JPH0422864B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention is a tough ceramic material, for example, a ceramic material in the field of engineering ceramics, which has excellent wear resistance and chipping resistance, and is suitable for use in cutting tool materials such as tips for heavy cutting and interrupted cutting such as milling cutters. This invention relates to a method for manufacturing materials. (Prior Art) In the field of processing tools, especially cutting tools, improvements in sintering technology have made it possible to utilize various materials that could not be used in the past, and ceramic tools have been attracting attention in recent years. Ceramic tools can be roughly divided into two types: pure alumina ceramics (99% Al ₂ O ₃ or more) and TiC-added ceramics (TiC 20 to 40W%). Of these, the former pure alumina ceramics can be mass-produced and has excellent durability. Although its advantage is high abrasion resistance, it has the disadvantage of poor toughness, so it is mainly used for finish continuous turning. On the other hand, the latter ceramics, which are made by dispersing TiC particles in an Al ₂ O ₃ sintered body, have superior toughness and strength compared to pure Al ₂ O ₃ , and are particularly useful as materials for interrupted cutting tools such as milling. has been done. Moreover, recently, a material in which ZrO ₂ is dispersed in Al ₂ O ₃ is known as a material that similarly improves the mechanical properties of Al ₂ O ₃ , and attempts have been made to utilize this material. (Problems to be Solved by the Invention) By the way, in producing a dispersion-strengthened material such as Al ₂ O ₃ −ZrO ₂ (Y ₂ O ₃ ), what is necessary is to make the dispersed particles finer, and to make the _dispersed particles finer. The goal is to uniformly disperse the particles in the O ₃ matrix, but in the past, the dispersion of such particles was mainly due to mechanical mixing of the raw material oxide particles, and although the dispersed particles were not necessarily homogeneously dispersed, Nakatsuta. In view of this situation, the present invention provides a method for ideally making ZrO ₂ particles fine and uniformly dispersing them in a matrix. (Means for Solving the Problems) That is, the present invention is characterized by using Al and Zr alkoxides as raw materials, creating a completely homogeneous mixed state at the atomic level in a solution, and then hydrolyzing this. By doing this, a completely homogeneous mixed raw material of Al ₂ O ₃ -ZrO ₂ is obtained, and by performing a calcination treatment using this, it is made into a raw material powder for sintering, which is then shaped and fired using a normal ceramic manufacturing process. The purpose is to produce a final tough ceramic sintered body. To explain this more specifically, a homogeneous mixed solution of metal alkoxides is hydrolyzed to form Al ₂ O ₃
, ZrO ₂ , and at least one selected from _the group consisting of _{Y 2} O ₃ , MgO, _and CaO.
A coprecipitate having a composition of 5 mol% or less of one or more selected from MgO and CaO based on the ZrO ₂ and the balance consisting of Al ₂ O ₃ and unavoidable impurities is prepared, and this is heated at 900 to 1300°C. This method consists of calcination to obtain a ceramic raw material powder, which is molded according to a normal ceramic manufacturing process, and then normal sintered and/or high pressure sintered at 1400 to 1650°C. This will be further explained in detail below. First, the present invention uses Al(i-OC ₃ H ₇ ) ₃ as a raw material.
(aluminum isopropoxide) and (OC ₄ H ₉ ) ₄ (zirconium butoxide), Y
A predetermined amount of (OC ₄ H ₉ ) ₃ (yztrium butoxide) is dissolved in ethanol. In this case, the alkoxide used as the raw material is, for example,
Al(OC ₄ H ₉ ) ₃ other than Al(i-OC ₃ H ₇ ) ₃ may be used,
In short, it is possible as long as it can be completely dissolved and hydrolyzed, but usually Al(i-OC ₃ H ₇ ) ₃ , Zr
(OC ₄ H ₉ ) ₃ is used because it is common and easily available. Then, water was added dropwise to the solution dissolved as above while stirring to perform hydrolysis.
ZrO ₂ 5 to 30 Vol% and one or more selected from Y ₂ O ₃ , MgO, CaO Here, Y ₂ O ₃ is added to the ZrO ₂
A precipitate having a composition of less than tmol% and the remainder consisting of Al ₂ O ₃ and inevitable impurities is produced. At this time, the amount of ZrO ₂ was set to 5 to 30 Vol% because if it was less than 5%, it would not be possible to fill all the grain boundary points of the Al ₂ O ₃ matrix particles and the grain growth of Al ₂ O ₃ could not be suppressed. Abnormal grain growth of Al ₂ O ₃ occurs in the composition, which makes it non-uniform and reduces mechanical strength.On the other hand, when it exceeds 30%, the characteristics of ZrO ₂ become apparent and the hardness decreases significantly, resulting in poor wear resistance. Because it will be. Furthermore, adding 5 mol% or less of one or more of Y ₂ O ₃ , MgO, and CaO to ZrO ₂ makes the dispersed ZrO ₂ particles in the sintered body stable or metastable in the tetragonal state. This is to keep it safe. Tetragonal Zr particles undergo a phase transition to monoclinic crystal at the tip of the crack, and have a transition-strengthening effect that prevents crack propagation by absorbing fracture pressure. However, when Y ₂ O ₃ or the like is increased to 5 mol % or more, the proportion of complete stabilization as cubic ZrO ₂ increases, and the above-mentioned dislocation strengthening effect disappears, resulting in a significant increase in toughness and strength. Therefore, it is preferable to limit Y ₂ O ₃ etc. to 5 mol % or less. By the way, hydrolysis produces very fine particles of several tens of angstroms in size, which have a low bulk density and are difficult to form. For this reason, it is possible to subsequently perform the calcination treatment at an appropriate temperature. Of course, the outside is used for the calcination process.
Since the Al (OC ₃ H ₇ ) hydrolysis product is in a water-containing state like AlOOH, it also means dehydrating it. Therefore, the obtained precipitate is filtered and dried, and then subjected to a calcining treatment to obtain a raw material powder for sintering. In this case, a range of 900 to 1300°C is applied as the calcination temperature. _For example, the relationship between the calcination temperature and the specific surface area value _is shown in _{Figure 1 .}
65m ² /g - 15m ² /g when calcined for 1 hour at 900 - 1300℃
This is estimated based on the fact that the raw material powder is ready for use in subsequent molding operations. Note that below 900°C, the BET value is large (particle size is small) and forming is difficult; on the other hand, when the temperature exceeds 1300°C, crystallization of particles becomes noticeable, making it difficult to crush after calcination. Therefore, the temperature is preferably 900 to 1300°C, more preferably 1100°C.
~1300°C is preferred. Henceforth, the powder obtained as described above,
The final sintered body is formed through the addition of a binder, molding, and sintering using the usual ceramic manufacturing process, but the sintering process can be performed using conventional sintering, a combination of sintering and hot isostatic pressing (HIP), hot pressing, etc. Each of the above means can be used alone or in combination as appropriate. FIG. 2 shows the relationship between sintering temperature and density during sintering. In the figure, the composition of _the sintered body is _Al2O3-20 % _ZrO2 ( _3mol % _Y2O3 ), the sintering time is 2 hours, and the HIP condition is 1450℃.
150MPa, 1hr. As is clear from the figure, in the case of normal sintering (white circles in the figure), the TD is 92% at temperatures above 1400℃, and a density of 97% or higher is preferably obtained for practical use.
A temperature of 1450℃ or higher is required. On the other hand, in order to achieve densification of 99% or more by HIP treatment, it is preferable that the sintering before HIP achieves 95% or more, and the sintered body should be sintered at a temperature of 1425℃ or higher.
For HIP use. Therefore, it is effective to normally sinter the molded body of the raw material powder at a temperature below 1450 to 1650°C, and then directly subject the sintered body to HIP treatment. Here, the upper limit of the firing temperature is set to less than 1650°C because the material is sufficiently densified at this temperature, and a temperature higher than this is not only unnecessary, but also causes deterioration of mechanical properties due to grain growth. More specific examples are listed below. (Example) 80Vol% and 80Vol% respectively in terms of Al ₂ O ₃ and ZrO ₂
20Vol% Al(i- _OC3H7 ) ₃ and _{Zr ( OC4H9} ) ₄ , and
Y corresponding to 3 mol% Y ₂ O ₃ based on ZrO ₂
(OC ₄ H ₉ ) ₃ was dissolved at an alkoxide concentration of 20WT% in a three-necked flask using ethanol as a solvent. Distilled water was then added dropwise to the solution while stirring it with a stirrer to hydrolyze the alkoxide. The obtained hydrolysis product has a specific surface area of 100
The powder frame was extremely fine and had a low bulk density of m ² /g. This powder frame was then calcined in an air furnace at 1200°C for 1 hour to obtain a raw material powder with a specific surface area of 30 m ² /g.
(See Figure 1) After mixing paraffin wax with the above raw material powder,
It was molded into a mold with a size of 50 x 50 x 8 ^tons at 1000 kg/cm ² .
The bulk density of this molded body was 45%. In this way, the molded product obtained above is further exposed to the atmosphere.
When fired at 1500℃ for 2 hours, the density of the sintered body after firing was 98.5%, and the bending strength (3-point bending) was 3rd grade.
From the diagram, 90Kg/Kg, KIC (Bitzkers indentation method)
10MN/m ^3/2 , Bitkers hardness (Hv) 1680Kg/
mm ² and had superior properties compared to conventional materials.
(See Figures 2 and 3) Therefore, the above sintered body was further heated at 1450℃ and 15MPa.
After HIP treatment for 1 hour, Figures 2 and 3
As shown by each black circle in the figure, the resistance strength is 142Kg/mm ² ,
SIC12MN/m ^3/2 , Bitkers hardness (Hv) 1740
Kg/mm ² , which showed significantly superior properties compared to conventional materials. Hereinafter, the above example will be referred to as Example 1, and Examples 2 to 2 will be described as Example 1.
6. Comparative Examples 1 to 7 are summarized in Table 1. In the table, the other compositions are ZrO ₂ mol%,
The HIP treatment conditions are 1450° C., 150 MPa, 1 hr, and the hot press pressure is 250 Kg/cm ² , 1 hr.

