JPH1025154A - Ceramic excellent in sliding characteristic and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sliding characteristics of the surface structure of a ceramic by forming long-periodic unevennesses so as to retain a lubricating oil and short-periodically reducing the surface roughness. SOLUTION: This ceramic has a surface structure thereof in which long- periodic unevenesses so as to hold a lubrication oil are formed on the surface and the surface roughness is short-periodically small. Si3 N4 , SiC, Al2 O3 or ZrO2 or a composite ceramic prepared by dispersing other ceramics in the ceramic as a substrate, e.g. an Al2 O3 /ZrO2 -based, an A2 O3 /TiC-based or an Al2 O3 /SiC whisker/ZrO2 -based ceramic is used as the ceramic. The surface roughness of the long-periodic surface part is 0.1-1.0μm and the average roughness indicating the roughness of the short-periodic surface part is 0.01-0.1μm. Furthermore, the average roughness for 10 points of the roughness in the short-periodic surface part is 0.2-0.6μm and the maximum roughness is 0.3-1.5μm. The surface structure can be changed with the surface roughness of a grindstone in a barrel grinding method used herein. For example, a coarse grindstone having about No. 400 grain size is initially used and then a grindstone composed of abrasive grains is then used. A grindstone composed of fine grains is finally used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic having excellent sliding characteristics such as wear resistance and seizure resistance, and a method for producing the same. The ceramics provided by the present invention are used in ceramic engine parts which are required to have excellent sliding properties, tools which are required to have excellent wear resistance, and the like.

[0002]

2. Description of the Related Art Ceramics may exhibit very good sliding characteristics against metals due to wear resistance due to high hardness of ceramics and seizure resistance due to low reactivity with metals. Has been pointed out in the past. However, at present, the application area is still limited because of the low fracture toughness, that is, the fragility that ceramics are a brittle material.

[0003]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a surface structure which does not break down when ceramic is used as a sliding member or a tool, and a method of adjusting the surface structure. Things.

[0004]

Means for Solving the Problems A ceramic which achieves the above-mentioned object has a surface structure in which long-period irregularities are formed on the surface so as to hold a lubricating oil, and the surface structure is short-periodally. It is a ceramic having excellent sliding characteristics characterized by a small roughness, and in the method for manufacturing a ceramic for a sliding material according to the present invention, first, long-period irregularities are formed so that lubricating oil is retained. Is a method for producing a ceramic having a surface structure excellent in sliding characteristics, characterized in that roughness is formed in a short period while substantially maintaining the irregularities on a surface.

Hereinafter, analysis and consideration performed by the inventor in the process of devising the above-described surface structure will be described. First, when using ceramic as a sliding member, a metal component as a mating material reciprocates in a state pressed against the ceramic surface. At this time, what kind of stress is generated near the ceramic surface which is a starting point of ceramic breakage Calculated what would happen.

As the calculation model, a compression load model shown in FIG. 1 and a shear load model shown in FIG. 2 are used. In Figure 1, q: pressing load a per unit area: per width of the ceramic and metallic O: contact surface leftmost O _1: contact surface rightmost theta: angle theta ₁ made of ON and OM: angle formed by the ON and O ₁ N r: distance between O and M r ₁ : distance between O ₁ and N α: angle formed by OM and MN M: point to be analyzed N: intersection of a vertical line from O and O ₁ M In FIG. 2, S is a shear load.

As a calculation model, a compression load model and a shear model are adopted, and by analyzing these analysis results, fracture under actual sliding conditions in which both compression and shear loads are applied to the ceramic is considered. 1 and 2, the mating material is in contact with the ceramic material in a direction perpendicular to the paper surface. Therefore, it is assumed that the contact portion with the counterpart material is a belt shape perpendicular to the paper surface. Therefore, if the longitudinal direction of the band is taken along the Z axis, 2
The model can be set as a two-dimensional plane stress problem. The coordinate axes in this model are as shown in FIGS.

