JP3367165B2 - Ceramic sliding member - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic sliding member in which compound whiskers or fibers are dispersed in a ceramic matrix. 2. Description of the Related Art Conventionally, there is a sliding member made of ceramics. In addition, silicon nitride Si ₃ N
_{A method} of dispersing a solid lubricant such as boron nitride BN in the material ₄ to reduce the coefficient of friction is disclosed in, for example, JP-A-59-30769.
No. 6,086,045. In addition, as a sintering aid, Fe
Silicon nitride Si ₃ added with an oxide of iron Fe such as ₃ O ₄
N _4, for example, JP 58-64268, JP-Sho 59-88374 and JP disclosed in JP-61-72685 Publication. In addition, Al ₂ O ₃ , Y
A method of performing reaction sintering mainly to increase strength by adding an oxide such as ₂ O ₃ is disclosed in, for example, JP-A-59-1522.
No. 71, JP-A-59-207875 and JP-A-59-207876. Further, as a composite sliding member, there has been known a composite sliding member in which ceramic is composited with an alloy such as Al by various methods, for example, a ceramic preform is prepared, and then metal and ceramic are composited by impregnation or the like. Therefore, such a composite sliding member has been partially put into practical use as a piston ring. When coating a metal substrate with ceramics, thermal spraying or the like is generally put to practical use. [0004] However, the above-mentioned composite sliding member uses ceramics mainly as a wear-resistant material, and is not intended to reduce the friction coefficient μ. It is not intended to significantly reduce μ. Also, Al ₂ O ₃ and Y ₂ O are used for Si.
Addition of additives such as ₃ cannot sufficiently reduce the friction coefficient μ. In addition, solid lubricant such as BN
When it is contained in i ₃ N ₄ , the strength is significantly reduced.
It cannot be used for engine parts that require a certain level of strength. [0005] Meanwhile, silicon nitride ceramics having a low friction coefficient are desired. In general, when silicon carbide, boron nitride, or oxide particles are dispersed in Si ₃ N ₄ , the reactivity at the bonding interface is poor, and the strength of the material itself is reduced. Further, in a material in which boron nitride is compounded, the portion is oxidized at a high temperature, the crystal structure is changed, and the friction coefficient may be increased. As disclosed in the above publication, Fe ₃ O _{4 is} used as a sintering aid.
In the case where a metal oxide such as that described above is added, the amount of addition is small and low friction characteristics cannot be obtained. Furthermore, ceramics do not always have low friction characteristics in the boundary lubrication region, and in the case of a material containing boron nitride, boron oxide is formed at a temperature of 600 ° C. or more, and the crystal structure changes. There is a problem that the coefficient increases. In addition, in the case of a composite of Si ₃ N ₄ and an oxide of iron Fe, a reduction reaction occurs during firing, and FeO, Fe ₂ O
Even if it is added at the mixing stage in the form of ₃ , Fe ₃ O ₄ , it changes to an Fe—Si compound after firing. Such a compound is also excellent in adsorptivity to lubricating oil, but is desirably left in the form of an oxide in order to further enhance the adsorptivity and reduce friction. [0008] In order to solve the above-mentioned problems, the present applicant has developed a low-friction ceramic and filed an application [Japanese Patent Application No. 5-95048 (Japanese Patent Application Laid-Open No. Hei 6-234564)]. The low friction ceramic is made of Si ₃ N ₄ or S
iC, FeO, Fe
Fe oxides such as ₂ O ₃ and Fe ₃ O ₄ are dispersed and oxidized from the surface to the inside in the air, and the Fe-Si compound existing as a compound is excellent in adsorbability with oil. The friction is reduced by changing to an Fe-O-based oxide. However, Fe in the ceramic matrix
In the case of a ceramic sliding member in which compound particles are dispersed, for example, in Si ₃ N ₄ , grain growth is suppressed, and the fracture toughness value K _{1 C} is lowered to 6.4 MPam ^1/2 . In addition, an attempt to control the firing pattern of the ceramic compact, that is, to increase the sintering temperature and the maximum temperature holding time or to increase the maximum temperature holding time, to increase the grain growth and increase the fracture toughness. However, at present, good results have not been obtained. [0010] An object of the present invention is to solve the above-mentioned problems, and uses ceramics as a mother phase and contains Fe in the mother phase.
By dispersing whiskers or fibers of oxides and silicides, it is possible to prevent the oil film from breaking off from the surface with excellent oil-absorbing property, to have a low friction coefficient, and especially to improve the fracture toughness. It is to provide a member. SUMMARY OF THE INVENTION The present invention provides ZrO ₂ ,
A ceramic, which is Al ₂ O ₃ , Si ₃ N ₄ or SiC, is used as a mother phase, and an oxide of Fe or silicidation of Fe is contained in the mother phase.
