Tungsten metallurgy and processing technology
The preparation methods of dense tungsten mainly include powder metallurgy and melting. Because of the high melting point of tungsten, the early preparation methods were mainly limited to powder metallurgy. 1909 laid the foundation for modern powder metallurgy of tungsten by reducing tungstate with hydrogen at 800-900℃, then pressing the tungsten powder, pre-sintering at 1000℃, and vertical melting. Although various improvements have been made to the powder metallurgy process over the past century, it is still by far the main method for preparing dense tungsten metals. With the development of melting technology, high quality tungsten billet with high purity can be prepared by using electron beam melting technology, especially electron beam local melting technology has opened a new world for the preparation of tungsten single crystal. However, the smelting process has some insuperable disadvantages (such as large grain size), which bring great difficulties to the further plastic processing of tungsten.
1.1 Powder Metallurgy
The advantages of powder metallurgy are as follows: the billet microstructure is uniform and the grain is fine, which is convenient for further processing. Low metal loss, high yield; Small investment, quick effect, production has great flexibility, can directly produce finished products and meet certain size requirements of the blank.
1.2 Smelting method
With the development of electron beam melting technology and regional purification technology, it is now possible to use melting technology to produce tungsten which can only be produced by powder metallurgy. However, powder metallurgy is still the most important method for the production of tungsten and its alloys because of the relatively low yield of molten alloy and the coarse grain of billet, which makes further processing more difficult.
On the other hand, the electron beam region melting can purify tungsten, greatly reduce its impurity content, and also provide the possibility for the preparation of single crystal.
