JP3142022B2 - Cutting tool made of silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon nitride sintered body
Become a cutting tool About.

[0002]

2. Description of the Related Art Since silicon nitride sintered bodies have high mechanical strength, application to structural materials such as automobile engine parts and gas turbine engines has been attempted. In order to use silicon nitride as a structural material, it is necessary to improve fracture toughness, and many inventions have been disclosed (JP-A-63-15 / 1988).
9259, JP-A-1-157466, JP-A-2-263664, and JP-A-2-157162. Further, since sintering of silicon nitride alone is difficult, a method of sintering by adding a sintering aid such as MgO, ZrO ₂ and rare earth oxide has been used, and many inventions have been disclosed. (JP-B-61-4788, JP-A-62-4788, etc.).

[0003]

However, the techniques described in JP-B-61-4788 and JP-A-62-153170 still have insufficient toughness. Also,
The cutting edge workability and tool life when these materials are used as cutting tools have not been determined yet. An object of the present invention is to provide a cutting tool made of a silicon nitride sintered body having an optimized type and amount of a sintering aid and excellent in fracture toughness and characteristics as a cutting tool .

[0004]

Means for solving the problem include a cutting tool and
To 0.5 the weight composition of the sintered body, the Mg in terms of MgO
10%, and 0.5 to 10% of Zr in terms of ZrO ₂ ,
And 1-20% in their oxide conversion at least one or more selected from Pr and Er, in that it consists of a balance _Si 3 _{N 4} and inevitable impurities.

[0005]

The oxides of the elements Mg and Zr and Pr and Er
Si ₃ Si, with N and O oxide during the firing process of
A liquid phase is generated between the N ₄ particles and contributes to densification,
The glass is vitrified in the course of lowering the temperature, and the Si ₃ N ₄ particles are bonded by a moderate force. If the content of any one of the Mg and Zr elements is less than 0.5% in terms of oxide, it will not be densified, and if any one of the elements exceeds 10%, the grain boundary phase will be excessive, and the bonding strength will increase. Becomes inappropriate and high toughness and high strength cannot be obtained.

If the Pr and Er element components are mixed together with other raw materials in the form of an oxide, they melt into the liquid phase during the firing process, change the viscosity of the liquid phase during sintering, and change the Si ₃ N ₄ (α, dissolves and precipitates in the liquid phase to grow Si ₃ N ₄ particles. However, if the content of these components is less than 1%, the effect is poor, while if it exceeds 20%, the grain boundary phase becomes excessive and high toughness cannot be obtained. Therefore, by making Mg, Zr, and at least one of Pr and Er essential as the respective oxides, the promotion of the grain growth of silicon nitride and the bonding force of the grain boundary glass phase are optimized, and high toughness is achieved. can do. That is, for example, high toughness cannot be obtained even if oxides of other rare earth elements Y ₂ O ₃ and CeO ₂ are added instead of Pr and Er.

[0007] For example, the following method is conceivable for producing a sintered body to be a cutting tool of the present invention. 0.5 to 10 wt% of the Mg element oxide powder and 0.
5 to 10 wt% and a 1 to 20 wt% of at least one or more kinds of powder selected from the oxides of Pr and Er, blending the remainder _Si 3 _{N 4} powder, molded, nitrogen pressure 1
0 atm or less, primary firing at a temperature of 1700 to 1900 ° C., and then the same atmospheric pressure of 10 atm or more and a temperature of 1600
The secondary firing is performed at a temperature of at least ℃. The firing conditions are preferably two-step gas pressure firing as described above, but are not limited thereto. It should be noted that the raw material other than silicon nitride may be any material that can become an oxide by firing, and may be, for example, a carbonate or an alkoxide.

[0008]

EXAMPLE A BET specific surface area of 10 m ² / g of Si ₃ N ₄ powder was mixed with 10 m ² / g of magnesium carbonate and 14 m ² / g of magnesium carbonate.
² / g zirconium dioxide and Pr ₆ O ₁₁ , Er ₂ O
Each powder of No. ₃ was blended in the ratios shown in Tables 1 and 2.

[Table 1]

[0009]

[Table 2]

[0010] The dried compounded powder is 1.5 ton / cm ²
, And formed by a static pressure press to a thickness of 6 mm, a width of 10 mm and a length of 35 mm, and sintered under the following conditions to obtain a silicon nitride sintered body. Sintering method: Gas pressure sintering (two-step sintering) Primary sintering: ₂ atm-1750 ° C. for 4 hours in N ₂ , secondary sintering: described in the table Material strength is measured by a three-point bending test according to JISR1601, and broken Toughness value is SEPB according to JISR1607
It was measured by the method. Tables 3 and 4 show the obtained results.

[0011]

[Table 3]

[0012]

[Table 4]

As shown in Tables 3 and 4, by adding one of Pr ₆ O ₁₁ and Er ₂ O ₃ in addition to MgO and ZrO ₂ as a sintering aid, Comparative Example No. 16,
The fracture toughness values are improved with respect to the additive systems shown in Nos. 22 and 23. When Pr ₆ O ₁₁ and Er ₂ O ₃ are less than 1 wt% or more than 20 wt%, the comparative example No. As shown in Nos. 17 to 19, the effect of the composite addition does not appear, and no improvement in fracture toughness is observed.

Next, a rectangular parallelepiped sample having the same composition as that of the above Examples and Comparative Examples was ground using a diamond wheel by the following method. Then, this sample was estimated as a cutting tool, and the tipping workability of the cutting tool made of the silicon nitride based sintered body of the present invention was evaluated by measuring the chipping length of the obtained cutting edge (ridge line portion of the sample). . FIG. 1 shows a cross section in the direction perpendicular to the ground surface where the grinding is being performed. The figure shows a state where chipping of a length t has occurred at the ridge of the sample when the main surface of the sample 1 is ground by the diamond wheel 2.

(Grinding method) Depth of cut: 20 μm, Wheel rotation speed: 3600 rpm
m, diamond wheel: particle size # 200, outer diameter 180m
m, front-back feed amount: 1.25 mm / sec left-right feed speed: 20 cm / sec Surface grinding was performed under the above conditions, and the obtained cutting edge was observed with a SEM. The chipping length was determined from the cutting edge photograph. (Evaluation Results) Table 5 shows the chipping length at the tip of the cutting edge obtained by the above measurement method.

[0016]

[Table 5]

As shown in the results of Table 5, the tip of the cutting edge of the present embodiment is sharp, and is larger in the comparative example. Therefore,
When using a cutting tool made of silicon nitride sintered body of the present invention, in addition to finishing of the cutting material is improved, since the cutting edge resistance decreases, it can be seen that the tool life is prolonged.

[0018]

The cutting made of the silicon nitride sintered body of the present invention
The tool was cut from another sintered body as shown in the example.
Superior in fracture toughness compared to cutting tools , so it has excellent reliability, The finish of the material to be cut is improved, and the tool life can be extended.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing that a sample of an example is subjected to surface grinding with a diamond wheel.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/584-35/596 B23B 27/14

Claims (1)

(57) [Claims] 1. Mg is converted to MgO by 0.5 on a weight basis.
-10%, and 0.5-10% of Zr in terms of ZrO ₂
And at least one selected from the group consisting of Pr and Er in an amount of 1 to 20% in terms of their oxides, with the balance being Si ₃ N
₄ and silicon nitride sintered material consisting of inevitable impurities
Become a cutting tool .