JPH04261702A - Tool made of silicon nitride sintered body - Google Patents

Abstract

PURPOSE:To provide a tool made of a silicon nitride sintered body excellent in wear resistance and toughness and capable of being manufactured at low cost. CONSTITUTION:It is a tool made of a silicon nitride sintered body, containing a silicon nitride and sintering assistant, is composed of the silicon nitride sintered body sintered with no pressure, and removed with beta-Si3N4(beta'-sialon included) freely developed on the surface, from the sintered skin.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool made of a silicon nitride sintered body, in which at least the working part of the tool is made of a silicon nitride sintered body having excellent wear resistance and toughness.

0002

[Prior Art] Conventionally, in the field of cutting tools and polishing tools,
Attempts were made to use ceramic tools in place of high-speed machining, carbide tools, and coated tools from the viewpoint of high-speed, high-efficiency machining, and first, Al2 O3-based tools were used.
It appeared in the 1950s. However, it was not put into practical use at first due to its low toughness, and after that, the addition of TiC,
Addition of ZrO2 (Japanese Patent Publication No. 59-6279), S
Improvements were made with the aim of improving toughness, such as by adding iC whiskers (Japanese Patent Application Laid-Open No. 61-274803), and it came into practical use mainly for finishing cutting of cast iron. However, its toughness is still insufficient and its reliability is low, making it impossible to use it for rough cutting or interrupted cutting. On the other hand, silicon nitride sintered body is Al2O3
Compared to sintered bodies, it has high toughness and a small coefficient of thermal expansion, so it has high thermal shock resistance, and can be widely used for rough/finish cutting of cast iron, wet cutting, etc., and is highly reliable, so it has rapidly become popular. ing.

[0003] Conventionally, with regard to this silicon nitride sintered body, research and development on sintering aids have been actively conducted for the purpose of improving the strength. This is because silicon nitride is a compound with strong covalent bonds, has a large ratio of grain boundary energy to surface energy compared to ionic crystals and metal crystals, self-diffusion is extremely slow, and decomposes and evaporates at high temperatures. This is because it is a substance that is difficult to sinter. That is, MgO, Y2 O3
, Al2 O3 , ZrO2 , AlN, CaO, C
A technique has been developed in which a sintering aid such as eO2 or SiO2 is used to form a glass phase with a low melting point and a dense sintered body is obtained by liquid phase sintering. In the history of the development of such auxiliaries, sintering auxiliaries such as Y2O3 not only densify the sintered body, but also develop silicon nitride crystal grains into columnar shapes, and according to the theory of fiber reinforcement, sintering auxiliaries such as Y2O3 This was a very important technological development in that it increased the strength of silicon nitride sintered bodies (see Japanese Patent Publication No. 48-7486). This sintering mechanism is that α-Si3N4 dissolves in the molten glass phase generated at high temperature, and β-Si3N
4 (or β'-sialon) and precipitates as Y2
Columnar silicon nitride particles are produced by growing in the C-axis direction of hexagonal crystals in the presence of O3. This technological development has made it possible to increase the strength of silicon nitride, and it is now being put into practical use as a ceramic tool capable of rough cutting, interrupted cutting, and rough milling of cast iron.

Furthermore, the development of such a sintering aid and the adoption of nitrogen gas pressure sintering have made it possible to perform evaporative sintering of silicon nitride, which could previously only be produced by hot pressing, making it possible to produce products with complex shapes in a near-field manner. It is now possible to easily manufacture net-shape products that closely approximate the shape of the final product.

[0005]

[Problems to be Solved by the Invention] However, even though near-net shaping has progressed through the above-mentioned technological developments, silicon nitride-based tools do not utilize the sintered skin as is, as in carbide and cermet tools. The development of products that can be used as tools has been slow, and currently the desired shape is achieved through grinding. Therefore, the strength of the sintered body decreases due to cracks caused by machining scratches generated during grinding, and silicon nitride is extremely difficult to process, leading to an increase in manufacturing costs.

