JPH0339989B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high toughness ceramic tool mainly made of silicon nitride. Al ₂ O ₃ is the most commonly used ceramic tool for cutting black scales of cast metals at high speeds of 100 m/min or more.
and Al ₂ O ₃ --TiC, etc., sintered by hot pressing or hot isostatic pressing (HIP method), etc., have been mainly used. However, these tools are prone to chipping, cracking, etc. during use, which is the biggest cause of reduced operating rates when cutting with automatic machines. Furthermore, the life of the tool was affected by chipping and cracking, and it often had to be replaced even when the amount of wear was very small. In order to eliminate these drawbacks, we first focused on silicon nitride, which has higher impact strength, thermal shock strength, and toughness than Al ₂ O ₃ -based materials, and as a result of research, we found that MgO and stabilized ZrO ₂ were sintered. By using hot pressing as an auxiliary agent, we have developed a highly tough silicon nitride tool that does not chip or crack during use (see JP-A-55-62857). This tool sinters a three-component composition of Si ₃ N ₄ , ZrO ₂ , and MgO, but it uses pressure sintering using a hot press and is extremely expensive. Therefore, it has been desired to develop a highly tough ceramic tool that has a composition that can be normally sintered at low cost without pressure sintering. Furthermore, as a sintered body having a similar three-component composition of Si ₃ N ₄ , ZrO ₂ , and MgO, the one described in JP-A-55-109276 is known. However, this material had a low transverse rupture strength of about 78 kg/mm ² at maximum, and could not be used for ceramic tools that required high toughness. On the other hand, for Si ₃ N ₄ ceramic tools, a method described in Japanese Patent Application Laid-open No. 73670/1983 is known as a method for ordinary sintering without using hot pressing. ₃ N ₄ as a second powder, Y ₂ O ₃ , MgO,
A material selected from ZrO ₂ , CeO ₂ and a mixture thereof is added, and a third powder of Al ₂ O ₃ , WC,
After adding a material selected from WSi ₂ , W, TiC, and a mixture thereof, mixing and adjusting the particle size, the mixture of these three types of powder is normally sintered, and the addition of this third powder is essential. , Si ₃ N ₄ ,
It is not possible to achieve densification by selectively mixing ZrO ₂ , MgO, Y ₂ O ₃ , and CeO ₂ without pressure sintering.
It has not been possible to create ceramic tools with high toughness. Furthermore, as another method for increasing the strength of Si ₃ N ₄ based ceramics, for example, Japanese Patent Publication No. 56-388 (this method involves mixing rare earth oxides such as Y ₂ O ₃ with Si ₃ N ₄ matrix powder) and sintered in the presence of AlN) and JP-A-Sho
No. 54-99115 (in which a heat-resistant hearth roll is manufactured by sintering a mixed powder of Si ₃ N ₄ , MgO, and lanthanum group oxides) is known, but all of them require sintering under special conditions. The purpose is not to bind or increase toughness, but to improve heat resistance. To the best of the inventors' knowledge, Si ₃ N ₄ ,
In addition to the three-component composition of MgO and ZrO ₂ , Y ₂ O ₃ and/or
By adding Dy ₂ O ₃ to create a four-component or five-component composition, it is shown that a high-toughness ceramic suitable for use in cutting tools, which could previously only be obtained by hot pressing, can be obtained by ordinary sintering. There are no known examples. As a result of intensive studies, the present inventors succeeded in developing such a highly tough ceramic tool. In other words, the gist of the present _invention is that _point A ₍ Si ₃ N ₄ 94% by weight, MgO3% by weight,
ZrO ₂ 3% by weight), point B (Si ₃ N ₄ 85% by weight, MgO 12% by weight, ZrO ₂ 3% by weight), point C (Si ₃ N ₄ 80% by weight,
MgO 10% by weight, ZrO ₂ 10% by weight) and point D
( _Si3N4 85% by weight, MgO3% by weight, _ZrO2 12% by _weight )
Si ₃ N ₄ , MgO in the range surrounded by the solid line connecting
and stabilized ZrO ₂ powder.
A mixed powder of 85 to 98% by weight powder and 2 to 15% by weight of a second powder consisting of at least one of Dy ₂ O ₃ and Y ₂ O ₃ is molded and sintered without hot pressing. There is a method for manufacturing high-toughness ceramic tools. The present invention will be explained in detail below. In the present invention, three components of Si ₃ N ₄ , MgO and ZrO ₂ are used as raw materials.
