Short carbon fiber-reinforced composite material and method for producing same

Abstract

The present invention relates to a short carbon fiber-reinforced composite material, including a base material part and at least one sliding part contacting the base material part, in which each of the base material part and the sliding part has a plurality of short carbon fiber bundles in which at least a part thereof has been converted into SiC and a SiC matrix present among the plurality of short carbon fiber bundles, as constituent components, and the short carbon fiber bundles of the sliding part have a SiC conversion higher than that of the short carbon fiber bundles of the base material part.

Claims

1. A short carbon fiber-reinforced composite material, comprising a base material part and at least one sliding part contacting the base material part, wherein: each of the base material part and the sliding part has a plurality of short carbon fiber bundles in which at least a part thereof has been converted into SiC, and a SiC matrix present among the plurality of short carbon fiber bundles, as constituent components; and the short carbon fiber bundles of the sliding part have a SiC conversion higher than that of the short carbon fiber bundles of the base material part, wherein the SiC conversion of the short carbon fiber bundles of the sliding part is 45% or more and 80% or less, and the SiC conversion of the short carbon fiber bundles of the base material part is 5% or more and 25% or less.

2. A method for producing a short carbon fiber-reinforced composite material according to claim 1, comprising: a step of mixing a phenol resin with short carbon fiber bundles for a base material part, wherein the short carbon fiber bundles are carbon-coated with a pitch, to obtain a mixture for a base material part; a step of mixing SiC and a phenol resin with short carbon fiber bundles for a sliding part, wherein the short carbon fiber bundles are resin-coated with a phenol resin, to obtain a mixture for a sliding part; a step of placing the mixture for a sliding, part and the mixture for a base material part in a molding die, followed by a pressure-molding under heating to obtain a cured body; a step of baking the cured body at 2000 C. or higher to obtain a baked body; and a step of infiltrating the baked body with silicon by a silicon melt infiltration process at about 1500 C. in vacuum.

Description

EXAMPLES

(1) The present invention is further specifically described below based on Examples, but the present invention is not construed as being limited to the following Examples.

Example 1

(2) Short carbon fiber bundles (diameter: 7 m or more and 15 m or less, length: 4 mm or more and 14 mm or less, 4,000 fibers per bundle) for a base material part were dipped in a solution obtained by diluting pitch with ethanol to 50 wt % such that the bundles were sufficiently dipped in the solution. The bundles were then taken out of the solution and dried at 100 C. or lower for 100 minutes or more. Thus, carbon-coated short carbon bundles for a base material part were obtained.

(3) Short carbon fiber bundles (diameter: 7 m or more and 15 m or less, length: 4 mm or more and 14 mm or less, 4,000 fibers per bundle) for a sliding part were dipped in a solution obtained by diluting a phenol resin with ethanol to 50 wt % such that the bundles were sufficiently dipped in the solution. The bundles were then taken out of the solution and dried at 100 C. or lower for 100 minutes or more. Thus, resin-coated short carbon bundles for a sliding part were obtained.

(4) Next, 70 to 80 wt % of the short carbon fiber bundles for a base material part were mixed with 20 to 30 wt % of phenol resin (the total of short carbon fiber bundles for base material part and phenol resin is 100 wt %) and ethanol to obtain a mixture for a base material part.

(5) Similarly, 65 to 75 wt % of the short carbon fiber bundles for a sliding part were mixed with 10 to 30 wt % of SiC (average particle diameter: 0.5 m), 5 to 15 wt % of phenol resin (the total of short carbon fiber bundles for sliding part, SiC and phenol resin is 100 wt %), and ethanol to obtain a mixture for a sliding part.

(6) The mixture for a sliding part, the mixture for a base material part and the mixture for a sliding part were placed in a molding die in this order, molded at 100 C. or higher under a pressure of 100 kgf/cm.sup.2 or more, and then heated at 800 C. or higher for 100 minutes or more. Thus, a cured body having 150 mm diameter and 15 mm thickness was obtained.

