Production method of super large tungsten crucible
Since the service temperature of high temperature vessel of single crystal furnace is over 2000 ℃, tungsten crucible is the only choice for high temperature vessel of single crystal furnace. Because of the high requirements of service conditions, higher requirements are put forward for the size and density of tungsten crucible: the size is developed to 300 ~ 500mm, and the density is required to be above 18.3 g/cm3. According to the literature reports, the maximum diameter of the tungsten crucible in the prior art is 280mm, and the density is only required to be more than 18.0 g/cm3.
However, the production of super large tungsten crucible, especially the production of super large tungsten crucible for single crystal furnace, has a certain contradiction in compactability and product density. In general, the powder can meet the requirements of large tungsten crucible with good compactability, and its sintering density is lower (generally lower than 18.3 g/cm3), while the powder with higher sintering density has poor compactability. At home and abroad, the use of powders with various particle sizes is generally used to find a balance between sintering density and compactability. In China, 1 ~ 3 kinds of powder are commonly used. Generally, the compactability is good, but the density is only 17.8 ~ 18.3 g/cm3.
The problem solved by the invention lies in providing a method for producing super large size tungsten crucible, which can improve the compactability of powder under the premise of high sintering density ≥ 18.3 g/ cm3, the strength of powder compact is between 1.8 ~ 2.8 MPa, and the specification of tungsten crucible reaches the diameter of φ 300 ~ 500mm and the height of 350 ~ 600mm.
The production method of the super large tungsten crucible of the invention mainly includes mixing of ingredients, isostatic pressing, shaping, sintering and finishing, which is characterized in that the ingredients are made of four different tungsten powders with the Fischer particle size in the range of 1.0 ~ 5.0 μ m. The four kinds of particle sizes are 1.2 ~ 1.8 μ m, 2.2 ~ 2.8 μ m, 3.0 ~ 3.6 μ m and 4 ~ 4.6 μ m respectively, and the mass ratio is 18 ~ 22: 28 ~ 32: 28 ~ 32: 18 ~ 22.
The isostatic pressure is 200 ± 10 MPa, the holding time is 5 ~ 8 minutes, the sintering temperature is 2300 ℃, the sintering time is 6 ~ 8 hours.
Four kinds of tungsten powders with different particle sizes were mixed and mixed according to the proportion, combined with reasonable isostatic pressing, shaping and sintering process, which ensured the production of ultra large size tungsten crucible with a diameter of 300 ~ 500mm and a height of 350 ~ 600mm. The compact strength met the pressing forming requirements and the sintering density was above 18.3 g/cm3.