The solution for the compressive load of the model of FIG.
EORY OF ELASTICITY, SPTIMOSHENKO, JNGOODIER
(Publisher McGraw Hill, 1970) at pages 104-108. The stress function φ is given by the following equation. φ = q / 2π · (r 2 θ-r 1 2 θ 1) ········ _{^{However, r 1 2 = r 2 +}} a 2 -2r acos (π / 2 + θ) θ 1 = θ + α (α < 90 °) As the stress solution, using this stress function, σ _r = 1 / r∂φ / ∂r + 1 / r ² ∂φ / ∂θ ² = -q / π ・ (α + 2 acos θ / r)・ ・ ・ ・ ・ ・ ・

[0009]

(Equation 1)

[0010]

(Equation 2)

Here, σ _r , σ due to stress solution, and σ due to stress solution are r direction, θ direction, r direction in FIG.
This is the stress in the θ direction.

Now, considering the portion on the left side of O, θ = 0 to
π / 2, α = 0 to π / 2. This value is the stress solution,
Substituting into

[0013]

(Equation 3)

That is, the stress of σ _r and the stress solution are all compression, and the ceramic chip is practically not broken by this stress (breakage is most likely to occur under tensile stress). The possibility of failure is when the shear stress due to the stress solution exceeds the shear strength of the ceramic. On the surface of the ceramic chip, that is, r → 0, the stress solution diverges and becomes ∞. However, this is a mathematical contradiction, and actually saturates at a certain finite value by inducing microcracks, plastic deformation, and the like. Therefore, in order to find this finite value, q = 8
It is assumed that 0 kg / mm ² and a = 0.5 mm, and r is changed to see the change in σ due to the stress solution.

Σ by stress solution at r = 0.5 mm
Is

[0016]

(Equation 4)

Σ by stress solution at r = 0.4 mm
Is

[0018]

(Equation 5)

Σ by stress solution at r = 0.3 mm
Is

[0020]

(Equation 6)

Σ by stress solution at r = 0.2 mm
Is

[0022]

(Equation 6)

Σ by stress solution at r = 0.1 mm
Is

[0024]

(Equation 7)

Σ from the stress solution at r = 0.01 mm is

[0026]

(Equation 8)

## EQU1 ## In the above calculation, r = 0.1 to
Since σ due to the stress solution at 0.01 mm exceeds the shear strength of ordinary ceramics, there is a possibility that breakage or wear due to shear stress may occur only in a portion very close to the surface of the ceramic chip.

Next, the solution to the shear load of the model in FIG. 2 is also given as a stress function on page 147 of THEORY OF ELASTICITY. Specifically, φ = S / π · [１ ／ · y ² log (x ² + y ² ) + xy arctan (y / x) −y ² ] ·········· _x = S / _π · ^{[log (x 2 + y 2)} + (2x 2 + 3y 2) / (x 2 + y 2) -2 ] ^{_{········ σ y = -y 2 / (}} x 2 + y ² ) ······ σ _xy = (2-x ² −y ² ) / (x ² + y ² ) ² + tan ^-1 (x / y) It is.

The stress at position 0 in FIG. 2 is x = 0, y → 0
Given by

[0030]

(Equation 10)

Σ _y = 1 σ _xy = π / 2, and it can be seen that the tensile stress that causes breakage is infinite at this point, and that breakage is very likely to occur at this point. However, since σ _x is a function of log y in the y direction, σ _x sharply decreases when going slightly downward from the surface, and therefore this tensile stress is also a problem only in a portion very close to the surface.

From the above stress solutions, it can be said that when the metal component slides on the ceramic, a very large tensile / shear stress is generated only on the surface of the ceramic sliding surface.

As mentioned above, very high tensile and shear stresses occur on the ceramic surface. In order to prevent ceramics from becoming tribological problems such as seizure and wear by using an appropriate lubricating oil type in order to make ceramic a sliding member, lubrication and the surface of ceramics have been proposed. There are no known studies that have related structures.

The ceramic surface structure for improving the tribology, which the present inventors have found, satisfies the following conditions. Surface structure 1: Long-period unevenness is formed on the surface so that lubricating oil is held. Surface structure 2: The surface roughness should be small in a short period so that abrasion does not occur in direct contact during sliding.

