Tungsten possesses several outstanding properties such as high melting point, high density, high recrystallization temperature, excellent high-temperature conductivity, resistance to thermal shock, and erosion resistance. However, tungsten has poor room-temperature ductility and a high ductile-to-brittle transition temperature ranging from 150 to 450°C, making it difficult to achieve machining and cold deformation at room temperature.

On the other hand, rhenium has a high melting point, large elastic modulus, no brittle-to-ductile transition temperature, and exhibits excellent tensile strength, creep resistance, endurance strength, and resistance to thermal shock. By adding rhenium to tungsten, the tungsten-rhenium alloy benefits from the "rhenium effect" and demonstrates a range of excellent properties including high melting point, high hardness, high strength, high ductility, high electrical resistivity, high thermoelectric potential, high recrystallization temperature, low vapor pressure, low electron emission work function, and low ductile-to-brittle transition temperature.

Tungsten-rhenium alloy is one of the best-performing alloys in terms of overall properties. It has extensive application prospects in cutting-edge fields such as aerospace, nuclear industry, electronics industry, and medical applications.

1、The strengthening effect of rhenium in tungsten-based alloys

（1）Solid solution strengthening tungsten-rhenium alloy

Solid solution strengthening tungsten-rhenium alloy. Tungsten-rhenium (W-Re) alloy is a solid solution alloy where rhenium is added to tungsten, significantly improving the room-temperature ductility and high-temperature creep resistance of pure tungsten. The added rhenium content is typically in the range of 3% to 26%, with commonly used compositions including W-3Re, W-5Re, W-10Re, and W-25Re. Figure 1 shows the binary phase diagram of tungsten-rhenium alloy, indicating that tungsten and rhenium have a wide range of solubility in each other, forming an α-solid solution in tungsten. Solid solutions can be classified into interstitial solid solutions and substitutional solid solutions. Due to the similar atomic radii of tungsten and rhenium, rhenium forms a substitutional solid solution in tungsten, which has little effect on the lattice constant of the matrix. Tungsten alloy is a body-centered cubic structure of solid solution, as shown in Figure 2. During the formation of the solid solution, tungsten atoms and rhenium atoms migrate to each other, which can repair a considerable number of microcracks. The maximum solubility of rhenium in tungsten is 37% Re (atomic ratio) at 3000°C, and the minimum solubility is 28% Re (atomic ratio) at 1600°C. In practical production, when the rhenium content exceeds 26%, a second phase called W2Re3 precipitates in tungsten alloy. W2Re3 is a high-strength and high-hardness structure, which brings difficulties in the pressure processing and heat treatment of tungsten-rhenium alloys and significantly affects the properties of tungsten-rhenium alloys, especially in terms of material uniformity.

The improvement in properties of solid solution W-Re alloy compared to pure tungsten is mainly attributed to the "rhenium effect." When rhenium is added to tungsten, it forms complex oxide compounds with high surface tension. These oxides do not wet grain boundaries but instead aggregate into spherical shapes, enhancing the grain boundary strength of tungsten-rhenium alloy. This, in turn, improves the ductility of the alloy and promotes the formation of dislocation cells during deformation, reducing the energy of stacking faults.

Fig.1 Tungsten-Rhenium alloy phase diagram

Fig.2 solid solution crystal structure of tungsten-rhenium alloy

（2）Second-phase particle strengthening in tungsten-rhenium alloy

The addition of finely dispersed second-phase particles in W-Re alloy can further enhance the high-temperature mechanical properties of tungsten-rhenium alloy. The second-phase particles are typically oxides and carbides.

Uniformly distributed second-phase particles serve multiple purposes. On one hand, they act as pinning points for dislocations and grain boundaries, leading to grain refinement and increased strength of the tungsten-rhenium alloy. At the same time, they increase the interfacial area of grain boundaries, reducing the concentration of impurities and lowering the ductile-to-brittle transition temperature of the alloy.