[Table] In the above table, Comparative Example 1 uses a hydrolysis product obtained in the same manner as Example 1, and the calcination temperature is
At 900℃, the BET specific surface area value is 60m ² /g
It is. (See Figure 1) This could not be molded beyond the lamination when press molded with a mold of 1000 kg/cm ² . When the pressure was lowered to 500 Kg/cm ² , molding was possible, but the bulk density was 32%, and this molded product was not sintered to more than 95% at temperatures up to 1650°C. Further, as seen in Comparative Example 2, at a calcination temperature of 850°C, the compressibility of the powder was extremely poor and molding was impossible. On the other hand, in Comparative Example 3, which was calcined at 1350°C, sintering occurred between the powders, making it difficult to break up the secondary particles. For this reason, large defects (bores) tend to remain in the sintered body, and the strength is relatively low at 62 kg/cm ² .
Almost no effect of dispersion reinforcement was observed. Moreover, even with HIP treatment, large diameter pores cannot be removed and no improvement in strength can be expected. Next, Table 2 lists examples of use in which sample sintered bodies in each of the above examples were extracted and used as a cutting tool for milling the upper surface of a cylinder block. Work material: Cylinder block top surface (200 x 500) Material: FC-25 Cutting speed V = 500 m/min Depth of cut t0.5 mm Feed f = 0.15 mm/t Tool SNGNTST (15.875 x 15.875 x 6.35 mm,
Corner R2.0mm Cutting edge chamfer 0.13mm×
20 In the table, the sample number indicates the sample number in Table 1.

