JP3561736B2 - Method for producing SiC particle dispersion-reinforced composite material and product produced by the method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention belongs to the field of high-strength composite materials and a method for producing the same. Specifically, this is a technique of dispersing fine particles of 1 μm or less, further 0.6 μm or less, particularly 0.3 μm or less in aluminum by agitating a molten aluminum without agglomeration.
[0002]
[Prior art]
In general, it has been theoretically clarified that the strength of the composite material increases as the particles dispersed in the metal become finer (1 μm or less, further 0.6 μm or less, particularly 0.3 μm or less). However, since the particles are actually agglomerated when the particles are miniaturized, a theoretically expected high-strength composite material has not been obtained. The reason for this is that the aggregated particles act as a kind of defect to reduce the strength. The prior art (Publication Publication No. 56-141960, a method for producing a ceramic-metal composite) discloses a method in which 0.05 to 5% of calcium metal is added to a molten metal and the ceramic is dispersed by stirring. However, in the case of fine particles unlike the fibrous material, a composite material without aggregation cannot be obtained by this method. As a method of compounding the fine particles, there is known a method in which particles in which SiC fine particles are dispersed in solid metal particles in advance by, for example, a ball mill, are added to molten aluminum and stirred. This method is not enough. SiC aggregates with fine particles of 1 μm or less, further 0.6 μm or less, especially 0.3 μm or less.
[0003]
[Problems to be solved by the invention]
The problem to be solved is to disperse fine particles of 1 μm or less, further 0.6 μm or less, especially 0.3 μm or less in aluminum without agglomeration.
[0004]
[Means for Solving the Problems]
In order to solve the above problems and obtain a composite material without aggregation, the following methods (1) to (11) are required.
(1) A method for producing a composite material, comprising the following steps (a) to (d).
(A) A cleaning step of cleaning impurities in the SiC powder.
(B) a removing step of removing impurities on the surface of the SiC with an acid;
(C) A crushing step in which the SiC is crushed to have a bulk density of 0.24 g / cm ³ or less.
(D) a stirring step of stirring the SiC in completely molten aluminum and then stirring in a solid-liquid coexistence region.
(2) The method according to the above (1), wherein the diameter of the SiC powder is 1 μm or less, further 0.6 μm or less, especially 0.3 μm or less. The method (4) according to the above (1), wherein the slurry having a SiC content of 0.2 to 4% by weight is a washing step of washing with an ultrasonic washing machine. (6) The method according to the above (1), which is a removing step of immersing in a hydrofluoric acid having a concentration of 10% by weight or more at room temperature for at least one day to remove. The method according to the above (1), wherein the water content of the SiC slurry of fine particles having an acid content of 1.0 mol / m ³ particles or less is evaporated to be used as a raw material for the crushing step (8). Crushed by a jet mill with the supply amount of The SiC of but fine particles (1) Bulk Density method (9) is disintegrated according became 0.24 g / cm ³ or less is more solutions砕工to be 0.24 g / cm ³ or less, per minute 500 It is added to a completely melted aluminum at 720 ° C. or higher, which is stirred with a propeller at ２０００2,000 rpm, and stirred for 30 minutes or more as it is, and then continuously at 645 to 650 ° C., at a solid phase of 10 to 80 vol% crystallized. The method (10) according to the above (1), which is a stirring step of stirring at a speed of 300 to 1000 revolutions per minute and a stirring time of 1 hour or more in the liquid coexistence region, adding 0.5% by weight or more of calcium to the above (9). (11) The method according to (1), wherein the content of impurities, especially free silicon and free carbon, is 0.1 to 1.0% by weight based on the SiC powder, and silicon dioxide and other Silicon oxide It said SiC fine particles Yes amount is 0.1 to 1.0 wt% with respect to SiC powder as a raw material (9), (10) said agitation is carried out step according (1) A method according [0005]
DETAILED DESCRIPTION OF THE INVENTION
A description will be given below with reference to FIGS.
[Washing process]
FIG. 1 shows a cleaning step of cleaning and removing impurities in the fine SiC powder. When cleaning is performed by an ultrasonic cleaner, free silicon and free carbon mixed in the SiC powder are separated and float on the water surface. In order to avoid agglomeration, contamination with impurities is not preferred. This requires a cleaning step.
[0006]
[Removal process]
FIG. 2 shows a removing step for removing silicon dioxide and other silicon oxide on the surface of the fine SiC. Hydrofluoric acid dissolves and removes silicon dioxide and other silicon oxide on the surface. The reason for this is that silicon dioxide and other silicon oxides on the surface are the main components of glass and therefore have the property of softening when heated to high temperatures. Therefore, the particles in the powder are likely to adhere to each other, which causes particle aggregation.
