JPH10291866A - Method for sintering powdery brittle material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an HIP method by which shrinkage anisotropy is reduced at the time of sintering a powdery brittle material having brittleness even at the sintering temp. SOLUTION: When a capsule is filled with a powdery brittle material such as Y2 O3 , Si3 N4 or Nb5 Si3 and the material is subjected to HIP by which it is sintered by heating under isostatic pressure, isostatic pressure is applied after the material attains to a temp. >=0.8 time as high as the sintering temp. (expressed in terms of absolute temp.). Since shrinkage anisotropy is remarkably reduced at the time of sintering the powdery brittle material such as ceramics or an intermetallic compd. having brittleness even at the sintering temp., parts having a complex shape are easily obtd. by sintering in a near-net shape with the powdery brittle material, the number of precision finishing processes is reduced and a superior economical effect is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for sintering brittle materials such as ceramics and intermetallic compounds.

[0002]

2. Description of the Related Art Ceramics, intermetallic compounds, and the like are extremely useful materials as heat-resistant materials, but are generally hard and brittle over a wide temperature range, so that forming processes such as plastic working and cutting are difficult. In order to form a part shape using such a brittle material, usually, the material powder is filled and sealed in a metal capsule, inserted into a high-pressure vessel, and a high-pressure gas is introduced into the high-pressure vessel. High temperature heating while applying high hydrostatic pressure to the metal capsule filled with the material powder,
Sintering of the material powder is performed by a so-called HIP process. By sintering under hydrostatic pressure, a high-strength sintered product with few internal defects such as microcavities can be obtained. Also, at this time, by appropriately selecting the shape of the metal capsule, the shape of the sintered product can be made into a near net shape product close to the component shape, and the labor of precision finishing such as grinding can be reduced.

By the way, when performing the above HIP processing,
Conventionally, a gas has been introduced into a high-pressure vessel at a relatively low temperature, and then heated to a high temperature. According to this method, since the pressure increase due to the heat expansion of the gas can be used, there is an advantage that the capacity of the pump for increasing the pressure in the high-pressure container can be small. However, when ceramics and intermetallic compound powders that still exhibit brittleness even at the sintering temperature of the material are sintered by the above-described conventional HIP processing method, anisotropic shrinkage occurs during sintering. There was a problem. In other words, the shrinkage rate in the long direction of the sintered body is greater than the shrinkage rate in the short direction, so that it is difficult to sinter and mold parts having a complicated shape into a near net shape, which is often used for precision finishing. Man-hours were required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the anisotropy of the shrinkage caused when sintering a brittle material powder that is brittle even at a sintering temperature.
P processing method is provided.

[0005]

In order to solve the above-mentioned problems, a method of sintering brittle material powder according to the present invention comprises filling a capsule with brittle material powder, heating and sintering while applying hydrostatic pressure. In the treatment step, the hydrostatic pressure is applied after the temperature of the brittle material powder reaches 0.8 times or more of the sintering heating holding temperature of the brittle material powder in absolute temperature.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION
For example, Y_TwoO_Three, Si_ThreeN_Four, Nb_FiveSi _ThreeAs
In addition, these materials are still brittle even at the sintering temperature.
It should be a material that exhibits properties. Capsules are used for powder HIP processing
What is usually used, at the sintering temperature of the powder,
Heat-resistant strength and materials that have gas tightness and withstand the applied hydrostatic pressure
It has ductility that can follow the shrinkage of the material powder and reacts with the material powder.
Shall not do so.

