Introduction
Vacuum arc remelting (VAR) is a widely used process in the production of high-performance alloys of non-ferrous metals and their alloys, where the properties of the alloys are often critical for the final applications. This process relies on the use of a high-temperature electric arc, which is generated in a sealed chamber where the pressure is maintained at a low level. The process is widely used for the production of aerospace alloys, medical alloys and superalloys.
Principles
The vacuum arc remelting process utilizes a direct current electric arc between two electrodes in a vacuum chamber. The electrodes are usually made of the same material as the melt and one of them is usually the pre-melted ingot, while the other is a consumable graphite or tungsten carbide electrode. When the electric arc is struck, the required electric resistance melts the material. The arc is adjusted and stabilized by the electrode angle, air gap and arc voltage.
The molten droplets spray onto the cool walls of the crucible and solidify to form an ingot.
Another electrode is sent into the crucible to provide additional heating and remelting of the solid ingot. This ensures homogeneity, low porosity and fine grain structure of the remelted ingot. The reaction force of the arc is converted into heat by the refractory lining on the inner wall of the vacuum chamber that is subjected to the radiation of the arc. The vented vacuum chamber and the use of a graphite crucible minimizes the contamination that occur during the VAR process.
Advantages
VAR offers numerous advantages, such as minimal oxidation of the metal, low ingot porosity and a fine grain structure. Additionally, very high melting rates can also be achieved, as the electric arc itself can reach temperatures in the range of 5000 to 8000°C. On the other hand, cost and equipment related limitations can be associated with the process, when it comes to the embedding metal control and melt control.
Above all, VAR offers an important advantage that nickel-based superalloys, titanium alloys and aluminum alloys are all amenable to VAR. In addition to improving the homogeneity, it also enables the addition of trace elements such as boron and silicon, as well as other alloys such as elements and alloy powders, to the molten metal bath.
Conclusion
Vacuum arc remelting is a widely-used process for the production of high-performance non-ferrous alloys. The process offers a wide range of advantages when it comes to the improvement of the homogeneity, porosity and grain structure of metallic alloys. Additionally, it also allows the addition of trace elements to the alloy. Due to its advantages, the VAR process is increasingly being utilized in the production of aerospace, medical and superalloys.