When the molten aluminum is agitated to form fine particles as in the present invention, the fine particles are present together with the bubbles entrained during the stirring. And since SiC is more strongly oxidized in hot bubbles, the amount of silicon dioxide and other silicon oxides increases. As a result, the particles aggregate more strongly. Therefore, a removal step is required in which silicon dioxide and other silicon oxide on the surface of SiC are removed in advance.
[0007]
By performing this removing step, silicon dioxide and other silicon oxide on the surface of the SiC particles are reduced. FIG. 3 shows the result of analyzing the surface of the SiC particles by ESCA (surface analyzer) to confirm this. (1) and (2) in FIG. 3 respectively show the results obtained by performing the removal process on the SiC powder without cleaning / removal process, and (2) on the SiC powder obtained by (1).
In (1), SiC, silicon dioxide, and other silicon oxides are recognized. When the removal step is performed on this, the peak of silicon dioxide becomes lower and the peaks of other silicon oxides disappear as shown in (2). When the removal step is performed in this manner, silicon dioxide and other silicon oxide on the SiC surface are dissolved and removed, and the amounts thereof are reduced as compared with those without the cleaning / removal step. Therefore, when the hydrofluoric acid treatment is carried out, the powder becomes less likely to cause aggregation.
[0008]
The above-mentioned powder was heated to 700 ° C. in the atmosphere in order to assume the state of oxidation of the SiC particles in the high-temperature bubbles of aluminum. (3) and (4) in FIG. 3 respectively represent (3) a powder obtained by heating the SiC powder of (1) to 700 ° C. in the atmosphere for 1 hour and cooling to room temperature, and (4) a powder of (2). This is a powder obtained by heating SiC powder to 700 ° C. in the atmosphere for one hour and cooling it to room temperature. When heated to 700 ° C., the peak indicating the amount of silicon dioxide and other silicon oxide in (3) becomes larger than that in the case of non-heating in (1). The same applies to (4) and (2). However, when comparing (3) and (4), the powder of (4) has lower peak values indicating the amounts of silicon dioxide and other silicon oxides than the powder of (3). And it is almost the same amount as (1). In other words, the powder subjected to the removal step has a small amount of silicon dioxide and other silicon oxides even when heated to 700 ° C. Therefore, the powder that has undergone the removal step is less likely to agglomerate.
[0009]
The above-mentioned heating at 700 ° C. is performed in the atmosphere. Thus, the amount of silicon dioxide and other silicon oxides that cause agglomeration is increased by the presence of atmospheric oxygen, which may be sufficient. However, in a non-oxidizing atmosphere, the amounts of silicon dioxide and other silicon oxides do not increase. Therefore, when stirring is performed in a non-oxidizing atmosphere, aggregation is less likely to occur.
[0010]
[Crushing process]
In order to obtain a composite material without aggregation, it is necessary that the particles to be added are sufficiently pulverized.
[0011]
Fine particles are agglomerated in the atmosphere. In order to reduce the agglomeration as much as possible or to pulverize it to such an extent that it can be dispersed with a weak force, the powder is pulverized with a jet mill to obtain fluffy powder. That is, particles that have been in close contact with each other are dispersed in a coarse state. By doing so, the SiC particles are likely to be uniformly dispersed in the subsequent stirring step. For this reason, a particle crushing step is required.
[0012]
[Stirring process]
After mixing the SiC powder that has been subjected to the above-mentioned washing, removal and crushing treatments into high-temperature aluminum that has been completely melted and has improved wettability, a stirring step is performed in a solid-liquid coexisting region at 645 ° C. to 650 ° C. Then, it is cast into a mold to form an aluminum composite material. In the solid-liquid coexistence region, the solid phase is scattered in the molten aluminum. When stirring is performed in this state, SiC that has aggregated due to the collision force between the solid phases is uniformly dispersed. Therefore, aggregation is less likely to occur than in the case of stirring in the state of only the liquid phase. As a result, the SiC particles are uniformly dispersed, and a composite material without aggregation is formed (see FIG. 4).
[0013]
Embodiments of the present invention will be described below.
0.3 μm SiC having a minimum particle size was used as the fine particles.