Oxides such as ThO2, Y2O3, and CeO2 are commonly used for dispersion strengthening of tungsten alloys. The principle behind this is the use of dispersed oxides to impede dislocation motion and refine grain size, thereby achieving strengthening and toughening effects. The commonly used W-Re-ThO2 series alloys include WRe-1ThO2 and W-Re-2ThO2. However, when the amount of ThO2 exceeds 4%, it can lead to a decline in the alloy's performance. Nevertheless, the size of oxide particles is relatively large, limiting the strengthening effect. Although oxides can improve the strength and lower the ductile-to-brittle transition temperature of tungsten-rhenium alloys, they exhibit lower high-temperature strength and poor resistance to erosion. Since tungsten-rhenium alloys are primarily used in high-temperature applications, the development of oxide-strengthened tungsten-rhenium alloys is limited.

Carbides, on the other hand, possess characteristics such as high hardness, high melting point, and strong thermal stability. By adding carbides, grain refinement can be achieved, leading to improved strength and deformation resistance of tungsten alloys. Additionally, they maintain good resistance to irradiation. The carbides commonly used for precipitation strengthening of tungsten-rhenium alloys include HfC, TaC, NbC, and ZrC. Among them, HfC has the highest melting point, lowest formation energy, and strongest thermodynamic stability. Therefore, W-Re-HfC alloys have been extensively studied, including W-3.6Re-HfC, W-4Re-HfC, W-23.4Re-HfC, and W-24.5Re-HfC alloys.

2、Applications of tungsten-rhenium alloy

The traditional applications mainly include the following three aspects: 

（1）Thermocouple Wires:

Tungsten-rhenium thermocouple wires are widely used in temperature measurement instruments. They offer a broad temperature range (0 to 2500°C), high thermal electromotive force, fast response speed, and excellent corrosion resistance. These thermocouple wires are used not only in vacuum, reducing, and inert atmospheres but also in oxidizing atmospheres with appropriate oxidation protection measures as a substitute for platinum-rhodium thermocouples.

（2）Manufacturing of Single Crystal Sapphire:

Tungsten-rhenium alloy is used for binding during the manufacturing process of single crystal sapphire.

（3）Electron Tubes, Imaging Tubes, and Lamp Filaments:

Tungsten-rhenium alloy is employed as a material for electrical contact points in electron tubes, imaging tubes, lamp filaments, and other electrical switches. Tungsten-rhenium alloy possesses good low-temperature ductility (favorable for initial wire forming), good low-temperature annealing ductility (favorable for secondary wire forming), good high-temperature ductility (after secondary recrystallization), and excellent high-temperature sag resistance. Therefore, it is particularly suitable for manufacturing high-end lamp filaments. Electrical switches commonly use various contact materials, such as automotive horn contacts, ignition contacts, voltage regulator contacts, telephone contacts, and various other electrical switch contacts. During operation, these contacts experience characteristics such as friction, electrical arcing corrosion, and frequent high-frequency contacts. Consequently, contact materials need to meet the following requirements: low contact resistance, low arc volt-ampere characteristics, and low erosion rates.

Rhniumet Ltd., has been dedicated to the research and development of rhenium and rhenium alloy materials for a long time. In addition to the conventional applications mentioned above, the company has also developed more advanced applications in the aerospace, semiconductor, and friction stir welding industries.

1、Aerospace High-Temperature Structural Materials:

Tungsten-rhenium alloys are used in aerospace applications such as heat shields, rocket nozzle components, cone parts, and coatings for engines or engine components. Tungsten-rhenium alloy containers, when heated to 2000°C, show no reaction with UO2 and are used as crucible materials for uranium refining. Tungsten-rhenium alloys are also employed in heating elements and insulation screens of high-temperature furnaces, crucibles for evaporating high-purity metals, and components like springs, screws, nuts, support rods, and connecting rods in high-temperature environments, benefiting from their good plasticity.

2、Semiconductor MOCVD Equipment Components:

In MOCVD (Metal-Organic Chemical Vapor Deposition) equipment, heating components require rapid temperature changes and can reach temperatures as high as 2000°C. Tungsten-rhenium alloys are used to extend the lifespan of these components, and tungsten-rhenium alloy wires with good elongation can also serve as supports for heating filaments.

3、Friction Stir Welding Tungsten-Rhenium Stirring Heads:

Due to its high hardness, strength, wear resistance, and corrosion resistance, tungsten-rhenium alloys are suitable for manufacturing stirring heads used in friction stir welding. Additionally, these alloys' properties make them suitable for applications such as printer pins, pen tips, plumb bobs for surveying instruments, and wear-resistant components.