[0006]Therefore, there have been attempts to form the desired shape during molding and finish it as a product without grinding or by post-processing using a low-cost method other than grinding. The product has problems such as deterioration in strength and reduction in wear resistance due to the presence of abnormal phases on the surface of the sintered body. Further, the abnormal phase on the surface of the sintered body may be caused by sublimation and decomposition of Si3N4, scattering of grain boundary glass phase, etc. To solve these problems, we oxidized the surface of the silicon nitride sintered body to form a film mainly composed of silicon dioxide to cover the abnormal phase on the sintered body surface and bring out the characteristics of the silicon nitride sintered body itself. An attempt to do so has also been proposed (Japanese Unexamined Patent Publication No. 2-164773). However, even if a tool is manufactured using a sintered body treated in this way and put into practical use, the low melting point silicate glass phase formed on the surface of the sintered body tends to cause welding with the workpiece. This results in a phenomenon such as a decrease in wear resistance. In addition, a container made of a specific material in which a pressed silicon nitride body is inserted with silicon nitride-based powder underneath,
A method has been proposed in which a sintered material that can be used for practical use in the sintered state is obtained by embedding it in silicon nitride-based powder in a black smoke crucible and sintering it (Japanese Patent Publication No. 30152/1982). . However, on the surface of the sintered body manufactured by this method, freely grown columnar silicon nitride crystal grains as seen in FIGS. 1(a) and 1(b) are generated, as in the case of the normal evaporative sintering method. These columnar silicon nitride crystal grains are β-Si3 N4
(or β'-Sialon), and as mentioned above, as a result of these crystal grains intertwining inside the sintered body, the silicon nitride sintered body has a high strength due to the fiber reinforcement mechanism, and is used for ceramic tools. However, it is possible to carry out cutting operations such as rough milling and cut-off turning of cast iron. This phenomenon is unique to highly strengthened silicon nitride sintered bodies, and is not observed in the sintered skin of cermet tools or cemented carbide tools.

[0007] β-Si3 freely grew on the surface of this sintered body.
N4 (or β'-Sialon) is unstable because it grows freely, and is only fixed by a glass phase mainly composed of sintering aid components at the ends of columnar crystal grains. Therefore, when external stress is applied, it is easy to cause a falling-off phenomenon, and the surface roughness is also rough due to the presence of voids between the columnar particles.

As a result, when a sintered body having such a surface phase is used as a tool, there is a problem in that wear resistance and strength deteriorate due to shedding of columnar crystal grains.

The present invention has been made in view of the above points, and by improving the surface of the silicon nitride sintered body, a silicon nitride sintered body that has excellent wear resistance and toughness and can be manufactured at a low cost. The purpose is to provide tools.

0010

[Means for Solving the Problems and Their Effects] In order to solve the above problems, the present invention provides a silicon nitride sintered body highly strengthened by β-Si3N4 (or β'-Sialon). Columnar β-Si grown freely on
It has been discovered that by using a silicon nitride sintered body from which 3N4 (or β'-Sialon) has been removed as a tool, the inherent characteristics of the silicon nitride sintered body can be exhibited.

[0011] Furthermore, in the present invention, as a means for removing freely grown columnar β-Si3N4 (or β'-Sialon), blasting, barrel processing, or ultrasonic vibration processing is used, and grinding is used. This enables low-cost processing.

The silicon nitride sintered body used in the present invention is produced by a well-known method, for example, a mixture of silicon nitride powder and a sintering aid is mixed at 1 ton/cm2.
It is manufactured by mold pressing at a pressure of 1,700 to 1,900° C. in a nitrogen atmosphere under normal pressure sintering or hot isostatic pressing after normal pressure sintering. The silicon nitride powder used in the present invention has an α rate, that is, α
-It is desirable that the wt% of Si3N4 is 90% or more. This is a columnar β-Si3 N4 (or β'-
This is because, in order to obtain a silicon nitride sintered body with excellent strength in which SiAlON) are entangled, it is preferable to use a silicon nitride raw material powder with an α rate of 90% or more. Further, it is desirable to use a raw material powder of silicon nitride made by an imide decomposition method. This is because the silicon nitride raw material powder produced by the imide decomposition method has a small amount and high purity and is easily dissolved in the liquid phase by the sintering aid. This is because it is easy to manufacture a silicon nitride sintered body in which the particles (sialon) are intertwined.

