JPS62207767A - High temperature high strength silicon nitride ceramics and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is in the field of engineering ceramics, and more specifically, it is used as a high-temperature structural material to provide high-temperature strength and oxidation resistance for use in engine parts, heat-resistant jigs and tools for steel manufacturing, blades for gas turbines, etc. The present invention relates to high-temperature, high-strength silicon nitride ceramics used in members requiring corrosion resistance, and a method for manufacturing the same.

(Conventional technology) Recently, high-temperature gas turbines, diesel engines,
The importance of high-temperature structural materials is recognized for the purpose of developing equipment that operates at high temperatures, such as HD power generation, and for use as highly hard materials such as tools and corrosion-resistant materials. However, silicon nitride (Si, 1N4) is attracting attention as one of the most important materials as it is chemically stable and resistant to thermal shock.

By the way, 5iJ4 has excellent physical properties as mentioned above, but this is because 5iJa is composed of silicon (Si) and nitrogen (
This is due to the fact that it is a compound consisting of a strong covalent bond with N).

At the same time, this also means that it is difficult to manufacture products with high density and high strength because they are difficult to sinter using Si or N alone. Therefore, Yz is usually used for sintering 5iJ4.
It is necessary to add a sintering aid such as Os, Al zOs 9Mg0.

However, these sintering aids generally bind Si3N by forming glass particles at the interface of Si, N4 powder particles.

Although it is possible to obtain a dense sintered body by adding a sintering aid because it has the role of bonding particles together, on the other hand, at high temperatures of 1000°C or higher, the sintered body formed by the additive auxiliary Since the grain boundary phase (glass phase) is softened, there is a drawback that the high-temperature strength decreases to 1/2 or less of the room-temperature strength.

In addition, Y2O, which has relatively excellent high-temperature strength, and Si3N
.

There is a problem in the material that oxidation occurs through grain boundaries in the temperature range of 900 to 1000°C, resulting in significant property deterioration.

Therefore, it has been considered to obtain a sintered body without the addition of sintering aids, and since the strength of a sintered body generally tends to be proportional to its density, hot isostatic pressing (hot isostatic pressing), which has recently attracted attention, has been
An attempt was made to sinter Si and N without the addition of a sintering aid under an inert gas at high temperature and high pressure using a method (hereinafter abbreviated as HIP).

The results show that additive-free Si3 obtained by HIP sintering
N, there was no decrease in strength up to 1300°C, but 14
It showed a decreasing tendency at 00°C. However, the intensity level was low, ranging from 20 to 40 kg/mn+2.

Therefore, when we tried to find the cause of the low strength level, we found that the reason was Fe contained in the raw material.

Although the amount of impurities such as Ni, As, and Sb (~200 ppm) is not a problem at all in the usual auxiliary-added Si 2N4, they aggregate during the HIP process and cause inclusion particles that become the starting point of fracture. It turns out that the purpose is to form
It was found that this phenomenon is unique to Si and N without additives.

In addition, it was found that the strength deterioration at 1400°C was due to the use of raw materials with a large amount of 0□.

(Problems to be Solved by the Invention) The present invention solves the problem that SiJ in an actual state such as soft soil and with no additives shows that although the strength does not decrease at high temperatures up to 1300°C, the reason for the low strength level is due to impurities in the raw material. Something (Fe,
This is based on the knowledge that strength deterioration at 1400°C is due to the use of a large amount of raw materials such as Fe, Ni, Cr, etc.). It is necessary to remove impurity elements such as iron group metals and Va group metals such as As and Sb, and in order to maintain strength up to 1400°C, 0□
Considering the need to control the amount, ultra-high purity 5ix
By using Na as a raw material, we can create ideal high-temperature, high-strength Si3N4 sintered bodies, especially Si3 whose strength does not deteriorate substantially up to 1400°C, which will be required for future gas turbine components.
The purpose is to obtain an N4 sintered body.

(Means for Solving the Problems) That is, the features of the present invention are the removal of the impurity elements mentioned above and the regulation of 02 materials in the raw materials. Sintering aid-free 5IJn H with metal element 50ppm or less and oxygen content 2% or less
The other one is an IP sintered body, and the other one is a 5i3Na raw material or a molded body thereof that is heat-treated in dry chlorine and/or vacuum heat-treated to contain impurity iron group elements and Vaa metal elements of 50 ppm or less.

High-temperature, high-strength, sintering aid-free Si, N produced by HIP treatment after reducing the oxygen content to 2% or less.