Hereinafter, the surface structures 1 and 2 will be described in detail. The presence of the lubricating oil between the metal parts and the ceramic surface greatly reduces the stress generated on the sliding surface, but the problem is how to keep this lubricating oil. It is considered that when only the periodic irregularities are present, when the lubrication is cut off on the sliding surface between the metal and the ceramic (it is considered that the lubrication is cut off at a certain probability), a very large amount of wear occurs. Therefore, it is the meaning of the surface structures 1 and 2 that the irregularities on the surface are reduced in a short period and the lubricating oil is retained by the irregularities in a long period.

Here, the long period is a period of the surface irregularities, and is a period having a width (measured in the sliding direction) capable of holding an amount of lubricating oil that substantially reduces the stress applied to the ceramic from the mating material. Indicates a state in which is repeatedly formed. That is, a very small amount of lubricating oil is held in the concave portion of the very microscopic unevenness by the attraction between molecules or atoms, but since such a small amount of lubricating oil does not contribute to stress reduction, In the present invention, a long period is determined so as to exclude microscopic irregularities.

The short cycle is the length of the sliding surface shorter than the long cycle. When the ceramic and the mating material come into contact with each other, breakage and wear of the ceramic analyzed with reference to FIGS. This is the length of the sliding surface to be obtained. That is, the lubricating oil is always held on the surface of the sliding ceramic according to the present invention by long-period irregularities, but with a shorter length, the lubricating oil runs out with a certain probability (that is, the lubricating oil exists at the atomic or molecular level). Even if it does not contribute to lubrication)
Here, it is assumed that the ceramic and the mating material are in contact with each other, and such a contact length is called a short cycle.

The second surface structure having a small roughness in a short period has another meaning. This is related to the fact that the shear load S generated in FIG. 2 is represented by the product of the compressive load (q) and the coefficient of friction (μ). This is because if the short-period irregularities are large, the friction coefficient μ becomes large, and as a result, S becomes large, so that the tensile stress at the point 0 in FIG.

As described above, since the surface is flat in the long period, but a rough surface structure is not preferable in the short period, the present invention requires that the roughness be large in the long period and small in the short period. . In the latter case, a rough surface in a long cycle usually has a short cycle roughness that is small.However, the short cycle roughness specified in the present invention is smaller than that of a counterpart material, and the microscopic fracture described in the preceding paragraph occurs. It points to difficult things.

On the other hand, if the irregularities have a long period, the number of contact points in sliding decreases, so that μ cannot be increased, and as a result, S also decreases. From such a viewpoint, it can be said that long-period irregularities are more preferable than short-period irregularities from the viewpoint of holding the lubricating oil.

The method of the surface structure according to the present invention relates to a method of preparing a surface having irregularities in a long period and having a small amount of irregularities in a short period, which comprises subjecting a ceramic to a special barrel treatment. Is possible.

In the present invention, ceramic refers to Si ₃
N ₄ , SiC, Al ₂ O ₃ , ZrO ₂ , and composite ceramics based on these and having other ceramics dispersed therein, as a typical example, an Al ₂ O ₃ / ZrO ₂ system,
Al ₂ O ₃ / TiC type, Al ₂ O ₃ / SiC whisker / ZrO ₂ type, etc.

The average roughness (Ra) of the long-period surface portion can be 0.1 to 1.0 μm as measured by a roughness meter. Similarly, the average roughness (R
a) can be 0.01 to 0.1 μm as measured by a roughness meter. Other, Rz representing the ten point average roughness in the short period surface portion roughness R _max representing 0.2 to 0.6 [mu] m, a maximum roughness can be 0.3 to 1.5 .mu.m.

Next, a description will be given of the barrel treatment used for carrying out the method of the present invention. The barrel treatment is a treatment in which the surface is polished with a polishing stone, and the surface structure can be variously changed depending on the roughness of the polishing stone. The surface structure proposed in the present invention having irregularities in a long period and having no irregularities in a short period can be realized by the following process. (1) A plane is formed by grinding a ceramic fired body. However, in this case, a coarse grindstone having a grain size of about 400 may be used (see FIG. 3A). (2) Using a grinding stone composed of abrasive grains, rough-polishing is performed on the ceramic that has been ground with a grinding stone to provide long-period irregularities on the surface (see FIG. 3B). (3) Short-period irregularities are reduced by performing finish polishing in the barrel using a polishing stone composed of fine grains (see FIG. 3C).

