JP3992474B2 - Method for producing boron carbide-aluminum nitride sintered body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a boron carbide (B ₄ C) -aluminum nitride (AlN) sintered body having a high relative density.
[0002]
[Prior art]
Since the boron carbide sintered body is a material that is lightweight and has high hardness and excellent wear resistance and corrosion resistance, it is used for sandblast nozzles, wire drawing dies, extrusion dies, and the like. Since the boron carbide sintered body is difficult to sinter, it is usually manufactured by a hot press method in a high temperature range of 2100 ° C. or higher and a large pressure of 30 MPa or higher. The application is hindered.
[0003]
On the other hand, in Japanese Patent Laid-Open No. 59-184767, Al, an Al alloy, and an Al compound are added to boron carbide as a sintering aid. However, Al, Al alloy and Al compound decompose and evaporate during normal pressure sintering in vacuum or inert gas atmosphere, so not only the sinterability is improved but also the weight is reduced to 95% or more. The relative density of is not obtained.
[0004]
[Problems to be solved by the invention]
As described above, since the boron carbide sintered body is difficult to sinter, a high-density and high-strength material cannot be provided at a low cost, and the use is restricted. An object of the present invention is to provide a boron carbide-aluminum nitride sintered body having a relative density of 95% or more at a low cost. The object of the present invention can be achieved by hot-press sintering or normal-pressure sintering of a compact of a mixed powder composed of boron carbide powder and aluminum nitride powder under specific conditions.
[0005]
[Means for Solving the Problems]
The present invention raises the temperature of a mixed powder formed of a boron carbide powder having an average particle diameter (D ₅₀ ) measured by a laser diffraction scattering analyzer of 10 μm or less and an aluminum nitride powder, In hot press sintering or normal pressure sintering in a temperature range of 2200 ° C. or lower, an atmosphere of 1000 ° C. or higher is a mixed atmosphere of argon gas and nitrogen gas, and the N ₂ partial pressure is higher than the decomposition N ₂ pressure of aluminum nitride. Boron carbide-aluminum nitride sintered with boron carbide (B ₄ C) of 99.5 to 70 mol%, aluminum nitride (AlN) of 0.5 to 30 mol%, and a relative density of 95% or more. It is a manufacturing method of a body. In the present invention, it is preferable to perform hot press sintering at a pressure of 20 MPa or less.
[0006]
[Form of the present invention]
The boron carbide-aluminum nitride sintered body produced in the present invention has a boron carbide (B ₄ C) content of 99.5 to 70 mol%, aluminum nitride (AlN) content of 0.5 to 30 mol%, and a relative density of 95% or more. is there. If the aluminum nitride (AlN) is less than 0.5 mol%, the effect as a sintering aid is not sufficiently exhibited in a practical sintering schedule, and if it exceeds 30 mol%, the light weight of the boron carbide sintered body is reduced. It is difficult to maintain characteristics such as high hardness, excellent wear resistance and corrosion resistance, particularly high elasticity. Also, those having a relative density of less than 95% have low strength, and their use is limited when they are put to practical use. A sintered body having a four-point bending strength of 600 MPa or more is suitable for applications such as a sandblast nozzle, a drawing die, and an extrusion die.
[0007]
In the present invention, in order to improve the sinterability of boron carbide powder, Ru is added 0.5～30Mol% aluminum nitride powder to boron carbide powder as a sintering aid. The molded body of the mixed powder of this Upon be heated sintering, because the aluminum nitride to decompose and evaporate an odd, heating and sintering the above 1000 ° C. is a mixed atmosphere of argon gas and nitrogen gas In addition, it is performed in an atmosphere in which the N ₂ partial pressure is maintained at or above the decomposition N ₂ pressure of aluminum nitride . As a result, a part of the surface of the aluminum nitride powder reacts with the boron carbide powder to form a grain boundary reaction phase, and the diffusion during the sintering is activated to promote the sintering. On the other hand, in the conventional technique, since sintering is performed in a vacuum or in an inert atmosphere, aluminum nitride is decomposed (2AlN → 2Al + N ₂ ) and the effect as a sintering aid is not sufficiently exhibited. large weight loss by evaporation even Al content with N ₂ occurs, the sintered body is sufficiently densified obtained such an off. Moreover, the reason why the temperature rise and sintering at 1000 ° C. or higher is made to be a mixed atmosphere of argon gas and nitrogen gas is that when excessive nitrogen pressure is applied, adverse effects such as reaction with the materials constituting the furnace occur at high temperatures. This is to avoid this.
