Iridium has a melting point of 2450℃ and a working temperature of 2200℃. It does not exhibit obvious oxidation at atmospheric conditions below 1000℃, and has good high temperature durable strength and creep strength. It still has good mechanical properties at 1600℃, so iridium is an ideal coating material for 238Pu isotope power sources. Pure iridium, however, is poorly processed and brittle at high temperatures, requiring alloying with other elements. The main preparation process of iridium alloy used in 238Pu isotope power supply in the United States is as follows: first add tungsten element to iridium material and prepare iridium tungsten alloy by electron beam melting, then add thorium and aluminum elements for arc melting, and finally obtain iridium tungsten alloy by electron beam melting and arc melting. The preparation process is complicated and it is difficult to control the uniformity of trace elements added in melting process. Therefore, improving the preparation process of tungsten-thorium alloy and obtaining thorium-containing iridium alloy with uniform composition and excellent properties is of great significance to the development of 238Pu isotope power supply in China.
Tungsten and thorium alloy as electrode is melted with pressed and sintered iridium block in an electric arc furnace, and then electron beam melting is used to remove impurities, so that uniform iridium alloy containing thorium can be obtained. Tungsten and thorium doped elements are introduced simultaneously through the tungsten and thorium electrodes in the arc melting process, which can simplify the preparation process of the existing thorium-containing iridium alloy. After repeated arc melting, the homogeneity of the doped elements can be guaranteed to the greatest extent. Thorium content in iridium alloy can be controlled by adjusting thorium content in tungsten-thorium electrode. In addition, compared with the POWDER metallurgy method, this method does not need to carry out ball milling, reducing the loss of ball milling process; Compared with pure arc smelting, this method can further remove volatile impurities, eliminate dendrite segregation and internal stress, improve the ductility of iridium alloy, iridium alloy has better properties.
