JPH04108663A - Production of fiber reinforced alumina ceramics - Google Patents

Abstract

PURPOSE:To obtain ceramics having superior toughness and wear resistance and fit for a cutting tool by adding a prescribed percentage of whiskers of the carbide, nitride or carbonitride of titanium having a prescribed oxygen content to alumina powder and firing them. CONSTITUTION:Whiskers of the carbide, nitride or carbonitride of titanium having <=3wt.% oxygen content are formed. A mixture consisting of 5-70vol.% of the whiskers and the balance alumina powder or further contg. 0.1-3wt.% sintering aid is prepd., molded and sintered. The sintering aid is selected among the oxides of Mg, Y, rare earth elements, Cr, Ni and Co.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to fiber-reinforced ceramics containing fibrous substances such as whiskers, and more particularly, to fiber-reinforced ceramics that have high toughness and are particularly useful for cutting tools and other wear-resistant parts. This invention relates to a method for manufacturing Ceramifukus suitable for.

(Prior art) Alumina (AlzOi) sintered bodies are used in various industrial machinery parts as a material with excellent wear resistance, but the drawback of poor toughness hinders the expansion of the field of use. has been done.

Therefore, various improvements have been proposed to improve toughness.

One example is JP-A No. 61-286271 and JP-A No. 62-Sho. 61-286271 and JP-A No. 62-1982, which suggest that toughness can be improved by incorporating fibrous substances such as silicon carbide (S i C) whiskers.
It has been proposed in No. 41776, etc.

Fiber-reinforced ceramics containing such SiC whiskers have high hardness and good thermal conductivity, so when used as a cutting tool, it is difficult to cut some super heat-resistant alloys, such as rough cutting Inconel 718. It shows excellent performance.

(Problem to be Solved by the Invention) However, since SiC has the property of easily reacting with iron and special iron oxide, A1.03-3iC whisker-based tools are often used with other A1□03 There is a tendency for the amount of wear to be greater compared to tools that are mainly made of For example, when cutting 5US304, conventional Al z O
If it is a J series tool, even if the conditions are sufficient for cutting, Si
Tools containing C whiskers have a problem in that they rapidly wear out and become impossible to cut. It has also been confirmed that the amount of wear is greater than that of A1°03 series tools when cutting cast iron.

As described above, the Al2O3SiC whisker-based tool has a problem in that its cutting performance varies greatly depending on the workpiece material.

However, recently, in order to prevent such reactivity with the work material, SiC whiskers have been replaced with
Titanium carbide (TiC) has lower reactivity with iron than SiC
It has been proposed to add titanium-based fibrous substances such as whiskers, but this has not yet been fully investigated in terms of the properties of ceramics such as flexural strength, toughness, and hardness, and has not yet reached a practical level. The current situation was that there was no such thing.

(Means for Solving the Problems) As a result of detailed studies on the AhOh-'r i-based whisker ceramics, the present inventors found that T
It has been found that the characteristics of i-type whiskers vary greatly depending on the amount of oxygen contained in them. Therefore, by controlling the oxygen content of these whiskers within a specific range, the hardness, fracture toughness, flexural strength, and sinterability of the sintered body can be adjusted to optimal conditions, and a ceramic with excellent properties can be obtained. The present invention was realized based on this finding.

That is, the present invention adds 5 to 70 whiskers made of titanium carbide, nitride, or carbonitride and having an oxygen content of 3% by weight or less to alumina powder.
It is characterized by molding and firing a mixture added in a proportion of % by volume, and further adding at least one selected from Mg, Y, rare earth elements, Ni, Co, and Cr as a sintering aid to the above system.
This method is characterized by molding and firing a mixture to which 0.1 to 3% by weight of a seed oxide is added.

The present invention will be explained in detail below.

The Ti-based whiskers used in the present invention are themselves single-crystal or polycrystalline, and have an average grain size (minor diameter) of 10 μm or less, particularly 0.2 to 1.0 μm.
It is preferable that This is because when the average particle size of the whiskers exceeds 10 μm, the whiskers themselves begin to break and the strength of the sintered body decreases significantly, and it becomes difficult to mix the whiskers uniformly into the matrix during the manufacturing process. This is because variations in strength and toughness tend to occur, and boundary wear on the flank surface becomes large when used as a cutting tool.

On the other hand, if the aspect ratio expressed by the long axis/breadth axis of the whisker is too small, the effect of fiber reinforcement will be reduced, making it difficult to obtain high toughness (on the other hand, if it is too large, it will not be possible to handle it as a raw material). This makes it difficult to obtain high toughness because the whiskers cannot be dispersed uniformly. Therefore, whiskers with an average aspect ratio of 3 to 100, especially 1
0 to 30 is preferably used. Note that any of TiC, TiN, and T1CN can be used as the Ti-based whisker.