It is in the method of manufacturing ceramics.

Below is a more detailed explanation of the present invention. First, the SisNa powder raw material used in the present invention is not only one obtained by the nitriding method of metal Si, but also a SisNa powder raw material used in the present invention. SiCj! by reduced powder, gas phase reaction method, or thermal decomposition method! ．． or Si(N
H) Those manufactured from z are used.

However, this 5iJa powder raw material contains Fe as described above.

Impurity elements such as iron group elements such as Ni and Cr and V'a group metal elements such as As and Sb are contained. It also contains oxygen 0□.

Therefore, it is necessary to remove these impurity elements and regulate the amount of 0□, and therefore the former is particularly subjected to heat treatment in dry chlorine and/or vacuum heat treatment.

In this case, the amount of impurity elements contained is up to 5
0 ppmAlso, although it is not particularly critical to set the amount of 02 to 2% or less, it is preferable from the experimental results shown in the examples below, and thus the 5iJ4 raw material powder can be highly purified. After that, sintering is performed by HIP processing, which is a known method, and is usually sintered under an inert atmosphere such as Ar gas or N2 gas.
It is carried out at a temperature of 600°C or higher, preferably 1700 to 2000°C, and under a pressure of 500 atmospheres or higher, preferably 700 atmospheres or higher.

Hereinafter, specific examples will be given to clarify how superior the present invention is compared to each comparative example.

(Example) First, a general table is shown.

(Hereinafter, blank space) Next, each example will be explained in sequence based on the above table.

(Example 1) After press-molding the raw material A in the above table into a size of 50 x 50 x 201111, the molded body was placed in a tube furnace for impurity purification treatment, and the temperature was gradually raised while flowing 2 Il of dry chlorine per minute. It was held at ℃ for 2 hours.

As a result of the analysis of the sample after treatment, it was as shown as X in the previous table, and a decrease in the impurity Fe was observed, and the amount of the impurity element became 5 oppm or less.

This sample was then glass-sealed using a press sealing method using Vycor glass powder, and heated at 2000°C for 15 minutes.
HIP treatment was performed under the conditions of 0 MPa and 2 hours, and sintering was performed.

The bending strength of the obtained sintered body is 6 at room temperature as shown in the previous table.
6 kg/mm', 78 kg/mm at 1200℃
", and furthermore, 75 kg/n++11" at 1400°C, demonstrating revolutionary high-temperature strength for a 5IJa sintered body.

Also 1. Weibull coefficient of room temperature strength (number of samples 15) m-1
It was 2.

(Comparative example) Sample C, which is a powder of Si3N produced by a commercially available silicon nitriding method, was press-molded, and without impurity purification treatment, it was glass-sealed by a breath-sealing method using Vycor glass powder, and heated at 2000°C and 150MP.
a, HIP treatment was performed under conditions of 2 hr.

The bending strength of the obtained sintered body is 2 at room temperature as shown in the previous table.
3 kg/mm”, 48 kg/mm at 1200℃
"and 32 kg/mm at 1400°C", which was considerably inferior to that of Example 1.

Moreover, in the sintered body of Comparative Example 1, as a result of observing the fragments of the bending test piece, all the fractures were found to originate from inclusions dispersed in the sintered body, and X-ray analysis revealed that the inclusions were Fe silicides. It turns out that there is something.

Further, although the appearance of this comparative example was good and the Weibull coefficient was high, the strength value itself was low and could not be put to practical use.Furthermore, the strength decreased at 1400°C.

The attached drawing is a chart comparing the above-mentioned Example 1 and Comparative Example 1 for the purpose of comparison, and the difference between the two can be clearly seen.

(Comparative Example 2) Next, 5iSN4 raw material A having the same composition as in the above example synthesized by the silicon diimide pyrolysis method was press-molded, and then press-sealed using Vycor glass powder without any impurity purification treatment. Seal the glass with
000℃, 150MPa.

HIP sintering was performed under conditions of 2 hours. Although the bending strength of the obtained sintered body was improved compared to that of Comparative Example 1, aggregates of inclusions were occasionally present in the sintered body, and inclusions were especially present near the surface on the tensile stress side of the test piece. If it exists and becomes the starting point of fracture, it will show an extremely low value, so the overall average value will be relatively low, and the strength will also vary widely, making it a somewhat unreliable material.

