Five common smelting methods for titanium alloys

Titanium alloys are widely used in various industries due to their excellent properties, such as high strength-to-weight ratio, corrosion resistance, and biocompatibility. However, the high melting point of titanium alloys presents processing challenges. Titanium alloy smelting methods are generally divided into: 1. Vacuum consumable electric arc furnace smelting method; 2. Non-consumable vacuum electric arc furnace smelting method; 3. Cold hearth smelting method; 4. Cold pot smelting method; 5. Electroslag smelting method. Five methods.

1. Vacuum consumable electric arc furnace melting method (referred to as VAR method)
It is an advanced metallurgical process used for the production of high-purity metals and alloys. This method is mainly used to improve the purity and uniformity of materials, and is usually used to produce high-quality special alloys, aluminum alloys and other high-demand metal materials. With the development of vacuum technology and the application of computers, the VAR method has quickly become a mature industrial production technology for titanium. Most of today's titanium and its alloy ingots are produced using this method. The salient features of the VAR method are low power consumption, high melting speed and good quality reproducibility. The ingot melted by the VAR method has a good crystal structure and uniform chemical composition. Usually, the finished ingot should be melted by VAR method. At least two remelts are required. The VAR method is used to produce titanium ingots. The processes used by manufacturers around the world are basically similar. The difference lies in the use of different electrode preparation methods and equipment. Electrode preparation can be divided into three major categories. One is the integral electrode that is continuously pressed by adding materials in portions, eliminating the electrode welding process; the other is the single-piece electrode that is pressed and welded into consumable electrodes. And welded together through plasma argon arc welding or vacuum welding; third, use other smelting methods to prepare cast electrodes.
In addition to the above two characteristics, modern VAR furnaces for titanium smelting have also realized the large-scale VAR furnace. Modern VAR furnaces can smelt large ingots with a diameter of 1.5m and a weight of 32t.
The vAR method is the standard industrial smelting method for modern titanium and titanium alloys.

2. Non-consumable vacuum electric arc furnace melting method (Jianni NC method)
Vacuum environment Like the consumable electric arc furnace, the CNC method is also performed in a vacuum environment. By sucking the air and gas in the furnace, high vacuum conditions are created to gradually reduce air and oxygen contamination and ensure the production of high-quality alloy materials.
Electrodes In CNC machining, the electrodes used are usually non-consumable and are usually made of tungsten or other high melting point materials. These electrodes are stable and able to withstand high temperature and high energy arc discharges without being consumed.
Arcing occurs by introducing an electric current, usually using two electrodes, producing an arc discharge. This arc is very hot and can heat materials to temperatures above their melting point.
Material melting Under the action of the arc, the material is heated to a high enough temperature to ignite and melt. Since non-consumable electrodes are used, the electrodes themselves are not consumed and can therefore be used continuously.
Alloy preparation: After the material is melted, the required alloy can be prepared by adjusting the intensity of the arc, the temperature in the furnace and the alloy composition. This makes the NC method very suitable for preparing alloys with high precision and precise composition control.
As a one-time smelting, the NC method is quite advantageous from the perspective of improving the recovery rate of residual materials and reducing costs. Usually, NC furnaces and VAR furnaces are used in conjunction to give full play to their respective advantages. The NC method is commonly used in research laboratories and for preparing specialty materials because it provides a high degree of material control and preparation flexibility. However, compared with consumable electric arc furnaces, the equipment and operation costs of the NC method are higher, so it is mainly used in applications that require high accuracy and precise component control, such as aerospace, energy, electronics, etc.

3. Cold hearth melting method (CHM method for short)
Metallurgical inclusion defects in titanium and titanium alloy ingots caused by raw material contamination and abnormal smelting processes have always affected the application of titanium and titanium alloy in the aerospace field. In order to eliminate metallurgical inclusions in titanium alloy aircraft engine rotating parts, cold hearth smelting technology came into being.
The biggest feature of the CHM method is the separation of the melting, refining and solidification processes, that is, the molten charge enters the cold hearth and is first melted, then enters the refining area of the cold hearth for refining, and finally solidifies into ingots in the crystallization area. The significant advantage of CHM technology is that it can form a condensation shell on the wall of the cold hearth. Its "viscous zone" can capture high-density inclusions (HDI) such as WC, Mo, Ta, etc. At the same time, in the refining zone, low-density inclusions The extended residence time of (LDI) particles in high-temperature liquids can ensure the complete dissolution of LDI, thereby effectively removing inclusion defects. That is to say. The purification mechanism of cold hearth smelting can be divided into two types: gravity separation and melting separation.

4. Cold crucible melting method (referred to as CCM method)
In the 1980s, the American Ferrosilicon Company developed a slag-free induction melting process and promoted the CCM method to industrial production applications for the production of titanium ingots and titanium precision castings. In recent years, in some economically developed countries, the CCM method has begun to enter the industrial production scale. The maximum diameter of the ingot is 1 m and the length is 2 m. Its development prospects are eye-catching. The CCM melting process is carried out in a metal crucible composed of water-cooled arc-shaped blocks or copper tubes that are non-conductive to each other. The biggest advantage of this combination is that the gap between each two blocks is an enhanced magnetic field, and the strong magnetic field generated Stirring brings chemical composition and temperature into consistency, thereby improving product quality. The CCM method combines the characteristics of the VAR method and crucible induction melting of refractory materials. It does not require refractory materials and electrodes, and can obtain high-quality ingots with uniform composition and no crucible contamination in one melting process. Compared with the VAR method, the CCM method has the advantages of low equipment cost and easy operation, but at present, this technology is still in the development stage.
5. Electroslag smelting method (ESR method for short)
The ESR method uses the collision of charged particles when electric current passes through conductive electroslag to convert electrical energy into thermal energy. It is a metal smelting and refining process, often used for high-temperature melting and refining of high-melting-point metals and alloys, such as steel, nickel, molybdenum, niobium, etc. It uses the heat energy generated by slag resistance to melt and refine the charge. The ESR method uses consumable electrodes for electroslag melting in inactive slag (CaF2). It can be directly cast into ingots of the same shape and has good surface quality, making it suitable for direct processing in the next process. General steps of electroslag smelting method:
Charging: Loading the metal or alloy to be melted and refined into the furnace. These materials are usually fed into the furnace in lumps or chunks.

Arc Ignition: An electric arc is created at the top of the furnace by two electrodes (usually carbon electrodes). The high temperature generated by the arc heats the metal to its melting temperature.

Electroforming slag: Metal slag that forms multiple dielectric layers on a metal surface. This slag is composed of metal oxides and other metal slag, which floats on the surface of the metal and prevents further diffusion.

Current passing: Passing high-intensity current through the resistance between the metal and the arc. This will continue to heat the metal, causing it to melt.

Oxidation and Refining: In the electroslag that forms on the metal surface, oxides and other impurities react with the metal and are removed or reduced to the desired level. This helps refine the metal to the desired level