Requires one or more components of Dy ₂ O ₃ and Y ₂ O ₃ ,
ZrO ₂ must be stabilized with Y ₂ O ₃ , CaO, or the like. If unstabilized ZrO ₂ is used, it will remain in the sintered body in a partially stabilized or monoclinic form after sintering, and the temperature at the tool tip will rise to more than 1000°C during cutting. When this happens, it undergoes a transformation into a high-temperature tetragonal system, accompanied by an abnormal volume change, which results in chipping due to thermal strain and reduced resistance to cracking. The blending amounts of the three components Si ₃ N ₄ , MgO, and ZrO ₂ mentioned above are determined at points A, B, and
It is required that it be within the range surrounded by the solid line connecting C and D. If it is within this range, the resistance to chipping will be high, and if it is outside this range, it will be reduced.
Additionally, as the MgO content decreases, wear resistance tends to decrease. 80% by weight or more and 94% by weight or less
The reason for adding Y ₂ O ₃ or CaO-stabilized _{ZrO 2} to Si ₃ N ₄ as an additive is 3% by weight or more and 12% by weight or less. No effect was observed, and when the amount exceeds 12% by weight, the hardness of the tool decreases and wear during cutting increases. Also, the reason for limiting Si ₃ N ₄ is
This is because if Si ₃ N ₄ exceeds 94% by weight, sintering properties are poor and the desired properties cannot be obtained, and if it is less than 80% by weight, wear resistance during cutting decreases. Also, MgO 3
The reason for adding more than 12% by weight is that less than 3% by weight is less effective as a sintering accelerator, and more than 12% by weight increases wear during cutting and makes it difficult to obtain properties as a tool. be. Densification by hot pressing is possible with the above three components, but in order to normally sinter it, at least one of Dy ₂ O ₃ and Y ₂ O ₃ is added to 85 to 98% by weight of the above three components. ~15% by weight must be added. The reason for limiting the amount of Dy ₂ O ₃ and Y ₂ O ₃ added is
If the amount added is less than 2% by weight, sintering cannot normally be performed, and if it exceeds 15% by weight, the hardness decreases and wear during cutting increases, making it impossible to use it as a tool. In order to manufacture a tool according to the present invention, an organic binder is added to the above mixed powder, molded into a predetermined shape using a die press, calcined to remove the organic binder, and heated at 1550 to 1800°C in a non-smoking environment. Fired in an oxidizing atmosphere without using a hot press. The reason for firing in a non-oxidizing atmosphere is that silicon nitride is easily oxidized, and if the temperature is less than 1550°C, sintering may be insufficient, and if it exceeds 1800°C, the evaporation of Si ₃ N ₄ will be significant. The present invention will be explained in more detail with reference to Examples below. Example 1 Powder consisting of 90% by weight of α-Si ₃ N ₄ and 10% by weight of β-Si ₃ N ₄ and ZrO ₂ stabilized with 20 mol% of CaO,
MgO, Dy ₂ O ₃ and Y ₂ O ₃ were mixed in the ratio shown in Table 1,
It was ground using a ball mill to give an average particle size of 1 μm.
5% by weight of paraffin was added to this and granulated, and molded into a predetermined shape using a die press at a press pressure of 1.5 ton/cm ² . After calcining this in vacuum at 800℃, _N2
Sintering was carried out in an air stream at the temperature shown in Table 1 for 1 hour. The obtained sintered body was polished to form SNGN432-TN (Change Fur 0.1) and SNGN455-TN (Change Fur 0.2).
Test pieces of 4 x 8 x 25 mm were prepared and various physical properties were measured. Notes in the table are as follows. *1 Using ZrO ₂ stabilized with Y ₂ O ₃ *2 Using a test piece of SNGN432-TN (Change Hua 0.1), a 100φ x 500L test piece was used as the work material.
Select FC25 and set cutting conditions to cutting speed 400m/
min, depth of cut 2.0mm, feed 0.3mm/rev, 1000
The flank wear width V _B after cutting mm was measured. *3 Using a test piece of SNGN455-TN (Change Fur 0.2), 200φ x 35l as the work material.
Select FC20 (black skin) and set the cutting conditions to the cutting speed.
400m/min, depth of cut 2.5mm, feed 0.3mm/rev
The outer surface of the disk was cut in the axial direction.