Next, as a sintering aid, MgO, Y2
O3, Al2 O3, ZrO2, AlN, CaO
, CeO2, SiO2, 1
It is desirable to contain it in a range of wt% or more and 20wt% or less. This is because by using these sintering aids, sinterability is improved and a dense sintered body can be obtained even by evaporation sintering. Addition of less than 1 wt% makes evaporation sintering difficult, and addition of more than 20 wt% reduces wear resistance, which is not preferred. In particular, Y2O3, Ce
Addition of O2 causes significant columnar crystallization of silicon nitride crystal grains, which is desirable from the viewpoint of increasing strength. In addition, Ti carbide,
When 1 to 30 wt% of at least one of nitrides, borides, and carbonitrides is added, the hardness of the sintered body is improved,
Wear resistance is improved. However, if it is less than 1 wt%, the effect is small, and if it is more than 30 wt%, the sinterability deteriorates, which is not preferable.

[0014] As a means for removing β-Si3N4 (or β'-Sialon) which has grown freely on the surface of the silicon nitride sintered body obtained in this way, any method with low processing cost other than grinding may be used. For example, any method may be used, including blasting, barrel treatment, and ultrasonic vibration. As a method of blasting, for example, #120 Al2 O3 is projected at a pressure of 4 kg/cm2. As a barrel treatment method, for example, water is added to #120 SiC and 200
Process by rotating at 0 rpm. As a processing method using the ultrasonic vibration method, for example, a 600 W ultrasonic vibrator is used and the processing is performed in water containing diamond abrasive grains for about 3 hours. As the propellant or media used for blasting and barrel processing, in addition to ceramics such as SiC and Ai2O3, glass-based materials such as SiO2 can also be used to perform the process favorably.

FIGS. 2(a) and 2(b) show SEM photographs showing the crystal structure of the surface structure of a silicon nitride sintered body from which columnar silicon nitride particles that had grown freely by blasting were removed. SEM photographs showing the crystal structure of the surface of the silicon nitride sintered body from which the columnar silicon nitride particles have been removed are shown in FIGS. 3(a) and 3(b). In this way, in the sintered skin from which the freely grown columnar silicon nitride particles have been removed, the grain boundary glass phase and the columnar silicon nitride particles are mixed, and the surface S
The presence or absence of treatment can be determined using EM photographs. Furthermore, whether or not the columnar silicon nitride particles that have grown freely on the surface are removed can be determined by X-ray diffraction, which shows that the half width of the diffraction peak of β-Si3N4 (or β'-Sialon), that is, the height of the diffraction peak, is halved. This can be determined by measuring the width of the diffraction angle when

The silicon nitride sintered body applied to the present invention has a 10-point average surface roughness Rz of 3 μm or less (detection distance is 2.0 μm or less).
5 mm). If Rz is larger than 3 μm, columnar β-Si3N4 (or β'-Sialon) that has grown freely on the surface of the sintered body will not be removed sufficiently, and this will reduce the durability when used as a tool. This is because the effect of improving abrasion properties is small.

[0017]

[Embodiment] An embodiment of the present invention will be described below.

[0018] Average particle size 0.4 μm, α crystallinity rate 96%,
A silicon nitride raw material with an oxygen content of 1.5 wt% and an average particle size of 0.
8μm Y2O3 powder 5wt%, 0.4μm Al
2 OI3 powder (3 wt%) was wet-mixed in ethanol for 100 hours in a nylon ball mill, and the resulting mixed powder was then dried and press-molded at 1 ton/CM2 using a mold with tool shape SNMN120408. This compact was placed in a pressure sintering furnace at 180° C. in a nitrogen gas atmosphere of 5 atm.
Sintering was carried out at 0° C. for 2 hours, and only the rake face was ground to obtain a silicon nitride sintered body X having a tool shape of SNMN120408.