[0007] Filling, degassing and sealing of the material powder into the capsule are performed by a usual method, and HIP processing is performed by a normal HIP device. In promoting sintering of the material powder, for example, Y ₂ O ₃ ultrafine powder,
A sintering aid such as Si, Nb powder can be added. The hydrostatic pressure in the HIP processing is performed after the material temperature reaches 0.8 times or more of the sintering heating holding temperature of the material powder in absolute temperature. When pressure is applied from a temperature lower than this, anisotropy occurs in the shrinkage ratio of the obtained sintered body.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for sintering brittle material powder of the present invention
Y ₂ O ₃ which is known to exhibit brittleness even at a temperature of 3K
A specific description will be given by taking the case of (1) as an example. Particle size -350me
sh Y ₂ O ₃ powder, inner diameter 114 mm, inner length 21
After filling into a cylindrical capsule made of SUS304 having a thickness of 0 mm and a thickness of 4.3 mm, the capsule was sealed by reducing the pressure to 10 ⁻³ torr. This capsule filler is heated by a HIP device,
The mixture was heated from room temperature to a sintering heating holding temperature of 1573K at the same time. During this time, hydrostatic pressure pressurization is started after the capsule filler material reaches the predetermined temperature T, and after the hydrostatic pressure reaches 2000 atm, the sintering is held at the sintering heating holding temperature for 3 hours and then at about 6 hours for 37 hours.
Cooled to a temperature below 3K. After cooling to room temperature, the capsule was removed by cutting to obtain a sintered body.

[0009] Both ends in the axial direction of the sintered body are recessed in a dish shape,
Although the side face is constricted in a drum shape, the length and diameter of the sintered body were taken as minimum dimensions. Table 1 shows the measurement results. Table 1 also shows similar test results for Nb ₃ Al which exhibits ductility at a temperature of 1473 K or higher. The shrinkage in the length direction is determined from the length of the powder filler before sintering and the length of the sintered body, and the shrinkage in the diameter direction is determined from the diameter of the powder filler before sintering and the diameter of the sintered body. The rates were calculated respectively. If the difference between the contraction ratio in the length direction and the contraction ratio in the diameter direction is defined as a contraction ratio anisotropy index, this is an index indicating the anisotropy of the contraction ratio.

[0010] Absolute temperature, temperature T at which hydrostatic pressurization starts
And the sintering heating holding temperature Ts are determined, and this is defined as the pressurization start temperature ratio.

[0011]

[Table 1]

From Table 1, it can be seen that in the sintering of H ₂ O ₃ , which exhibits brittleness at the sintering heating holding temperature of 1573 K, by the HIP treatment, the difference in the shrinkage ratios in Comparative Examples 1 and 2 in which the pressure start temperature ratio is less than 0.8. Anisotropy is observed, but the pressure start temperature ratio is 0.8
In Examples 1, 2, and 3 above, the anisotropy index is extremely small, and it can be seen that the anisotropy of the shrinkage ratio is not recognized. Nb ₅ Si ₃ showing brittleness at sintering heating holding temperature of 1573K
As a result of the same test, the anisotropy index was small in Example 4 in which the pressurization start temperature ratio was 0.8 or more, and no anisotropy of the shrinkage rate was observed. In Comparative Example 3 having a value of less than 0.8, the anisotropy index was large, and the anisotropy of the shrinkage was observed.

Table 1 also shows similar test results for Nb ₃ Al, which exhibits ductility at a temperature of 1473K or higher. In this case, the pressurization start temperature ratio is less than 0.8. Also, no anisotropy in shrinkage was observed.

[0014]

As described above, according to the method for sintering brittle material powder of the present invention, the difference in shrinkage caused when sintering brittle material powder that is brittle even at the sintering temperature. The anisotropy can be significantly reduced. by this,
It becomes easy to sinter and mold a component having a complicated shape with a brittle material powder into a near net shape, which brings about an excellent economic effect of saving man-hours for precision finishing.

Claims (1)

[Claims] In a HIP process of filling a capsule with brittle material powder and heating and sintering while applying hydrostatic pressure, the temperature of the brittle material powder is an absolute temperature, and the sintering of the brittle material powder is performed at an absolute temperature. A method for sintering a brittle material powder, wherein a hydrostatic pressure is applied after the holding temperature reaches 0.8 times or more.