JP7366707B2 - Sintered material and its manufacturing method - Google Patents

Description

The present invention relates to a sintered material and a method for manufacturing the same.

Sintered materials widely used for cutting tools and the like have a microstructure in which hard particles are dispersed in a matrix metal, and have excellent wear resistance. For example, as disclosed in Patent Documents 1 to 3, sintering in which metal carbide particles such as WC or metal boride particles such as WB or MoB are dispersed in a matrix metal such as a Co-based alloy or a Ni-based alloy The material is known.

Japanese Patent Application Publication No. 5-132734 Japanese Patent Application Publication No. 2018-111851 Japanese Patent Application Publication No. 2010-099693

The inventor discovered the following problem regarding a sintered material in which metal boride particles are dispersed as hard particles in a matrix metal.
Since metal boride particles are brittle, if the amount of metal boride particles added is increased in order to improve the wear resistance of the sintered material, cracks will easily occur and the strength will decrease. That is, such a sintered material has a problem in that it is difficult to achieve both wear resistance and strength.
Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

A method for producing a sintered material according to one embodiment is a method for producing a sintered material in which metal boride particles are dispersed in a matrix metal, in which powder having the composition of the sintered material to be produced is produced by an atomization method. Then, the powder is solid-phase sintered.

The sintered material according to one embodiment is a sintered material in which metal boride particles are dispersed in a matrix metal, the relative density is 99.0% or more, and the median diameter of the metal boride particles is 2. .0 μm or less.

According to the embodiment, it is possible to provide a sintered material that can achieve both wear resistance and strength, and a method for manufacturing the same.

3 is a flowchart showing a method for manufacturing a sintered material according to the first embodiment. 1 is a microstructure photograph of sintered materials according to Examples 1 to 3 and Comparative Examples 1 to 3. It is a graph showing the sintering temperature dependence of relative density and bending strength. 3 is a bar graph showing wear volume in sintered materials according to Examples 1 to 3 and Comparative Examples 1 to 3.

Hereinafter, specific embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Further, in order to clarify the explanation, the following description and drawings are appropriately simplified.

(First embodiment)
<Method for manufacturing sintered material>
With reference to FIG. 1, a method for manufacturing a sintered material according to a first embodiment will be described. FIG. 1 is a flowchart showing a method for manufacturing a sintered material according to a first embodiment. The sintered material according to the first embodiment is a sintered material in which boride particles of W (tungsten) and Mo (molybdenum) are dispersed in an alloy mainly composed of Ni (nickel) or Co (cobalt). . This sintered material is used, for example, in cutting tools.

Firstly, as shown in FIG. A powder consisting of one of the two is produced by an atomization method (step ST1). Specifically, the powder contains a total of 13.7 to 55.3% of W and Mo, 1.3 to 4.4% of B, 8.9 to 18.6% of Cr, and Cu. It contains 0 to 3.4% of Si, 0 to 2.0% of Si, and 0 to 1.3% of C, with the remainder consisting of at least one of Co and Ni and inevitable impurities.

Next, as shown in FIG. 1, the powder obtained in step ST1 is solid phase sintered at a temperature higher than 1050° C. (step ST2). In step ST2, the powder may be sintered while being pressurized. For example, a spark plasma sintering (SPS) method or a hot isostatic pressing (HIP) method can be used for solid phase sintering.
The sintered material according to the first embodiment is obtained by step ST2.

The inventors have found that when the sintering temperature in step ST2 is 1050° C. or lower, sintering defects such as voids increase, resulting in a sharp decline in wear resistance. Therefore, in the method for manufacturing a sintered material according to the present embodiment, solid phase sintering is performed at a temperature higher than 1050°C. As a result, a high-density sintered material with few sintering defects is obtained. Specifically, the relative density of the sintered material is 99.0% or more, making it possible to achieve both high levels of wear resistance and strength. The sintering temperature is more preferably 1100°C or higher.
Here, the relative density is expressed as a percentage based on the density calculated from the composition of the sintered material and the density of each element (ie, 100%).

On the other hand, the sintering temperature may be high as long as the sintered material does not melt. However, the higher the sintering temperature, the more likely the metal boride particles become coarse due to Ostwald growth. Therefore, from the viewpoint of keeping the metal boride particles fine, the sintering temperature is preferably lower. For example, the sintering temperature is preferably 1200°C or lower, more preferably 1180°C or lower.