(Example 2) As in Example 1, the B raw material shown in the table above was prepared in a 50×50×2
After press molding to 0 tm, the molded body was placed in a tube furnace for impurity purification treatment, the temperature was gradually raised while dry chlorine was flowed at 21 per minute, and the temperature was held at 900° C. for 2 hours. When the sample after treatment was analyzed, it was as shown as B in the above table, and a significant decrease in impurities, especially the ASI S b impurity element, was observed.

Next, the sample was glass-sealed using a press sealing method using Vycor glass powder, and then heated to 2000°C.
When HIP sintered under the conditions of 150 MPa and 2 hr, the bending strength of the obtained sintered body was 70 kg/kg at room temperature.
mm”, Si3 at 72 kg/vm” at 1200℃
N showed excellent high-temperature strength as a sintered body.

Further, the Weibull coefficient of the room temperature strength value was 8.

(Example 3) Next, the B raw material in Example 2 was molded and impurity purified in the same manner as in Example 1, and once again
The temperature was raised to 0.degree. C., and the vacuum was evacuated to 10-3 Trouble and maintained for 1 hour.

When the sample after treatment was analyzed, the results were as shown in the table above.
In this case, the purification was further improved than in the case of Example 2, and in particular, Va group elements were effectively removed.

This sample was then heated under the same conditions as in Example 2 above.
As a result of IP sintering, the bending strength of the HIP sintered body was further improved compared to Example 2 as shown in the table above, and the Weibull coefficient was also improved.

(Comparative Example 3) Using the 5iJa raw material B synthesized by the SiJn gas phase reaction method, H
IP sintered. The obtained sintered body was found to be much worse in bending strength than those of Examples 2 and 3.

(Comparative Example 4) Raw material
Surface oxidation of the powder was promoted to prepare a raw material with an oxygen content of 2.7%, and a HIP sintered body was obtained in the same manner as in Example 1 above.

When the bending strength of this sintered body was measured, it was found to be 82 kg/mm'' at room temperature, with a Weibull coefficient of 13 and raw material A' (1
Although better results were obtained than in Example 1), the temperature was 1200°C.

At 1400° C., the strength showed a sudden decrease, which was not preferable as a high-temperature structural material.

(Effect of the invention) As described above, the invention removes impurity elements and produces iron group elements,
It is made of high-purity Si+Na with a Va group element of 50 ppm or less and an oxygen content of 2% or less, and due to the reduction of the impurity elements, no inclusions that cause destruction are formed, making it a 5iJa material without the addition of sintering aids. It has the remarkable effect of being able to create a high-temperature, high-strength material that has never been reported before. Furthermore, by performing HIP treatment without adding a sintering aid and sintering at high temperature and high pressure, the entanglement of 5iiN4 particles is reduced. It is possible to provide a sintered body that is stronger and exhibits the heat resistance and strength of 5iJa itself, and is ideal as an engineering ceramic material that is expected to be developed.

[Brief explanation of drawings]

The figure is a comparison chart of temperature changes in bending strength of 5i3Na without sintering aid added according to the present invention and the conventional method.

Claims (1)

[Claims] 1. A sintered body obtained by hot isostatic pressing Si_3N_4 without the addition of sintering aids, which contains impurity elements of iron group and Va group metal elements of 50 ppm or less and an oxygen amount. is 2%
A high-temperature, high-strength silicon nitride ceramic characterized by: 2. Heat treatment and/or vacuum heat treatment of Si_3N_4 raw material without sintering aid additive or its molded body in dry chlorine,
After reducing the amount of impurity elements of iron group metal and Va group metal contained in the raw material or compact to 50 ppm or less and the amount of oxygen to 2% or less, hot isostatic pressing treatment is performed and sintering is performed. A method for producing high-temperature, high-strength silicon nitride ceramics. 3. Place the Si_3N_4 compact with no sintering aid added into a tube furnace and gradually raise the temperature to 900°C while flowing dry chlorine.
3. The method for producing high-temperature, high-strength silicon nitride ceramics according to claim 2, wherein impurity elements are reduced by holding the ceramic for 2 hours. 4. Place the Si_3N_4 compact with no sintering aid added into a tube furnace and gradually raise the temperature to 900°C while flowing dry chlorine.
After holding the temperature for 2 hours, the temperature was further increased to 1200℃.
3. The method for producing high-temperature, high-strength silicon nitride ceramics according to claim 2, wherein impurity elements are reduced by evacuation to 0^-^3 Torr and holding for 1 hour.