[ 0008 ]
The sintering temperature is selected in the range of 1900 ° C. or higher and 2200 ° C. or lower. If the temperature is lower than 1900 ° C., sintering does not proceed sufficiently. If the temperature exceeds 2200 ° C., boron carbide in the sintered body grows, and it becomes difficult to suppress decomposition of aluminum nitride.
[0009]
The pressure applied during hot press sintering is preferably 20 MPa or less. As a result, a relatively high density sintered body can be obtained without requiring an excessive pressurizing apparatus. In addition, when applying a conventional hot press apparatus, the problem that the shape of the product is restricted due to the need for a large pressing force is avoided, and a large size product is manufactured using the conventional apparatus as it is. Can do.
[0010]
Atmospheric pressure sintering is a method in which a mixed powder is sintered without pressing a compact obtained by a molding method such as pressing, extrusion, or injection molding. It is much cheaper and more massive than hot press sintering. A knot can be produced. Furthermore, since no pressure is applied in the sintering process, the raw material is made into a complex product shape or a shape close to it in advance and then sintered, or only after post-processing such as some processing, the complicated shape. The sintered body can be manufactured.
[ 0011 ]
The boron carbide powder used in the present invention has an average particle size (D ₅₀ ) of 10 μm or less measured with a laser diffraction / scattering analyzer (Microtrack). When the average particle diameter (D ₅₀ ) is larger than 10 μm, the sinterability is inferior and a dense sintered body cannot be obtained. Moreover, it is preferable that a specific surface area (BET) is 2 m < ² > / g or more.
[0012]
【Example】
Reference example 1
In this example, the temperature of a compact of a mixed powder composed of boron carbide powder and aluminum nitride powder is started in a vacuum atmosphere, and when reaching 1000 ° C. , argon gas and nitrogen gas are introduced, and N ₂ partial pressure is a mixed atmosphere of argon gas and nitrogen gas was maintained on the decomposition N ₂ pressure of aluminum nitride, and further the heating was 1700 ° C., the hot press sintering under a pressure 50 MPa.
[0013]
Boron carbide powder A shown in Table 1 is mixed with 10 mol% of aluminum nitride powder having an average particle diameter (D ₅₀ ) of 0.7 μm, and using a methanol solvent, the number of revolutions is 185 rpm in a planetary ball mill made of silicon carbide (SiC). After mixing for 30 minutes, the mixture was dried by an evaporator, further dried at 150 ° C. for 24 hours, and then passed through a sieve having an opening of 250 μm to prepare a boron carbide-aluminum nitride mixed powder.
[0014]
[Table 1]
[ 0015 ]
A graphite die was filled with boron carbide-aluminum nitride mixed powder, molded at 7.5 MPa, and then attached to a firing furnace. Heated at a rate of temperature increase of 40 ° C./min while evacuating to a pressure of 2.0 × 10 ^{−1 to} 2.0 × 10 ⁻² Pa using a diffusion pump in a state pressurized to 10 MPa. Went. 2 l / min and N ₂ gas Ar gas to exit vacuum when it reaches the 1000 ° C. were introduced into 0.006 l / min. This resulted in an atmosphere with a gas pressure of 0.103 MPa . The flow rate of the N ₂ gas is such that the decomposition pressure (N ₂ partial pressure) of aluminum nitride at a sintering temperature of 1700 ° C. is 6.2 × 10 ⁻⁶ MPa, so the N ₂ partial pressure in the firing furnace is 3.1. × is the flow rate for the ¹⁰ -4 MPa. The mixture was heated to 1500 ° C. under this atmosphere . Heating was performed from 1500 ° C. to 1700 ° C. at a temperature rising rate of 10 ° C./min. After reaching 1700 ° C., the applied pressure was increased to 50 MPa and held for 1 hour to perform hot press sintering to produce a boron carbide-aluminum nitride sintered body.