[0045]

The ceramic surface structure provided by the present invention has the following advantages. First, FIG.
Since the lubricating oil accumulates in the concave portion shown in (c), the lubricating oil exists during sliding between the metal component and the ceramic material. Since a thin film is formed by this lubricating action, the stress is sufficiently reduced as compared with the direct contact, and the probability of microscopic fracture of the ceramic is drastically reduced. In addition, since the unevenness is long-period, the number of contact points with the metal component is reduced, so that the friction coefficient between the metal and the ceramic is reduced. In addition, since the short-period unevenness is eliminated, the friction coefficient per unit area of the contacting portion is reduced.

The reason why the ceramic according to the present invention has such excellent wear resistance is considered as follows. That is,
Since the wear of the ceramic is caused by the aggregation of microscopic fractures (such as grain boundaries), the surface structure proposed in the present invention does not cause direct contact between the metal surface and the ceramic surface due to the presence of the lubricating oil. This is because the contact load applied from the metal side can generate only a stress greatly attenuated compared to the stress at the time of direct contact on the ceramic surface separated by the thickness of the lubricating layer. In addition, the surface structure according to the present invention, which has long-period irregularities and few short-period irregularities, reduces the number of metal / ceramic contact areas as compared with a smooth surface, and reduces the friction coefficient of the contacted portions. It is considered that the frictional coefficient μ shown in the equation is significantly reduced because the two effects of being small are simultaneously obtained. This means that the S (shear load), which is the fundamental load of fracture, is extremely small, so that micro-fracture has occurred at S, which is a certain point or more, which is the zero point in FIG. As a result, it is possible to suppress the stress below the stress at which destruction occurs, and it is possible to prevent the destruction from occurring.

The reason why the ceramic according to the present invention is so excellent in seizure resistance is considered as follows. That is,
The metal / ceramic seizure first cracks on the surface of the ceramic, abrasion progresses, and the metal penetrates into the abraded part, rather than the lubrication between the metal / ceramic being cut off. This is because it is easy to occur due to sliding of. In other words, it can be said that the root cause of seizure is unevenness (short-period) of the ceramic surface due to wear. With the surface structure as in the present invention, destruction hardly occurs, so that surface roughness due to abrasion hardly occurs, and as a result, seizure resistance improves. Hereinafter, the present invention will be described more specifically with reference to examples.

[0048]

EXAMPLE A sample having the surface structure shown in the present invention was produced by the following process. Raw material powder Si ₃ N ₄ -15 wt% Y ₂ O ₃ -2.5 wt% Al ₂
Add 5 wt% of molding binder to the compounded powder of O ₃ , mix with a ball mill, and use a spray dryer to
m was granulated. 1.5t After uniaxial molding the granulated powder at 150 kg / m ²
Rubber pressing was performed at a pressure of on / cm ² . Heat treatment is performed by the temperature control program shown in FIG.
Degreasing was performed by evaporating the binder at a temperature of 3 ° C for 3 hours. Thereafter, heat treatment was performed by the temperature and pressure control program shown in FIG. 5, and pressure firing was performed at 1800 ° C. for 70 minutes at 8 atm.
The size of the fired material is about 50φ × 6t. After firing, surface grinding was performed with a diamond grindstone of about 400 (see FIG. 3A). The surface roughness at this time was as follows. Ra = 0.43 μm, R _max = 3.09 μm, Rz =
2.59 μm

Thereafter, a disc for reciprocating sliding test was cut out from the disc. Next, the test piece was subjected to barrel treatment. The barrel processing used three processes of rough finishing, medium finishing, and finishing (see FIGS. 6A, 6B, and 6C). The time required for rough finishing 3h, medium finishing 1h and finishing 8h. FIG.
As can be seen from the above, the short-period unevenness, that is, the surface roughness, became thinner while the long-period unevenness was maintained as the rough, medium, and finish progressed. The surface roughness was as follows by this barrel treatment. Ra = 0.055 µm N = 16, δ = 0.017 µm R _max = 0.72 µm N = 16, δ = 0.027 µm Rz = 0.387 µm N = 16, δ = 0.387 µm Gloss as an evaluation method was also measured.
As a result, the gloss was 74.3, N = 8, σ _SD = 5.56. The long period of this sample directly measured from the surface roughness measurement data is 74 to 680 μm, and the short period is 6 to 8
μm. The long period roughness was 0.25 to 1.0 μm, and the short period roughness was 0.06 μm.