The present invention relates to a ceramic sliding member in which whiskers or fibers are dispersed. [0012] Since this ceramic sliding member is configured as described above, it has a dispersed phase having excellent oil adsorbing properties, has an extremely low friction coefficient, and has a fracture toughness value of K _IC. Can be improved. That is, since Fe oxide or silicide is excellent in adsorptivity, when the compound is dispersed in the ceramic matrix, the oil film on the surface is hard to be cut, and as a result, excellent wear resistance is exhibited. It will exhibit a low coefficient of friction. The ceramic sliding member is made of Al.
Ceramics such as ₂ O ₃ , ZrO ₂ , Si ₃ N ₄ , and SiC are used as a mother phase, and FeO, Fe ₂ O ₃ , Fe
_It has a structure in which a phase having excellent adsorptivity such as ₃ O ₄ is included as whiskers or fibers, and can be produced by using a whisker such as Fe ₃ O ₄ as a raw material of the whiskers or fibers. Note that the fracture toughness value K
_IC is the critical stress intensity factor, a material constant for evaluating the mechanical function of ceramics. According to Griffith, the fracture strength of ceramics depends on the size of cracks that are latent in the material. The tensile strength σ _f at which a crack grows and breaks in ceramics is expressed by the following equation. σ _f = K
_{1 C} / (πc) ^1/2 , where K _{1 C} is the fracture toughness, the critical value of the stress intensity factor, and c is the length of a surface crack or the radius of an internal circular crack. Hereinafter, an embodiment of a ceramic sliding member according to the present invention will be described with reference to the drawings. As shown in FIG. 1, this ceramic sliding member has ceramics as a mother phase 1 and contains, in the mother phase 1, elements of group 8 in the periodic table.
Compound whiskers and fibers 3 of elemental oxides of Fe or silicides of Fe are dispersed. ZrO ₂ , Al ₂ O ₃ , Si
₃ N _4, is either SiC. The compound of the group VIII element is either Fe oxide or Fe silicide. Reference numeral 2 denotes the surface of the ceramic sliding member. [0015] In general, for low fracture toughness K _{1 C} ceramics, as a method to enhance the fracture toughness value K _{1 C,} it is grain growth, or short fibers, or the like can be conjugated the long fibers are known ing. All of them attempt to increase the fracture toughness value K _{1 C} by increasing the amount of energy required for crack propagation by crack deflection. On the other hand, substances such as FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ can enhance oil adsorbability and have a low friction coefficient. Therefore, in this ceramic sliding member, a whisker of Fe ₃ O ₄ or the like is used to improve the fracture toughness value K _{1 C} to a high value and improve the adsorptivity to reduce the friction coefficient. An embodiment (Embodiment 1) of the ceramic sliding member according to the present invention will be described. [Example 1] This ceramic sliding member was produced as follows.
First, La-βAl ₂ O ₃ -added CeO ₂ -stabilized ZrO ₂
A whisker (20 μm length) of Fe ₃ O ₄ was added to the powder, and the mixture was kneaded for about 5 hours by a kneader equipped with a means capable of measuring torque and the like to prepare a mixture. In this case, water was used as the mixing medium, and the number of revolutions of the kneader was set to 60 rpm. Here, La-βAl ₂ O ₃ added CeO ₂ stabilized Z
rO ₂ powder is composed of ZrO ₂ stabilized with CeO ₂ and La-
This is a ceramic powder produced by mixing and firing with βAl ₂ O ₃ and pulverizing the sintered body. The mixture was taken out of the kneader, and the mixture was put into a mold and preformed to prepare a preform. The preform was dried at 150 ° C., and the dried preform was CIP-molded under a pressure of about 2000 kgf / cm ² to produce a formed body. Next, the compact was fired at a maximum temperature of 1650 ° C. to produce a dense sintered body, that is, a ceramic sliding member. With respect to the sintered body produced by the above-described manufacturing process, the fracture toughness value K _{1 C} (MP) with respect to the amount (wt%) of the whisker of Fe ₃ O ₄ added to the above ceramic powder.
FIG. 2 shows the relationship of (a · m ^1/2 ). As can be seen from FIG. 2, the fracture toughness value K _{1 C} gradually increases as the amount of Fe ₃ O ₄ whiskers added to the ceramic powder increases. Further, the addition amount of the whisker of Fe ₃ O ₄ to the above ceramic powder was 8 wt%.