【table】

[Table] As shown in Table 1, the ceramic tool of the present invention has excellent toughness, especially resistance to tool chipping and chipping for rough cuts of castings, and can greatly improve the reliability of tools in automatic machines. . The reason for this cannot be determined, but firstly, in interrupted cutting as shown in Table 1, the temperature of the cutting edge is 1000
The temperature rises above ℃ repeatedly, and at this time
The thermal expansion coefficient of Al ₂ O ₃ −TiC tools is approximately 7×10 ^-6 /
This is thought to be due to the fact that the tool mainly made of Si ₃ N ₄ of the present invention has a small value of about 3.5×10 ^-6 /°C, which is strong against thermal shock. Second, when microstructurally observed, the tool mainly composed of Si ₃ N ₄ exhibits a fibrous structure;
This is thought to be due to its high fracture toughness. In addition, by adding Dy ₂ O ₃ or Y ₂ O ₃ to Si ₃ N ₄ -MgO-ZrO ₂ , normal sintering becomes possible, cutting is not required compared to hot pressing, and the polishing time is significantly reduced. At the same time, cutting tools with complex shapes, such as tips with holes, became easily available. Example 2 Comparative sample No. 2R was manufactured using unstabilized monoclinic zirconia instead of using stabilized zirconia with the same composition as sample No. 2 of Example 1. In particular, 10 samples were made to investigate the number of pieces cut before chipping or cracking of the product occurred, and the results compared with No. 2 were as shown in Table 2.

[Table] As is clear from Table 2, although there is no difference in transverse rupture strength, hardness, and wear resistance between the two, out of 10 samples, No. 2 had the highest number of cuts before chipping or cracking occurred.
All 10 pieces were able to cut more than 150 pieces, while No. 2R was able to cut 4 pieces.
It was possible to cut more than 150 pieces only in 1, while the rest varied between 32 and 131. Although the reason for this cannot be determined, a small amount of monoclinic low-temperature ZrO ₂ was detected in No. 2R by X-ray diffraction, whereas in No. 2R of the present invention.
Since only stabilized ZrO ₂ was detected in all cases of No. 2, it is thought that this is because the strength against chipping and cracking is stable. All recent cutting machines are highly automated, and sudden chipping and cracking of tools can cause serious problems. Therefore, the stable tool of the present invention is No. 2R, which has a large variation in strength against chipping and cracking.
It has great advantages compared to . Furthermore, when we investigated thermal expansion from room temperature to 1200℃, we found that
For No. 2R, a change point in the coefficient of thermal expansion was observed between 900°C and 1000°C, but for No. 2, no change point was observed and a linear expansion curve was observed. Furthermore, due to the excellent physical properties mentioned above, the ceramic tool of the present invention can be used as a cutting tool for metals other than cast metals, such as aluminum and steel, as well as heat-resistant parts for machines that are subject to vibration and heat during cutting. can be used.

[Brief explanation of the drawing]

The drawing is a triangular coordinate diagram showing the blending ratio of each element constituting the mixed powder to be sintered.

Claims (1)

[Claims] 1 As shown in the drawing, in the triangular coordinates where the weight percentages of Si ₃ N ₄ , MgO and stabilized ZrO ₂ are indicated on the three axes intersecting the equilateral triangle, point A is
( _{Si3N4 94} % by weight, MgO3% by weight, _ZrO2 3% by weight),
Point B (Si ₃ N ₄ 85% by weight, MgO 12% by weight, ZrO ₂ 3% by weight), Point C (Si ₃ N ₄ 80% by weight, MgO 10% by weight,
ZrO ₂ 10% by weight) and point D (Si ₃ N ₄ 85% by weight,
85 to 98% by weight of the first powder containing each powder of Si ₃ N ₄ , MgO and stabilized ZrO ₂ and Dy ₂ O ₃ in the range surrounded by the solid _line connecting MgO 3 weight %, ZrO 2 12 weight %). A method for manufacturing a high-toughness ceramic tool, which comprises molding a mixed powder containing 2 to 15% by weight of a second powder consisting of at least one of Y _{2 O 3 and Y 2} O ₃ and sintering it without hot pressing.