JPH07126791A - Cermet alloy - Google Patents

Abstract

PURPOSE:To obtain a cermet alloy material having high hardness and superior toughness by preparing a powder mixture consisting of powder of hard carbides of specific metals and powder of hard metal boride and sintering this powder mixture by using Co powder as a binding material. CONSTITUTION:A hard WB powder or MoB powder is mixed with a powder of hard carbides of the group IVa metals (Ti, Zr, Hf), group Va metals (V, Nb, Ta), group VIa metals (Cr, Mo, W), etc., of the Periodic Table. A Co powder is added as a binding material at the time of sintering to the resulting powder mixture, which is compacted and then sintered at 1300-1600 deg.C. As to the grain size of the hard metal carbides, the grains of >=2.0mum comprise 20-70% of the whole grains and the other grains have <=2mum grain size, and the powder of hard metal borides, such as WB and MoB, and the Co powder as a binding material are added to the hard metal carbide powder. By this method, the cermet alloy material, composed essentially of the hard carbides of the group IVa-VIa metals in the Periodic Table and the W-Co-B or Mo-Co-B type hard compound and having high hardness and superior toughness, can be obtained.

Description

Detailed Description of the Invention

[0001]

This invention relates to cermet alloys,
In particular, it relates to improvement in toughness of cermet alloys containing double borides.

[0002]

2. Description of the Related Art Various proposals have been made for cermet alloys containing double boride.
(Provided that M is one or more of metal elements belonging to Groups 4a, 5a and 6a of the Periodic Table) and a hard phase mainly composed of a W-Co-B compound and a cermet alloy composed of a binder phase mainly composed of Co. (US Pat. No. 5,149,5
95, European Patent Publication 477685). This cermet alloy contains WB powder, Co powder, and MC as raw material powders.
It can be obtained by sintering the powder at 1300-1600 ° C. after mixing and molding, but the following behavior is performed during sintering. That is, Co is melted during sintering, promotes sintering, and is densified.
C grains, WB grains and Co grains are strongly bonded. Moreover,
This Co not only fills the gaps of hard particles,
A part of it reacts with WB and enters the inside, and CoW ₂
B ₂ is formed, and further CoWB is formed on the surface of CoW ₂ B ₂ . Since this cermet alloy has a Vickers hardness of 1800 or more, its application to tools is under study. Further, since the amount of metallic Co in the binder phase is small, it is also considered as a promising substrate for forming a diamond film. In addition, based on the same idea as this cermet alloy, MC (where M is one or more of the metal elements of the 4a, 5a, and 6a group of the periodic table) and a hard phase mainly composed of a Mo-Co-B compound, and A cermet alloy composed of a binder phase containing Co as a main component is also proposed (Japanese Patent Laid-Open No. 5-2).
09247).

[0003]

However, this cermet alloy is insufficient in toughness due to the small amount of metallic Co in the binder phase. Therefore, there is a problem that chipping occurs during grinding into a predetermined shape, not to mention when used as a tool. This problem can be avoided by grading the grinding processing conditions, but the processing time increases, which is not preferable for industrial production. Therefore, the present invention provides MC (where M is one or more of the metal elements of Group 4a, 5a, and 6a of the Periodic Table) and a hard phase mainly composed of a W-Co-B compound or a Mo-Co-B compound, Another object is to improve the toughness of a cermet alloy composed of a binder phase mainly composed of Co.

[0004]

As a result of various studies to solve the above problems, the present inventor did not add MC powder as a single particle size but rather relatively fine particles and relatively coarse particles. By mixing and adding M in the sintered body
It has been found that the C phase has a structure in which relatively fine MC grains and relatively coarse MC grains coexist, and such a structure improves toughness. The present invention has been made based on the above findings, and MC (where M is the fourth periodic table
a, one or more of metal elements of 5a, 6a) and W-
A sintered body composed of a hard phase mainly composed of a Co-B compound and a binder phase mainly composed of Co, in which MC particles having an average particle size of 2.0 μm or more have an area ratio of 20 to 70%,
A cermet alloy characterized in that the remaining MC grains have an average grain size of less than 2.0 μm, or MC (where M is one or more of the metal elements of Groups 4a, 5a, and 6a of the Periodic Table) and Mo−. A hard phase mainly composed of a Co-B compound,
And a sintered body composed of a binder phase mainly composed of Co, in which MC grains having an average grain size of 2.0 μm or more have an area ratio of 20 to 70%, and the remaining MC grains have an average grain size of 2.0 μm.
It is a cermet alloy characterized by being less than.

[0005]

The present invention will be described in more detail below. The sintered body according to the present invention is prepared by mixing and molding WB powder or MoB powder, Co powder, and MC powder as raw material powder, and then
It can be obtained by sintering at 300 to 1600 ° C. The amount of WB powder or MoB powder is 2
˜45% by volume, Co2˜20% by volume, and the balance MC powder. 2 to 45% by volume of WB powder or MoB powder
When the content is less than 2% by volume, the W-Co-B compound or the Mo-Co-B compound is not sufficiently formed to secure the hardness, and when it exceeds 45% by volume, uniform sintering becomes difficult. This is because there is a tendency. The reason why the Co content is 2 to 20% by volume is that if the content is less than 2% by volume, the density is hard to increase and the strength and toughness are deteriorated. This is to allow it.

The present invention is characterized in that the grain size of the raw material powder, particularly the MC powder, is specified. That is, as the MC powder, by using a fine powder having an average particle size of less than 2 μm and a coarse powder having an average particle size of 2 μm or more, an average particle size of 2.
The area ratio of MC particles of 0 μm or more is 20 to 70%, and the balance is M.
It is possible to obtain a structure in which C grains have an average grain size of less than 2.0 μm, which contributes to improvement in toughness. However, if the particle size of the powder becomes extremely large, the activity of the powder becomes small and the sintering does not proceed, so the particle size is preferably 10 μm or less. WB powder, C
The particle size of the powder may be selected within the range of 10 μm or less.