(7) The cured body is baked at 2000 C. or higher for 40 minutes or more in a reducing atmosphere to obtain a baked body. The baked body obtained was further infiltrated with molten silicon at about 1500 C. in vacuum to obtain a short carbon fiber-reinforced composite material.

(8) The SiC conversion, bending strength and fracture energy of the short carbon fiber-reinforced composite material obtained were measured by the following methods.

(9) [SiC Conversion]

(10) Short carbon fiber-reinforced composite material was cut and polished to expose the cross-section of short carbon fiber bundles. Adjustment was performed such that X-ray points the center of the short carbon fiber bundles, and EDX analysis was performed. SiC proportion of the short carbon fiber bundles was calculated from peak intensity ratio of Si and C obtained. Cross-sections at optional different 10 places of the short carbon fiber bundles were subjected to EDX analysis, and the average value of the SiC proportions calculated was defined as SiC conversion.

(11) [Bending Strength]

(12) Test piece of 3 mm4 mm40 mm was prepared, and 3-point bending strength (MPa) was measured under crosshead speed of 0.5 mm/min by the method according to JIS R1601:2008.

(13) [Fracture Energy]

(14) Test piece of 3 mm4 mm40 mm was prepared, a straight notch having a depth of about 2 mm was formed at a central part thereof by using a diamond blade having a thickness of 0.1 mm, and fracture energy was measured according to JCRS-201. Distance between supporting points was 30 mm, crosshead speed was 0.01 mm/min, and fracture energy (J/cm.sup.2) per unit area until 5% of maximum load value was obtained.

Example 2

(15) A short carbon fiber-reinforced composite material was obtained in the same manner as in Example 1, except that the short carbon fiber bundles for a base material part were dipped in a solution obtained by diluting pitch with ethanol to 60 wt % and the short carbon fiber bundles for a sliding part were dipped in a solution obtained by diluting a phenol resin with ethanol to 60 wt %.

(16) The SiC conversion, bending strength and fracture energy of the short carbon fiber-reinforced composite material were measured in the same manners as in Example 1.

Example 3

(17) A short carbon fiber-reinforced composite material was obtained in the same manner as in Example 1, except that the short carbon fiber bundles for a base material part were dipped in a solution obtained by diluting pitch with ethanol to 35 wt % and the short carbon fiber bundles for a sliding part were dipped in a solution obtained by diluting a phenol resin with ethanol to 35 wt %.

(18) The SiC conversion, bending strength and fracture energy of the short carbon fiber-reinforced composite material were measured in the same manners as in Example 1.

Comparative Example 1

(19) The same short carbon fiber bundles (diameter: 7 m or more and 15 m or less, length: 4 mm or more and 14 mm or less, 4,000 fibers per bundle) were used in the base material part and the sliding part, and dipped in a solution obtained by diluting a phenol resin with ethanol to 50 wt % such that the carbon fiber bundles were sufficiently dipped in the solution. The bundles were then taken out of the solution and dried at 100 C. or lower for 100 minutes or more to obtain resin-coated short carbon fiber bundles. Then, 70 to 80 wt % of the short carbon fiber bundles were mixed with 20 to 30 wt % of phenol resin (the total of short carbon fiber bundles and phenol resin is 100 wt %) to obtain a mixture for a base material part. A short carbon fiber-reinforced composite material was then obtained in the same manner as in Example 1.

(20) The SiC conversion, bending strength and fracture energy of the short carbon fiber-reinforced composite material were measured in the same manners as in Example 1.

(21) The results of Examples 1 to 3 and Comparative Example 1 are shown below.

(22) TABLE-US-00001 TABLE 1 SiC conversion of SiC conversion of Bending Fracture carbon fibers of carbon fibers of base strength energy sliding part (%) material part (%) (MPa) (J/m.sup.2) Example 1 55 12 175 2020 Example 2 46 7 134 1960 Example 3 78 25 191 1460 Comparative 55 56 45 825 Example 1

(23) While the present invention has been explained in detail with reference to specific embodiments, it is apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the present invention.

(24) This application is based on Japanese Patent Application (No. 2017-090225) filed on Apr. 28, 2017, the contents of which are incorporated herein by reference.