As described above, in the method for producing a sintered material according to the present embodiment, a powder having the same composition as the sintered material to be produced is produced by the atomization method (step ST1), and the powder is solid-phase sintered (step ST2). ). In the atomization method, high-pressure gas or water is sprayed onto a molten alloy having the above composition, causing the molten metal to scatter and solidify into powder. Therefore, the obtained powder has a structure in which extremely fine metal boride particles such as WB and MoB are dispersed in the metal, or W, Mo, B, etc. that make up the metal boride particles are supersaturated and solidified in the metal. It has dissolved tissue.

Therefore, in the solid phase sintering process (step ST2), either the fine metal boride particles in the raw material powder are dispersed as they are in the matrix metal, or the fine metal boride particles are dispersed in the matrix metal from a supersaturated solid solution state. It precipitates out. As a result, the manufactured sintered material has a structure in which fine metal boride particles are uniformly dispersed in the matrix metal. Further, solid-phase sintering at a temperature higher than 1050° C. provides a high-density sintered material with fewer sintering defects.

As explained above, the method for manufacturing the sintered material according to the present embodiment allows the sintered material to have a structure with few sintering defects, high density, and fine metal boride particles uniformly dispersed in the matrix metal. A binding material is obtained. Therefore, the sintered material can achieve both wear resistance and strength at a higher level than before.

<Composition of sintered material>
Next, the structure of the sintered material according to the first embodiment will be explained. The sintered material according to the first embodiment is a sintered material manufactured by, for example, the method for manufacturing a sintered material according to the above-described first embodiment.

The sintered material according to the first embodiment contains predetermined amounts of W, Mo, B, Cr, Cu, Si, and C, and the remainder consists of at least one of Co and Ni. In detail, the sintered material contains a total of 13.7 to 55.3% of W and Mo, 1.3 to 4.4% of B, and 8.9 to 18.6% of Cr in mass%. , contains 0 to 3.4% of Cu, 0 to 2.0% of Si, and 0 to 1.3% of C, with the remainder consisting of at least one of Co and Ni and inevitable impurities.

The sintered material contains a total of 8.0 to 22.5% of W and Mo, 8.0 to 22.5% of B, 12.0 to 24.0% of Cr, and Cu in terms of atomic percent. It is preferable to contain 0 to 3.5% of Si, 0 to 4.5% of Si, and 0 to 6.0% of C.

Co and Ni constitute the matrix metal of the sintered material and enhance the corrosion resistance of the sintered material.
W and Mo combine with B to form a WB type boride, a WCoB type or a W ₂ CoB ₂ type hard double boride, and improve the wear resistance of the sintered material.
Cr and Cu form a solid solution in the matrix metal and enhance the corrosion resistance of the sintered material.
Note that, as shown in the above composition, addition of Cu to the sintered material is not essential.

B forms the above-mentioned boride, and also forms a solid solution in the matrix metal at high temperatures, and has the effect of lowering the melting point of the matrix metal. On the other hand, excess B forms brittle borides with low hardness such as Ni ₃ B, so the ratio of the total number of W and Mo atoms to the number of B atoms, that is, (total number of W and Mo atoms)/ (Number of atoms of B) is preferably close to 1. For example, (total number of atoms of W and Mo)/(number of atoms of B)=0.75 to 2.0.

Since Si lowers the melting point of the matrix metal together with B, the addition of Si facilitates the atomization method. However, excessive Si combines with Cr in the matrix metal to form a brittle Laves phase. Therefore, if the amount of Si added is too large, the toughness of the sintered material will be impaired.
Note that, as shown in the above composition, addition of Si to the sintered material is not essential.

C forms metal carbides such as WC and contributes to wear resistance. However, since metal carbides are difficult to melt into the matrix metal even at high temperatures, if the amount of C added is too large, it becomes difficult to produce powder by the atomization method.
Note that, as shown in the above composition, addition of C to the sintered material is not essential.

The inventors have found that when the relative density is less than 99.0%, sintering defects such as voids increase, resulting in a sharp decline in wear resistance. In contrast, the sintered material according to the first embodiment has a relative density of 99.0% or more and has few sintering defects. Further, in the sintered material, the median diameter of metal boride particles dispersed in the matrix metal is 2.0 μm or less. That is, the sintered material has a structure in which fine metal boride particles are uniformly dispersed in the matrix metal. The median diameter of the metal boride particles is more preferably 1.5 μm or less.