The above raw material powders are mixed and molded and then sintered, and a non-pressure sintering method can be applied to this sintering.
If the sintering temperature is lower than 1300 ° C, the sintering does not proceed sufficiently, and if it exceeds 1600 ° C, the grain growth of the hard phase becomes remarkable. Therefore, the temperature is preferably set to 1300 to 1600 ° C.
When the sintering time is less than 10 minutes, the sintering does not proceed sufficiently, and when it exceeds 120 minutes, the grain growth of the hard phase becomes remarkable.
Therefore, the sintering time is preferably 10 to 120 minutes. The following behavior occurs during sintering. That is, Co is melted at the time of sintering, promotes sintering, and is densified, and hard particles such as MC particles, WB particles (or MoB particles) and Co particles
It is firmly bonded to the grains. Moreover, this Co not only fills the gaps between the hard particles, but a part thereof reacts with WB (or MoB) and enters the inside thereof, and CoW ₂ B ₂
(Or CoMo ₂ B ₂ ) and then CoW ₂ B
CoWB (or CoMoB) is formed on the surface of ₂ (or CoMo ₂ B ₂ ).

[0008]

EXAMPLES The present invention will be described below based on examples. (Example 1) W having an average particle size of 0.6 μm and 3.5 μm
C powder, WB powder with an average particle size of 2.5 μm, average particle size of 8 μ
Prepare the Co powder m, (90-X) vol % WC 1 -Xvol
% Were mixed so that the composition of _{WC 2 -5vol% WB-5vol%} Co. In addition, WC ₁ is W having an average particle size of 0.6 μm.
C powder and WC ₂ mean WC powder having an average particle size of 3.5 μm. This mixture was press-molded at a pressure of 1500 kgf / cm ² , and the molded body was sintered in a vacuum at 1500 ° C. for 1 hour to obtain a sintered body. The Vickers hardness (Hv) and crack resistance (CR) of the sintered body were measured. The results are shown in Table 1.

[0009]

[Table 1]

From Table 1, it can be seen that the No. 1 material using only WC powder having an average particle size of 0.6 μm and a small particle size has high hardness but low toughness, and the hardness increases as the amount of WC powder having an average particle size of 3.5 μm increases. It can be seen that the toughness decreases but the toughness increases. No. The material of No. 5 has improved toughness, but its hardness is too low, and the characteristics of this material are impaired. The No. 1 and No. 2 microstructures in Table 1 were observed. No. 1 in FIG. 1 and No. 1 in FIG. The metal microstructure photograph of 2 is shown. No.
The WC grains of No. 1 are almost uniform in the range of 1 μm or less, whereas the WC grains of No. It was confirmed that No. 2 has a structure in which coarse WC grains exceeding 3 μm and fine WC grains of 1 μm or less are mixed. In addition, No. 3 and 4 had the same organization.

Next, No. 1-No. The maximum dimension of the chip generated when the material of No. 5 was ground was measured, and the grindability was evaluated. The results are shown in Table 2.

[0012]

[Table 2]

From Table 2, it can be seen that the chip size of the material having a structure in which coarse WC grains of more than 3 μm and fine WC grains of 1 μm or less are mixed is small.

(Example 2) WC powders having an average particle size of 0.6 μm and 3.0 μm, MoB powder having an average particle size of 2.5 μm, and Co powder having an average particle size of 8 μm were prepared and prepared in the same manner as in Example 1. A material having a compounding composition shown in 3 was obtained.

[0015]

[Table 3]

Next, the area ratio of WC grains having an average grain size of 2.0 μm or more in the WC phase was obtained by observing the microstructure of this sintered body. The results are shown in Table 4.

[0017]

[Table 4]

From Tables 3 and 4, as the area ratio of WC grains having an average grain size of 2.0 μm or more increases, the toughness of the material improves. However, if the area ratio is too high, the hardness is remarkably lowered, and therefore, in the present invention, the average particle size is 2.0 μm.
The area ratio of the above WC grains is set to 20 to 70%.

[0019]

As described above, according to the present invention, M
C (provided that M is one or more of the metal elements of Groups 4a, 5a, and 6a of the Periodic Table), a hard phase containing a W-Co-B compound or a Mo-Co-B compound as a main component, and Co as a main component. It is possible to improve the toughness of the cermet alloy composed of the binder phase.

[Brief description of drawings]

FIG. 1 is a photograph of a metal microstructure of a cermet alloy including a conventional hard phase mainly composed of WC and a W—Co—B compound and a binder phase mainly composed of Co.

FIG. 2 is a photograph of a metal microstructure of a cermet alloy including a hard phase mainly containing WC and a W—Co—B compound according to the present invention and a binder phase mainly containing Co.

Claims (2)

[Claims] 1. MC (where M is 4a, 5 of the periodic table)
a, one or more of 6a group metal elements) and W-Co-
A sintered body comprising a hard phase mainly composed of a B compound and a binder phase mainly composed of Co, wherein MC particles having an average particle diameter of 2.0 μm or more are present in an area ratio of 20 to 70%. A characteristic cermet alloy. 2. MC (where M is 4a, 5 of the periodic table)
a, one or more of 6a group metal elements) and Mo-Co
-A sintered body composed of a hard phase mainly composed of a B compound and a binder phase mainly composed of Co, and 20 to 70% of MC particles having an average particle diameter of 2.0 µm or more are present in an area ratio. A cermet alloy characterized by.