[0019]

[Table 1]

Cutting tests were conducted using the silicon nitride sintered tool thus obtained under the following two conditions.

(Cutting test 1) Work material: FC25 Cutting speed: 600 m/min Feed: 0.4 mm/rev Depth of cut: 1.5 mm Cutting water: DRY Cutting time: 10 min (Cutting test 2) Work material: FC25 Cutting Speed: 200 m/min Feed: 0.2 mm/blade depth of cut: 2.5 mm Cutting fluid: DRY Cutting time: 10 min Table 2 shows the results of each of the above cutting tests. From the results in Table 2, tool samples A to D, which are products of the present invention, are different from E, which is outside the invention.
, F shows superior wear resistance and chipping resistance. However, in sample tool A, freely grown β-
Since the removal of Si3N4 (or β'-sialon) was not sufficient, the surface of the sintered body was rougher than in tool samples B to D, and the cutting test results also showed relatively large flank wear. In addition, in the case of tool sample E, in which the sintered body surface was subjected to oxidation treatment, the surface roughness Rz was the smallest value of 1.5 μm, but the cutting test results showed that flank wear was extremely large. . This is due to the fact that although the surface of the sintered body becomes flat with the oxidation treatment, an oxide film (
This is thought to be because the abrasion resistance deteriorated due to the low melting point of silicate glass.

[0022]

[Table 2]

[0023]

Effects of the Invention As explained above, according to the present invention, β-Si3 N4 (or β
By removing ´-Sialon), wear resistance,
A tool made of silicon nitride sintered body with excellent toughness can be manufactured at low manufacturing cost, which has a great industrial effect.

[Brief explanation of the drawing]

[Figure 1] (a) is a 4800x scanning electron microscope photograph showing the crystal structure of the sintered skin on the surface of the silicon nitride sintered body, and (b) is the same sintered skin on the surface of the silicon nitride sintered body. This is a photograph taken by a scanning electron microscope at a magnification of 1200 times, showing the crystal structure of .

FIG. 2(a) shows the crystal structure of the sintered body surface when the surface of the silicon nitride sintered body is subjected to blasting treatment, 480
Photographs taken with a scanning electron microscope at 0x magnification, (b) and (a)
This is a 1200x scanning electron microscope photograph showing the same crystal structure on the surface.

[Fig. 3] (a) is a photograph taken by a scanning electron microscope at a magnification of 4800 times showing the crystal structure of the surface of a silicon nitride sintered body subjected to barrel treatment; (b) is a photograph of (a) This is a 1200x scanning electron microscope photograph showing the same crystal structure on the surface.

Claims (4)

[Claims] Claim 1: A tool made of a silicon nitride sintered body, in which at least the working part as a tool is made of a silicon nitride sintered body containing silicon nitride and a sintering aid and sintered under pressure; β-Si3 N4 that has grown freely on the surface from at least a part of the sintered skin of the silicon nitride sintered body at the position where
A tool made of a sintered silicon nitride body, characterized in that (including β'-SiAlON) is removed. [Claim 2] β-Si3 N4 grown freely on the surface
(including β´-sialon) from the sintered skin.
The tool made of silicon nitride sintered body according to claim 1, characterized in that the tool is processed by blasting, barrel processing, or ultrasonic vibration method. [Claim 3] The 10-point average surface roughness Rz of the sintered skin is 3μ.
The tool made of silicon nitride sintered body according to claim 1, characterized in that the diameter is less than or equal to m. 4. The silicon nitride sintered body contains 1 to 30 wt% of at least one selected from Ti carbides, nitrides, carbonitrides, and borides as a sintering aid.
Or MgO, Y2 O3, Al2 O3, ZrO2
2. The silicon nitride sintered tool according to claim 1, comprising 1 to 20 wt% of at least one selected from , AlN, CaO, CeO2 and SiO2.