As described above, the sintered material according to the first embodiment has a high density with few sintering defects, and has a structure in which fine metal boride particles are uniformly dispersed in the matrix metal. Therefore, the sintered material according to the first embodiment can achieve both wear resistance and strength at a higher level than conventional ones.

Hereinafter, the sintered material and the manufacturing method thereof according to the first embodiment will be described in detail using examples. However, the sintered material and the manufacturing method thereof according to the first embodiment are not limited to the following examples.
Table 1 shows the compositions of the sintered materials according to all Examples and Comparative Examples in mass % and atomic %. The composition of the sintered materials in all Examples and Comparative Examples is the same.

<Example 1>
A method for manufacturing a sintered material according to Example 1 will be described.
A master alloy having the composition shown in Table 1 was melted, and a powder having the composition shown in Table 1 was produced by a gas atomization method. The hot water temperature during gas atomization was 1520°C. Ar (argon) gas was used as the injection gas and replacement gas in gas atomization, and the injection gas flow rate was 4000 L/min.

Next, the obtained powder was classified using a sieve, and powder with a particle size of 20 to 106 μm was used as a raw material. The powder used as the raw material was solid phase sintered using the Spark Plasma Sintering (SPS) method. The sintering conditions were a sintering temperature of 1100° C., a pressure of 30 MPa, and a holding time of 60 minutes.
Through the above manufacturing process, a sintered material according to Example 1 was obtained.

<Example 2>
A sintered material according to Example 2 was obtained in the same manner as in Example 1 except that the sintering temperature was 1150°C.
<Example 3>
A sintered material according to Example 3 was obtained in the same manner as Example 1 except that the sintering temperature was 1180°C.

<Comparative example 1>
A sintered material according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the sintering temperature was 1000°C.
<Comparative example 2>
A sintered material according to Comparative Example 2 was obtained in the same manner as in Example 1 except that the sintering temperature was 1050°C.

<Comparative example 3>
Co, Ni, Mo, Cr, Cu, and Si metal powders and hard particle powders (WB powder with an average particle size of 3 μm and Mo ₂ C powder with an average particle size of 2.4 μm) were prepared to have the same composition as in Table 1. and mixed for 15 minutes using a mortar.
A sintered material according to Comparative Example 3 was obtained by solid-phase sintering using the mixed powder as a raw material using the SPS method. The sintering conditions were the same as in Example 2, with a sintering temperature of 1150° C., a pressure of 30 MPa, and a holding time of 60 minutes.

Table 2 shows the manufacturing conditions (raw materials, sintering temperature, pressure) and the properties of the sintered materials (relative density, hard particle diameter, The bending strength and wear volume are shown together.

The measurement of density was based on the geometric measurement specified in JIS standard Z8807. Table 2 shows the relative density as a percentage based on the density calculated from the composition of the sintered material shown in Table 1 and the density of each element.
The measurement of bending strength was based on the three-point bending test specified in JIS standard R1601.
The measurement of wear volume was based on the rubber wheel wear test specified in ASTM standard G65.

The hard particle diameter was determined by measuring the hard particle diameter in an SEM (Scanning Electron Microscope) image using image analysis software. QuickGrain PadPlus ver. 5.15 manufactured by Innotek was used as image analysis software for particle size measurement. Specifically, hard particles were extracted from the contrast in the SEM image, and the diameter of a circle equal to the area of the hard particle (area circle equivalent diameter) was defined as the particle diameter of the hard particle. In each of the sintered materials according to Examples 1 to 3 and Comparative Examples 1 to 3, the particle diameters of 300 or more hard particles were measured, and the median diameter was taken as the hard particle diameter.

FIG. 2 is a photograph of the microstructure of the sintered materials according to Examples 1 to 3 and Comparative Examples 1 to 3.
As shown in FIG. 2, each sintered material has a structure in which white hard particles (metal boride particles) are dispersed in a black matrix metal that is a Co-based alloy.

The sintered materials according to Examples 1 to 3 and Comparative Examples 1 and 2 (i.e., other than Comparative Example 3), which used atomized powder as a raw material, had a structure in which fine hard particles were uniformly dispersed in the matrix metal. There is. As shown in FIG. 2, as the sintering temperature Ts became higher, the hard particles grew and the particle size became larger. However, even in the sintered material according to Example 3, which has the largest hard particle diameter, the hard particle diameter is 1.43 μm, which is less than half the hard particle diameter (3.86 μm) of the sintered material according to Comparative Example 3. and was sufficiently fine.