The above-mentioned whiskers are usually susceptible to oxidation and the like, so oxygen is present on their surfaces. According to the present invention, it is important to control the oxygen content contained in the whisker to 3% by weight or less. The reason why the amount of oxygen was limited to the above range is that if the amount of oxygen exceeds 3% by weight, adhesion due to the reaction between matrix components and whiskers will increase, the whisker extraction effect will decrease, and the grain growth of Al t O3 will be reduced. This is because toughness, flexural strength, and hardness decrease as this occurs more easily.

Such whiskers can be synthesized, for example, by carbonizing or nitriding titanium oxide whiskers, or by CVD.

The oxygen content in the whiskers can be adjusted by introducing a certain amount of oxygen during the manufacturing process, or by heating the manufactured whiskers in the atmosphere at a temperature below about 500°C for a certain period of time to oxidize them. It can be carried out.

The whiskers are dispersed and contained in a matrix component mainly composed of alumina in an amount of 5 to 70% by volume, particularly 25 to 50% by volume based on the total amount.

The reason why the amount of whiskers is set in the above range is that if the amount of whiskers is less than 5% by volume, the effect of improving toughness by whisker addition is small, and if it exceeds 70% by volume, the sinterability of the entire system will decrease. In addition, in consideration of mechanical properties and ease of sintering, the amount of whiskers added is preferably 25 to 45% by volume, and optimally 30 to 40% by volume.

Also, the matrix for dispersing whiskers is A 1
202 as the main component, but by adding at least one or more oxides selected from Mg, Y, rare earth elements, Ni, Co, and Cr as a sintering aid, the sinterability as a matrix component is improved and the characteristics are improved. It is possible to improve the

However, if the amount of this auxiliary agent is too large, the toughness of the sintered body decreases. Therefore, these sintering aids account for 0.1 to 3% by weight of the total amount.
It is particularly preferable to add it in a proportion of 0.5 to 2% by weight. The rare earth elements used here include Yb, Nd,
Examples include Er, Ce, Sm, Cd and Dy.

To produce the fiber-reinforced ceramics of the present invention, first, the whiskers, alumina powder, and if necessary, a sintering aid are mixed in the above-mentioned proportions, pulverized, and then molded using a desired molding method, die press, extrusion molding, or injection molding. After shaping by molding, cold isostatic pressing, etc., it is fired.

For firing, ordinary firing, hot press method, hot isostatic pressure firing method, etc. are applied, and Ar
The reaction is carried out for 0.5 to 6 hours in a reducing atmosphere in which an inert gas such as or He or carbon exists, and in a pressurized or reduced pressure atmosphere thereof. In order to obtain a particularly high-density sintered body, a sintered body having a theoretical density ratio of 96% or more may be prepared by normal firing or the real press method, and this sintered body may be further subjected to hot isostatic pressure firing.

(Function) According to the present invention, by adjusting the amount of oxygen contained in the whiskers, the matrix component A L203
The aim is to control the interfacial reaction between the whisker and the whisker. When the amount of oxygen in the whisker decreases, A I
The reaction at the interface between z 03 and the whisker is reduced, and A1
The bonding force between □03 and the whiskers becomes smaller, and strengthening mechanisms such as pull-out and day bonding work to improve the toughness of the sintered body, but the strength, hardness, and sinterability of the sintered body decrease. On the other hand, when the amount of oxygen in the whisker increases, the oxide present on the whisker surface and the matrix A1□0
3 reacts, increasing the bonding strength of crystal particles and improving strength and hardness, but if the oxygen amount exceeds 3% by weight, AIt.

The reaction between No. 3 and the whiskers becomes excessive and the effect of pulling out the whiskers, which is responsible for improving toughness, decreases, resulting in a decrease in the toughness of the sintered body. Also, as the amount of oxygen increases, A1□030
Since grain growth tends to occur, the bending strength and hardness also decrease.

The desired amount of oxygen varies depending on the characteristics desired for the sintered body, but
If high fracture toughness is desired, O to 0.3% by weight is good;
If high hardness is desired, 0.2 to 2% by weight is preferred, and if ease of manufacture is desired, 2 to 3% by weight is preferred. Considering the balance of strength, hardness, fracture toughness, etc., the amount of oxygen is 0.
．． It is preferably 1 to 1.5% by weight. Also, for cutting tools, 0
, 05~], 0% by weight is suitable.

The invention will now be explained with the following examples.

