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Method for preparing large scale ceramic ball

A ceramic ball and large-size technology, which is applied in the field of preparation of large-size silicon nitride ceramic balls, can solve problems such as difficult sintering, excessive grain growth, and difficulty in controlling the uniformity of sintered materials to achieve high strength and structural uniformity Effect

Inactive Publication Date: 2008-02-20
SHANGHAI RES INST OF MATERIAL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0005] However, there are certain difficulties in the preparation technology of large-sized ceramic balls. The special difficulty lies in: it is difficult to control the uniformity of the green body during molding; deformation or cracking easily occurs during the process; it is difficult to densify during sintering, and pores and The control of defects is difficult, and the uniformity of sintered materials is difficult to control
In particular, the sintering of large-sized ceramic balls is very difficult. For silicon nitride ceramic balls with a diameter greater than 20 mm, it is difficult to densify them by conventional sintering methods. Increasing the sintering temperature for sintering densification can easily cause excessive growth of grains and the formation of small gap

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0020] 1. With Si 3 N 4 powder as the main raw material, with (Y 2 o 3 、Al 2 o 3 , La 2 o 3 , CeO 2 ) as an additive, Si 3 N 4 The mass ratio of powder and additive is 100:15-5; wherein Si3N4 powder Si 3 N 4 Content ≥ 95%, median particle size D 50 ≤1μm, oxygen content ≤2%; purity of additives ≥99.9%, median particle size D 50 ≤1μm;

[0021] 2. Mix the silicon nitride powder and additives in step 1 by means of ball mill wet mixing. The mixing time is ≥18h. After the mixture is dried, it is dry-pressed and formed. The forming pressure is 2-10MPa. The green body after dry-pressed After vacuuming and plastic sealing, carry out cold isostatic pressing treatment, and the cold isostatic pressure is 100-450MPa;

[0022] 3. Sintering the cold isostatic pressed green body in step 2 by hot isostatic pressing. The hot isostatic pressing sintering method adopts the glass sheathing process; the sheathing glass is made of borosilicate glass, B 2 o 3 Content 10-18%, SiO 2 T...

Embodiment 2

[0026] Will add (5wt%Y 2 o 3 +2wt%Al 2 o 3 ) The silicon nitride powder of the sintering aid is mixed evenly, and after drying is complete, it is dry-pressed under a pressure of 2MPa to form a ceramic ball green body with a diameter of 35mm, and then cold isostatic pressed at 200MPa to further compact it. Composed of (SiO 2 77wt%, B 2 o 3 15wt%, Al 2 o 3 3wt%, Na 2 O 4wt%, K 2 O 0.6wt%, CaO 0.4wt%) glass powder, hot isostatic pressing sintering at 130MPa, 1750°C, holding time 1.5 hours, nitrogen or argon atmosphere, controlled cooling after sintering.

[0027] The surface of the silicon nitride ceramic ball prepared by the above process has no defects such as pores and cracks, the microstructure is uniform, and the microhardness is 1550kg / mm 2 , indentation fracture toughness 5.4MPa m 1 / 2 .

Embodiment 3

[0029] Will add (6wt%Y 2 o 3 +4wt%La 2 o 3 +3wt%CeO 2 ) The silicon nitride powder of the sintering aid is mixed evenly, and after drying completely, it is dry-pressed under a pressure of 2MPa to form a ceramic ball green body with a diameter of 55mm. (SiO 2 82wt%, B 2 o 3 10wt%, Al 2 o 3 2.7wt%, Na 2 O 4.3wt%, K 2 O 0.7wt%, CaO 0.3wt%) glass powder, hot isostatic pressing sintering at 150MPa, 1730°C, holding time 2 hours, nitrogen or argon atmosphere, controlled cooling after sintering.

[0030] The surface of the silicon nitride ceramic ball prepared by the above process has no defects such as pores and cracks, the microstructure is uniform, and the microhardness is 1500kg / mm 2 , indentation fracture toughness 6.3MPa m 1 / 2 .

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Abstract

The invention relates to a preparation method of a large size ceramic ball, comprising the steps of material mixing, moulding and sintering. The method takes silicon nitride powder and additive as raw materials, of which the weight ratio is 100:15-5; certain amount of raw materials are weighted, evenly mixed by a ball milling method, dry pressed and then treated by cold isostatic pressure to get rough-body; the rough-body is hot isostatic pressure sintered under the protection of nitrogen and argon by adopting glass canning process; after a period of insulation and sintering, the temperature is reduced and the finished products are obtained. Compared with the prior art, the silicon nitride ceramic ball prepared by the invention has no stomata and gape on the surface, has even micro structure, 1500kg / mm2 of microhardness, above 5.4MPa.m1 / 2 of indentation and fracture toughness, and the invention can be widely applied to fields such as bearing ball, etc.

Description

technical field [0001] The invention relates to the field of preparation of engineering ceramics, in particular to a method for preparing large-size silicon nitride ceramic balls. Background technique [0002] Silicon nitride material has a series of excellent properties such as wear resistance, corrosion resistance, high temperature resistance, electrical insulation, magnetic insulation, high strength, high rigidity, low specific gravity, and low expansion. It is the preferred material for ceramic balls at present. Silicon nitride ceramic balls can be used as ceramic bearing balls, valve balls, measuring balls, etc., and are widely used in aviation, aerospace, electronics, machinery and other fields. [0003] At present, the preparation of silicon nitride ceramic balls mainly focuses on the production of products with a diameter of less than 20mm, and there is a certain difficulty in the preparation of large-size silicon nitride ceramic balls. [0004] Large-size ceramic b...

Claims

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Application Information

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IPC IPC(8): C04B35/584C04B35/622
Inventor 张培志何万保
Owner SHANGHAI RES INST OF MATERIAL
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