[Table] As can be seen from the above table, materials 1a, 3a, and 4a produced by the method of the present invention have superior toughness and fracture resistance compared to other materials, and are optimal as tool materials for interrupted cutting such as milling. . (Effects of the Invention) As described above, according to the method of the present invention, ideal uniform dispersion of Al ₂ O ₃ and ZrO ₂ was achieved by the alkoxide method, so a uniform fine composition was obtained, and as a result, it was superior to conventional ceramic materials. In addition to being able to obtain a material with significantly higher density and toughness compared to other materials, the optimization of the calcination process facilitates the formation of alkoxide hydrolyzed raw materials, which were previously thought to be difficult to handle. This material was used in cutting tools that were required to improve performance along with high-speed machining, and it also provided excellent cutting performance (durability) even when cutting oil was required in interrupted cutting such as rice processing and NC processing. The method of the present invention is expected to have remarkable effects on improving the properties of this material and expanding its applications as a chip material for heavy cutting and interrupted cutting.

[Brief explanation of drawings]

Figure 1 is a chart showing the influence of calcination temperature on the specific surface area value, Figure 2 is a chart showing the relationship between sintered compact density and sintering temperature, and Figure 3 is a chart showing normal sintered compact (white circles).
It is a chart showing the bending strength against the sintering temperature of the HIP treatment (black circles).

Claims (1)

[Claims] 1. By hydrolyzing a homogeneous mixed solution of metal alkoxides, Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ ,
A mixture containing at least one selected from the group consisting of MgO and CaO is obtained, and the composition of the obtained mixture is 5 to 30 Vol% of ZrO ₂ and 5 mol of the component selected from the group relative to ZrO _2. % or less and the remainder consists of Al ₂ O ₃ and inevitable impurities,
Moreover, using the ceramic raw material powder obtained by calcining this mixture at 900 to 1300°C, and molding it according to the normal ceramic manufacturing process,
A method for producing a tough ceramic material, characterized by normal sintering and/or pressure sintering at a temperature below 1650°C. 2. The method for producing a tough ceramic material according to claim 1, wherein the calcination temperature is 1100 to 1300°C. 3. The tough ceramic material according to claim 1 or 2, wherein the raw material powder formed body is normally sintered at a temperature of 1450 to less than 1650°C, and then the sintered body is directly subjected to hot isostatic pressing. Production method.