[ 0016 ]
The four-point bending strength of the boron carbide-aluminum nitride sintered body was measured based on JIS R1601. The surface of the test piece was finished with a surface grinder # 400. Moreover, the density of the test piece was measured by the Archimedes method, and the relative density was calculated. The surface of the test piece was lapped, etched, and then observed by SEM to determine the maximum particle size of boron carbide. Furthermore, the crystal phase in the sintered body was identified by the X-ray diffraction method . As a result, boron carbide - aluminum nitride sintered body, a density of 2.50 g / cm ^3, having a 98.0% relative density, the maximum particle size is 2.7 .mu.m, four-point bending strength 615MPa Met. As the crystal phase, an aluminum nitride phase was detected in addition to the boron carbide phase.
[0017]
Examples 1 and 2
In this example, the same procedure as in Reference Example 1 was performed, except that the type of boron carbide powder and the amount of aluminum nitride powder added were changed, and hot press sintering was performed at 2000 ° C. and a pressure of 10 MPa .
[0018]
Table 1 shows that using a boron carbide powder B and C, and this was the aluminum nitride powder by blending 7 mol%, the temperature was raised to 2000 ° C., the flow rate of _{N 2} gas, the decomposition pressure of nitride aluminum definitive to 2000 ° C. Since (N ₂ partial pressure) is 0.0013 MPa, in order to set the N ₂ partial pressure in the firing furnace to 0.0040 MPa, it was set to 0.08 liter / min , the hot press temperature was 2000 ° C. , and the applied pressure was A boron carbide-aluminum nitride sintered body was produced in the same manner as in Reference Example 1 except that the pressure was 10 MPa. The results are shown in Table 2. All examples had a high density of 95% or more, and an aluminum nitride phase was detected.
[0019]
[Table 2]
[0020]
Comparative Example 1
A boron carbide sintered body was produced in the same manner as in Example 1 except that the aluminum nitride powder was not added. The results are shown in Table 2. The sintered body of Comparative Example 1 had a low density of 77.0%.
[0021]
Example 3
In this example, instead of performing hot press sintering at 1700 ° C. and a pressing force of 50 MPa, it was performed in the same manner as Reference Example 1 except that normal pressure sintering at 2000 ° C. was performed.
[0022]
In the same manner as in Reference Example 1, a boron carbide-aluminum nitride mixed powder was prepared. This was die-molded at 20 MPa, and then 200 MPa CIP molding was performed to produce a molded body. This molded body was put into a graphite container, heated to 1000 ° C. in the same manner as in Reference Example 1 under normal pressure without applying pressure, and Ar gas and N ₂ gas were introduced. _{N 2} gas flow rate at that time, since the decomposition pressure of nitride aluminum definitive sintered temperature 2 000 ° C. _{(N 2} partial pressure) is 0.0013MPa, 0.0040MPa the _{N 2} partial pressure in the firing furnace to the, it was 0.08 l / min. In the same procedure as in Reference Example 1, the temperature was increased to 2000 ° C. and normal pressure sintering was performed to produce a boron carbide-aluminum nitride sintered body. The results are shown in Table 3.
[0023]
[Table 3]
[0024]
Comparative Example 2
A boron carbide sintered body was produced in the same manner as in Example 3 except that N ₂ gas was not introduced. The results are shown in Table 3. The sintered body of Comparative Example 2 had a relative density as low as 92.9%, and no aluminum nitride phase was detected.
[0025]
【The invention's effect】
According to the present invention, a boron carbide-aluminum nitride sintered body having boron carbide (B ₄ C) of 99.5 to 70 mol%, aluminum nitride (AlN) of 0.5 to 30 mol%, and a relative density of 95% or more. Can be manufactured by an inexpensive process compared to the prior art. The sintered body produced by the present invention can be used for applications such as sliding parts, cutting tools, and new wear-resistant parts.

Claims (2)

The temperature of a compact of a mixed powder composed of boron carbide powder having an average particle diameter (D ₅₀ ) of 10 μm or less and an aluminum nitride powder measured with a laser diffraction / scattering analyzer is raised to 1900 ° C. or higher and 2200 ° C. or lower. In hot press sintering or normal pressure sintering in a temperature range, an atmosphere of 1000 ° C. or higher is a mixed atmosphere of argon gas and nitrogen gas, and an N ₂ partial pressure is set to a decomposition N ₂ pressure of aluminum nitride or higher. A method for producing a boron carbide-aluminum nitride sintered body in which boron carbide (B ₄ C) is 99.5 to 70 mol%, aluminum nitride (AlN) is 0.5 to 30 mol%, and the relative density is 95% or more. . The manufacturing method of Claim 1 which performs hot press sintering by the applied pressure of 20 Mpa or less.