(Example) AlzO3 with an average particle size of 1 μm or less and a purity of 99.9% or more
After weighing the powder and, if necessary, the sintering aid powder shown in Table 1, the powder was mixed and pulverized in a rotary mill for 366 hours. A predetermined amount of various TiC whiskers with an average particle size of 1 μm, an aspect ratio of 10 to 30, and different amounts of oxygen were added to this mixed powder, sealed in a nylon pot with nylon balls, and heated in a rotary mill for 6 hours.
Mixed for an hour. The slurry after mixing was dried and used as a raw material for hot pressing.

This raw material was filled into a carbon mold and fired at a predetermined temperature for 71 hours at a pressure of 300 kg/cm2 to produce bending test specimens based on JIS standards. Each sample was polished. Based on JIS1601S, the three-point bending strength is determined by Pinkers hardness, and the mirror surface is processed with Polyno Song.
Toughness (K+c) was measured by M method.

In addition, the structure was observed from microscopic photographs and the sinterability was evaluated.

The results are shown in Table 1.

In addition, as another example, instead of the TiC whiskers, an oxygen amount of 0.2% by weight, an average particle diameter (minor diameter) of 1.5 μm,
TiN whiskers with an aspect ratio of 20 and an oxygen content of 0.2
Weight %, average particle diameter (minor diameter) 1.5 μm, aspect ratio 2
A sample was prepared in exactly the same manner as in Example 1 except that 0 T1CN whiskers were used, and the characteristics were evaluated in the same manner.

(Yuzu bottom margin) According to Table 1 (2), in the comparison of samples N11l to 9, which differ only in the amount of oxygen in the TiC whiskers, the amount of oxygen was 3% by weight.
All of the sample seeds exceeding 8.9 had deteriorated properties in terms of strength and fracture toughness compared to the other samples.

On the other hand, in comparing samples 10 to 17 regarding the amount of TiC whiskers added to alumina, the amount was 5% by volume.
No toughness improvement effect was observed on sample level 10 with no drops, and 70
In sample NCL17, which exceeds the volume %, sinterability decreased, voids were observed, and the characteristics became thicker (decreased).

In addition, with sample N1128 without the addition of a sintering aid, excellent properties can be obtained by increasing the sintering temperature, but by adding an appropriate amount of a sintering aid, the sintering temperature can be lowered and the stability of properties can be improved. I was able to figure it out. However, in sample No. 34 in which the amount of sintering aid exceeded 3% by weight, both the flexural strength and toughness decreased.

In Table 1, all the samples prepared based on the present invention have a bending strength of 60 kg/mm! Above, toughness 5.0 MP
a-m"" or more, Vickers hardness 1800 kg/m
m2 or more was achieved.

(Example 2) In Table 1, as a comparative example with the composition of Sample Review 9, SiC whiskers with a diameter of 0.7 μI and an aspect ratio of 30 were used instead of the TiC whiskers in Example 1, and fired.
A tool of RNGN 1204 shape was obtained.

Using these tool test pieces, Inconel 718 (solution treated product) was cut with a depth of 2 mm, a feed rate of 0.3 mm/rev,
When cut for 5 minutes at a cutting speed of 300 m/min, the grade 9 tool showed slightly better wear resistance than the comparative product.

Similarly, create a tool of 5NGNI 20412 shape and 5
Cut US304 2mm, feed 0.3mm/re
When cutting was performed at a cutting speed of 300 m/mtn, the comparative product showed rapid wear, whereas the Nt19 tool was capable of cutting for more than 10 minutes.

(Effects of the invention) As detailed above, the AhCh Tic whisker-based ceramics of the present invention is superior to the conventional A1□03-3tC
This is because the toughness, wear resistance, and strength of TiC whiskers can be further improved by controlling the amount of oxygen in TiC whiskers, while maintaining the effect of reducing reactivity with iron oxide compared to whisker systems. The use of fiber-reinforced ceramics can be expanded as tool materials that can be used with all kinds of work materials, or as other machine parts.

Patent applicant (663) Kyocera Corporation

Claims (2)

[Claims] (1) Molding a mixture in which whiskers made of titanium carbide, nitride, or carbonitride and having an oxygen content of 3% by weight or less are added to alumina powder at a ratio of 5 to 70% by volume. , a method for producing alumina fiber-reinforced ceramics, characterized by firing. (2) Whiskers made of titanium carbide, nitride, or carbonitride and having an oxygen content of 3% by weight or less are added to the alumina powder at a ratio of 5 to 70% by volume, and then sintered. Alumina characterized by molding and firing a mixture to which at least one oxide selected from Mg, Y, rare earth elements, Cr, Ni, and Co is added as a binding agent at a ratio of 0.1 to 3% by weight. A method for producing quality fiber-reinforced ceramics.