[0014]
[Washing process]
In the washing step, 1 to 20 g of SiC (SiC content: 0.2 to 4.0% by weight) is added to 500 ml of water in a beaker or the like, and washing is performed by an ultrasonic washing machine for 5 to 10 minutes. At this time, it is better to add an acid such as nitric acid at 1 to 10 vol%. Then, wait until the SiC precipitates, and then discard the supernatant. The supernatant liquid to be discarded contains a lot of impurities such as free silicon and free carbon. These impurities mixed in the powder are removed by this washing step. This washing step may be repeated, and the content of free silicon and free carbon may be finally 0.1 to 1.0% by weight based on the SiC powder.
[0015]
FIG. 5 shows an equilibrium diagram of silicon and carbon. It can be seen that silicon and carbon are present as impurities when SiC is produced by reaction, regardless of whether the generated SiC is α-type or β-type. The free silicon and free carbon as impurities can be separated and floated and removed by the above-mentioned washing step.
[0016]
[Removing Step] In the removing step of removing the residual liquid, SiC is immersed in hydrofluoric acid having a concentration of 10% by weight or more at room temperature for one day or more. Thereafter, if the residual amount of hydrofluoric acid adhering to SiC is large, the inconvenience described later occurs in the next crushing step. Therefore, this content must be 1.0 mol / m ³ · particle or less. Washing is performed to remove the residue until the value is reached.
[0017]
The unit is 1.0 mol / m ³ · particle, but when the slurry is dried, only the water evaporates, and the number of moles of hydrofluoric acid before drying remains. Therefore, since the concentration in each drying step changes every moment, it is inappropriate to display the concentration in mol / l. On the other hand, the mol / m ³ · particle display indicates how many moles of hydrofluoric acid is present per 1 m ³ of SiC particles in the slurry. is there.
[0018]
When hydrofluoric acid remains, the liquid crosslinking force formed between the particles generally increases. The strength of the powder in the atmosphere is substantially determined by this liquid crosslinking force. In order for the crushing by the jet mill to be effective, the crushing force by the jet mill must exceed this powder strength. For this purpose, it is necessary to reduce the residual amount of hydrofluoric acid to minimize the liquid crosslinking power.
[0019]
It was found that the limit value for that was 1.0 mol / m ³ · particle. And it became clear that if it is less than that, it will be sufficiently crushed by the jet mill.
[0020]
FIG. 6 shows the results of calculating the adhesive force between two particles due to liquid crosslinking at a relative humidity of 90%, 70%, and 40%. The strength of the powder can be calculated from the adhesion between the two particles. There is a point where the adhesion between the two particles becomes almost equal at any humidity, and this is the limit value. Below this limit, the adhesion between the two particles decreases. Therefore, the crushing force of the jet mill exceeds the strength of the SiC powder, and as a result, crushing can be sufficiently performed.
[0021]
[Crushing process]
After evaporating the water content of the SiC slurry obtained in the removing step, the powder is supplied by a jet mill at a rate of 1 to 10 g per minute in order to disintegrate it in a mortar or the like and further disintegrate it finely. To disintegrate. The bulk density of SiC is reduced by this crushing step to about 1/2 to 1/4 before crushing. Accordingly, the volume is increased by a factor of 2 to 4 and a fluffy powder with less aggregation is obtained.
[0022]
[Relationship between degree of crushing and aggregation]
The bulk density of the SiC powder not subjected to the washing, removing and crushing steps is about 0.7 g / cm ³ , whereas the bulk density after washing, removing and crushing steps is 0.24 g / cm ³ or less. To decrease. The particles that have been in close contact with each other are dispersed in a coarse state, resulting in a coagulated powder. In the case of powder having a bulk density exceeding 0.24 g / cm ³ , agglomeration occurs when the powder is composited.
[0023]
After the washing step and the removing step, a powder sample was prepared in which the degree of pulverization was changed into three stages of weak, medium and strong, and a stirring process was performed to form a composite with the aluminum alloy (see FIG. C, D, see FIG. Weak / medium / strong crushing was obtained by the difference in the residual amount of the removal solution during the removal process. The weakness is about 10.0 mol / m ³ · particle, the inside is about 1.0 mol / m ³ · particle, and the strong is about 0.01 mol / m ³ · particle. Sample No. Calcium was not added to C, D and E. When strongly crushed, a composite material with almost no aggregation can be manufactured by performing washing, removal, crushing, and stirring steps (see FIG. 8 sample No. E). Photos (C) to (E) show the results when washing and removal were performed, and the degree of crushing was changed to weak, medium, and strong, respectively. In the photograph (C), aggregated particles having a size of about 30 to 300 μm are present at a rate of about 20 to 50 particles / mm ² . In the photograph (D), aggregated particles having a size of about 30 to 200 μm are present at a rate of about 10 to 20 particles / mm ² . In the photograph (E), particles having a size of about 30 μm or less exist at a rate of 10 particles / mm ² or less. At this level, it cannot be said that the particles are agglomerated particles.