The sliding characteristics of the added ceramic sliding members were investigated. The result is shown in FIG. The sliding test was performed under the following conditions. A pin made of cast iron was used as a mating material for the sliding test. The sliding characteristics of this ceramic sliding member were evaluated using a reciprocating motion tester at 170 ° C. in the air at an average sliding speed of 2 m / s. In the sliding test, the test was performed by changing the load variously. The results are shown in the graph of FIG. In FIG. 3, the vertical axis represents the friction coefficient μ, and the horizontal axis represents P = log (η × V / F). Regarding the parameter P, F indicates load, V indicates speed, η and viscosity of lubricating oil, and the unit of P is [× 10
⁻⁶ · (m ² / S) · (m / S) / kgf]. Further, in order to know the sliding characteristics of the ceramic sliding member of the first embodiment, as a comparative example 1, Fe ₃ O ₄
The above ceramics without added whiskers, namely L
A ceramic sliding member was produced from a-βAl ₂ O ₃ -added CeO ₂ stabilized ZrO ₂ powder. A sliding test of the ceramic sliding member of Comparative Example 1 was performed in the same manner as in Example 1 above.
The results are shown in the graph of FIG. As can be seen from FIG. 3, the ceramic sliding member of Example 1 has a lower friction coefficient μ than the ceramic sliding member of Comparative Example 1. Another embodiment (Embodiment 2) of the ceramic sliding member according to the present invention will be described. [Embodiment 2] The ceramic sliding member in this embodiment 2 is made of Al ₂
Using O ₃ powder as a raw material, Fe ₃
8% by weight of O ₄ (iron oxide) whiskers or Fe—Si (iron silicide) whiskers, Cr ₂ O ₃ whiskers, and CrN whiskers were added, and test pieces were prepared under the same conditions as in Example 1. . The sliding characteristics of this test piece were evaluated. It was found that the fracture toughness value K _{1 C} of the ceramic sliding member of Example 2 was 15 to 25% higher than that of the original ceramic sliding member to which no whisker was added, and was improved. Also, it was confirmed that the friction coefficient μ of the ceramic sliding member of Example 2 was 10% lower than that of the original ceramic sliding member. Next, another embodiment (Embodiment 3) of the ceramic sliding member according to the present invention will be described. [Embodiment 3] This ceramic sliding member is formed by adding Al ₂ powder to Si ₃ N ₄ powder.
Ceramics produced by adding O ₃ and Y ₂ O ₃ were pulverized to produce ceramic powder. After mixing this ceramic powder with Fe ₃ O ₄ whiskers, the mixture was molded to form a molded body, which was fired at 1700 ° C. 8w of Fe ₃ O ₄ whisker is added to the ceramic powder.
The ceramic sliding member manufactured by adding t% had a fracture toughness value K _{1 C} = 7.8 MPa · m ^1/2 , and the original ceramic sliding member without the addition of Fe ₃ O ₄ whisker was: Fracture toughness value K _{1 C} = 6.4 MPa · m
It was ^1/2 . Further, it was confirmed that the friction coefficient μ of the ceramic sliding member of Example 3 was reduced by about 12% as compared with the original ceramic sliding member. The ceramic sliding member according to the present invention is configured as described above, so that a low friction can be achieved and, in particular, a high fracture toughness value can be improved. It is very preferable to apply as a sliding member. Moreover, the compound whisker of Fe element functions as a dispersant having excellent adsorptivity, can secure a low friction in which an oil film is not interrupted, and has a stable and rich wear resistance. Also, troubles such as sticks do not occur. This ceramic sliding member is made of Al ₂ O ₃ , ZrO ₂ , Si ₃ N ₄ , SiC
In other words, in the structure of ceramics such as above, that is, a phase having excellent adsorbability such as Fe ₃ O ₄ is contained in the form of whiskers with the ceramic as a mother phase, and the fracture toughness can be improved. In addition, this ceramic sliding member can be easily manufactured by using whiskers such as Fe ₃ O ₄ .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural view showing one embodiment of a ceramic sliding member according to the present invention. FIG. 2 is a graph showing the relationship between the fracture toughness value K _{IC and} the amount of Fe ₃ O ₄ whisker added to the ceramic sliding member. FIG. 3 is a graph showing a friction coefficient with respect to a parameter P of a ceramic sliding member according to the present invention. [Description of Signs] 1 Mother phase 2 Surface 3 Compound whisker

Claims (1)

(57) [Claims 1] A ceramic which is ZrO ₂ , Al ₂ O ₃ , Si ₃ N ₄ or SiC is used as a matrix, and F is contained in the matrix.
ceramic sliding member whiskers or fibers is an oxide or silicide of Fe e is characterized in that it dispersed.