanium nitride, being different in thermal expansion coefficient from silicon nitride, cause residual compressive stress in the grains of silicon nitride. Such residual compressive stress works as resistance to a progress of crack, resulting in higher fracture toughness. However, in the use of external stress being continuously applied as in the case of a bearing member, the residual stress in the silicon nitride grains may cause peeling, on the contrary.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide wear resistant member that is, in addition to high strength and toughness, excellent in sliding characteristics, and a manufacturing method thereof. The present invention intends to provide wear resistant member that is improved in rolling fatigue life in particular to be suitable for bearing member, and a manufacturing method thereof.
The wear resistant member of the present invention is one comprising a silicon nitride sintered body, the silicon nitride sintered body comprising silicon nitride, titanium nitride particles having long axis is 1 &mgr;m or less, and a grain boundary phase mainly containing a Si—R—Al—O—N compound (here, R denotes a rare earth element) in the ranges of from 75 to 97% by mass, from 0.2 to 5% by mass and from 2 to 20% by mass, respectively.
In the wear resistant member of the present invention, the titanium nitride particles are preferable to be singly particle-dispersed in the silicon nitride sintered body. In other words, titanium nitride, without being dissolved as a solid solution in silicon nitride or grain boundary phase, is present as titanium nitride particles. The titanium nitride particles are particularly preferable to be dispersed mainly in the grain boundary phase.
A method of manufacturing the wear resistant member of the present invention is one of manufacturing wear resistant member comprising silicon nitride sintered body, having the following steps. That is, the present method of manufacturing a silicon nitride sintered body comprises the steps of preparing a mixture of raw material, molding the mixture of raw material into a desired shape, heat-treating after degreasing, and sintering to prepare a silicon nitride sintered body. In the step of preparing a mixture of raw material, to silicon nitride powder that contains oxygen by 1.7% by mass or less and &agr;-silicon nitride by 90% by mass or more and of which average particle diameter is 1.0 &mgr;m or less, rare earth compound, titanium nitride or titanium compound converting into the titanium nitride due to the sintering, aluminum oxide and aluminum nitride are added by the following amounts, respectively. That is, the rare earth compound is added by 0.5 to 10% by mass in terms of oxide thereof. The titanium nitride of which average particle diameter is 0.7 &mgr;m or less or titanium compound converting into titanium nitride due to the sintering is added by 0.1 to 5% by mass in terms of titaniu
Group Karl
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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