[0024]
After strong crushing in the crushing step, 2% by weight of calcium was added. A composite material without aggregation is obtained (see FIG. 8 sample No. F). The photograph (F) is the result of adding 2% by weight of calcium to the above photograph (E). The tissue has almost no aggregation.
[0025]
[Stirring process]
The above-mentioned SiC is added while stirring the aluminum in a completely molten state at 720 ° C. or higher with a propeller. The stirring propeller rotates 500 to 2,000 rpm, and the stirring time is 30 minutes or more. Thereafter, the temperature is lowered, and stirring is performed at 300 to 1,000 revolutions per minute for 1 hour or more in a solid-liquid coexisting region at 645 to 650 ° C. In the stirring step in the solid-liquid coexistence region, the solid phase is crystallized at 10 to 80 vol%, and a strong dispersing force is obtained by collision between the solid phases. Therefore, the SiC particles are more uniformly dispersed and are less likely to be agglomerated than when only the liquid phase is stirred. Aggregation is observed in the composite material manufactured by the manufacturing method that does not perform stirring in the solid-liquid coexistence region. Stirring in the solid-liquid coexistence region is necessary for producing a composite material without aggregation (see FIG. 8 sample No. H). The photograph (H) shows the result when the stirring step was not performed in the solid-liquid coexistence region. Agglomerated particles having a size of about 30 to 100 μm are present at a rate of about 50 to 100 particles / mm ² .
[0026]
[Pouring process]
The aluminum in which SiC is dispersed is cast into a preheated mold, and a composite material is formed by applying a pressure of, for example, 49 to 147 N / mm ² . After the solidification is completed, the composite material of the present invention is obtained by taking out from the mold.
[0027]
[Relationship between washing and removal processes and aggregation]
Compared to the manufacturing process of the photograph (F) in which aggregation is hardly possible, aggregation is more frequently observed in the composite material manufactured by omitting only the washing and removing steps (see FIG. 8 sample No. G). The photograph (G) is a result of the above-mentioned photograph (F) manufactured by omitting only the washing and removing steps. Agglomerated particles having a size of about 30 to 300 μm exist at a rate of about 30 to 80 particles / mm ² .
[0028]
FIGS. 7 to 10 show the results of the washing, removal, crushing, stirring step, and the elimination of aggregation by adding calcium.
[0029]
The photograph (A) shows the result when only the stirring step was performed without performing the washing, removal, crushing step, and calcium addition. Agglomerated particles having a size of about 30 to 300 μm are present at a rate of about 50 to 120 particles / mm ² .
[0030]
The photograph (B) shows the result when calcium was added at 2% by weight and the stirring step was performed without performing the washing, removing, and crushing steps. Agglomerated particles having a size of about 30 to 300 μm exist at a rate of about 40 to 100 particles / mm ² . The degree and ratio of aggregation are almost the same as in the case of the photograph (A).
[0031]
The photographs (C) to (E) show the results when the washing, removal, and stirring steps were performed, and the degree of crushing was changed to weak, medium, and strong, respectively. No calcium was added. In the photograph (C), aggregated particles having a size of about 30 to 300 μm are present at a rate of about 20 to 50 particles / mm ² . The degree and ratio of aggregation are smaller than those in the photographs (A) and (B).
[0032]
In the photograph (D), aggregated particles having a size of about 30 to 200 μm are present at a rate of about 10 to 20 particles / mm ² . The degree and ratio of aggregation are smaller than those in the photographs (A), (B) and (C).
[0033]
In the photograph (E), particles having a size of about 30 μm or less exist at a rate of 10 particles / mm ² or less. At this level, it cannot be said that the particles are agglomerated particles.
[0034]
The photograph (F) is the result of adding 2% by weight of calcium to the photograph (E). It is a tissue without aggregation.
[0035]
Photograph (G) shows the result when only the washing and removing steps were omitted from photograph (F). Agglomerated particles having a size of about 30 to 300 μm exist at a rate of about 30 to 80 particles / mm ² . The ratio of aggregation is slightly smaller than that of the photographs (A) and (B), but not much different.
[0036]
The photograph (H) shows the result when only the stirring in the solid-liquid coexistence region was omitted from the photograph (F). Agglomerated particles having a size of about 30 to 100 μm are present at a rate of about 50 to 100 particles / mm ² .