A reciprocating sliding wear test was performed as an evaluation. The evaluation method and results are shown below.

FIG. 7 shows a reciprocating sliding wear test method test apparatus. In the figure, 1 is a movable-side test piece (a mating material pin), 2 is a test piece (a ceramic test piece), and an arrow indicates a pressing load. The test conditions were as follows. Sliding surface speed: 0.1265 m / s Load: 784 MPa (Hertz stress) Sliding distance: 1.2 km Amplitude width: 25 mm Lubrication: Sniso 5G, 400 mL / min, 80 ° C Test pin side (partner material) Material: S50C (Induction hardening) Dimensions: □ 5 × 30mm, tip R = 6mm (tip roughness, R
a = 0.24 μm, Rz = 0.8 μm, R _max = 1.0
μm). The measuring method was as follows. Pin material: Measure the weight before and after the test and compare by weight loss due to abrasion. Ceramic specimen: Measure the wear depth. The results of the measurement are shown in Table 1 together with the results of the comparative example.

Comparative Example 1 After firing the ceramic by the same process as in the example,
Surface grinding was performed with the number one diamond grindstone. The surface roughness at this time was as follows. Ra = 0.14 μm, Rz = 1.12 μm, R _max =
1.62 μm, and the surface structure of the fired body was as shown in FIG. 8, and there was no long-period unevenness.

Comparative Example 2 After firing the ceramic in the same process as in the example, 700
Surface grinding was performed with the number one diamond grindstone. The surface roughness at this time was as follows. Ra = 0.14 μm, Rz = 0.97 μm, R _max =
The surface structure of the fired body was the same as that shown in FIG. 8 except for the roughness.

Comparative Example 3 After the treatment of Comparative Example 2, lapping was performed. The surface roughness at this time was as follows. Ra = 0.06 μm, Rz = 0.14 μm, R _max =
The surface structure of this fired body was the same as that shown in FIG. 8 except for the roughness.

[0055]

Table 1 Ceramic Wear (μm) Counter Material Wear (mg) Inventive Example 2 0.9 Comparative Example 1 3.4 1 Comparative Example 2 2.9 0.8 Comparative Example 3 2.5 1.2

As can be seen from Table 1, in the embodiment of the present invention, the wear of both the ceramic and the mating material is small.

[0057]

As described above, according to the present invention, it is possible to improve the sliding characteristics of ceramics, which had a problem in terms of brittleness. Sex is enhanced.

[Brief description of the drawings]

FIG. 1 is a stress analysis diagram based on a compression load model.

FIG. 2 is a stress analysis diagram based on a shear load model.

FIG. 3 is a conceptual diagram illustrating a change in roughness by a barrel polishing method according to the present invention.

FIG. 4 is a graph showing a degreasing temperature control program.

FIG. 5 is a graph showing a temperature and pressure control program in firing.

FIG. 6 is an example of a surface roughness measurement result of a barrel-treated product in Example 1.

FIG. 7 is a schematic view of a reciprocating sliding wear test apparatus.

FIG. 8 is an example of a surface roughness measurement result in Comparative Example 1.

[Description of reference numerals]

 1 Movable side test (Material pin) 2 Ceramic test piece

(Equation 9)

Claims (2)

[Claims] 1. A sliding characteristic of a ceramic having a surface structure in which long-period irregularities are formed on the surface so as to hold a lubricating oil, and surface roughness is small in a short period. Excellent ceramic. 2. A method of manufacturing a ceramic for a sliding material by polishing a surface of a ceramic, wherein firstly, long-period irregularities are formed on the surface so as to hold a lubricating oil.
A method for producing a ceramic having a surface structure with excellent sliding characteristics, characterized by reducing roughness in a short period while substantially maintaining the irregularities.