On the other hand, the sintered material according to Comparative Example 3, which used a mixed powder of metal powder and hard particle powder as the raw material, had lower It has a structure in which coarse hard particles are unevenly dispersed.

FIG. 3 is a graph showing the dependence of relative density and bending strength on sintering temperature. The horizontal axis of FIG. 3 is the sintering temperature, and the vertical axis is the relative density and bending strength, and the relative density and bending strength are shown side by side in the vertical direction. In FIG. 3, Comparative Examples 1 and 2 are indicated by white circles, Examples 1 to 3 are indicated by black circles, and Comparative Example 3 is indicated by white squares.

As shown in Table 2 and FIG. 3, in the sintered materials according to all Examples 1 to 3 and Comparative Examples 1 to 3, including Comparative Example 3 using different raw materials, the higher the sintering temperature Ts, the more voids The number of sintering defects such as sintering defects decreased and the density increased. Specifically, at a sintering temperature Ts of 1100° C. or higher, the relative density was 99.0% or higher.

Furthermore, as shown in Table 2 and FIG. 3, the sintered materials according to Examples 1 to 3 and Comparative Examples 1 and 2 using atomized powder are the same as the sintered materials according to Comparative Example 3 using mixed powder. The bending strength was greater than that of In the sintered materials according to Examples 1 to 3 and Comparative Examples 1 and 2 using atomized powder, the bending strength increases as the density increases up to a sintering temperature Ts of 1150°C, but when the sintering temperature Ts reaches 1180°C It has declined. It is presumed that the bending strength decreased due to grain growth of the hard particles.

FIG. 4 is a bar graph showing the wear volumes of the sintered materials according to Examples 1 to 3 and Comparative Examples 1 to 3. In FIG. 4, the bars of Examples 1 to 3 are displayed as dots. As shown in FIG. 4, the sintered materials according to Comparative Examples 1 and 2, in which the sintering temperature Ts is 1050°C or less and the relative density is less than 99.0%, have a larger wear volume than Comparative Example 3, and have higher durability. It had poor abrasion resistance. On the other hand, the sintered materials according to Examples 1 to 3 whose sintering temperature Ts is 1100°C or higher and whose relative density is 99.0% or higher are stable with wear volumes equal to or lower than that of Comparative Example 3. It had excellent wear resistance.

As explained above, by the method for manufacturing the sintered material according to the first embodiment described above, the sintered material has few sintering defects and has a high density, and fine hard particles (metal boride particles) are formed in the matrix metal. A sintered material with a uniformly distributed structure was obtained. Therefore, the sintered material can achieve both wear resistance and strength at a higher level than before.

Although the invention made by the present inventor has been specifically explained based on the embodiments above, the present invention is not limited to the embodiments already described, and various changes can be made without departing from the gist thereof. It goes without saying that it is possible.

Claims (6)

A method for producing a sintered material in which metal boride particles are dispersed in a matrix metal, the method comprising:
(a) In terms of mass %, the total content of W and Mo is 13.7 to 55.3%, B is 1.3 to 4.4%, Cr is 8.9 to 18.6%, and Cu is 0 to 3. 4% of Si, 0 to 2.0% of C, and 0 to 1.3% of C, with the balance consisting of at least one of Co and Ni and unavoidable impurities, by an atomization method, and ( b) solid phase sintering the powder at a temperature higher than 1100 °C and lower than 1200 °C ,
Method of manufacturing sintered materials. The atomization method is a gas atomization method,
A method for manufacturing the sintered material according to claim 1. In the step (b), solid phase sintering is performed while pressurizing.
A method for manufacturing the sintered material according to claim 1. In the step (b), solid phase sintering is performed using a discharge plasma sintering method.
A method for producing a sintered material according to claim 3. The relative density of the produced sintered material is 99.0% or more, and the median diameter of the metal boride particles is 2.0 μm or less,
A method for manufacturing the sintered material according to claim 1. The ratio of the total number of atoms of W and Mo to the number of atoms of B is 0.75 to 2.0,
A method for manufacturing the sintered material according to claim 1.

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