[0037]
Photo (I) is the result when 0.5% calcium was added to photo (E). Particles of approximately 30 μm or less are present at a rate of 10 particles / mm ² or less. At this level, it cannot be said that the particles are agglomerated particles, and is almost satisfactory.
[0038]
Photographs (F ′) and (G ′) are the results of magnifying observation of the circles in the photographs (F) and (G) with a scanning electron microscope. In the photograph (F ′), the SiC particles are coarsely dispersed. On the contrary, in the photograph (G ′), the SiC particles are densely aggregated. The state without aggregation in the present invention is a state where SiC particles are coarsely dispersed as shown in the photograph (F ′).
[0039]
As described above, according to the method for producing a composite material of the present invention, it is possible to obtain a non-agglomerated composite material using SiC of fine particles as a reinforcing phase, which cannot be obtained by the above-mentioned [Prior Art].
[Brief description of the drawings]
FIG. 1 is a cleaning process diagram for cleaning fine SiC particles. FIG. 2 is a removal process diagram for removing silicon dioxide and other silicon oxide on the surface of fine SiC particles. FIG. 3 is an untreated SiC surface after the removal process. FIG. 4 is a stirring process diagram showing stirring in a solid-liquid coexistence region. FIG. 5 is a diagram showing an equilibrium state of silicon and carbon. FIG. 6 is a diagram showing residual hydrogen at each relative humidity. Fig. 7 is a micrograph showing the effect of cohesion and elimination by washing, removing, crushing, and stirring processes, etc. [Fig. 8] Cohesion and elimination by washing, removal, crushing, and stirring processes. Micrograph showing the effect [FIG. 9] Micrograph showing aggregation and disappearance effects by washing, removing, crushing, stirring steps, etc. [FIG. 10] Micrograph showing aggregation and elimination effect by washing, removal, crushing, stirring steps, etc.

Claims (14)

A method for producing a composite material, comprising the following steps (1) to (5).
(1) A cleaning step of cleaning impurities in the SiC powder.
(2) A removing step of removing impurities on the surface of the SiC with an acid.
(3) A crushing step in which the SiC is crushed to have a bulk density of 0.24 g / cm ³ or less.
(4) A stirring step of stirring the SiC in completely molten aluminum and then stirring in a solid-liquid coexistence region.
(5) A step of performing the stirring step and then casting the mixture into a mold. The method according to claim 1, wherein the diameter of the SiC powder is 1 µm or less. The method according to claim 1, wherein the diameter of the SiC powder is 0.6 µm or less. The method according to claim 1, wherein the diameter of the SiC powder is 0.3 µm or less. 2. The method according to claim 1, wherein the cleaning step is a step of cleaning the fine particle SiC with an ultrasonic cleaner. The method according to claim 1, which is a washing step of washing a slurry having an SiC content of 0.2 to 4% by weight with an ultrasonic washing machine. The method according to claim 1, wherein the removing step is a step of removing with hydrofluoric acid. 2. The method according to claim 1, wherein the removing step is a step of immersing in a hydrofluoric acid having a concentration of 10% by weight or more at room temperature for at least one day to remove. Hydrofluoric acid, the SiC slurry of water particles is less than SiC particles 1 m ³ per 1.0mol in the slurry is evaporated, the method of claim 1 wherein the raw material of about solutions砕工. The method according to claim 1, wherein the method is a crushing step in which fine particles of SiC are crushed by a jet mill at a supply rate of 1 to 10 g per minute, and the bulk density becomes 0.24 g / cm ³ or less. Finely divided SiC having a bulk density of 0.24 g / cm ³ or less after being crushed is added to a completely melted aluminum at 720 ° C. or higher, which is stirred with a propeller at 500 to 2,000 revolutions per minute. This is a stirring step of stirring for 30 minutes or more, and subsequently, stirring at 645 to 650 ° C., a solid-liquid coexistence region where the solid phase is crystallized at 10 to 80 vol%, at 300 to 1000 rotations per minute, and a stirring time of 1 hour or more. Item 7. The method according to Item 1. The method according to claim 11, wherein the stirring step is performed by adding 0.5% by weight or more of calcium. The free silicon content and free carbon content as impurities are 0.1 to 1.0% by weight based on the SiC powder, and the content of silicon dioxide and other silicon oxides is 0.1 to 1.0% based on the SiC powder. The method according to claim 11 or 12, wherein the stirring step is performed using fine particles of SiC of 1 to 1.0% by weight as a raw material. A composite material produced by the method according to claim 1.

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